Kitava is a Melanesian island that has maintained an almost entirely traditional, non-industrial diet until very recently. It was the subject of a study by Dr. Staffan Lindeberg and colleagues, which I have written about many times, in which they demonstrated that Kitavans have a very low (undetectable) rate of heart attack, stroke, diabetes and overweight. Dr. Lindeberg described their diet as consisting mostly of yam, sweet potato, taro, cassava, coconut, fruit, fish and vegetables. Over the seven days that Dr. Lindeberg measured food intake, they ate 69% of their calories as carbohydrate, 21% as fat (mostly from coconut) and 10% as protein.
I recently received an e-mail from a Kitavan by the name of Job Daniel. He's working at the Papua New Guinea Institute of Medical Research in Madang, studying the social and economic impacts of malaria and related health issues in Papua New Guinea. He recalls many details of Dr. Lindeberg's visit to Kitava, which Dr. Lindeberg has confirmed are correct. Job generously offered to answer some of my questions about the traditional Kitavan diet. My questions are in bold, and his responses are below.
How many meals a day do Kitavans eat?
People on the island eat mostly two meals a day. But nowadays, breakfast is mainly comprised of tubers (yam and sweet potato and greens all cooked in coconut cream and salt) and dinner is the same with the inclusion of fish as protein most often. In between these two meals, lunch is seen as a light refreshment with fruits or young coconut only to mention these two popular ones. In between the morning and the evening, we mostly eat fruits as snack or lunch. Generally speaking, there are only two main meals per day, i.e breakfast and dinner.
Do Kitavans eat any fermented food?
There are fermented fruits and nuts like you've said for breadfruit, nuts, yams and not forgetting fish. We ferment them by using the traditional method of drying them over the fire for months. And this fermented foods last for almost one to two years without getting stale or spoiled. Food preservation is a skill inherited from our great grand fathers taking into consideration the island's location and availability of food. Foods such as bread fruit and fish are fermented and preserved to serve as substitutes to fresh food in times of trouble or shortage. Otherwise, they're eaten along the way.
Is this really fermentation or simply drying?
To your query about the fermentation methods we use, apart from drying food over the fire, we also use this method like the Hawaiians do with taro [poi- SJG]. For our case we bury a special kind of fruit collected from the tree and buried in the ground to ripen, which takes about 2 - 3 days. I don't really know the English name, but we call it 'Natu' in vernecular. There's also a certain nut when it falls from the tree, women collect them and peel off the rotten skin, then mumu [earth oven- SJG] them in the ground covered with leaves to protect them from burning from the extreme heat of the fire, both from the open fire on top and hot stones underneath. After a day, the nuts are removed from the mumu and loaded into very big baskets which are then shifted to the sea for fermentation. This takes a week (minimum) to ferment or be ready for consumption at last. After the fermentation period is over, i.e one week some days or two
weeks to be exact, then the nuts are finally ready for eating. The length of time it takes before the nuts are no longer edible is roughly one week.
What parts of the fish are eaten?
As islanders, we eat almost every creature and body part of a sea creature. Especially fish eggs, it is one of the favorites of children. They always prefer it burnt on the fire and consumed greedily. Every part of the fish is eaten except for the feces, gall bladder, bones and the scales.
Is food shortage really rare on Kitava?
Generally speaking it is rare. BUT sometimes we run out of food only if there is a drought and the sea is useless. Otherwise, we tend to use the preserved or fermented foods on the dryer in the kitchen. As you would understand, we have seasons and they affect the type and availability of food on the island. In the beginning of the year, we eat sweet potato, cassava and mostly tuna for protein. During mid year, before yam comes in to replace sweet potato and cassava, taro is then ready for harvest. And then yams are ready for harvesting so the food supply is continued on. OK when yams are harvested, some are eaten, some are stored away for reserve and seedlings. In this way, we don't run out food towards the end of the year before sweet potato would be ready for harvest. So as you can see, the food supply on the island is somewhat planned by our ancestral economists where it continues throughout the year without stopping.
Do Kitavans traditionally eat pork, and if so, how often?
We do eat pork but not that often because pork meat is chiefly regarded important on the island. We only eat pork on special occasions so I'd rather say that pork is only eaten occasionally. In most cases in the middle of the year when the yams are harvested (yam harvest celebrations and towards the end of the year for certain rites and activities). Otherwise the everyday meal is always topped with fish.
How long are infants breast fed on Kitava?
Women breast feed for a minimum of 2 years. But breast feeding is again determined by the size and health situation of the baby. If the baby is looking healthy and big, it is most likely that this baby would be adopted temporarily by someone else so as to be removed from breast milk after two years of age minimum. Child care nowadays is paramount as people start to realize the importance of health and hygiene in general. But Kitavans are well known in that part of the country for their hygiene practices. They also got the provincial and district awards for a 'clean community' in early 90s and right now, they still maintain their hygiene level and awareness.
Are there any other foods that are commonly eaten on Kitava that I might not be aware of?
Bananas, pineapple, corn and watermelons. For watermelon and corn, they are plentiful especially at this time of the year.
Thanks for your help, Job! I know many people will appreciate reading these responses.
Showing posts sorted by relevance for query sweet potato. Sort by date Show all posts
Showing posts sorted by relevance for query sweet potato. Sort by date Show all posts
Sunday, December 5, 2010
Tuesday, May 25, 2010
Sweet Potatoes
We can debate the nutritional qualities of a food until we're blue in the face, but in the end, we still may not have a very accurate prediction of the health effects of that food. The question we need to answer is this one: has this food sustained healthy traditional cultures?
I'm currently reading a great book edited by Drs. Hugh Trowell and Denis Burkitt, titled Western Diseases: Their Emergence and Prevention. It's a compilation of chapters describing the diet and health of traditional populations around the world as they modernize.
The book contains a chapter on Papua New Guinea highlanders. Here's a description of their diet:
How was their health? Like many non-industrial societies, they had a high infant/child mortality rate, such that 43 percent of children died before growing old enough to marry. Surprisingly, protein deficiency was rare. No obvious malnutrition was observed in this population, although iodine-deficiency cretinism occurs in some highlands populations:
There was no evidence of coronary heart disease or diabetes. Average blood pressure was on the high side, but did not increase with age. Investigators administered 100 gram glucose tolerance tests and only 3.8 percent of the population had glucose readings above 160 mg/dL, compared to 21 percent of Americans. A study of 7,512 Papuans from several regions with minimal European contact indicated a diabetes prevalence of 0.1 percent, a strikingly low rate. For comparison, in 2007, 10.7 percent of American adults had diabetes (1).
I'm not claiming it's optimal to eat nothing but sweet potatoes. But this is the strongest evidence we're going to come by that sweet potatoes can be eaten in quantity as part of a healthy diet. However, I wish I knew more about the varieties this group ate. Sweet potatoes aren't necessarily sweet. Caribbean 'boniato' sweet potatoes are dry, starchy and off-white. In the US, I prefer the yellow sweet potatoes to the orange variety of sweet potato labeled 'yams', because the former are starchier and less sweet. If I could get my hands on locally grown boniatos here, I'd eat those, but boniatos are decidedly tropical.
Instead, I eat potatoes, but I'm reluctant to recommend them whole-heartedly because I don't know enough about the traditional cultures that consumed them. I believe there are some low-CHD, low-obesity African populations that eat potatoes as part of a starch-based diet, but I haven't looked into it closely enough to make any broad statements. Potatoes have some nutritional advantages over sweet potatoes (higher protein content, better amino acid profile), but also some disadvantages (lower fiber, lower in most micronutrients, toxic glycoalkaloids).
I'm currently reading a great book edited by Drs. Hugh Trowell and Denis Burkitt, titled Western Diseases: Their Emergence and Prevention. It's a compilation of chapters describing the diet and health of traditional populations around the world as they modernize.
The book contains a chapter on Papua New Guinea highlanders. Here's a description of their diet:
A diet survey was undertaken involving 90 subjects, in which all food consumed by each individual was weighed over a period of seven consecutive days. Sweet potato supplied over 90 percent of their total food intake, while non-tuberous vegetables accounted for less than 5 percent of the food consumed and the intake of meat was negligible... Extensive herds of pigs are maintained and, during exchange ceremonies, large amounts of pork are consumed.They ate no salt. Their calories were almost entirely supplied by sweet potatoes, with occasional feasts on pork.
