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:
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).


Chris Sturdy said...

I just had an orange sweet potato/yam tonight with dinner (I think this was a sweet potato; not too huge the way yams often are). I really like them but can't imagine eating them as 90% of of my diet! Thanks for the interesting post. I'll have to get a copy of that book.

Ed said...

Yet another post without traditional grain preparation recipes! :-) perhaps you can make up for that by telling us how the New Guineans prepared their sweet potatos? Any fermenting? I would assume they roasted them, at least.

Ed said...

With or without skin?

Me said...

Is there any possibility they were eating true yams (which are unrelated to sweet potatoes or what we in the U.S. sometimes call "yams")?

stephen said...

Sweet potato is known here in New Zealand as "kumara" and widely eaten. They were a very important staple for New Zealand Māori, although definitely not the only starch. When Māori came here, they found that most of New Zealand was too cold for taro or yams but kumara can be grown with care in many places. The only significant other sources of starch I know of in the traditional diet were fern root or palm hearts (maybe some taro in the far north). The old varieties were abandoned shortly after contact with Europeans as American whalers introduced superior strains -- a few people still grow the old kinds but you can't get them in shops.

We seem to get three kinds here. A purple-skinned, yellow-fleshed one that reminds me of chestnuts in taste; a russet-skinned one with orange flesh that's moister and sweeter; and a white skinned one that's also orange and moist inside.

A local cooking tip is to bake at a low temperature for a long time. After an hour or so at 150 C the starches undergo some kind of reaction and start turning to sugars and the flesh is noticeably sweeter. Traditional earth-oven (umu/hangi) techniques would produce this effect too, since they basically slowly steam with a little smoke flavour.

Ed: I don't know what they do in New Guinea, but here they are scrubbed but not peeled, wrapped in foil or leaves, and cooked in an earth oven ("hāngī"). That is, you have a pit lined with dense stones, a fire is built on the stones, the embers and ash are swept aside when the stones are really hot, then wrapped food is placed on the stones, and the pit is filled in with earth and left for a few hours before you dig it up. Food steams slowly -- it's delicious. Pretty much anything can be cooked this way. No fermentation process that I know of.

I have seen warnings to be careful about cutting out any discoloured skin and surrounding flesh. The bacteria and fungi that cause black spots etc produce nasty carcinogens.

Nutritionists here often recommend sweet potatoes because of their GI.

I often have a few sitting around at work because in a pinch you can cook one in a microwave oven in a few minutes and get a pretty tasty healthy snack.

Tucker Goodrich said...

We also had sweet potatoes for dinner. (Fried in tallow.)

I'm interested in why you want to examine African consumption of potatoes, as I understood that the potato was originally of South American provenance. Wouldn't that be the place to study consumption patterns?

Dave Riley said...

I used to grow them and love them. But stopped eating them because I became diabetic and they are high carb.If I can go back without consequence to eating them, I'd be delighted.

I now substitute chayote, egg plant and pumpkin to get that bulk feel in a dish.

And while I have no desire to go back to rice, and other grains in a big way -- I'm pragmatic and would love to be opportunistic.

Anonymous said...

Hello Stephan(and fellow commenters),

I've read that sweet potatoes contain goitrogens which can suppress the function of the thyroid gland resulting in a goitre. Are the goitrogens removed when cooking(i.e.- baking in the oven for an hour or so)?
I consume plenty of sweet potatoes in a given week(5 or more) and was wondering if maybe I should cut back. By the way, this is a wonderful blog. Thanks for all the great info.

Anonymous said...

Great post Stephan on my favourite starch!

I'm a Kiwi like Stephen and love our kumara, with the golden kumara being my favourite (although I'm quite partial to the smaller purple 'kumara sweeties'). A favourite recipe is to use the stock from a roast and cook the kumara in this (I normally add purple onion and parsnip too). Once soft, everything goes in the blender and the soup that comes from this is stunning - particularly if you have left the bones in with the initial cooking.

David L said...

It is important to understand the history of the sweet potato in Polynesia. It blew across the region like wildfire, some say beginning in 700 AD. All Pacific islands have fertility festivals based around the introduction of yams to their cultures, and the coincident rise in their populations.

So whatever was the traditional diet, it was overwhelmed by the sweet potato. That suggests that it provided a substantial nutritional benefit over the traditional diet. Of course, this assumption is wrong in the case of cereal grains. Introduction of grains in hunter-gatherer societies markedly diminished the physical well-being of the populace, but it allowed for bigger armies, which was what was more important at the time.

Dave Riley said...

Its' a bit of a misnomer to compare the diet of the short stocky Melanesians of New Guinea, to the much larger built Polynesians. A better indication would be to log the transition impact of Western diets on both food cultures that lead to the developing prevalence of diseases like diabetes. It may not be so simple as simply a change in diet but it needs to be considered that what may impact so well on the Melanesians in terms of health consequences may not be the same in other conditions.
The post begs the question that if a diet so high in sweet potato is so good, why isn't it replicated in demonstrable form?
The Irish lived on potatoes and milk but they suffered for it gravely.And if sweet potato is the clincher vegetable, then studies in its home neighborhood -- e Yucatán Peninsula of Mexico -- Impomea Central -- should suggest similar conslusions as Burkitt's. But do they?

Todd Hargrove said...

