The debate rages on over whether dietary salt (NaCl) increases the risk of cardiovascular events, with no clear answer in sight. Yet few people are paying attention to another, more insidious effect of salt: it may increase our calorie intake, and eventually, the size of our waistlines.
Introduction
Humans are born with specific hard-wired food motivations, which guide us to food properties that kept our ancestors alive and fertile in times past. We have an instinctive attraction to sweetness because, in the world of our ancestors, it indicated ripe fruit or honey-- both important sources of calories and other nutrients. Most of the other food properties we're instinctively drawn to, such as starch, fat, and glutamate, signify high-calorie foods.
Yet one of our hard-wired food motivations stands out from the rest: our attraction to salt. Since salt is calorie-free, salt appetite is one of the few instinctive food drives that doesn't relate directly to acquiring calories. Interestingly, salt is the only essential micronutrient (vitamin/mineral) we can taste at the concentrations normally found in food. Not only our brains, but also our tongues, are hard-wired to seek salt above all other micronutrients.
Sodium and chloride are essential micronutrients for all animals, but not all animals find dietary salt appealing. For example, rats don't exhibit a salt appetite unless they've been deprived of salt intermittently (1). Yet humans are so drawn to salt that when there are no constraints on our behavior, we eat many times more of it than our hunter-gatherer ancestors did (presumably, as judged by modern and historical hunter-gatherers).
Although salt itself doesn't contain calories, it is a powerful reward factor. If you don't believe that, try eating food that contains no added salt for a day. This is just another way of saying that the human brain instinctively values salt. And when the brain places a high instinctive value on food, it tends to drive us to eat more of it. We know that applies to other food reward factors, but does it apply to salt as well?
The Study
To test the hypothesis, Dieuwerke Bolhuis and colleagues recruited 48 volunteers and fed them a standardized breakfast, followed by an experimental lunch of elbow macaroni and sauce. Volunteers were randomized to four different versions of the experimental lunch, and each person ate each version on a different day (2):
1) low-fat (0.02% fat, wt:wt)/low-salt (0.06% NaCl, wt:wt)
2) low-fat/high-salt (0.5% NaCl, wt:wt)
3) high-fat (34% fat, wt:/wt)/low-salt
4) high-fat/high-salt
Volunteers were allowed to eat as much as they wanted of the experimental lunch, and calorie intake was recorded.
The Results
As expected, volunteers served the calorie-dense high-fat pasta consumed more calories-- in fact, a full 60 percent more. This is consistent with previous findings that people tend to overeat foods that are calorie-dense.
Yet salt also increased calorie intake, by a smaller but still meaningful 11 percent. This held true in both the low-fat and the high-fat context.
Discussion
This straightforward study adds to the evidence that food reward factors can increase calorie intake. Yet it also extends the evidence, showing that even non-caloric reward factors can indirectly increase calorie intake when they're added to caloric foods, by increasing the overall reward value of the meal.
The 11 percent difference in calorie intake may not seem like much, but keep in mind that 11 percent is approximately the difference in calorie intake between a lean person and an overweight person.
I don't know whether this effect would persist over weeks, months, and years-- which is what really matters for body weight. Hopefully, future research will address this. Yet judging by the ability of other types of food reward restriction to cause long-term weight loss, including low-carbohydrate, low-fat, and vegan diets, it seems plausible.
Despite countless studies and massive funding, we still don't have a very clear view of the role of dietary salt in human health. About the only thing researchers agree on is that very high intakes are probably harmful. The fact that so much controversy remains after so much research suggests to me that salt intake probably isn't a major determinant of health, at least cardiovascular health, which has been the primary focus. But in the absence of clear evidence, I tend to fall back on the evolutionary view, which suggests that it may not be a good idea to eat a quantity of salt that far exceeds what our ancestors would have eaten for nearly all of our evolutionary history.
34 comments:
Which ancestors? Our African ancestors probably had little salt, but our European ancestors regularly used salt to preserve food and probably had much higher consumption than modern humans.
Sodium is really a fascinating subject, and I hope you write more about it.
Hi normalcarb,
That's a valid question and I acknowledge that the issue isn't black and white. Some lineages do have a history of higher salt intake. However, it's likely a very short history compared to the long span of human evolution. Even in ancient Rome, salt was so expensive that it was used as a currency, and that was only 2,000 years ago.
Not sure about calorie intake but it'll surely add water to your body. ANd more water means more weight and worse looks. I've lost 30 lbs so far with the Loaded Gun Diet just eating a bit less than usually and using a few simple rules.