How was their health? Like many non-industrial societies, they had a high infant/child mortality rate, such that 43 percent of children died before growing old enough to marry. Surprisingly, protein deficiency was rare. No obvious malnutrition was observed in this population, although iodine-deficiency cretinism occurs in some highlands populations:
Young adults were well built and physically fit and had normal levels of haemoglobin and serum albumin. Further, adult females showed no evidence of malnutrition in spite of the demands by repeated cycles of pregnancy and lactation. On the basis of American standards (Society of Actuaries, 1959), both sexes were close to 100 percent standard weight in their twenties.
The Harvard Pack Test carried out on 152 consecutive subjects demonstrated a high level of physical fitness which was maintained well into middle-age. Use of a bicycle ergometer gave an estimated maximum oxygen uptake of 45.2 ml per kilogram per minute and thus confirmed the high level of cardiopulmonary fitness in this group.Body weight decreased with age, which is typical of many non-industrial cultures and reflects declining muscle mass but continued leanness.
There was no evidence of coronary heart disease or diabetes. Average blood pressure was on the high side, but did not increase with age. Investigators administered 100 gram glucose tolerance tests and only 3.8 percent of the population had glucose readings above 160 mg/dL, compared to 21 percent of Americans. A study of 7,512 Papuans from several regions with minimal European contact indicated a diabetes prevalence of 0.1 percent, a strikingly low rate. For comparison, in 2007, 10.7 percent of American adults had diabetes (1).
I'm not claiming it's optimal to eat nothing but sweet potatoes. But this is the strongest evidence we're going to come by that sweet potatoes can be eaten in quantity as part of a healthy diet. However, I wish I knew more about the varieties this group ate. Sweet potatoes aren't necessarily sweet. Caribbean 'boniato' sweet potatoes are dry, starchy and off-white. In the US, I prefer the yellow sweet potatoes to the orange variety of sweet potato labeled 'yams', because the former are starchier and less sweet. If I could get my hands on locally grown boniatos here, I'd eat those, but boniatos are decidedly tropical.
Instead, I eat potatoes, but I'm reluctant to recommend them whole-heartedly because I don't know enough about the traditional cultures that consumed them. I believe there are some low-CHD, low-obesity African populations that eat potatoes as part of a starch-based diet, but I haven't looked into it closely enough to make any broad statements. Potatoes have some nutritional advantages over sweet potatoes (higher protein content, better amino acid profile), but also some disadvantages (lower fiber, lower in most micronutrients, toxic glycoalkaloids).
Tuesday, June 22, 2010
In Search of Traditional Asian Diets
It's been difficult for me to find good information on Asian diets prior to modernization. Traditional Chinese, Taiwanese and Japanese diets are sometimes portrayed as consisting mostly of white rice, with vegetables and a bit of meat and soy, but I find that implausible. Rice doesn't grow everywhere, and removing all the bran was prohibitively labor-intensive before the introduction of modern machine milling. One hundred years ago, bran was partially removed by beating or grinding in a mortar and pestle, as it still is in parts of rural Asia today. Only the wealthy could afford true white rice.
Given the difficulty of growing rice in most places, and hand milling it, the modern widespread consumption of white rice in Asia must be a 20th century phenomenon, originating in the last 20-100 years depending on location. Therefore, white rice consumption does not predate the emergence of the "diseases of civilization" in Asia.
Taiwan in 1980
Traditionally, coronary heart disease and high blood pressure were rare, but the prevalence is now increasing rapidly. Stroke is common. Diabetes was rare but is increasing gradually.
Mainland China
China is a diverse country, and the food culture varies by region.
Symptoms of vitamin A, C and D deficiency were common in the poor, although coronary heart disease and high blood pressure were rare. Diabetes occurred at a higher rate than in most traditionally-living populations.
Japan
On the Japanese island of Okinawa, the traditional staple is the sweet potato, with a smaller amount of rice eaten as well. Seafood, vegetables, pork and soy are also on the menu. In Akira Kurosawa’s movie Seven Samurai, set in 16th century mainland Japan, peasants ate home-processed millet and barley, while the wealthy ate white rice. Although a movie may not be the best source of information, I suspect it has some historical basis.
White Rice: a Traditional Asian Staple?
It depends on your perspective. How far back do you have to go before you can call a food traditional? Many peoples' grandparents ate white rice, but I doubt their great great grandparents ate it frequently. White rice may have been a staple for the wealthy for hundreds of years in some places. But for most of Asia, in the last few thousand years, it was probably a rare treat. The diet most likely resembled that of many non-industrial African cultures: an assortment of traditionally prepared grains, root vegetables, legumes, vegetables and a little meat.
Given the difficulty of growing rice in most places, and hand milling it, the modern widespread consumption of white rice in Asia must be a 20th century phenomenon, originating in the last 20-100 years depending on location. Therefore, white rice consumption does not predate the emergence of the "diseases of civilization" in Asia.
In the book Western Diseases: Their Emergence and Prevention, there are several accounts of traditional Asian diets I find interesting.
Taiwan in 1980
The staple constituent of the diet is polished white rice. Formerly in the poorer areas along the sea coast the staple diet was sweet potato, with small amounts of white rice added. Formerly in the mountains sweet potato, millet and taro were the staple foods. During the last 15 years, with the general economic development of the whole island, white polished rice has largely replaced other foods. There is almost universal disinclination to eat brown (unpolished) rice, because white rice is more palatable, it bears kudos, cooking is easier and quicker, and it can be stored for a much longer period.
Traditionally, coronary heart disease and high blood pressure were rare, but the prevalence is now increasing rapidly. Stroke is common. Diabetes was rare but is increasing gradually.
Mainland China
China is a diverse country, and the food culture varies by region.
Snapper (1965)… quoted an analysis by Guy and Yeh of Peiping (Peking) diets in 1938. There was a whole cereal/legume/vegetable diet for poorer people and a milled-cereal/meat/vegetable diet for the richer people.
Symptoms of vitamin A, C and D deficiency were common in the poor, although coronary heart disease and high blood pressure were rare. Diabetes occurred at a higher rate than in most traditionally-living populations.
Japan
On the Japanese island of Okinawa, the traditional staple is the sweet potato, with a smaller amount of rice eaten as well. Seafood, vegetables, pork and soy are also on the menu. In Akira Kurosawa’s movie Seven Samurai, set in 16th century mainland Japan, peasants ate home-processed millet and barley, while the wealthy ate white rice. Although a movie may not be the best source of information, I suspect it has some historical basis.
White Rice: a Traditional Asian Staple?
It depends on your perspective. How far back do you have to go before you can call a food traditional? Many peoples' grandparents ate white rice, but I doubt their great great grandparents ate it frequently. White rice may have been a staple for the wealthy for hundreds of years in some places. But for most of Asia, in the last few thousand years, it was probably a rare treat. The diet most likely resembled that of many non-industrial African cultures: an assortment of traditionally prepared grains, root vegetables, legumes, vegetables and a little meat.
Please add any additional information you may have about traditional Asian diets to the comments section.
Tuesday, November 3, 2009
Impressions of Hawai'i
I recently went to Hawai'i for the American Society of Human Genetics meeting in Waikiki, followed by a one-week vacation on Kaua'i with friends. It was my first time in Hawai'i and I really enjoyed it. The Hawai'ians I encountered were kind and generous people.Early European explorers remarked on the beauty, strength, good nature and exellent physical development of the native Hawai'ians. The traditional Hawai'ian diet consisted mostly of taro root, sweet potatoes, yams, breadfruit, coconut, fish, occasional pork, fowl including chicken, taro leaves, seaweed and a few sweet fruits. It would have been very low (but adequate) in omega-6, because there simply isn't much of it available in this environment. Root crops and most fruit are virtually devoid of fat; seafood and coconut contain very little omega-6; and even the pork and chicken would have been low in omega-6 due to their diets. Omega-3 would have been plentiful from marine foods, and saturated fats would have come from coconut. All foods were fresh and unrefined. Abundant exercise and sunlight would have completed their salubrious lifestyle.
The traditional Hawai'ian diet was rich in easily digested starch, mainly in the form of poi, which is fermented mashed taro. I ate poi a number of times while I was on Kaua'i, and really liked it. It's mild, similar to mashed potatoes, but with a slightly sticky consistency and a purple color (due to the particular variety of taro that's traditionally used to make it).
I had the opportunity to try a number of traditional Polynesian foods while I was on Kaua'i. One plant that particularly impressed me is breadfruit. It's a big tree that makes cantaloupe-sized starchy green fruit. Breadfruit is incredibly versatile, because it can be used at different stages of ripeness for different purposes. Very young, it's like a vegetable, at full size, it's a bland starch, and fully ripe it's starchy and sweet like a sweet potato. It can be baked, boiled, fried and even dried for later use. It has a mild flavor and a texture similar to soft white bread. It's satisfying and fairly rich in micronutrients. On the right are breadfruit, coconut and sugarcane, three traditional Hawai'ian foods.