Have you ever had Japanese sweet potatoes? They are available at the Seattle Whole Foods seasonally. They look like the red yams but taste more like the yellow sweet potatoes. They are the tastiest variety of sweet potato I have ever had.

Gord said...

I've been reading your blog for about a year now and have enjoyed it very much. It's getting more interesting all the time. You provide a unique voice in providing research to back up the radical claims.

As for the Yam/Sweet Potato thing: most North Americans have never seen or tasted a yam. Almost exclusively, we have sweet potatoes available to us.

And they are very different things. Useful links which explain the difference clearly...

Library of Congress: http://www.loc.gov/rr/scitech/mysteries/sweetpotato.html

Texas A&M University: http://aggie-horticulture.tamu.edu/archives/parsons/vegetables/sweetpotato.html

The Wikipedia articles on each offer much more detailed information for the interested...

praguestepchild said...

Wikipedia says that sweet potatoes were introduced 300 years ago, replacing taro. That doesn't seem long enough for a food to pass the 'traditional' test, as say miso or olive oil does, at least in my mind.

It also says "Agriculture was independently developed in the New Guinea highlands around 7,000 BC, making it one of the few areas of original plant domestication in the world." So they might just be better adapted to high starch neolithic diet than, say, Northern Europeans. Or it could be that the sweet potatoes work well for them in the overall context: plenty of exercise, occasional SFA/protein feasts, high altitude living, proper mineral intake, high social cohesion, who knows?

Matt Stone said...

Thanks Stephan. I've always appreciated the work of Trowell and Burkitt. Most seem to resent them, as a great deal of our low-fat, high-carbohydrate, high-fiber dogma that dominates government nutrition standards stemmed from their work. I ain't mad at 'em though. Here are some great quotes from one of their other works...

Burkitt, Denis, Hugh Trowell, and Kenneth Heaton. Dietary Fibre, Fibre-Depleted Foods and Disease. Academic Press: London, 1985.

p. 152 Thus, diverticular disease was almost unknown in 1900 but is now the most common disorder of the colon in Western man. This change happened in only 70 years, the traditional life span of man.

p. 210 “Shortly after this report, another German group, using personal interviews and even closer matching of controls, found that Crohn’s patients ate twice as much sugar as healthy people.”

p. 281 “It is of interest that diets high in fibre-rich cereals and tuberous vegetables tend to result in an improvement in basal blood glucoses.”

p. 401 “…consumption of fibre-free sucrose does considerably inflate energy intake and promotes weight gain. Fibre-depleted starch seems to have little or no effect on energy intake.”

praguestepchild said...

By traditional foods such as miso or olive oil I mean in their traditional context, which includes some genetics in my opinion. Sweet potatoes might be a traditional food for South Americans, but not really for New Guinea Highlanders, and even traditional foods in context still might not be optimal foods (perhaps the occasional salad might have helped prevent apparent osteoporosis in HG Inuit, vitamin K1 perhaps?).

Of course, it could be that the way they prepared taro just happened to be the healthiest way to prepare sweet potatoes (assuming they used the same method), and/or the nutritional profile was close enough or better to supersede taro in their diet.

Michael said...

We can measure the nutrient and toxin content of a food, and debate the health effects of each of its constituents until we're out of breath. But in the end, we still won't 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?

Good stuff! Quotes from Trowel and Burkitt are one of the hidden gems over at the WAPF website that I point people to when they want to insist that the "Weston Price Diet" is a low carb diet or that removing a good portion of the bran from certain grains before consumption is somehow antithetical to a healthy non-industrial diet.

Their work also contradicts the sometimes perceived official position of the WAPF which at times appears to ignore the high carbohydrate consuming groups that Price observed and reported on, though again you can find contradictory gems throughout their website.

And that is as it should be, since Price's work covers every macro-nutrient ratio under the sun.

Anonymous said...

For someone who is not metabolically challenged, it seems that sweet potatoes of some variety may be perfectly fine to eat. However, I am a diabetic and I know that any potato of any kind has a disastrous effect on my blood sugars.

Eric said...

Yum! Timely post as tonight on the menu I was planning for yams deep-fried in lard :)

Medjoub said...

@ Praguestepchild -

This is OT, but are you a Czech Republic resident? I just moved to Prague and am struggling to adapt to grocery/eating style. If you'd be willing, I'd love to exchange an email or two about your strategies...

chris said...

Tubers have a bit less protein than grains, and much less than legumes, and i don't really like the asparagine in potatoes.

Aaron said...

Someone eating lots and lots of the orange sweet potatoes would be getting ungodly amounts of vitamin a (b-carotene), not so sure this is a good thing (and we know your skin would tint to orange). I wish there were more of the white sweet potatoes by me (which would be less vitamin a).

Secondly, what about the AGE formation from baking? Even if it tastes better, boiling sweet potatoes would be a safer process.

Ned Kock said...

Thanks Stephan for this interesting analysis. I do think that sweet potatoes are healthy overall. Reading your post I was reminded a bit of the Okinawan diet:


However, I have one concern about looking into the habits of isolated populations and extrapolating from them. That is that food-related traits can evolve fast, in as little as 396 years or less:


There is also the possibility of a founder effect, which leads to similar results.

Unknown said...

BG reading above 160? That's already in the severe consequences category. I'd love to know how many had 1hr and 2hr post-prandial readings above 120. THAT would indicate something to observe, in children and adults.

