Why Did We Evolve a Taste for Sweetness?

After I did my post on Seth Roberts’s new therapies for circadian rhythm disorders, Seth learned of my experience with scurvy and blogged about a similar experience of his own.

Seth made the important point that food cravings are driven by nutritional deficiencies – a point I heartily agree with, which is why it’s so important for those seeking to lose weight to be well nourished – and asked, “Why do we like sweet foods?” His suggested answer was that the taste for sweetness encouraged Paleo man “to eat more fruit so that we will get enough Vitamin C.”

This led to a fascinating contribution from Tomas in the comment thread:

I have read several books on the Traditional Chinese Medicine and they attributed that increased craving for sweets is in fact signaling some serious nutritious deficiencies. They said that it’s in fact meat or starches or other nutritionally dense foods that will soothe the craving, but sweets are more readily available. The taste of meat is in fact sweet as well.

In my experience this seems (the TCM view) to be true. I always have been very skinny, but eating enormous amounts of sweets. After I switched to a proper, paleo-like diet, the situation changed in many aspects and I no longer have such strong cravings and slowly I am gaining some weight.

Shou-Ching and I have great respect for the empirical claims of Traditional Chinese Medicine, and so I found this a fascinating idea. Is our modern taste for sweets actually derived from a taste that evolved to encourage meat eating?

Human tastes

It is generally agreed that animals evolved the sense of taste to detect nutrients and toxins:

Taste helps animals to decide whether a food is beneficial for them and should be consumed or whether it is dangerous for them and should be rejected. Probably, taste evolved to insure animals choose food appropriate for body needs. [1]

The five basic human tastes are sweet, salty, sour, bitter, and umami. Each taste detects either a nutrient class we need or toxins we should avoid:

  • Sweet – carbohydrate.
  • Salty – electrolytes.
  • Sour – acids.
  • Bitter – toxins.
  • Umami – glutamate and nucleotides.

Electrolytes are essential to life, and toxins best avoided, so the evolution of salty and bitter tastes is easy to understand. The umami taste is mainly a sensor for natural (healthy) protein. The sour taste is interesting, in that it is attractive in small doses but aversive in large. Seth argues that low-dose sourness is desirable because it leads us to seek out fermented foods, which supply probiotic bacteria and their fermentation products such as vitamin K2. If so, it is natural that strong sourness, indicating high bacterial populations, would be aversive.

But what of the sweet taste? Is it really a sensor for carbohydrates? If so it does a rather poor job. The healthiest carbohydrate source – starch, which is fructose-free – hardly activates this taste, while fructose, a toxin, activates it in spades. If this taste evolved to be a carbohydrate sensor, it should have made us aversive to the carbohydrates it detects, as the bitter taste makes us avoid toxins. But sweet tastes are attractive!

Sweetness activators

It turns out that the sweetness receptors are complex; many things activate them, and they appear to serve multiple functions.

Wikipedia (“Sweetness”) notes:

A great diversity of chemical compounds, such as aldehydes and ketones, are sweet.

Some of the amino acids are mildly sweet: alanine, glycine, and serine are the sweetest. Some other amino acids are perceived as both sweet and bitter.

The sweetness of some amino acids would seem to support Tomas’s assertions that sweetness detect meat: perhaps it is detecting amino acids. But this seems a bit odd: there is another taste, umami, that detects protein. Would we really need two taste receptors for protein? And lean meats don’t taste sweet.

A possible clue is that the sweet tasting amino acids are hydrophobic, while hydrophilic (or polar) amino acids are not sweet.

Proteins that are hydrophobic end up lodging in cell membranes alongside lipids; proteins that are hydrophilic dissolve in water and reside apart from the fat. Glutamate and nucleotides, which are detected by the umami taste, are hydrophilic and water-soluble.

So maybe the umami taste detects proteins that aren’t associated with fat, while the sweet taste detects proteins that are associated with fat.