I find perennial staple crops such as breadfruit very interesting, because they're much less destructive to soil quality than annual crops, and they're a breeze to maintain. I could walk into the backyard of the apartment I was renting and pick a breadfruit, soak it, throw it in the oven and I had something nutritious to eat in just over an hour. It's like picking a bag of potatoes right off a tree. Insects and birds didn't seem to like it at all, possibly because the raw fruit exudes a bitter, rubbery sap when damaged. Unfortunatley, breadfruit is a tropical plant. Temperate starchy staples that were exploited by native North Americans include the majestic American chestnut in the Appalachians, and acorns in the West. These are both more work than breadfruit to prepare, particularly acorns which must be extensively soaked to remove bitter tannins.
One of the foods Polynesian settlers brought to Hawai'i was sugar cane. I had the opportunity to try fresh sugar cane for the first time while I was on Kaua'i. You cut off the outer skin, then cut it into strips and chew to get the sweet juice. It was mild but tasty. I don't know if it was a coincidence or not, but I ended up feeling unwell after eating several pieces. It may simply have been too much sugar for me.
Modern Hawai'i is a hunter-gatherer's dream. There are fruit trees everywhere, including papayas, wild and cultivated guavas, mangoes, avocados, passion fruit, breadfruit, bananas, citrus fruits and many others. Many of those fruits did not predate European contact however. Even pineapples were introduced to Hawai'i after European contact. Coconuts are everywhere, and we could pick one up for a drink and snack on almost any beach. The forests are full of wild chickens (such as the one at left) and pigs, both having resulted from the escape and subsequent mixing of Polynesian and European breeds. Kaua'ians frequently hunt the pigs, which are environmentally damaging due to their habit of rooting through topsoil for food. Large areas of forest on Kaua'i look like they've been ploughed due to the pigs' rooting. Humans are their only predators and their food is abundant.While I was on Kaua'i, I ate mostly seafood (including delicious raw tuna poke), poi, breadfruit, coconut and sweet fruits-- a real Polynesian style hunter-gatherer diet! I swam every day, hiked in the lovely interior, and kayaked. It was a great trip, and I hope to return someday.
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Saturday, February 2, 2013
Why Do We Eat? A Neurobiological Perspective. Part V
In previous posts, I explained that food intake is determined by a variety of factors that are detected by the brain, and integrated by circuits in the mesolimbic system to determine the overall motivation to eat. These factors include 'homeostatic factors' that reflect a true energy need by the body, and 'non-homeostatic factors' that are independent of the body's energy needs (e.g. palatability, habit, and the social environment).
In this post, we'll explore the hedonic system, which governs pleasure. This includes the pleasure associated with food, called palatability. The palatability of food is one of the factors that determines food intake.
The Hedonic System
In this post, we'll explore the hedonic system, which governs pleasure. This includes the pleasure associated with food, called palatability. The palatability of food is one of the factors that determines food intake.
The Hedonic System
Tuesday, June 28, 2011
Food Reward: a Dominant Factor in Obesity, Part VII
Now that I've explained the importance of food reward to obesity, and you're tired of reading about it, it's time to share my ideas on how to prevent and perhaps reverse fat gain. First, I want to point out that although food reward is important, it's not the only factor. Heritable factors (genetics and epigenetics), developmental factors (uterine environment, childhood diet), lifestyle factors (exercise, sleep, stress) and dietary factors besides reward also play a role. That's why I called this series "a dominant factor in obesity", rather than "the dominant factor in obesity".
Sunday, September 19, 2010
Potatoes and Human Health, Part I
Potatoes: an Introduction
Over 10,000 years ago, on the shores of lake Titicaca in what is now Peru, a culture began to cultivate a species of wild potato, Solanum tuberosum. They gradually transformed it into a plant that efficiently produces roundish starchy tubers, in a variety of strains that suited the climactic and gastronomic needs of various populations. These early farmers could not have understood at the time that the plant they were selecting would become the most productive crop in the world*, and eventually feed billions of people around the globe.
Wild potatoes, which were likely consumed by hunter-gatherers before domestication, are higher in toxic glycoalkaloids. These are defensive compounds that protect against insects, infections and... hungry animals. Early farmers selected varieties that are low in bitter glycoalkaloids, which are the ancestors of most modern potatoes, however they didn't abandon the high-glycoalkaloid varieties. These were hardier and more tolerant of high altitudes, cold temperatures and pests. Cultures living high in the Andes developed a method to take advantage of these hardy but toxic potatoes, as well as their own harsh climate: they invented chuños. These are made by leaving potatoes out in the open, where they are frozen at night, stomped underfoot and dried in the sun for many days**. What results is a dried potato with a low glycoalkaloid content that can be stored for a year or more.
Nutritional Qualities
From a nutritional standpoint, potatoes have a bad reputation, but this is undeserved in my opinion. If I had to pick a single food to eat exclusively for an extended period of time, potatoes would be high on the list. One reason is that they contain an adequate amount of complete protein, meaning they don't have to be mixed with another protein source as with grains and legumes. Another reason is that a number of cultures throughout history have successfully relied on the potato as their principal source of calories, and several continue to do so. A third reason is that they're eaten in an unrefined, fresh state.
Potatoes contain an adequate amount of many essential minerals, and due to their low phytic acid content (1), the minerals they contain are well absorbed. They're rich in magnesium and copper, two minerals that are important for insulin sensitivity and cardiovascular health (2, 3). They're also high in potassium, which helps control blood pressure, and vitamin C. Overall, they have a micronutrient content that compares favorably with other starchy root vegetables such as taro and cassava (4, 5, 6), and they offer considerably more micronutrients than refined carbohydrates such as white flour, white rice and white sugar.
On the other hand, I don't have to eat potatoes exclusively, so what do they have to offer a mixed diet? They have a high glycemic index, which means they raise blood sugar more than an equivalent serving of most carbohydrate foods, although I'm not convinced that's a problem in people with good blood sugar control (7, 8). They contain adequate fiber, but less than some other sources of starch. For example, sweet potatoes, an unrelated species, contain more micronutrients and fiber, and have been a central food source for healthy cultures (9). However, the main reasons temperate-climate cultures throughout the world eat potatoes is they yield well, they're easily digested, they fill you up and they taste good.
In the next post, I'll delve into the biology and toxicology of potato glycoalkaloids, and review some animal data. In further posts, I'll address the most important question of all: what happens when a person eats mostly potatoes... for months, years, and generations?
* In terms of calories produced per acre.
** A simplified description. The process can actually be rather involved, with several different drying, stomping and leaching steps.
Over 10,000 years ago, on the shores of lake Titicaca in what is now Peru, a culture began to cultivate a species of wild potato, Solanum tuberosum. They gradually transformed it into a plant that efficiently produces roundish starchy tubers, in a variety of strains that suited the climactic and gastronomic needs of various populations. These early farmers could not have understood at the time that the plant they were selecting would become the most productive crop in the world*, and eventually feed billions of people around the globe.
Wild potatoes, which were likely consumed by hunter-gatherers before domestication, are higher in toxic glycoalkaloids. These are defensive compounds that protect against insects, infections and... hungry animals. Early farmers selected varieties that are low in bitter glycoalkaloids, which are the ancestors of most modern potatoes, however they didn't abandon the high-glycoalkaloid varieties. These were hardier and more tolerant of high altitudes, cold temperatures and pests. Cultures living high in the Andes developed a method to take advantage of these hardy but toxic potatoes, as well as their own harsh climate: they invented chuños. These are made by leaving potatoes out in the open, where they are frozen at night, stomped underfoot and dried in the sun for many days**. What results is a dried potato with a low glycoalkaloid content that can be stored for a year or more.
Nutritional Qualities
From a nutritional standpoint, potatoes have a bad reputation, but this is undeserved in my opinion. If I had to pick a single food to eat exclusively for an extended period of time, potatoes would be high on the list. One reason is that they contain an adequate amount of complete protein, meaning they don't have to be mixed with another protein source as with grains and legumes. Another reason is that a number of cultures throughout history have successfully relied on the potato as their principal source of calories, and several continue to do so. A third reason is that they're eaten in an unrefined, fresh state.
Potatoes contain an adequate amount of many essential minerals, and due to their low phytic acid content (1), the minerals they contain are well absorbed. They're rich in magnesium and copper, two minerals that are important for insulin sensitivity and cardiovascular health (2, 3). They're also high in potassium, which helps control blood pressure, and vitamin C. Overall, they have a micronutrient content that compares favorably with other starchy root vegetables such as taro and cassava (4, 5, 6), and they offer considerably more micronutrients than refined carbohydrates such as white flour, white rice and white sugar.