The type of sweet potato eaten may have an effect, but I'd put my money on their overall daily activity keeping their insulin sensitivity high, and insulin resistance low.

Ned Kock said...

Cheryl, a BG reading of 160 or so is not really that abnormal:


SimonPure said...

According to Wikipedia Papua New Guinea entry:

"the sweet potato entered New Guinea having been introduced to the Moluccas from South America by the locally dominant colonial power, Portugal. The far higher crop yields from sweet potato gardens radically transformed traditional agriculture; sweet potato largely supplanted the previous staple, taro, and gave rise to a significant increase in population in the highlands."

Unknown said...

Ned, I read your post earlier this month. I understand spikes happen. The trouble, when it presents itself within the diabetic population, is when the average continues to trend up (or trend high). 160 and above are where the conditions for complications accumulate. It takes time, but when a physician says an average of 160 is acceptable, over time this causes an individual to have to take more meds, and heads toward beta cell cessation, insulin presription, and other complications of diabetes, including heart disease.

I don't care that it is not "abnormal" to see the readings. What I care about are the consequences of such. And, I do agree that there are many factors beyond 'control' that contribute to in range and out of range BG levels.

And as you say, if you can do something about it, please do. And, if despite best efforts BG remains out of range, then continue efforts to the best of your ability, without guilt or shame.

I appreciate the dialogue. Love to learn!

Mavis said...

Sweet potatoes are my favorite starch. Unfortunately, I just found out I have diabetes. Now I can have 1/4 cup of them at a time.

If it turns out to be the type I think it is (MODY 2), this kind of diabetes is 100% genetic, though it can be made worse or better depending on one's diet and insulin resistance.

Just putting in a plug, somewhat reluctantly (because I think, generally, environmental and dietary factors influencing genetic expression, metabolism, etc., trump genetic propensities for disease), for considering that, while we are all very much alike under the skin, it could be that some populations are blessed with fewer diabetic genes. I'd be prediabetic or diabetic on any diet.

praguestepchild said...

@Aaron, it is my understanding that tons of beta carotene is fine since it is just a precursor to Vit A, so our bodies will make as much as they need from it. Rather like Vit D and sunlight: tons of sunlight doesn't cause Vit D poisoning, we stop making it when we have enough.

You talk about turning orange as if that's a bad thing. I for one welcome our new pumpkin overlords.

Anne E said...

Dave, you mentioned that the "The Irish lived on potatoes and milk but they suffered for it gravely." But surely that was a political issue rather than a nutritional one? I am Irish and my understanding of the Irish diet pre-famine was that it consisted of potatoes (up to 14 lbs per day of a variety called lumper) and milk and very little occasional bacon. On that diet they were supposedly strong and healthy but I'd be interested to read otherwise. They suffered gravely when they no longer had access to potatoes not because of them.


Ned Kock said...

Hi Cheryl.

Yes, we both agree that one should aim for small glucose increases after meals.

Now, the 100 g of glucose given in the OGTT to these folks is a lot. (Usually the dose is 75 g for an OGTT.) So I am rather impressed with the very small number getting the high reading.

rmarie said...

Stephan, it seems to me that you have a diet right here in the US, consumed by a large number of people (for over 30 years) which highly recommends the frequent consumption of sweet potatoes and potatoes. It is of course the McDougall diet which is not often mentioned. It’s always Ornish that we hear about.

The McDougall diet is vegan, lowfat and based on 70-90% ‘starch’ in the form of sweet potatoes, potatoes, grains, etc. along with lots of vegetables and moderate fruit. Dr. McDougall is convinced (with studies to prove his point) and with his own success stories that humans are made to consume starch and not meat (well, here we go again …who to believe?)

I was on this diet for about 15 months only because I wanted to see if eating NO cholesterol would lower my cholesterol (and it did…went from 250/280 down to 156 even though everywhere I read it says dietary cholesterol does NOT raise your cholesterol (I guess I’m the exception) Now, since going low carb my cholesterol is back up…go figure!)

During this time, I found that sweet potatoes (I preferred the orange kind – baked – eaten with skin) filled me up and satisfied my hunger more than anything. So I kept them on hand and ate them throughout the day as snacks.

I finally had to stop this way of eating as I lost too much weight even though I ate a lot of food throughout the day and still tended to became hungry soon after eating. I needed more substance and that’s when I turned my attention to the low-carb community. I’m also pre-diabetic and yet found that the sweet potatoes usually did not raise my BS more than 10 points or so which surprised me. Now that I’ve switched to lower carb eating sweet potatoes (and of course grains, etc) produce much higher spikes.

I’m still looking for the perfect diet! I guess most of us are. I'm still puzzled over the fact that diets so diverse (low-fat/high carb vs. high fat/low carb such as McDougall/Ornish/Fuhrmann vs. Atkins/Eades etc) do benefit so many people – both in weight loss/heart disease and diabetes.

I like reading your blog for the excellent information/analysis it provides in a variety of subjects pertaining health. Thank you!

For more info on McDougall here are some links to get you started.

McDougall Hot Topics: http://www.drmcdougall.com/medical_hottopics.html
McDougall home page: http://www.drmcdougall.com/

Ed said...


There is some evidence to suggest that if you catch type 1 diabetes early enough, and apply a Paleo-type diet, you may be able to reverse it.


In particular, I think I understand that the most critical components are eliminating wheat and dairy. The basic concept is to heal the gut so that foreign proteins stop entering the bloodstream, triggering immune and auto-immune responses.