Indeed, a leading theories of sweetness holds that compounds must be hydrophobic, or fat-associated, in order to invoke the sweetness taste:

B-X theory proposed by Lemont Kier in 1972. While previous researchers had noted that among some groups of compounds, there seemed to be a correlation between hydrophobicity and sweetness, this theory formalized these observations by proposing that to be sweet, a compound must have a third binding site (labeled X) that could interact with a hydrophobic site on the sweetness receptor via London dispersion forces. Wikipedia (“Sweetness”)

The sweet taste seems to work in collaboration with the bitter taste to regulate toxin avoidance. Wikipedia (“Sweetness”) again:

Sweetness appears to have the highest taste recognition threshold, being detectable at around 1 part in 200 of sucrose in solution. By comparison, bitterness appears to have the lowest detection threshold, at about 1 part in 2 million for quinine in solution.[4] In the natural settings that human primate ancestors evolved in, sweetness intensity should indicate energy density, while bitterness tends to indicate toxicity[5][6][7] The high sweetness detection threshold and low bitterness detection threshold would have predisposed our primate ancestors to seek out sweet-tasting (and energy-dense) foods and avoid bitter-tasting foods. Even amongst leaf-eating primates, there is a tendency to prefer immature leaves, which tend to be higher in protein and lower in fibre and poisons than mature leaves.[8]

This makes some sense: we need a certain number of calories per day, and since “the dose makes the poison,” what determines the toxicity of the diet as a whole is not the amount of toxins in a food, but the ratio of toxins to calories. In an evolutionary setting, our ancestors needed to eat foods with a low toxin-to-calorie ratio in order to minimize daily toxin intake.

So if sweetness is an “energy density” detector, it should be especially strongly activated by fatty foods. If it detects fat-associated compounds, then it would do so.

Why not detect fats directly? In natural foods, fats are bound in triglycerides or phospholipids which are chemically inert. So they won’t bond to taste receptors. Free fatty acids will, but these are not present in fresh foods and would probably indicate some kind of degradation of the food. In fact there seems to be a taste receptor for free fatty acids, CD36 [2], but this may be an aversive sensor for decayed food.

Interestingly, color also affects sweetness:

The color of food can affect sweetness perception. Adding more red color to a drink increases its sweetness with darker colored solutions being rated 2–10% higher than lighter ones even though it had 1% less sucrose concentration.[26] Wikipedia (“Sweetness”)

So red meats are sweetest. Richard Nikoley would approve.

Summary and A Puzzle

A plausible inference would be:

1.      The sweet taste evolved primarily to encourage the eating of fatty, energy-dense meats; and of essential fat-associated micronutrients such as choline and inositol.

2.      The sweetness of fruit may result from plants having evolved a way to hijack the sweetness receptors, and animal food preferences, for their own purposes.

This still leaves a few puzzles. Why, Seth asks, do we tend to neglect sweet tastes when we are hungry, but after dinner is done crave sweet desserts?

Here’s something to consider. Fats are a special macronutrient. We have unlimited storage space for fats, in our adipose tissue, but very limited storage space for other calories. Once we’re full, of course we should lose our appetite for calories we cannot store. But for fats, why not get a little extra in case food is scarce in days to come? There’s always room for a little more fat.

Implications for Binge Eaters

Correct me if I’m wrong, but when people go on an eating binge, they go for sweets.

Presumably, they have a craving for the sweet taste – which, evolutionarily, may be a craving for fatty meats and fat-associated micronutrients.

But if they’ve imbibed the anti-fat propaganda of recent decades and are afraid to eat fat, binge eaters must follow their taste buds to sugars – which unfortunately fail to satisfy any of the micronutrient deficiencies the sweet craving is designed to redress.

Perhaps, then, a good fatty steak, preferably accompanied by some liver and cream sauce, would be the best cure for binge eating. It would satisfy the craving, but also satisfy the underlying nutritional need that generated the craving.

Implications for Weight Loss

If, as I believe, the key to weight loss and curing obesity is eliminating appetite, then it’s important to eliminate any deficiencies of fat-associated micronutrients. Micronutrient deficiencies trigger food cravings, and deficiencies of fat-associated micronutrients will trigger a craving for sweets.

In the modern world, we know how a craving for sweets is likely to be satisfied – by eating sugary, nutrient-poor foods. Unfortunately these foods do not contain the fat-associated nutrients (such as choline) whose deficiency is probably driving the craving. So the craving persists unabated no matter how many sugars are eaten.