On the other hand, I don't have to eat potatoes exclusively, so what do they have to offer a mixed diet? They have a high glycemic index, which means they raise blood sugar more than an equivalent serving of most carbohydrate foods, although I'm not convinced that's a problem in people with good blood sugar control (7, 8). They contain adequate fiber, but less than some other sources of starch. For example, sweet potatoes, an unrelated species, contain more micronutrients and fiber, and have been a central food source for healthy cultures (9). However, the main reasons temperate-climate cultures throughout the world eat potatoes is they yield well, they're easily digested, they fill you up and they taste good.
In the next post, I'll delve into the biology and toxicology of potato glycoalkaloids, and review some animal data. In further posts, I'll address the most important question of all: what happens when a person eats mostly potatoes... for months, years, and generations?
* In terms of calories produced per acre.
** A simplified description. The process can actually be rather involved, with several different drying, stomping and leaching steps.
Tuesday, November 16, 2010
Impressions from the Wise Traditions Conference
I spent last weekend at the Weston A. Price Foundation Wise Traditions conference in King of Prussia, PA. Here are some highlights:
Spending time with several people in the diet-health community who I’ve been wanting to meet in person, including Chris Masterjohn, Melissa McEwen and John Durant. John and Melissa are the public face of the New York city paleo movement. The four of us spent most of the weekend together tossing around ideas and making merry. I’ve been corresponding with Chris quite a bit lately and we’ve been thinking through some important diet-health questions together. He is brimming with good ideas. I also got to meet Sally Fallon Morell, the founder and president of the WAPF.
Attending talks. The highlight was Chris Masterjohn’s talk “Heart Disease and Molecular Degeneration: the New Paradigm”, in which he described his compelling theory on oxidative damage and cardiovascular disease, among other things. You can read some of his earlier ideas on the subject here. Another talk I really enjoyed was by Anore Jones, who lived with an isolated Inuit group in Alaska for 23 years and ate a mostly traditional hunter-gatherer diet. The food and preparation techniques they used were really interesting, including various techniques for extracting fats and preserving meats, berries and greens by fermentation. Jones has published books on the subject that I suspect would be very interesting, including Nauriat Niginaqtuat, Plants that We Eat, and Iqaluich Niginaqtuat, Fish that We Eat. The latter is freely available on the web here.
I attended a speech by Joel Salatin, the prolific Virginia farmer, writer and agricultural innovator, which was fun. I enjoyed Sally Fallon Morell’s talk on US school lunches and the politics surrounding them. I also attended a talk on food politics by Judith McGeary, a farmer, attorney and and activist, in which she described the reasons to oppose or modify senate bill 510. The gist is that it will be disproportionately hard on small farmers who are already disfavored by current regulations, making high quality food more difficult to obtain, more expensive or even illegal. It’s designed to improve food safety by targeting sources of food-borne pathogens, but how much are we going to have to cripple national food quality and farmer livelihood to achieve this, and will it even be effective? I don’t remember which speaker said this quote, and I’m paraphrasing, but it stuck with me: “I just want to be able to eat the same food my grandmother ate.” In 2010, that’s already difficult to achieve. Will it be impossible in 2030?
Giving my own talk. I thought it went well, although attendance was not as high as I had hoped. The talk was titled “Kakana Dina: Diet and Health in the Pacific Islands”, and in it I examined the relationship between diet and health in Pacific island cultures with different diets and at various stages of modernization. I’ve covered some of this material on my blog, in my posts on Kitava, Tokelau and sweet potato eating cultures in New Guinea, but other material was new and I went into greater detail on food habits and preparation methods. I also dug up a number of historical photos dating back as far as the 1870s.
The food. All the meat was pasture-raised, organic and locally sourced if possible. There was raw pasture-raised cheese, milk and butter. There was wild-caught fish. There were many fermented foods, including sauerkraut, kombucha and sourdough bread. I was really impressed that they were able to put this together for an entire conference.
The vendors. There was an assortment of wholesome and traditional foods, particularly fermented foods, quality dairy and pastured meats. There was an entire farmer’s market on-site on Saturday, with a number of Mennonite vendors selling traditional foods. I bought a bottle of beet kvass, a traditional Russian drink used for flavor and medicine, which was much better than the beet kvass I’ve made myself in the past. Beets are a remarkable food, in part due to their high nitrate content—beet juice has been shown to reduce high blood pressure substantially, possibly by increasing the important signaling molecule nitric oxide. I got to meet Sandeep Agarwal and his family, owners of the company Pure Indian Foods, which domestically produces top-quality pasture-fed ghee (Indian-style clarified butter). They now make tasty spiced ghee in addition to the plain flavor. Sandeep and family donated ghee for the big dinner on Saturday, which was used to cook delicious wild-caught salmon steaks donated by Vital Choice.
There were some elements of the conference that were not to my taste. But overall I’m glad I was able to go, meet some interesting people, give my talk and learn a thing or two.
Wednesday, August 13, 2008
The Kitavans: Wisdom from the Pacific Islands
There are very few cultures left on this planet that have not been affected by modern food habits. There are even fewer that have been studied thoroughly. The island of Kitava in Papua New Guinea is host to one such culture, and its inhabitants have many profound things to teach us about diet and health.
The Kitava study, a series of papers produced primarily by Dr. Staffan Lindeberg and his collaborators, offers a glimpse into the nutrition and health of an ancient society, using modern scientific methods. This study is one of the most complete and useful characterizations of the diet and health of a non-industrial society I have come across. It's also the study that created, and ultimately resolved, my cognitive dissonance over the health effects of carbohydrate.
From the photos I've seen, the Kitavans are beautiful people. They have the broad, attractive faces, smooth skin and excellent teeth typical of healthy non-industrial peoples.
Like the Kuna, Kitavans straddle the line between agricultural and hunter-gatherer lifestyles. They eat a diet primarily composed of tubers (yam, sweet potato, taro and cassava), fruit, vegetables, coconut and fish, in order of calories. This is typical of traditional Pacific island cultures, although the relative amounts differ.
Grains, refined sugar, vegetable oils and other processed foods are virtually nonexistent on Kitava. They get an estimated 69% of their calories from carbohydrate, 21% from fat, 17% from saturated fat and 10% from protein. Most of their fat intake is saturated because it comes from coconuts. They have an omega-6 : omega-3 ratio of approximately 1:2. Average caloric intake is 2,200 calories per day (9,200 kJ). By Western standards, their diet is high in carbohydrate, high in saturated fat, low in total fat, a bit low in protein and high in calories.
Now for a few relevant facts before we really start diving in:
Overall, Kitavans possess a resistance to degenerative diseases that is baffling to industrialized societies. Not only is this typical of non-industrial cultures, I believe it represents the natural state of existence for Homo sapiens. Like all other animals, humans are healthy and robust when occupying their preferred ecological niche. Our niche happens to be a particularly broad one, ranging from near-complete carnivory to plant-rich omnivory. But it does not include large amounts of industrial foods.
In the next few posts, I'll discuss more specific data about the health of the Kitavans.
The Kitava study, a series of papers produced primarily by Dr. Staffan Lindeberg and his collaborators, offers a glimpse into the nutrition and health of an ancient society, using modern scientific methods. This study is one of the most complete and useful characterizations of the diet and health of a non-industrial society I have come across. It's also the study that created, and ultimately resolved, my cognitive dissonance over the health effects of carbohydrate.
From the photos I've seen, the Kitavans are beautiful people. They have the broad, attractive faces, smooth skin and excellent teeth typical of healthy non-industrial peoples.
Like the Kuna, Kitavans straddle the line between agricultural and hunter-gatherer lifestyles. They eat a diet primarily composed of tubers (yam, sweet potato, taro and cassava), fruit, vegetables, coconut and fish, in order of calories. This is typical of traditional Pacific island cultures, although the relative amounts differ.
Grains, refined sugar, vegetable oils and other processed foods are virtually nonexistent on Kitava. They get an estimated 69% of their calories from carbohydrate, 21% from fat, 17% from saturated fat and 10% from protein. Most of their fat intake is saturated because it comes from coconuts. They have an omega-6 : omega-3 ratio of approximately 1:2. Average caloric intake is 2,200 calories per day (9,200 kJ). By Western standards, their diet is high in carbohydrate, high in saturated fat, low in total fat, a bit low in protein and high in calories.
Now for a few relevant facts before we really start diving in:
- Kitavans are moderately active. They have an activity level comparable to a moderately active Swede, the population to which Dr. Lindeberg draws frequent comparisons.
- They have abundant food, and shortage is uncommon.