Good luck with your new diagnosis. There is a ton of good information on Stephan's blog and through his linked blogroll to help you educate yourself on your options and management.

Michael said...


In the beginning of this post Stephan wrote:

The question we need to answer is this one: has this food sustained healthy traditional cultures?

And then he talks about the Highlanders, who largely ate sweet potatoes with occasional feasts of pork.

They weren't the only group who had a similar pattern. The Swiss of the Loetschental Valley, for example, ate meat only one day a week (Sundays) and yet they thrived.

And frankly that is where McDougall goes wrong. As Price observed he found no vegan/vegetarian group that was thriving. There has been no observable healthy traditional cultures surviving let alone thriving on vegan fare. Sure you can get certain results with those types of diets, especially within the cultural context of SAD, but notice you couldn't maintain it long term. As Matt Stone noted in his vegan experiment on the Furhman Diet:

So you be the judge. Is a vegan diet good because I had low fasting glucose levels? Or is it sinister for causing me to have a poorer glucose response to normal food?

I think it’s probably just like calorie restriction. You lose weight, you feel good at first, your digestion is better, your skin is clearer, you have verifiable improvements in disease markers – but returning to normal food seems to be almost catastrophic. And you will, of course, return to normal food because you crave it more and more by the day just like I did while eating vegan.

And his take away point:

The vegan diet has one and only purpose, and that is to provide relief for very serious, imminent, and urgent health conditions. And just because it may in many cases achieve results, doesn’t mean that it is the most prudent strategy, or the only strategy, to enhance health. Any form of fasting will have similar results...

McDougall goes wrong long term because he is fat phobic and meat phobic despite whatever short term successes people might achieve. His ideology is coloring his observations, not the evidence from what we have seen work in actual people groups. Such an approach is certainly a recipe for drawing the wrong conclusions.

It is certainly possible to eat a high carbohydrate low fat diet and maintain good health long term. This post and several other posts by Stephan certainly demonstrate such a possibility. But none of the healthy traditional groups that eat/ate that way eschewed animal foods. None. In the long run, for most folks, a vegan diet is a recipe for disaster.

PJS said...

This is a decidedly non-scientific question, but I consider the occasional potato (sweet or white) as basically a butter-delivery mechanism. Does eating butter with the starch do much to change the profile, or is this just wishful thinking? Is potatoes (or sweet potatoes) with butter a recent/Western practice?

JBG said...
This comment has been removed by the author.
Mavis said...

Hi Ed,

Thank you. Yes, I understand that about autoimmune diabetes, but I probably have a different kind altogether, MODY 2.

To make a long story short, I underproduce an enzyme that lets the pancreas know when to start producing insulin. My blood glucose "set point" is higher. I don't know if any environmental factors mediate gene expression here. Possibly they can, but it's not clear to me how.

It's something I have probably had all of my life - a fairly mild (for diabetes) form, that tends to show up in women who have gestational diabetes despite being thin when they started their pregnancy. I think I changed from a healthy person with unexplained high fasting glucose levels (but good A1C five years ago) to someone with higher fasting levels and worse A1C due to some weight gain, stress, and age. Insulin resistance makes the already iffy glucose control iffier.

So, low-carb, paleo, weight training, and high intensity interval training it is for me. And, destressing. So I guess the take-home message is essentially the same, except that I will probably have to be at least moderately low-carb all my life, unlike the Papauns who thrived on sweet potatoes for breakfast, lunch and dinner.

Anna said...


How did you come to the conclusion you had MODY 2? I'm not questioning it, just curious. Did you have a particular test for that enzyme?

I have a somewhat similar history/diabetes situation (and strategy for managing it), but couldn't get my endo to even discuss "why" my blood glucose went awry, except to speculate some insulin insufficiency (my own observation is my 1st phase insulin response is insufficient). So I don't know if it is MODY, LADA, or run of the mill T2.

When I was diagnosed with GDM in 1998 there was NO diabetes history in my family on either side and we were all shocked. Turns out my sister would have been diagnosed with GDM a few years earlier but the 1 and 3 hr OGTT cutoff numbers were higher then. Since that time, 3 of my family members now are T2 diabetics - a parent, an uncle, and a cousin (all same side of the family). So I have a profound curiosity about what is going on in the family, but the no one else shares the curiosity.

Have you read Jenny Ruhl's Blood Sugar 101website /Diabetes Update blog info on MODY forms?

Xogenisis said...

Concerning the muscle mass decline with advancing age. I am wondering if this is the result of low protein consumption finally catching up with the aging body. We know that hormone replacement along with adequate protein consumption can slow this effect way down in aging humans. Not recommending exogenous hormone supplementation. Jack LaLanne (www.jacklalanne.com/) is a good example of intense physical exercise along with diet maintaining muscle and hormone balance into the 90's.

Stephan Guyenet said...

Hi Ed,

It's coming, I promise! I don't know how they prepared them, but I assume simply roasting or baking in the skin, then peeling, like most other groups.

Hi Me,

They were eating sweet potatoes, not yams.

Hi Tuck,

The reason is simply that I'm more familiar with the health of well-documented African cultures. I don't know where I'd find detailed info on the health of traditionally-living Peruvians, for example.

Hi la lintik,

I think the goitrogens probably aren't a problem in the context of a varied diet that contains enough iodine. Otherwise, these people would all have had goiters.