Persistent food cravings despite an excess of caloric intake is probably a necessary (though not sufficient) condition for obesity to develop. Unsatisfied cravings probably make weight loss extremely difficult.

What of Vitamin C?

Vitamin C – ascorbic acid – is an acid so it directly activates the sour taste.

So perhaps the sour taste evolved to help us get vitamin C. This would actually complement Seth’s idea that the sour taste encourages us to eat fermented foods. Fermented foods are high in vitamin C.

I had a fairly severe case of scurvy and don’t recall being attracted to sweet flavors. Instead, I was ravenously hungry. My appetite generally, not craving for any particular taste, was promoted. If anything, I was less attracted to sweet tastes. So I think it’s plausible that vitamin C deficiencies may lead to a general appetite upregulation, or to cravings for sour foods, rather than a craving for sweets.

Conclusion

Our evolved taste receptors can tell us a lot about what our bodies need. Food cravings are a pretty good sign of an unsatisfied nutrient deficiency.

But sometimes, it’s less than obvious what a craving signifies. Our modern food environment is so different from the Paleolithic: We have many industrially produced foods designed to fool our Paleolithic taste buds into eating nutritionally unsatisfying calories.

Humans evolved, not in the forests where fruit was available, but in open woodlands where tubers and other tasteless starch sources were abundant but fruit rare. In this context, our cravings for sweet foods may have been directing us to eat animal fats.

It may be that the cravings for sweets often experienced by binge eaters and the obese are really a craving for animal fats. If you feel drawn to sugar, perhaps you should ask yourself: Steak or salmon?

References

[1] Bachmanov AA, Beauchamp GK. Taste receptor genes. Annu Rev Nutr. 2007;27:389-414. http://pmid.us/17444812.

[2] Laugerette F et al. CD36 involvement in orosensory detection of dietary lipids, spontaneous fat preference, and digestive secretions. J Clin Invest. 2005 Nov;115(11):3177-84. http://pmid.us/16276419.

Leave a comment ?

81 Comments.

  1. Having lived this crazy craving roller coaster for decades (and finding lots o’ relief in a nutrient-rich diet that’s very PHD-like), I’d have to say I suspect you’re right … that some/much of the cravings (or other appetite disproportionate to energy intake) are related to missing micro-nutrients, *especially* the fat-soluble vitamins.

    That said, I think a lot of overeating is related to other aspects of the SAD diet … the ones that start getting into the addiction/dependency space (I still haven’t dug into this, http://bit.ly/gD4deV, which I find very compelling given the excess omega 6s in our diets today). But of course there are the other potential problematic pathways with dopamine, serotonin, and opiod peptides in wheat etc.

    But putting the two together is a bit of a perfect storm. Something that we evolved to use before industrial food now really bites us in the butt because what’s now “sweet” is really toxic!

  2. Fascinating! I’ve always believed that fructose was a hijack of our taste buds, but I was never totally clear on exactly what was hijacked.

    However, I must point out that starches can indeed taste sweet: the longer you chew them, the sweeter they get, as the amylase in your saliva breaks them down into glucose. So it may be that the human taste for starch is a misapplication of a fat taste receptor as well: but where fruits intentionally hijack the receptor, the tuber/starch craving is purely an evolutionary accident. Tubers don’t want to be eaten, unlike fruit.

    “There’s always room for a little more fat.” Ha! I just wrote an article about this, which I think you’ll find amusing and relevant:

    “Why Humans Crave Fat”
    http://www.gnolls.org/1763/why-humans-crave-fat/

    JS

  3. it seems to me from observation that when protein intake is adequate sweet intake is minimized or absent. Women who try to diet a lot and do not take in adequate protein seem to crave sweets. I have notice this with the females both in my office and huosehold: adequate protein; little to no sweet cravings; protein absence mainly through cutting calories and fear of fat, carb craving, usually sweets.
    I just wonder whether the search for sweets is related to breast milk in humans in any way.