- Their good health is probably not related to genetics, since genetically similar groups in the same region are exquisitely sensitive to the ravages of industrial food. Furthermore, the only Kitavan who moved away from the island to live a modern life is also the only fat Kitavan.
- Their life expectancy at birth is estimated at 45 years (includes infant mortality), and life expectancy at age 50 is an additional 25 years. This is remarkable for a culture with limited access to modern medicine.
- Over 75% of Kitavans smoke cigarettes, although in small amounts. Even the most isolated societies have their modern vices.
For the whole of PNG, no case of IHD or atherothrombotic stroke has been reported in clinical investigations and autopsy studies among traditionally living Melanesians for more than seven decades, though an increasing number of myocardial infarctions [heart attacks] and angina pectoris in urbanized populations have been reported since the 1960s.Dementia was not found except in in two young Kitavans, who were born handicapped. The elderly remained sharp until death, including one man who reached 100 years of age. Kitavans are also unfamiliar with external cancers, with the exception of one possible case of breast cancer in an elderly woman.
Overall, Kitavans possess a resistance to degenerative diseases that is baffling to industrialized societies. Not only is this typical of non-industrial cultures, I believe it represents the natural state of existence for Homo sapiens. Like all other animals, humans are healthy and robust when occupying their preferred ecological niche. Our niche happens to be a particularly broad one, ranging from near-complete carnivory to plant-rich omnivory. But it does not include large amounts of industrial foods.
In the next few posts, I'll discuss more specific data about the health of the Kitavans.
Tuesday, December 16, 2014
Is Meat Unhealthy? Part V
In this post, I'll examine the possible relationship between meat intake and type 2 diabetes. Type 2 diabetes is the most common form of diabetes, and it is strongly linked to lifestyle factors.
Non-industrial cultures
Non-industrial cultures have an extremely low prevalence of diabetes, whether they are near-vegan or near-carnivorous. This is supported by blood glucose measurements in a variety of cultures, from the sweet potato farmers of the New Guinea highlands to the arctic Inuit hunters. Here is what Otto Schaefer, director of the Northern Medical Research Unit at Charles Camsell hospital in Edmonton, Canada, had to say about the Inuit in the excellent book Western Diseases (Trowell and Burkitt, 1981):
Non-industrial cultures
Non-industrial cultures have an extremely low prevalence of diabetes, whether they are near-vegan or near-carnivorous. This is supported by blood glucose measurements in a variety of cultures, from the sweet potato farmers of the New Guinea highlands to the arctic Inuit hunters. Here is what Otto Schaefer, director of the Northern Medical Research Unit at Charles Camsell hospital in Edmonton, Canada, had to say about the Inuit in the excellent book Western Diseases (Trowell and Burkitt, 1981):
Monday, January 30, 2012
Paleo Diet Article in Sound Consumer
I recently wrote an article for my local natural foods grocery store, PCC, about the "Paleolithic" diet. You can read it online here. I explain the basic rationale for Paleo diets, some of the scientific support behind it, and how it can be helpful for people with certain health problems. I focused in particular on the research of Dr. Staffan Lindeberg at the University of Lund, who has studied non-industrial populations using modern medical techniques and also conducted clinical diet trials using the Paleo diet.
Wednesday, February 17, 2016
What I Eat
People often ask me what I eat. I've been reluctant to share, because it feels egocentric and I'm a private person by nature. I also don't want people to view my diet as a universal prescription for others. But in the end, as someone who shares my opinions about nutrition, it's only fair that I answer the question. So here we go.
In my food choices, I try to strike a balance between nutrition, cost, time efficiency, animal welfare, pleasure, and environmental impact. I'm the chef of my household of two, and I cook two meals a day, almost every day, typically from single ingredients. I prefer organic, but I don't insist on it.
My diet changes seasonally because I grow much of my own food. This started out with vegetables, but recently has expanded to staple foods such as potatoes, flour corn, and winter squash. I also have a small flock of laying hens that turn table scraps, bugs, grass, and chicken feed into delicious eggs.
The primary guiding principle of my diet is to eat somewhere between a "Paleolithic"-style diet and a traditional agricultural/horticultural diet. I think of it as a broad ancestral diet. Because it's partially inspired by agricultural/horticultural diets, starch is the main calorie source.
My meals are organized around three food groups: a protein, a starch, and vegetables/fruit. If any of those three are missing, the meal doesn't feel complete. I'll start with those categories and move on from there.
In my food choices, I try to strike a balance between nutrition, cost, time efficiency, animal welfare, pleasure, and environmental impact. I'm the chef of my household of two, and I cook two meals a day, almost every day, typically from single ingredients. I prefer organic, but I don't insist on it.
 |
| Eggs from my hens |
The primary guiding principle of my diet is to eat somewhere between a "Paleolithic"-style diet and a traditional agricultural/horticultural diet. I think of it as a broad ancestral diet. Because it's partially inspired by agricultural/horticultural diets, starch is the main calorie source.
My meals are organized around three food groups: a protein, a starch, and vegetables/fruit. If any of those three are missing, the meal doesn't feel complete. I'll start with those categories and move on from there.
Saturday, November 20, 2010
Glucose Tolerance in Non-industrial Cultures
Background
Glucose is the predominant blood sugar and one of the body's two main fuel sources (the other is fatty acids). Glucose, in one form or another, is also the main form of digestible dietary carbohydrate in nearly all human diets. Starch is made of long chains of glucose molecules, which are rapidly liberated and absorbed during digestion. Sucrose, or table sugar, is made of one glucose and one fructose molecule, which are separated before absorption.
Blood glucose is essential for life, but it can also be damaging if there is too much of it. Therefore, the body tries to keep it within a relatively tight range. Normal fasting glucose is roughly between 70 and 90 mg/dL*, but in the same individual it's usually within about 5 mg/dL on any given day. Sustained glucose above 160 mg/dL or so causes damage to multiple organ systems. Some people would put that number closer to 140 mg/dL.
The amount of glucose contained in a potato far exceeds the amount contained in the blood, so if all that glucose were to enter the blood at once, it would lead to a highly damaging blood glucose level. Fortunately, the body has a hormone designed to keep this from happening: insulin. Insulin tells cells to internalize glucose from the blood, and suppresses glucose release by the liver. It's released by the pancreas in response to eating carbohydrate, and protein to a lesser extent. The amount of insulin released is proportional to the amount of carbohydrate ingested, so that glucose entering the blood is cleared before it can accumulate.
Insulin doesn't clear all the glucose as it enters the bloodstream, however. Some of it does accumulate, leading to a spike in blood glucose. This usually doesn't exceed 130 mg/dL in a truly healthy person, and even if it approaches that level it's only briefly. However, diabetics have reduced insulin signaling, and eating a typical meal can cause their glucose to exceed 300 mg/dL due to reduced insulin action and/or insulin secretion. In affluent nations, this is typically due to type II diabetes, which begins as insulin resistance, a condition in which insulin is actually higher than normal but cells fail to respond to it. The next step is the failure of insulin-secreting beta cells, which is what generally precipitates actual diabetes.
The precursor to diabetes is called glucose intolerance, or pre-diabetes. In someone with glucose intolerance, blood glucose after a typical meal will exceed that of a healthy person, but will not reach the diabetic range (a common definition of diabetes is 200 mg/dL or higher, 2 hours after ingesting 75g of glucose). Glucose tolerance refers to a person's ability to control blood glucose when challenged with dietary glucose, and can be used in some contexts as a useful predictor of diabetes risk and general metabolic health. Doctors use the oral glucose tolerance test (OGTT), which involves drinking 60-100g glucose and measuring blood glucose after one or two hours, to determine glucose tolerance.
Why do we care about glucose tolerance in non-industrial cultures?
One of the problems with modern medical research is that so many people in our culture are metabolically sick that it can be difficult to know if what we consider "normal" is really normal or healthy in the broader sense. Non-industrial cultures allow us to examine what the human metabolism is like in the absence of metabolic disease. I admit this rests on certain assumptions, particularly that these people aren't sick themselves. I don't think all non-industrial cultures are necessarily healthy, but I'm going to stick with those that research has shown have an exceptionally low prevalence of diabetes (by Western standards) and other "diseases of civilization" for the purposes of this post.
Here's the question I really want to answer in this post: do healthy non-industrial cultures with a very high carbohydrate intake have an excellent glucose tolerance, such that their blood glucose doesn't rise to a high level, or are they simply resistant to the damaging effects of high blood glucose?