Salt is needed to make cooked foods taste good. Most foods that we eat raw have plenty of flavor without salt.
OK, some of the salad foods are improved by salt, but my contention stands.
I should amend somewhat: edible raw foods are generally tasty when you are hungry for them. For many such foods -- especially vegetables -- there is a taste change after you have had enough. Overeating becomes difficult.
What would be a "very high intake"?
Is the usual 1500 mg/day guidelines reliable?
The 7 Nations Japan studies are interesting because of the high salt and low fat content in the traditional diet. Neither appears to reduce longevity or result in increased CVD, though the high salt appears to cause a lot of stomach cancer. Whether the salt is added for reward is hard to guess, but starchy noodles and rice do taste better with salt.
http://www.epi.umn.edu/cvdepi/study-synopsis/seven-countries-study-in-japan/
American Japanese, who eat a higher fat version of the traditional salty diet, have much higher CVD rates.
Did the Romans really pay in salt, or did they just supply a salt and food ration to troops, and also pay them with money, as the US Army does today?
https://www.quora.com/Why-did-the-Romans-pay-in-salt
Human migration paths were often littoral in the past, and large parts of the human population would have had access to salt water at some stage in our evolution. Those living in archipelagos would have adapted to a constant higher salt level; it seems likely that we adapted to a very wide range of salt intakes indeed. Certainly the environment our distant hominid ancestors evolved in was likely very low in Na (but not necessarily Cl, which is commonly found with K and MG in plants). (@Carl M, these other salts and also nitrates may account for the extra taste of raw veges).
I reckon that if salt makes you eat more food, just eat salt without food when food isn't around. Then when you're offered salt with a meal, you can just say "Yeah, Na."
Hi Stephan,
An interesting question to me is, say you had a fixed size meal (e.g. lunch) and you can add salt. Should you add salt as desired? You can't overeat anyway (as you are restricted in portion size) so that you will be less wired to eat salt later on?
Best, Nils
Salt preferences can be changed. I once read about some Europeans who found a tribe in South America that didn't have salt and sprinkled some kind of burned grass on their food. When they gave the people some salty food, the Indians reacted with disgust. But by the second day, the Indians wanted more of the salty food.
I've always liked salty food. Used to suck bouillion cubes as a child. As an adult I've occasionally experimented with giving up salt. For about 3 days all the food seems tasteless. Then I begin tasting sweetness in things like vegetables. And I don't want sweet food after dinner.
Then I return to normal salt habits. Like the SA Indians, I find that the first meal tastes terrible. But it takes less than 24 hours to go back to old salt preferences. Unfortunately, I didn't track how much I ate. But if after a salty meal one would tend to want a nonsalty food like fruit or other dessert, that could explain weight gain.
Another interesting thing about salty food. I've always salted food before tasting it. Once when we were eating in a restaurant, my sister asked why I hadn't salted the food. I said, "Oh. I guess I forgot" and added some salt. Turned out the dish was very salty to begin with. Somehow I had been able to tell that by looking at it. Maybe salt changes the look of a sauce.
Dear Stephan,
How much salt do we need per day? Can we skip salt totally, is it healthy?
Thanks in advance for your reply.
Thanks for the article! What would be the recommended amount based on what our ancestor did???
Thanks Stephan!
Hi Bebidoo,
I'm talking about >90th percentile of typical Western intakes. 7+ grams/d of sodium. That's 17.5+ g/d of salt, or about 1 tablespoon/d.
I honestly don't know whether the 1,500 mg guidelines are beneficial; the evidence is conflicting.
Hi George,
I'm no expert on ancient Rome so I can't vouch for the relevance of that story; it's just something I've read. I agree with you that many groups would have had access to salt, but I suspect that they still would have eaten less of it than we do, in large part because it was a lot more "expensive" (often either requiring work, or significant money/bartering, to obtain). Today, table salt is so cheap it's effectively free.
In the Pacific islands they do use seawater to flavor some foods, although according to the Kitava study their total salt intake was still something like 1/3 of ours, IIRC.
Hi Nils,
Certainly in the situation you describe, salt wouldn't make you overeat. I can't answer your question of whether or not to add salt, because I'm still unsure of what the optimal intake is.
Hi Gretchen,
Interesting. I do find that my salt appetite changes somewhat based on how much of it I eat. I think there may have been some research on this?