  4. This has many good ideas. Donny of naivenutrition has some very interesting blog posts on tastes and foods/nutrients.

  5. Fascinating.

    What do you think about Seth’s theories regarding the non nutritional factors, such as palatability, that tend to promote a different weight set point?

  6. Hi Beth,

    Thanks for the link, neat ppt. I agree – toxins are killing us!

    Hi JS,

    Great post!

    Somehow I overlooked your blog before – I’ve added it to the blogroll.

    Hi Steve,

    Proteins are convertible to glucose and can substitute for it, so definitely high protein intake should reduce carb needs; and protein satisfies both sweet and umami tastes, so it addresses the taste desire.

    I do think the sweet taste is adapted for both carbs and fats … thus human milk sugars activate the sweet taste. But while the literature emphasizes the carb sensing, I suspect the fat sensing may be as or more important evolutionarily.

    Hi John,

    Looks like an interesting blog, thanks for introducing it.

    Hi Todd,

    I think they’re very interesting and clearly they work for a lot of people.

    This whole issue of appetite has a lot of subtleties to it. Thank goodness people like Seth are exploring them – if we waited for NIH-funded scientists to explore these issues, we’d have to live to 200 to get answers.

  7. Interesting ideas.

    Also, as Wiki writes: “Even amongst leaf-eating primates, there is a tendency to prefer immature leaves, which tend to be higher in protein and lower in fibre and poisons than mature leaves.”

    The same idea could also apply to animal protein. Are the healthiest cuts of meat and fish, sweeter somehow due to their amino acid profile? Sushi quality tuna and salmon tastes sweet to me.

    Something else I find puzzling is the sensitivity, or perhaps gullibility, of our sweetness receptors. Why is sucrose so much sweeter than lactose despite both having the same chemical formula? Our salt receptors seem to be much less discerning (ie KCL vs NaCl).

  8. Hi Paul,

    the mother milk’s sweetness is actually what I thought to be the origin of our sweet taste.
    It’s essential to crave sweet mother milk for babies to survive the first months/year. And during this time there is a positive feedback loop (sweet=well beeing) which may last a lifetime. And human milk is much sweeter then cow milk (do cows crave sweets?).
    I agree that vitamine c is linked with the sour taste. You don’t even need fermented food because I suspect fruit in the good old paleo times was much less sweet and more sour (like today’s lemons), like fruits the chimpanzees still eat in the wilde.

  9. anand srivastava

    Fat could be a very big possibility for the sweet taste because our initial evolution from Chimps happened due to scavenging fatty brain and bone marrow.

  10. I read that once supplementing magnesium chocolate (rich in magnesium) craving disappeared for some people.

  11. Fats (a energy dense food) may not be so attractive like sweets because the latter are fast acting, fats needs more time to give us energy (not true for MCFA that act like carbs).

  12. Hi Paul,

    This reminds me of Vince Gironda who wrote in the 50s that if you’re craving sugar you need to eat more protein.

    Of course aimed at bodybuilders but I’ll try and dig out his original references to see his sources. As usual he was ahead of his time so I’m sure there’s something to it.

    WP

  13. Hi Paul,

    thank you for using my comment, it resulted into a terrific post.

    I also have respect for the TCM. I guess we will be seeing more TCM nutritional dogmas being explained by serious science.

  14. ha. I had a really *interesting* and alarming experience the other morning that relates to your taste reference for bitter.
    I was eating Greek yogurt mixed with a few frozen raspberries. First bite, I bit into something crunchy- following the crunch was a bitter taste explosion (not what I was expecting for yogurt and raspberries)– I removed the object from my mouth to inspect, thinking it was a raspberry stalk or leaf, and discovered I was chewing on a GRASSHOPPER. Very bitter! NOT supposed to be there! I guess it was in the bag of frozen (organic hahah yeah, no pesticides used here) raspberries (from Chile).

  15. Hey Ellen,

    it must have been a grasshopper gone bad! When I was eating them fresh as a kid (to win a bet here and there) they tasted nutty. Not too bad actually except of the chewiness (is this a word even?). I don’t remember them beeing overly bitter.

    kratos,

    good point! Actually coconut oil (more MCT’s then any other fat) does taste sweet to me.
    I really enjoy a spoon here and there.