Hi Todd,

I'm not sure I've tried the variety you mentioned. I've had purple "Okinawan" sweet potatoes, which are tasty but too sweet for me.

Hi Praguestepchild,

300 years is more than I need. All I want to see is a few generations grow up with it, and at least one generation grow old with it. So 90 years is plenty for me.

Stephan Guyenet said...

Hi Matt,

Yeah I started off with a bit of a chip on my shoulder about them, but the book is just awesome so I got over that in a hurry.

Hi Michael,

I agree. The WAPF is not anti-carb. In fact, Sally Fallon-Morell has invited me to speak at the 2010 conference (on South Pacific diets), specifically to dispel the myth that traditional cultures were all low-carb. It's an easy myth to dispel, as many more traditional cultures were high-carb then low-carb.

Hi Aaron,

As far as I know, baking tubers barely increases AGEs.

Hi rmarie,

I believe your diet lowered your cholesterol, but I doubt it had anything to do with reducing dietary cholesterol, because it has virtually no impact on serum cholesterol in humans. I agree with Michael that eliminating all animal food is going too far, into a place that no healthy traditional culture has ever gone, and it's asking for trouble.

Hi Will,

Even LaLanne has lost muscle mass over the years, it's evident in the pictures. He's a muscular 90+ year old, there's no doubt about that, but not as muscular as he was at 40. I suspect his weight has decreased over the years, since he's still lean. I think it's perfectly natural.

Unknown said...

"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."
Stephan, did the authors mention why they have such a high infant/child mortality rate?

Unknown said...

"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."
Stephan, did the authors mention why they have such a high infant/child mortality rate?

Mavis said...
This comment has been removed by the author.
Mavis said...


It's totally self-diagnosis at this point. I'm waiting to see an endocrinologist and hope to rule out LADA, since I do have autoimmune thyroiditis.

I'd love to correspond with you as another potential MODY 2. I have a feeling that, since so many MODY 2s are subclinical, and most of the rest are labeled Type II, that there are many more out there than thought.

Please write me at helen.harrison. at gmail.com.

And yes, Jenny Ruhl rules! That's where I learned about MODY and LADA.

Stephan Guyenet said...

Hi Luke,

Infectious disease. Especially diarrhea and pneumonia.

JBG said...

Helen, if there remains a possibility that your diabetes is a consequence of an ongoing autoimmune process, a way-far-out treatment possibility is helminthic therapy:


Warning: Helminthic therapy does violence to some strong cultural taboos. A good, moderately-long account of how the above site came to be is found at:


JBG said...

An interesting data point with respect to vegan diet is the case of Scott Nearing. Living the Good Life, by Helen & Scott Nearing, describes their life on a Vermont farm from the 30s forward. Chapter 5, Eating for Health, especially (in my copy) pages 133-6, describes their strictly vegan regime, letting go even of some residual use of dairy. Scott lived to an even 100, and only died then because in the final few years he had lost enough of his muscular strength that he could no longer do the hard physical labor that he considered part of life. Sensing possible disability ahead, he chose to check out on his own terms and stopped eating.

I have no idea how he/they survived without special attention to, eg, B12, omega-3s, and iodine. The book's index provides no clues, and it's been too many years since I read the book to recall if such things were mentioned.

But it is a wonderful book, and I recommend it to anyone, especially, who has back-to-the-land aspirations.

Anna said...


My email to you bounced back (tried with and without the . and I removed the spaces.

You can email me at againstthegrain at me dot com.

Mavis said...

Hi JBG -

Yes! I have read about that and am actually half-considering it for myself and my daughter. Can't quite work up to it yet. We both have other autoimmune and allergy stuff going on. We're going to try a Chinese remedy that is being tested for curing anaphylactic allergies first.


And we are also going to go gluten-free, but first my daughter will have a celiac test. Either way, we're going in that direction.

Plus, vitamin D and pro- and pre-biotics.

Damn all this hygiene.

Brandy Vencel said...

I am still confused about what variety was actually being eaten. It is so hard that our grocery stores insist on labeling many orange sweet potatoes as yams, even though they are botanically distinct. We are beginning to grow sweet potatoes--a vining relative of the morning glory which is very beautiful--here on our microhomestead, but I am wondering if this is actually what you are talking about?

Interesting note on iodine--it can be present in plants if the soil is rich in it. Often iodine deficiency is a soil deficiency. Our soil, for instance, is naturally deficient. Hence, we have resolved to collect seaweed for composting whenever we visit the coast.

Perhaps these people did not have goiters because their soil was rich in iodine and other trace minerals, plus had the correct ph to make it available to what they were growing?

Stephan Guyenet said...

Hi Brandy,

They were eating true sweet potatoes, the same species you're growing. Iodine is marginal in places in the Papua New Guinea highlands, as some groups suffer from iodine deficiency cretinism. I don't know what the soil iodine content was for this group, but apparently it was sufficient.

Nick Christensen said...

is there any danger in eating a high quantity of starch alongside a high quantity of sat. & monounsat fat? My diet right now tends to be around 1/3, 1/3, 1/3 for each macronutrient (all whole foods), and I'd hate to think I'm making things worse.

Paul Ericson said...

Not all produce is created equal. I'd love to see a detailed nutrient analysis of the sweet potatoes they were eating.