The data
I'm going to start with an extreme example. In the 1960s, when it was fashionable to study non-industrial cultures, researchers investigated the diet and health of a culture in Tukisenta, in the highlands of Papua New Guinea. The eat practically nothing but sweet potatoes, and their typical daily fare is 94.6 percent carbohydrate. Whether or not you believe that exact number, their diet was clearly extraordinarily high in carbohydrate. They administered 100g OGTTs and measured blood glucose at one hour, which is a very stringent OGTT. They compared the results to those obtained in the 1965 Tecumseh study (US) obtained by the same method. Here's what they found (1):
Compared to Americans, in Tukisenta they had an extraordinary glucose tolerance at all ages. At one hour, their blood glucose was scarcely above normal fasting values, and glucose tolerance only decreased modestly with age. In contrast, in Americans over 50 years old, the average one-hour value was around 180 mg/dL!
Now let's take a look at the African Bantu in the Lobaye region of the Central African Republic. The Bantu are a large ethnic group who primarily subsist on a diverse array of starchy foods including grains, beans, plantains and root crops. One hour after a 100g OGTT, their blood glucose was 113 mg/dL, compared to 139 mg/dL in American controls (2). Those numbers are comparable to what investigators found in Tukisenta, and indicate an excellent glucose tolerance in the Bantu.
In South America, different investigators studied a group of native Americans in central Brazil that subsist primarily on cassava (a starchy root crop) and freshwater fish. Average blood glucose one hour after a 100g OGTT was 94 mg/dl, and only 2 out of 106 people tested had a reading over 160 mg/dL (both were older women) (Western Diseases: Their Emergence and Prevention, p. 149). Again, that indicates a phenomenal glucose tolerance by Western standards.
I have to conclude that high-carbohydrate non-industrial cultures probably don't experience damaging high blood glucose levels, because their glucose tolerance is up to the task of shuttling a huge amount of glucose out of the bloodstream before that happens.
Not so fast...
Now let's turn our attention to another study that may throw a wrench in the gears. A while back, I found a paper containing OGTT data for the !Kung San (also called the Bushmen), a hunter-gatherer group living in the Kalahari desert of Africa. I reported in an earlier post that they had a good glucose tolerance. When I revisited the paper recently, I realized I had misread it and in fact, their glucose tolerance was actually pretty poor.
Investigators administered a 50g OGTT, half what the other studies used. At one hour, the San had blood glucose readings of 169 mg/dL, compared to 142 mg/dL in Caucasian controls (3)! I suspect a 100g OGTT would have put them close to the diabetic range.
Wait a minute, these guys are hunter-gatherers living the ancestral lifestyle; aren't they supposed to be super healthy?? First of all, like many hunter-gatherer groups the San are very small people: the men in this study were only 46 kg (101 lbs). The smaller you are, the more a given amount of carbohydrate will raise your blood glucose. Also, while I was mulling this over, I recalled a discussion where non-diabetic people were discussing their 'diabetic' OGTT values while on a low-carbohydrate diet. Apparently, carbohydrate refeeding for a few days generally reverses this and allows a normal OGTT in most people. It turns out this effect has been known for the better part of a century.
So what were the San eating? The study was conducted in October of 1970. The San diet changes seasonally, however their main staple food is the mongongo nut, which is mostly fat and which is available year-round (according to The !Kung San: Men, Women and Work in a Foraging Society). Their carbohydrate intake is generally low by Western standards, and at times of the year it is very low. This varies by the availability of other foods, but they generally don't seem to relish the fibrous starchy root crops that are available in the area, as they mostly eat them when other food is scarce. Jean-Louis Tu has posted a nice analysis of the San diet on BeyondVeg (4). Here's a photo of a San man collecting mongongo nuts from The !Kung San: Men, Women and Work in a Foraging Society:
What did the authors of the OGTT study have to say about their diet? Acknowledging that prior carbohydrate intake may have played a role in the OGTT results of the San, they made the following remark:
You can draw your own conclusions, but I think the high OGTT result of the San probably reflect a low habitual carbohydrate intake, and not pre-diabetes. I have a very hard time believing that this culture wasn't able to handle the moderate amount of carbohydrate in their diet effectively, as observers have never described diabetic complications among them.
Putting it all together
This brings me to my hypothesis. I think a healthy human body is extraordinarily flexible in its ability to adapt to a very broad range of carbohydrate intakes, and adjusts glucose tolerance accordingly to maintain carbohydrate handling in a healthy range. In the context of a healthy diet and lifestyle (from birth), I suspect that nearly anyone can adjust to a very high carbohydrate intake without getting dangerous blood glucose spikes. A low carbohydrate intake leads to impaired glucose handling and better fat handling, as one would expect. This can show up as impaired glucose tolerance or even 'diabetes' on an OGTT, but that does not necessarily reflect a pathological state in my opinion.
Every person is different based on lifestyle, diet, personal history and genetics. Not everyone in affluent nations has a good glucose tolerance, and some people will never be able to handle starch effectively under any circumstances. The best way to know how your body reacts to carbohydrate is to test your own post-meal blood glucose using a glucose meter. They are inexpensive and work well. For the most informative result, eat a relatively consistent amount of carbohydrate for a week to allow your body to adapt, then take a glucose measurement 1 and 2 hours after a meal. If you don't eat much carbohydrate, eating a potato might make you think you're diabetic, whereas after a week of adaptation you may find that a large potato does not spike your blood glucose beyond the healthy range.
Exercise is a powerful tool for combating glucose intolerance, as it increases the muscles' demand for glucose, causing them to transport it out of the blood greedily after a meal. Any exercise that depletes muscle glycogen should be effective.
* Assuming a typical carbohydrate intake. Chris Kresser recently argued, based on several studies, that true normal fasting glucose for a person eating a typical amount of carbohydrate is below 83 mg/dL. Low-carbohydrate eating may raise this number, but that doesn't necessarily indicate a pathological change. High-carbohydrate cultures such as the Kitavans, Aymara and New Guineans tend to have fasting values in the low 60s to low 70s. I suspect that a very high carbohydrate intake generally lowers fasting glucose in healthy people. That seems to be the case so far for Chris Voigt, on his diet of 20 potatoes a day. Stay tuned for an interview with Mr. Voigt in early December.
Glucose is the predominant blood sugar and one of the body's two main fuel sources (the other is fatty acids). Glucose, in one form or another, is also the main form of digestible dietary carbohydrate in nearly all human diets. Starch is made of long chains of glucose molecules, which are rapidly liberated and absorbed during digestion. Sucrose, or table sugar, is made of one glucose and one fructose molecule, which are separated before absorption.
Blood glucose is essential for life, but it can also be damaging if there is too much of it. Therefore, the body tries to keep it within a relatively tight range. Normal fasting glucose is roughly between 70 and 90 mg/dL*, but in the same individual it's usually within about 5 mg/dL on any given day. Sustained glucose above 160 mg/dL or so causes damage to multiple organ systems. Some people would put that number closer to 140 mg/dL.
The amount of glucose contained in a potato far exceeds the amount contained in the blood, so if all that glucose were to enter the blood at once, it would lead to a highly damaging blood glucose level. Fortunately, the body has a hormone designed to keep this from happening: insulin. Insulin tells cells to internalize glucose from the blood, and suppresses glucose release by the liver. It's released by the pancreas in response to eating carbohydrate, and protein to a lesser extent. The amount of insulin released is proportional to the amount of carbohydrate ingested, so that glucose entering the blood is cleared before it can accumulate.
Insulin doesn't clear all the glucose as it enters the bloodstream, however. Some of it does accumulate, leading to a spike in blood glucose. This usually doesn't exceed 130 mg/dL in a truly healthy person, and even if it approaches that level it's only briefly. However, diabetics have reduced insulin signaling, and eating a typical meal can cause their glucose to exceed 300 mg/dL due to reduced insulin action and/or insulin secretion. In affluent nations, this is typically due to type II diabetes, which begins as insulin resistance, a condition in which insulin is actually higher than normal but cells fail to respond to it. The next step is the failure of insulin-secreting beta cells, which is what generally precipitates actual diabetes.
The precursor to diabetes is called glucose intolerance, or pre-diabetes. In someone with glucose intolerance, blood glucose after a typical meal will exceed that of a healthy person, but will not reach the diabetic range (a common definition of diabetes is 200 mg/dL or higher, 2 hours after ingesting 75g of glucose). Glucose tolerance refers to a person's ability to control blood glucose when challenged with dietary glucose, and can be used in some contexts as a useful predictor of diabetes risk and general metabolic health. Doctors use the oral glucose tolerance test (OGTT), which involves drinking 60-100g glucose and measuring blood glucose after one or two hours, to determine glucose tolerance.
Why do we care about glucose tolerance in non-industrial cultures?