  16. Paul, found this post interesting because it really shows the two sides of PHD.

    What I don’t like about PHD is the idea of you and Shou-Chin as taoist monks, passing out little pills, saying, eat this, and you’ll live forever. Now, obviously I am drawing a bit of straw man (woman?) here. And I’m not condemning Chinese medicine either. There are a lots of interesting ideas from Chinese (as well as Western and Indian) traditional medicine. What I don’t like is the assumption that you are unwell and starting from the stance, rather (as I think Dr. Harris has said) the focus needs to be on eliminating poison.

    Now what is great about PHD isn’t so much the answers, but the questions you are posing. That being said, you may be over thinking this a bit much. Mothers milk, certain fruits, don’t need complex explanations. However, the process of answering the questions brings a lot of interesting science into play.

    My personal experience is when I have a good carb intake I am not craving sweets; however when I have too much protein in my diet (and not enough carbs) I do have a sweet tooth.

    Couple other ideas to throw out there:

    1) Quality matters: are there levels of quality in sweetness that will satiate the craving?

    2) Regional: Sugar evolved in India, spread to the mid-east then the west. My impression it is still low in Asia. Are there regional distinctions in sweet tooths, or is it a universal craving?

    3) Steak, salmon or EGGS?

  17. Hi all, very interesting thoughts, thank you!

    Tomas, thanks for the idea, it was very stimulating. What do you think is a good book in English on TCM?

    Hi Robert, we’re not really taoist monks, and we don’t assume people are unwell. But I think nearly everyone can be better; and almost everyone becomes unwell at some time or other. Since eliminating poison is our Step Two, there’s not much space between us and Dr. Harris.

    If we emphasize therapy on the blog, it’s because (a) I think we’ve figured out how healthy people can stay well, and it would be boring to keep blogging the same advice over and over; but there’s still a lot to learn about how to use diet and nutrition as therapy, and that’s what drives my research right now; and (b) there are a lot of people who can be helped by these ideas, since no one else is formulating or publicizing them, and most people with diseases use ineffective strategies, which is why diseases are rarely cured.

    Two days ago I would have agreed that this was overthinking the sense of taste. But Seth persuaded me otherwise. I think this is one issue where the Paleolithic (and earlier) environments were radically different from the modern human environment, and we need to do evolutionary thinking in the context of primates 20 million years ago.

    Your experience with carbs reducing the sweet craving makes sense – increasing carbs on a low-carb diet reduces protein and fat needs too. The sweet craving when you eat too much protein may be a sign of protein toxicity – your body is sensing that your diet is too high in protein and wants you to eat energy dense (carb+fat) foods. So maybe the sweet taste is intended to detect carbs and fats and shift diet away from protein.

    However, as Winalot / Vince Gironda point out, carbs and protein are substitutes to a degree and eating more protein reduces need for carbs, and may reduce a sweet craving. So it’s complex.

    Definitely I think there are regional differences in taste: Asians eat far fewer sweets and more sour. I don’t know if this is cultural or diet-context-dependent or genetic.

    Yes, eggs would have worked too!

  18. @Paul; How do we know you’re not Taoist? Prove it! 😉

    As I said before, every man over 40 has to be his own physician. I’d say there is a difference between this an therapy — asking yourself is your current habits are healthy. Certainly what I do now is different than 10 years ago.*

    Another PHD related though: all this talk about macronutriets is just confusion. Food is food, and it is the micronutrients that are important. The macro side is somewhat useful for weight loss, and to some degree weight maintenance, but other than than not helpful when looking at health.

    * I should tell you the reason I am a reader is your point about Vitamin C and scurvy. I always had bad gums that bled. Assumed it was dental issues. I noticed some small razor cuts that weren’t healing quickly, saw your post about scurvy, and thought, no, that’s not possible. Two days after taking Vitamin C the gums stopped bleeding.

  19. I have read just 3 or 4 and I definitely wouldn’t label myself as an expert. We have quite a lot books in our library, and upon inquiring my wife, it turns out that those books we had on TCM were borrowed from friends and we don’t have them anymore. However, I’ll try to track them down and let you know.