The USDA used to publish nutrient profiles of produce by region. But the poorer performing regions complained so the USDA started averaging everything.

I would be cautious about what conclusion you can draw from this with regard to any given sweet potato you can actually buy today, in a grocery store in the US.

In "War in the Country", Pawlick details the dismal downward spiral of nutrients in our food.

I also wonder if they were super-converters of beta-carotene and were thus eating a vitamin A-rich diet.

They were outside all day so I'm sure they had plenty of vitamin D. And the pork fat was a good source as well.

Nicky said...

@ Dave Riley - have you come across this website, and its information on diabetes and diet?

It's the website of the Diabetes 101 author, IMO one of the 3 top diabetes books currently.


Jane said...

David L

'Introduction of grains in hunter-gatherer societies markedly diminished the physical well-being of the populace ..'

Are you sure the grains did this? Might it not have been the increase in population, the introduction of monoculture, or some other circumstance that happened to coincide with cultivation of grains?

I ask because the healthiest people in the world, the Hunza as studied by McCarrison, ate large quantities of grain. I have been unable to find any evidence for the idea that grain is an unsuitable food for humans. On the contrary, grain is a rich source of minerals, which activate enzymes needed for germination. We have many of the same enzymes, and we need the same minerals.

Anna said...

Dave & Nicky,

I also highly recommend Jenny's excellent sites, Blood Sugar 101 (formerly What They Don't Tell You About Diabetes and Diabetes Update blog. It was finding Jenny's sites while browsing for new research on risk factors for future diabetes in women and their offspring from (gestational diabetes pregnancies) that really helped me understand that I still had a considerable blood glucose problem and wasn't being adequately monitored.

Bryan said...

Any info out there on the health of societies eating mainly rice, such as Thailand 90 years ago?

Stephan Guyenet said...

I have papers on 1950s-60s autopsy studies in Asia (Japan, Korea and Thailand) indicating low levels of atherosclerosis and an infarction rate of 10-20% what we were seeing in America at the time.

Stanley said...

"Sweet potato supplied over 90 percent of their total food intake". I assume you mean as a percent of total calories. Gasp! Dr. Atkins must be rolling over in his grave.

I'm stumped as to how these people _don't_ have diabetes. I guess they chop wood all day or something. I wonder how long they live (the ones who die of old age, that is).

I will admit that in "Blue Zones", the famous book about centenarian lifestyles, the author remarks how many very long-lived people seem to eat carbs, then take a mid-afternoon nap, which on the face of it sounds like a perfect recipe for diabetes and premature death. Perhaps the relaxation aspect and the high quality of the carbs compensates for the glycation damage somehow.

Anyway, I'm still in shock. Such a diet sounds unsurvivable. I really wish I had a clue how they end up with paleolithic-diet-like physiques. Perhaps it's just bad data?

Ed said...


I think one of the things you need to take into account is the function of the liver. I am no endocrinologist, I do not know for a fact that the body works this way. But my understanding is that a healthy liver soaks up all your digested glucose, and titrates it into the bloodstream, modulated by insulin from the pancreas.

So starch/ glucose isn't a problem for someone with a "healthy metabolism" ie healthy liver, pancreas, etc etc all the other organs that work in concert to modulate blood glucose levels.

Now, if your endocrine system is busted, you may be better off not eating 90% of your calories as starch.

Nut and see oils, high in omega-6 fats, damage the liver, particularly in conjunction with fructose. If 90% of their diet was sweet potatos, their omega-6 and fructose loads had to have been rather low.

I hope someone corrects me if I've got this wrong :-)

Anonymous said...

"Cheryl, a BG reading of 160 or so is not really that abnormal"

Wow, STRONGLY disagree. sorry. These are obviously undiagnosed diabetics/prediabetics.

Anecdotally many diabetics who have tested friends, family etc. find a significant number whose BG is absolutely nailed in a window of 80 - 110 and often varies less than that: these are true nondiabetics, anyone moving further from this baseline is starting on the "diabetic progression".

Anecdotally again many diabetics, self included, find that 140 - 150 is the point where symptoms occur or worsen - particularly peripheral neuropathy and polyuria.

Despite sweet ptoatoes being "sweet" I can tolerate more of them than ordinary potatoes, albeit that "more" isn't very much.

"his is a decidedly non-scientific question, but I consider the occasional potato (sweet or white) as basically a butter-delivery mechanism. Does eating butter with the starch do much to change the profile, or is this just wishful thinking?"

YMMV. Adding fats to starch can slow it's conversion to glucose. This "pizza effect" is well known to Type 1s as their bolus insulin may well outrun the input of glucose from such a meal and may lead to an immediate hypo, followed some hours later by hyperglycemia as the glucose is still being produced after the insulin has faded.

For a Type 2 like me with virtually no Phase 1 insulin but still adequate Phase 2 it works quite well as my BG will only go up slightly and stay up for several hours, which makes the combination good fuel for prolonged exercise.

But the other side of the coin is what the combination does to lipids subsequently, the combination of sat fats and excess carbs is probably not a good long term plan.

Probably the best source on MODY and diabetes genes


Neonomide said...