Hi RO,
It's commonly said that the minimum safe intake of sodium is 500 mg per day, which equals about 1.3g of salt. I haven't examined the evidence supporting that recommendation so I don't know how solid it is. There are certainly cultures that eat less than that, e.g. the Yanomamo.
It's certainly possible to get all your sodium and chloride from whole foods, without adding any salt. Whether or not it's healthier than adding salt, however, I don't know. There is an ongoing debate about this that hasn't yet been clearly resolved.
5000 mg/d sodium seems like the sweet spot:
http://jama.jamanetwork.com/article.aspx?articleid=1105553
When your intake is too low, you can both sense it (craving salt or simply liking the taste of salt), and you can sometimes feel it (light-headedness, fatigue, headaches).
The studies may be conflicting simply because they do not account for the different environments of our different ancestors. For those of European descent (like me), low sodium intake can have negative health consequences due to poor perfusion. The body will try to compensate by raising blood pressure.
Stephen
I just listened to your talk about bland diets as the solution to weight problems. I wonder if you are familiar with The Rice Diet, from 1939?
'Kempner described his diet as "a monotonous and tasteless diet which would never become popular.... Kempner's only defense of its use was the fact that “it works,” and that the diet was preferable to the alternative of certain death"[1]'
The Rice Diet prohibited all added salt.
I had dinner with some Rice Diet participants. One of the ladies was quite energetic and was getting ready to hike to the Base Camp on Mount Everest at the age of 75. The other people seemed to me to be quite depressed. The food we were served was really, really bland, although prepared by a professional chef.
The Rice Diet survived until a few years ago, and even placed a book on the New York Times best-seller list, but I think it is now defunct as a movement.
Don Stewart
Looks like the Rice Diet has been revived as the Rice House Healthcare Program: http://www.ricehouse.org/our-staff/
Hello Stephan
Thanks for all the great content you share.
ok so we can't tell for sure, but what is your "educated guess" about a potentiel ancestral explanation of our inner motivation for salt ?
I thought maybe it could be linked with the potentially very ancient appearance of fermentation.
Guillaume
Hi Don,
Yes, I've heard of the rice diet. It also reminds me of John McDougall's diet low-fat vegan diet. No offense intended to that community but the food is super bland. I went to a McDougall retreat once and my hunger level went down even though my kcal intake was lower.
Hi Guillaume,
As you said, there's no way to be sure, but it seems highly likely that we crave salt because it was an important and limiting nutrient in the environment of our ancestors. Most hunter-gatherers don't have added salt, and I have to guess that would have been particularly true in the area where Homo sapiens originally evolved (African rift valley area; the original humans probably were not coastal).
Sodium and chloride are essential nutrients, and we need higher levels of them than most other animals because we sweat a lot (at least, non-industrialized humans do). Presumably, we can't taste other essential vitamins/minerals like niacin, vitamin A, and magnesium, because as a hunter-gatherer eating a diverse omnivorous diet of whole foods, it's probably difficult to meet your energy needs without meeting all your micronutrient needs. Either that, or we have other proxy taste drives like sweetness and acidity as a stand-in for vitamin C.
Salt may be an exception to that. There may not be optimal levels in whole foods (even though we can survive without any added salt) so we have a drive to seek additional salt.
It's speculative but I think it's probably the reason.
Re salt craving. I keep sheep, and one year I shared a ram lamb with another woman. She kept him for a few months and then I got him. She hadn't provided and salt or minerals, and when I got him and put out salt and minerals, he gorged himself. I worried that he'd get sick, but he kept eating and eating for several days and then stopped.
Apparently the body knows when it needs salt or minerals. And of course salt licks are ways of attracting game animals.
Thank you Stephan, great content as usual :)
... and your explanation is coherent with the need of our ancestors to improve the control of their body-temperature, with sweat, after they left the tropical forest and started to hunt (7-8 millions years ago as I understood)
A lot of herbivores go to salt licks. Carnivores don't because it seems they get their sodium needs satisfied by eating other animals plus they don't sweat. Some herbivores sweat: Horses and donkeys. A lot of them don't. Cows, sheep, elephants.
I thought that humans, being sweaty omnivores, are someplace in between. Possibly the addition of grains to the diet necessitates added salt. There are people who consume a comparatively large amount of the diet in rice, for example.
The Greeks and Romans made a sauce from salt and rotting fish. Garum. Other peoples make similar. Fish sauces are common and popular in various Asian countries. So it's a condiment but also a way in which salt is added to the diet.