One of the problems with modern medical research is that so many people in our culture are metabolically sick that it can be difficult to know if what we consider "normal" is really normal or healthy in the broader sense. Non-industrial cultures allow us to examine what the human metabolism is like in the absence of metabolic disease. I admit this rests on certain assumptions, particularly that these people aren't sick themselves. I don't think all non-industrial cultures are necessarily healthy, but I'm going to stick with those that research has shown have an exceptionally low prevalence of diabetes (by Western standards) and other "diseases of civilization" for the purposes of this post.
Here's the question I really want to answer in this post: do healthy non-industrial cultures with a very high carbohydrate intake have an excellent glucose tolerance, such that their blood glucose doesn't rise to a high level, or are they simply resistant to the damaging effects of high blood glucose?
The data
I'm going to start with an extreme example. In the 1960s, when it was fashionable to study non-industrial cultures, researchers investigated the diet and health of a culture in Tukisenta, in the highlands of Papua New Guinea. The eat practically nothing but sweet potatoes, and their typical daily fare is 94.6 percent carbohydrate. Whether or not you believe that exact number, their diet was clearly extraordinarily high in carbohydrate. They administered 100g OGTTs and measured blood glucose at one hour, which is a very stringent OGTT. They compared the results to those obtained in the 1965 Tecumseh study (US) obtained by the same method. Here's what they found (1):
Compared to Americans, in Tukisenta they had an extraordinary glucose tolerance at all ages. At one hour, their blood glucose was scarcely above normal fasting values, and glucose tolerance only decreased modestly with age. In contrast, in Americans over 50 years old, the average one-hour value was around 180 mg/dL!Now let's take a look at the African Bantu in the Lobaye region of the Central African Republic. The Bantu are a large ethnic group who primarily subsist on a diverse array of starchy foods including grains, beans, plantains and root crops. One hour after a 100g OGTT, their blood glucose was 113 mg/dL, compared to 139 mg/dL in American controls (2). Those numbers are comparable to what investigators found in Tukisenta, and indicate an excellent glucose tolerance in the Bantu.
In South America, different investigators studied a group of native Americans in central Brazil that subsist primarily on cassava (a starchy root crop) and freshwater fish. Average blood glucose one hour after a 100g OGTT was 94 mg/dl, and only 2 out of 106 people tested had a reading over 160 mg/dL (both were older women) (Western Diseases: Their Emergence and Prevention, p. 149). Again, that indicates a phenomenal glucose tolerance by Western standards.
I have to conclude that high-carbohydrate non-industrial cultures probably don't experience damaging high blood glucose levels, because their glucose tolerance is up to the task of shuttling a huge amount of glucose out of the bloodstream before that happens.
Not so fast...
Now let's turn our attention to another study that may throw a wrench in the gears. A while back, I found a paper containing OGTT data for the !Kung San (also called the Bushmen), a hunter-gatherer group living in the Kalahari desert of Africa. I reported in an earlier post that they had a good glucose tolerance. When I revisited the paper recently, I realized I had misread it and in fact, their glucose tolerance was actually pretty poor.
Investigators administered a 50g OGTT, half what the other studies used. At one hour, the San had blood glucose readings of 169 mg/dL, compared to 142 mg/dL in Caucasian controls (3)! I suspect a 100g OGTT would have put them close to the diabetic range.
Wait a minute, these guys are hunter-gatherers living the ancestral lifestyle; aren't they supposed to be super healthy?? First of all, like many hunter-gatherer groups the San are very small people: the men in this study were only 46 kg (101 lbs). The smaller you are, the more a given amount of carbohydrate will raise your blood glucose. Also, while I was mulling this over, I recalled a discussion where non-diabetic people were discussing their 'diabetic' OGTT values while on a low-carbohydrate diet. Apparently, carbohydrate refeeding for a few days generally reverses this and allows a normal OGTT in most people. It turns out this effect has been known for the better part of a century.
So what were the San eating? The study was conducted in October of 1970. The San diet changes seasonally, however their main staple food is the mongongo nut, which is mostly fat and which is available year-round (according to The !Kung San: Men, Women and Work in a Foraging Society). Their carbohydrate intake is generally low by Western standards, and at times of the year it is very low. This varies by the availability of other foods, but they generally don't seem to relish the fibrous starchy root crops that are available in the area, as they mostly eat them when other food is scarce. Jean-Louis Tu has posted a nice analysis of the San diet on BeyondVeg (4). Here's a photo of a San man collecting mongongo nuts from The !Kung San: Men, Women and Work in a Foraging Society:
What did the authors of the OGTT study have to say about their diet? Acknowledging that prior carbohydrate intake may have played a role in the OGTT results of the San, they made the following remark:a retrospective dietary history (M. J. Konner, personal communication, 1971) indicated that the [San], in fact, consumed fairly large amounts of carbohydrate-rich vegetable food during the week before testing.However, the dietary history was not provided, nor has it been published, so we have no way to assess the statement's accuracy or what was meant by "fairly large amounts of carbohydrate-rich vegetable food." Given the fact that the San diet typically ranges from moderately low to very low in carbohydrate, I suspect they were not getting much carbohydrate as a percentage of calories. Looking at the nutritional value of the starchy root foods they typically eat in appendix D of The !Kung San: Men, Women and Work in a Foraging Society, they are fibrous and most contain a low concentration of starch compared to a potato for example. The investigators may have been misled by the volume of these foods eaten, not realizing that they are not as rich in carbohydrate as the starchy root crops they are more familiar with.
You can draw your own conclusions, but I think the high OGTT result of the San probably reflect a low habitual carbohydrate intake, and not pre-diabetes. I have a very hard time believing that this culture wasn't able to handle the moderate amount of carbohydrate in their diet effectively, as observers have never described diabetic complications among them.
Putting it all together
This brings me to my hypothesis. I think a healthy human body is extraordinarily flexible in its ability to adapt to a very broad range of carbohydrate intakes, and adjusts glucose tolerance accordingly to maintain carbohydrate handling in a healthy range. In the context of a healthy diet and lifestyle (from birth), I suspect that nearly anyone can adjust to a very high carbohydrate intake without getting dangerous blood glucose spikes. A low carbohydrate intake leads to impaired glucose handling and better fat handling, as one would expect. This can show up as impaired glucose tolerance or even 'diabetes' on an OGTT, but that does not necessarily reflect a pathological state in my opinion.
Every person is different based on lifestyle, diet, personal history and genetics. Not everyone in affluent nations has a good glucose tolerance, and some people will never be able to handle starch effectively under any circumstances. The best way to know how your body reacts to carbohydrate is to test your own post-meal blood glucose using a glucose meter. They are inexpensive and work well. For the most informative result, eat a relatively consistent amount of carbohydrate for a week to allow your body to adapt, then take a glucose measurement 1 and 2 hours after a meal. If you don't eat much carbohydrate, eating a potato might make you think you're diabetic, whereas after a week of adaptation you may find that a large potato does not spike your blood glucose beyond the healthy range.
Exercise is a powerful tool for combating glucose intolerance, as it increases the muscles' demand for glucose, causing them to transport it out of the blood greedily after a meal. Any exercise that depletes muscle glycogen should be effective.
* Assuming a typical carbohydrate intake. Chris Kresser recently argued, based on several studies, that true normal fasting glucose for a person eating a typical amount of carbohydrate is below 83 mg/dL. Low-carbohydrate eating may raise this number, but that doesn't necessarily indicate a pathological change. High-carbohydrate cultures such as the Kitavans, Aymara and New Guineans tend to have fasting values in the low 60s to low 70s. I suspect that a very high carbohydrate intake generally lowers fasting glucose in healthy people. That seems to be the case so far for Chris Voigt, on his diet of 20 potatoes a day. Stay tuned for an interview with Mr. Voigt in early December.
Tuesday, February 5, 2013
Why Do We Eat? A Neurobiological Perspective. Part VIII
In the (probably) last post of this series, I'll take the pieces that I've gradually outlined in previous posts, and put them together into a big-picture, common-sense framework for thinking about human eating behavior, and why we eat more today than ever before.
Why is Eating Behavior Regulated?
Let's start at the most fundamental level. To be competitive in a natural environment, organisms must find rational ways of interacting with their surroundings to promote survival and reproduction. One of the most important elements of survival is the acquisition of energy and chemical building blocks, either by photosynthesis, or (in the case of animals) eating other organisms. This imperative drove the evolution of rational food seeking behaviors long before the emergence of humans, mammals, reptiles, amphibians, fish, worms, and even eukaryotes (organisms with nuclei).
Why is Eating Behavior Regulated?