Cordain released an anti-potato newsletter just a few weeks ago. I'll put some interesting points here, ask if u need sources:

"Table 2 below shows the recent per capita consumption of commonly eaten nightshades. Potatoes come in first (126 lbs) followed by tomatoes (85.7 lbs, including both fresh and processed), peppers (15.5 lbs) and eggplant (0.8 lbs). These figures clearly show that nightshades are a staple food, universally consumed in the U.S. diet. This raises the question: Are there any health hazards associated with eating almost 230 pounds of nightshades on a yearly basis?"
- -
"Potatoes generally maintain one of the highest glycemic index and load values of any food 3-6"
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"in both of my books I do not recommend that potatoes be included as a regular component of Paleo Diets. Additionally, as you can see from Table 1, most of the potatoes consumed in the U.S. are highly processed in the form of french fries, mashed potatoes, dehydrated potato products, and potato chips. Processed potato foods typically are made with multiple additives (salt, vegetable oils, trans fats, refined sugars, dairy products, cereal grains, preservatives, and other food additives) that may adversely affect health in a variety of ways."
- -
"An additional nutritional property of potatoes that is rarely considered in regard to human health is their saponin content."
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"The primary function of saponins is to protect the plant from microbial and insect attack by dissolving cell membranes of these potential predators8. In mammals, including humans who consume saponin containing plants, these substances frequently create pores in the gut lining, thereby increasing intestinal permeability8-10. If they enter the bloodstream in sufficient concentrations, they cause hemolysis (destruction of the cell membrane) of red blood cells8-10."
- -
"Potatoes contain two glycoalkaloid saponins: α-chaconine and α-solanine which may adversely affect intestinal permeability and aggravate inflammatory bowel disease11, 12. Even in normal healthy adults, a meal of mashed potatoes results in the rapid appearance of both α-chaconine and α-solanine in the bloodstream13. The toxicity of these two glycoalkaloids is dose dependent – meaning that the greater the concentration in the bloodstream, the greater is their toxic effect. At least 12 separate cases of human poisoning from potato consumption, involving nearly 2000 people and 30 fatalities have been recorded10. Potato saponins can be lethally toxic once in the bloodstream in sufficient concentrations because these glycoalkaloids inhibit a key enzyme (acetyl cholinesterase) required for the synthesis of acetylcholine, a neurotransmitter required for nerve impulse conduction10."
- -
" So the next logical question arises: Should we be eating a food that contains two known toxins which rapidly enter the bloodstream, increase intestinal permeability and potentially impair the nervous system?

In the opinion of these authors: ". . . if the potato were to be introduced today as a novel food it is likely that its use would not be approved because of the presence of these toxic compounds." 11"

Stephan Guyenet said...

Hi Neonomide,

Yeah I saw that. I have a couple of points. First, sweet potatoes are not related to potatoes, so what Cordain said doesn't apply to sweet potatoes.

Second, I think Cordain is really overstating the case against potatoes. There is no evidence in humans that the amount of solanine and chaconine gotten from eating non-green potatoes has any adverse effect on health whatsoever. Potatoes definitely contain toxins, but so does every other plant we eat. Solanine and chaconine show up in the bloodstream (as do many other food molecules, both toxic and benign), but that doesn't mean there's enough of it to do anything. The dose makes the poison.

The studies he cited to support his argument that eating potatoes causes inflammation are not convincing. One used potato chips as the source of potatoes, and the other fed people a diet rich in potatoes and white flour and compared it to a lower gluten diet. Neither one looked at the effect of actual potatoes in a controlled manner.

I'm keeping my eyes on the solanine and chaconine issue, which is why I haven't whole-heartedly embraced potatoes on this blog. If a study comes out showing that actual non-green potatoes pose a human health risk, I'll be open to it. Until then, the evidence against taters is way too slim for me. I consider them safe enough to eat regularly myself. They're one of my main sources of starch. Of course, you should listen to what your body is telling you, so if they don't agree with you, then by all means avoid them.

Unknown said...


forgive me if this is a bit off-topic for Sweet Potatoes, but I don't think Michael and you should rubbish the vegan diet out of hand, as you both appear to do here. There are thousands of happy and healthy vegans in the UK, and more elsewhere, who are having a great time, minimising their carbon footprint, and living a healthier life than the omnivore majority (they also live in their own little ethical glow, but let's not go there!). I take your point about traditional societies; their primary aim has always been survival, and so could not ignore any source of food. But I'm reading your blog because I'm interested in optimal nutrition, which is a different thing. A well informed vegan diet is healthier than the standard first-world diet, but the challenge is to find an optimal diet which minimises the demand on the world's resources. In fact, we need to say diets, because I expect that we will increasingly need to tailor diet to our individual genetic characteristics. A vegan diet may feature as one of these, or it may not. If I can glow, and live to 100 as well, then fantastic, but if not, then I may have to make some compromises......

Elizabeth said...

I recall reading an anthropological account of an isolated people with a yam/pork diet that studied the way occasional amounts of pork were integrated into the diet. It was ceremonial, but not based on seasonal ceremonies, as Western ceremonial foods often are (Ceres - cereal - ceremony). Pork was eaten in times of stress: illness, death, warfare, conflict. The author hyposthesized that this cermonial structure reserved their limited amount of high-protein nutrient dense food for the times when they were needed most. Over a long period of time the author also noted a cyclical pattern in pork consumption. When pigs became overpopulated, they started straying farther from home, raiding other people's gardens. This triggered conflicts between neighbors, which triggered the slaughter of pigs and the ceremonial consumption of pork as part of the resolution of the conflict, which brought the garden/pig ratio back into a sustainable balance again.