The 60% higher consumption of the energy dense macaroni is interesting too. I consider fat to be a "stealth calorie", because I habitually eat the whole portion served. Equal volumes of low fat pasta soups like pho, udon or ramen are just as filling as high fat mac and cheese or chow mein, and are less calorie dense.
The ability of fat to suppress hunger is one major argument for HFLC dieting. In this study, the addition of fat to the carbs in the macaroni had the opposite effect. Is the high fat argument for reduced hunger valid only when the carbs are taken out? Bacon and eggs is a less rewarding meal without toast, juice and pancakes.
Finally, this article about high fat peanut snacks was interesting.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3144712/
The 300 kcal peanut snacks were null effect for either appetite suppression or overall daily calorie consumption. Again suggesting that fat is not an effective appetite suppressant.
Thinking about the NZ Satiety Index while watching a ball game, I noticed that kids around me were eating 3.5 ounce bags of Cheetos. No peanuts or crackerjacks. After the game I found an empty sack on the ground and read the nutritional information. Multiplying the suggested one ounce serving size by 3.5, I came up with about 550 kcal, of which 60% is fat. If the RDA for PUFA is 15g, and the frying oil is soy, you'd have your daily requirements amply supplied, along with 1/3 of your daily sodium.
Reading the bag, I wondered to what degree the oil had been oxidized, and I dug out a fryer patent for potato chips.
http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=/netahtml/PTO/search-bool.html&r=2&f=G&l=50&co1=AND&d=PG01&s1=20060019007&OS=20060019007&RS=20060019007
320 F max, dropping to 260 F for most of a 3 minute cook. From looking at the size of these things probably regulated to within a degree of that. In my experience soy will oxidize rapidly at 400F, generating fumes akin to drying paint. Frito Lay stays well away from that, and would not be able to sell rancid smelling chips anyway.
This in turn brought back memories of Plano and the stairwell full of patents such as these. The Hall of Food Reward.
I looked for an image of the great hall of food reward. This one in Wisconsin at Frito R&D is similar but not as vast.
http://margaretmsavino.photoshelter.com/image/I00003bOwRhz4T94
My mother was born before the arrival of refrigeration and she says that at least her grandparents, and surely long before that, ate mostly salted meat. The families living in the farm butchered three hogs a year, plus had rabbits and chickens. Every bit of the hog was cured (salted), except liver that had to be eaten fresh. I have the impression that my recent ancestors ate far more salt than I. The only fish they could get was salted cod, too.
Weston Price in his big book relates of a South American tribe, eating no salt, sodium intake measured at 100mg/day, in apparent good health. But I suspect some of us Caucasians have evolved to tolerating and needing more sodium. When the summer heat hits the Midwest, I note every year a sharply increased need for sodium for about a week, with strong symptoms, until the body adjusts to the new, sweatier metabolism.
@glib dry salt cod is inedible unless you soak it, with multiple water changes. For the French dishes (such as brandade), people used to drag the salt cod in sacks behind their ships headed upriver. In modern times they've used their toilet tanks for salt cod soakers. My Norwegian grandma soaked her salt cod with lye, followed by multiple water changes to get the lye and salt out, before cooking the lutefisk. Same thing with Italian bacalan and New England chowders. It takes a lot of water changes to remoisten the fish and get rid of the salt.
[references at the bottom] One interesting thing to consider is that salt appetite and tolerance may be related to *where* our ancestors lived. While you say prehistoric people didn't eat a lot of salt, that's probably not true for many. There is good evidence to think that the level of salt they consumed is a lot higher and closer to today's consumption level than you'd think. For example, when Europeans first encountered Polynesian cultures, they found they engaged in a practice of dipping their food into sea water to add flavoring [Cordain 2005]. Animals, like Japanese macaques, also do this, though they're taught. Other animals will voluntarily travel to "mineral licks" in order to lick salt and other minerals from the ground and human hunters likely hunted those animals at these gathering spots and there's evidence they also ate the earth (geophagy). Apart from a few places around the world that have no source of natural salt (like the West African and Chinese interiors) most prehistoric hunters, I think, would have access to good amounts of salt through deposits or just sea water. Perhaps the scarcity of salt in some places accounts for the racial disparity in salt sensitivity. Another aspect of this discussion (on which I can't find any research yet) is whether or not people put on a low salt diet will eat more calories to satisfy their salt appetite? Or, will they alter the types of food they eat, e.g. eating fewer vegetables which, I think most would agree, are far less palatable when unsalted? Based on the research I've done (I'm writing a book on the topic) I tend to agree with you that salt likely isn't a big determining factor on cardio health--at least not for the majority of individuals (UVA, which developed a new test for salt sensitivity, estimates 25% of the population is SS).