Let's start at the most fundamental level. To be competitive in a natural environment, organisms must find rational ways of interacting with their surroundings to promote survival and reproduction. One of the most important elements of survival is the acquisition of energy and chemical building blocks, either by photosynthesis, or (in the case of animals) eating other organisms. This imperative drove the evolution of rational food seeking behaviors long before the emergence of humans, mammals, reptiles, amphibians, fish, worms, and even eukaryotes (organisms with nuclei).
Friday, November 29, 2013
Friday, May 30, 2014
Wednesday, December 3, 2014
Is Meat Unhealthy? Part IV
In this post, I'll address the question: does eating meat contribute to weight gain?
Non-industrial cultures
I'll get right to the point: humans living in a non-industrialized setting tend to be lean, regardless of how much meat they eat. This applies equally to hunter-gatherers, herders, and farmers.
One of the leanest populations I've encountered in my reading is the 1960s Papua New Guinea highland farmers of Tukisenta. They ate a nearly vegan diet composed almost exclusively of sweet potatoes, occasionally punctuated by feasts including large amounts of pork. On average, they ate very little animal food. Visiting researchers noted that the residents of Tukisenta were "muscular and mostly very lean", and did not gain fat with age (1, Western Diseases, Trowell and Burkitt, 1981).
Another remarkably lean hunter-gatherer population is the !Kung San foragers of the Kalahari desert. The !Kung San are so lean that many of them would be considered underweight on the standard body mass index scale (BMI less than 18.5). Average BMI doesn't exceed 20 in any age category (The !Kung San, Richard Lee, 1979). Is this simply because they're starving? It is true that they don't always get as much food as they'd like, but on most days, they have the ability to gather more food than they need. The fact that they are able to reproduce normally suggests that they aren't starving. Richard Lee's detailed work with the !Kung San indicates that approximately 40 percent of their calories came from animal foods during his study period in the 1960s. This was mostly meat, with occasional eggs when available.
Non-industrial cultures
I'll get right to the point: humans living in a non-industrialized setting tend to be lean, regardless of how much meat they eat. This applies equally to hunter-gatherers, herders, and farmers.
One of the leanest populations I've encountered in my reading is the 1960s Papua New Guinea highland farmers of Tukisenta. They ate a nearly vegan diet composed almost exclusively of sweet potatoes, occasionally punctuated by feasts including large amounts of pork. On average, they ate very little animal food. Visiting researchers noted that the residents of Tukisenta were "muscular and mostly very lean", and did not gain fat with age (1, Western Diseases, Trowell and Burkitt, 1981).
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| !Kung man gathering mongongo fruit/nuts. From The !Kung San, by Richard B. Lee. |
Saturday, November 26, 2011
A Brief Response to Taubes's Food Reward Critique, and a Little Something Extra
It appears Gary Taubes has completed his series critiquing the food reward hypothesis of obesity (1). I have to hand it to him, it takes some cojones to critique an entire field of research, particularly when you have no scientific background in it, and have evidently not read any of the scientific literature on it. As of 2012, a Google Scholar search for the terms “food reward” and “obesity” turned up 2,790 papers.
The food reward hypothesis of obesity states that the reward and palatability value of food influence body fatness, and excess reward/palatability can promote body fat accumulation. If we want to test the hypothesis, the most direct way is to find experiments in which 1) the nutritional qualities of the experimental diet groups are kept the same or at least very similar, 2) some aspect of diet reward/palatability differs, and 3) changes in body fat/weight are measured (for example, 2, 3, 4, 5, 6, 7, 8, 9). In these experiments the hypothesis has both arms and one leg tied behind its back, because the most potent reward factors (energy density, sugar, fat) have nutritional value and therefore experiments that modify these cannot be tightly controlled for nutritional differences. Yet even with this severe disadvantage, the hypothesis is consistently supported by the scientific evidence. Taubes repeatedly stated in his series that controlled studies like these have not been conducted, apparently basing this belief on a 22-year-old review paper by Dr. Israel Ramirez and colleagues that does not contain the word 'reward' (10).
Another way to test the hypothesis is to see if people with higher food reward sensitivity (due to genetics or other factors) tend to gain more fat over time (for example, 11, 12, 13, 14, 15, 16). In addition, studies that have examined the effect of palatability/reward on food intake in a controlled manner are relevant (17, 18, 19, 20, 21, 22), as are studies that have identified some of the mechanisms by which these effects occur (reviewed in 23). Even if not all of the studies are perfect, at some point, one has to acknowledge that there are a lot of mutually buttressing lines of evidence here. It is notable that virtually none of these studies appeared in Taubes's posts, and he appeared unaware of them.
The food reward hypothesis of obesity states that the reward and palatability value of food influence body fatness, and excess reward/palatability can promote body fat accumulation. If we want to test the hypothesis, the most direct way is to find experiments in which 1) the nutritional qualities of the experimental diet groups are kept the same or at least very similar, 2) some aspect of diet reward/palatability differs, and 3) changes in body fat/weight are measured (for example, 2, 3, 4, 5, 6, 7, 8, 9). In these experiments the hypothesis has both arms and one leg tied behind its back, because the most potent reward factors (energy density, sugar, fat) have nutritional value and therefore experiments that modify these cannot be tightly controlled for nutritional differences. Yet even with this severe disadvantage, the hypothesis is consistently supported by the scientific evidence. Taubes repeatedly stated in his series that controlled studies like these have not been conducted, apparently basing this belief on a 22-year-old review paper by Dr. Israel Ramirez and colleagues that does not contain the word 'reward' (10).
Another way to test the hypothesis is to see if people with higher food reward sensitivity (due to genetics or other factors) tend to gain more fat over time (for example, 11, 12, 13, 14, 15, 16). In addition, studies that have examined the effect of palatability/reward on food intake in a controlled manner are relevant (17, 18, 19, 20, 21, 22), as are studies that have identified some of the mechanisms by which these effects occur (reviewed in 23). Even if not all of the studies are perfect, at some point, one has to acknowledge that there are a lot of mutually buttressing lines of evidence here. It is notable that virtually none of these studies appeared in Taubes's posts, and he appeared unaware of them.
Tuesday, April 15, 2014
Garden Update: A Banner Year
Things are warming up here in Seattle and the flowers are blooming. I just planted my first crops of the year-- potatoes and strawberries.
2013 was a banner year for my 500-square-foot urban vegetable garden, including my first experience growing and processing a grain. I never got around to posting about it last year-- so here it is.
Interbay mulch technique
In the fall of 2012, I tried a new technique for improving the soil called "Interbay mulching". This is a variation on sheet mulching, which involves placing uncomposted organic matter directly onto the garden soil in fall and letting it compost until the next growing season. To Interbay mulch, you simply cover your sheet mulch with burlap. This keeps everything moist, protects earthworms from bird predation so they can munch freely, and suppresses weeds. I used leaves (carbon) and spent coffee grounds from a local coffee shop (nitrogen) for my organic matter.
When I pulled back the burlap last spring, I was initially disappointed. The coffee grounds had disappeared completely, but there was still a lot of leaf matter left on the soil, indicating that it had only partially composted. However, I later decided that it had worked well, because the soil structure underneath was improved and it seemed to be enriched with significant organic matter as well as a large population of fat earthworms. The mulch suppressed weeds remarkably well, and the beds remained mostly clean for the rest of the season.
Those observations, combined with huge yields from the mulched beds, convinced me that it was worthwhile.
New tools
2013 was a banner year for my 500-square-foot urban vegetable garden, including my first experience growing and processing a grain. I never got around to posting about it last year-- so here it is.
Interbay mulch technique
.JPG) |
| The bed on the right has been mulched with leaves, spent coffee grounds, and burlap sacks ($1/sack at the local hardware store). The beds on the left were planted with a rye-clover-vetch-pea cover crop. Paths are mulched with wood chips. |
When I pulled back the burlap last spring, I was initially disappointed. The coffee grounds had disappeared completely, but there was still a lot of leaf matter left on the soil, indicating that it had only partially composted. However, I later decided that it had worked well, because the soil structure underneath was improved and it seemed to be enriched with significant organic matter as well as a large population of fat earthworms. The mulch suppressed weeds remarkably well, and the beds remained mostly clean for the rest of the season.
Those observations, combined with huge yields from the mulched beds, convinced me that it was worthwhile.
New tools
Thursday, July 12, 2012
Interview with Aitor Calero of Directo al Paladar
Aitor Calero writes for the popular Spanish cooking and nutrition blog, Directo al Paladar ("straight to the palate"). We did a written interview a while back, and he agreed to let me post the English version on my blog. The Spanish version is here and here.
Without further ado, here it is:
Without further ado, here it is:
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