    On a related note, right now I am reading all Stephan Guyenet’s posts and one of his early pieces touches the topic – and reading Stephan is never time lost:
    “Our brains are wired to respond to the stimuli with which they evolved. For example, our natural taste preferences tell us that fruit is good. But what happens when we concentrate that sugar tenfold? We get a superstimulus. Our brains are not designed to process that amount of stimulation constructively, and it often leads to a loss of control over the will, or addiction.”

    http://wholehealthsource.blogspot.com/2008/03/superstimuli.html

  20. Paul, re sense of taste, I’m in the first quarter of a nutritional therapy program that uses neuro-lingual testing as a way to identify solutions to nutrient deficiencies.

    I’m *very* skeptical about this, but the idea that we, like other animals, were able to taste things and determine whether or not they were good for us seems plausible. I’ll have to see if I can find the diagram online that’s in our notes. Curious!

  21. Hi Robert,

    I do think toxin avoidance and micronutrition, our Steps Two and Three, are the most important. But we put Step One, the macronutrients, first because it’s important for people to get over their fear of fats, and because it’s a lot easier to give up wheat if you believe in a low-carb diet.

    Still, there must be a reason why nearly all animals evolved to get low-carb nutrition. I don’t think macronutrients matter as much as some low-carb advocates, but I think there’s some modest health improvement when low-carbing – as long as it’s not too low carb.

    Glad your subclinical scurvy is finally fixed! It shouldn’t take decades to figure these things out … but with our current state of medical and dental knowledge, alas, people get no help.

    Hi Tomas,

    Yes, Stephan always rewards reading!

    My wife has an interest, if she ever gets so successful that she can research whatever she wants, in researching why and how Chinese medicines work. If there is a good resource to help us formulate some research ideas, then maybe that will actually happen. Life is short, though, and art long!

    Hi Beth,

    Sounds fascinating! Interesting if it works.

    Best, Paul

  22. Hey Paul,

    The traditional theory in the paleosphere is that the sweetness in fruit encouraged us to fatten up at the end of summer when fruit was available (by eating fat-storing fructose) for the sake of surviving the winter. In this theory, the food cravings are driven in the way that Taubes describes in GCBC, namely, calories in the diet are getting stored as fat rather than being available for fuel to the body, perpetuating hunger.

    This still seems the most plausible to me. The idea that the sweetness taste bud has evolved to detect anything other than fructose or very easily digestible glucose, seems pretty implausible given that it is activated in such a strong way by these compounds.

  23. Paul, oh, and one more thing re taste. This too goes in the “oh, really?” category, but we’re also being taught that you can check sensitivities to food by checking someone’s pulse for a full minute, then having them put the food in their mouths and then re-checking the pulse. An increase of more than 6 bpm is said to suggest sensitivity. It’s apparently a variant of the Coca Pulse Test (http://www.amazon.com/Pulse-Test-Secret-Building-Health/dp/0312956991)

  24. Interesting post.

    However, my mind is stuck in “new to diet” phase.

    I just finished your book. Thanks you, as I will be
    referencing it for years to come.

    I have a question that you may have addressed, if so please direct me to the post.

    I am trying to figure out iodine supplementation.

    I see the name Potassium iodide in your book. My question. Once you refer to the above mentioned you then say containing 4.6 gram iodine. My confusion, does this mean there are two types of iodine I need?
    I have read some reviews stating something about two different types, and that ratios need to be______, please fill in this blank.

    I have ordered Lugol’s 2% solution, as Idoral was too expensive right now. It will not be hear for another week.

    In the mean time I have a jar of Potassium iodide that I can dilute in water. I (to the best of my math) diluted it enough to take 1.8mg this am. I just want to know if it in itself is not sufficient coverage for the thyroid. (Hypothyroid symptoms)

    Thanks so much!

  25. Hi Beth,

    That’s true! I knew of that, thanks for reminding me. Hadn’t heard of the Coca Pulse Test though.

    Hi Betty,

    No, potassium iodide is just elemental potassium and iodine, united in a salt. Just like sodium and chlorine make sodium chloride salt. As soon as they dissolve in water they become elements again.