Cordain, et al 2005: http://ajcn.nutrition.org/content/81/2/341.full
UVA https://news.virginia.edu/content/uva-researchers-new-diagnostic-test-can-identify-each-person-s-optimal-salt-intake
Hi Michelle,
The UVA researcher who developed the salt sensitivity test, Robin Felder, is a friend of mine. It may have useful predictive value for CVD events, although more research is needed.
Regarding salt intake in non-industrial cultures, I agree that some would have had access to salt. The only quantification of salt intake in Pacific Islanders I've seen is from Staffan Lindeberg's work. The Kitavans use seawater in cooking, however their total salt intake is still only a fraction of what we eat in the US (something like 1/3, IIRC). So the fact that some people had access to salt doesn't mean they ate as much of it as we do today.
I've done a lot of reading about non-industrial diets, and the large majority of the cultures I've studied didn't have access to concentrated salt. This is not systematic or scientific of course, but that is the impression that my reading has left me with.
Stephan, thanks for you response (and I meant to thank you earlier for all your great writing on health).
I still have a lot of digging to see what the salt levels might be/have been for polynesians and other groups. As you know, the devil is in the details on these estimates not using urine excretion.
You may be right that non-industrial diets include much less salt. One piece of evidence I can find (with the caveat noted above) is here, where the author notes one estimate of Chinese sodium intake from 300 BCE was around 3,000 mg/d for women and 5,000mg for men http://www.ncbi.nlm.nih.gov/books/NBK50958/ Even if the estimate is accurate, they could be an outlier and not representative of past consumption.
My primary research concern isn't actually on salt's connection to weight, but its connection to hypertension/CVD. At the moment, I believe it probably isn't the most significant aspect of these health outcomes. Or, more importantly, there are far easier dietary approaches (increasing potassium, e.g.) to curtailing these risks.
I look forward to reading any further analysis you do on the salt issue! And I'll look into what we've discussed here more and get back if I find anything interesting.
-Michelle
Thanks for your reply Stephan! I'm not sure if I already submitted this response (if I did, my apologies), but getting data on prehistoric consumption of salt--or anything--is pretty hard, as you know. At least one paper I've read notes that "some cultures in China" in 300 BCE were consuming between 3,000 and 5,000 mg of sodium a day. That's not paleolithic, but it is pretty far back. Of course, these could be outliers, not representing the experience of most people in that age. Slighter closer to modern day, post industrial British/French in 1850 ate more sodium than Americans do now; an average of 4-5,000 mg (China/France/Britain reference at bottom).
There's some oral history that Native Americans used to boil water from salt springs to produce salt (but how much they ate and how widespread the practice was is unknown).
It's a super fascinating topic (my focus is on salt and blood pressure/CVD not so much weight) I'll definitely look into this historical aspect more and I look forward to reading follow up posts on the issue.
Since I forgot to say it my lat post: I've been enjoying your blog for a few years now. You are one of the only writers on nutrition that I trust to be even close to objective.
-M
IOM paper discussing pre-historic sodium consumption http://www.ncbi.nlm.nih.gov/books/NBK50958/
Hi Michelle,
Thanks for the additional information. I don't claim to be an expert on historical use of salt and perhaps the story will turn out to be different than what I thought. There is certainly genetic variability in salt retention genes, suggesting that some populations may have been exposed to more salt than others, historically. It does seem like an interesting question to get to the bottom of; I wonder if anyone has done a systematic review of the literature on salt intake in ancient and historical non-industrial cultures? The paper you referenced had some interesting information along those lines.
Awesome write up Stephen, it seems like a complicated subjects that needs more clarification. Appreciate your balanced on non dogmatic view on nutrition.
It's logical - high sodium intake (over the optimum) generates overeat (excess calories in carbohydrates, proteins too), leading by sodium-induced energy deficit. This is a part (one of the symptoms) of the ignored Sodium-Induced Disorder Syndrome.
Z. Sandor: Sodium-Induced Disorder Syndrome. Where have all the sciences gone?
BMJ Online (13 April 2016)
http://www.bmj.com/content/351/bmj.h4962/rr-45
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