Sorry I can't give you the source; I read it 30 years ago. But a quick search with some key terms on Google Scholar turned up "Highland Peoples of New Guinea" by Paula Brown, from 1978, which would have been hot off the presses when I was in school, and the intro pages available online sound very familiar.

pipparoni said...

Yep, there were some interesting points made here in the comments section that shouldn't be overlooked.
Sweet potatoes are a healthy food to eat but it all depends on the soil they were grown in.
If the soil is unhealthy then the food will not provide all the nutrients needed to provide us humans with good health.
It doesn't really matter what we eat as long as those foods are mineral dense.. Which is distinct from being nutrient dense.
Although I do not feel vegan diets are normal or natural to our species but there is clearly societies that thrived on little animal foods

Unknown said...


1. “Effect of added fat on plasma glucose and insulin ... [Diabetes Care. 1993] - PubMed result,” http://www.ncbi.nlm.nih.gov/pubmed/8325201.

I wonder why you said it was a "non-scientific question"?

Oh well, you're never going to read this, are you? That's what I hate about discussions in the comments of blogs. And there isn't even a way that I can see to get your email address so that I can send this to you. Oh well.

While I'm here: hey Stephan, keep up the good work! You are an excellent thinker and writer, and I'm grateful for your contributions. (I say this even though you upset me and complicate my thoughts by casting doubt on my favorite hypotheses and my chosen practices.)

Benjamin Eble said...

I do not have an academic background, like many here. But, here is my experience: I am 5'10" tall, and my weight crept up to 200 lbs, by the age of 40. During my teens, I weighed 155 lbs. In June 2011, I made the move to remove all sugar drinks, sugar, and sweetener from my diet. My weight dropped 20 lbs, to 180 lbs. Then, I removed milk from my diet, and I lost another ten pounds. Usually, I bake meat, with a little garlic salt, and eat it. Also, I eat fresh fruits, and veggies, regularly, and drink water, or watered down coffee. Recently, I started eating American sweet potatoes for the first time. And, I have been amazed by the effect. I simply bake the potatos in the oven, for up to an hour and a half, and then let them cool in the refrigerator, to conserve moisture. Anyway, what I discovered is that by eating sweet potatoes, it does two things. First, it knocks out my appetite completely. And, second, after eating an ample amount of sweet potatoes, I will have no desire to eat meat, for one or two days at a time. Also, I feel great, and do not gain weight. My weight is currently at 170 lbs. Also, it is worth mentioning that after cutting all sugar out of my diet, for just a week, my short term memory began to resurge, in a very unexpected manner. Currently, my memory may even be better than when I was a teenager. And, this appears to be linked to the removal of refined sugar/sweetener from my diet. For example, I have not "lost" my car in a parking lot for months, whereas before I had reached a point where I was "losing" my car more often than not. Anyway, unless I see some adverse side affects, I will be sticking with the sweet potatoes, due to the low fat content. Also, if you eat them regularly, they become somewhat addictive. When I was in the states, for a week, and had to eat at restaurants, each day I could only think about getting some baked sweet potatoes. That has been my experience. I hope to lose twenty more pounds, in part due to my interest, and study of ethnography. Thanks for the blog!

LMC said...

I was wondering if anyone had any problems eating sweet potato fries while taking coumadin? I was at 2.5 on the scale about 4 weeks ago and have been eating the sweet potato fries since then and today i had a 1.8 which is a bad level of blood thickness. Does anyone know if the fries were the culprit?--Thanks so much-Les

Brian said...

Stephan: I know this question is very late, but how does the Papua New Guinea tribe get their Vitamin A out of sweet potatoes, if they are not eating any fat along with it, to stimulate bile secretion?

Beibichepe said...

I live in uptown new york city, where theres a huge Dominican population. So we have lots of exotic starchy foods(plantains, yucca). I favor boniato over the American variety since its thicker therefore more satiating. Is the fact that it isn't local an issue? Should I stick with regular sweet potatoes?

Unknown said...

One of your readers posted: " just had an orange sweet potato/yam tonight with dinner (I think this was a sweet potato; not too huge the way yams often are). I really like them but can't imagine eating them as 90% of of my diet!"

True, the Papuans represent an extreme, but traditional societies did not know the kind of variety of foods that we have. Take a look at some of the most magnificent physical speciments among humans, such as the Nuba of Kau. Their diet is somewhat varied, but very far from "paleo." Or again, look at the very long-lived people in the Caucasus or in Guanacaste in Costa Rica. Again, the diet is very simple, and until recently no modern foods at all.

Personally, I think the key to the health of these people, as regards the aspect of diet, amounts to having food that is not degraded by modern agricultural-industrial practices and depleted soils, on the one hand, and simplicity on the other, combined with an outdoor and physical way of life, without the stressors of modern urban living.

One of the things I notice in blogs relating to diet is the obsession with making recipes. There is an undiminished need for variety, great palatability, pleasure, habits acquired from their environment. It is an inability to just eat very simply without a need for constant variety, "taste" treat, and the like. This may be a large factor in why people cannot lose weight reliably.

Fiona said...

Hi Stephan - curious to know - how many times have you tried purple (Okinawan) sweet potatoes? I find them much less sweet and also starchier than any other type, including the Japanese sweet potato (red ski, off-white interior) and not nearly as sweet as the Caribbean boniato.