    If you read the label on supplements it will tell you how much iodine there is. If I recall correctly, the 130 mg potassium iodide pills for radiation poisoning are 96 mg iodine, 34 mg potassium.

    I think 1.8 mg is a lot to start with, especially if you are hypothyroid. I would start with half or one-quarter that and work up slowly. You may notice thyroid symptoms.

    Hypothyroidism is not usually simply due to iodine deficiency, and you shouldn’t expect that the iodine will cure it … but supplementation will remove one factor, and improve health overall.

    Best, Paul

  26. Paul, I just read Datis Kharrazian’s book on thryoid for a class. His big thing is that for our generation, what looks like hypothryoidism is often Hashimoto’s, and in that case, iodine supplementation can actually be problematic (http://drknews.com/iodine-and-hashimotos/). Something to consider?

  27. re: “The sweetness of fruit may result from plants having evolved a way to hijack the sweetness receptors, and animal food preferences, for their own purposes.”

    This theory implies that fruit evolved fructose to get carnivores to eat them, mistaking their flavour for meat. What about herbivores? I’d assume that herbivores don’t have a natural inclination to eat meat.
    Wouldn’t the fruit trees main target for symbiosis be animals that naturally eat lots of plant matter anyways?

    Do herbivores have the same type of sweet sensors that omni/carnivores have?

  28. Hi Beth,

    Yes, something to consider, but:
    1) The cases of iodine supplementation causing harm in Hashimoto’s hypothyroidism are rare;
    2) They seem to be almost always associated with selenium deficiency and occur mainly in countries with widespread selenium and mineral deficiencies;
    3) The ill effects are obvious, immediately detected, and quickly reversed when iodine dose is dropped;
    4) So with selenium and other micronutrient supplementation and a gradual increase in iodine intake, monitoring for symptoms, either (a) there will be no cases of trouble since the selenium will prevent it, or (b) the trouble will be detected early and the iodine dose dropped before damage to thyroid tissue is significant.

    Meanwhile, many people with Hashimoto’s report benefits from iodine supplementation, including Mario. So there are benefits that have to be weighed against any risk.

    This is an actively debated topic on hypothyroid forums. Thyroid specialists disagree about it too. Kharrazian’s perspective is the mainstream, but the pro-iodine view has some vigorous advocates. As so often – “more research is needed.”

    I think slowly increasing iodine after fixing other micronutrients is generally beneficial with very low risk of side effects. But I think the thyroid doctors distrust their patients to follow a simple supplementation program.

    Hi DancinPete,

    Great questions. These taste receptors mostly evolved a long time ago, probably around the time of the herbivore-carnivore separation in mammals, but with modifications since; there are differences in taste receptors among the primates.

    Cattle do like sweet tastes, http://www.ncbi.nlm.nih.gov/pubmed/7972408. But I wouldn’t assume they don’t like fats. Cow’s milk is predominantly composed of fat, and I’m sure cows would enjoy eating fat in the wild if they had a chance!

    Palm oil is given to cows to improve their milk: http://www.alibaba.com/product-free/101208531/Animal_Feed_Feed_Nutritional_Supplement_Palm.html

    And ruminants get indigestion, potentially fatal, from eating pure sugars. (Too much gas produced by their bacteria!)

    So I don’t know that we can exclude fat from the reason cows evolved a taste for sweetness.

  29. Hello Paul!

    Once again a great article on your blog.

    But perhaps just a quick observation in regard to your explenations about the nature of carvings. I believe you are being very (too?) reducionistic, not looking at a whole picture with only biological reasons in mind.

    Of course you can argue that this is the sole object of your scientific approach, but your writings – at least latently – assume that some material/biological elements can and do explain human (behavior).

    Looking forward to your new blog posts,
    Boštjan

  30. Paul:

    ” modest health improvement when low-carbing” Modest improvement, or just some basic weight control? What we (NHMAS II) as Americans is so out of proportion to a weight control diet (wheat based deserts, pasta, pizza in the top 5?) that just cutting them out will help with any weight issues. Personally, still not convinced wheat, especially in a high quality form, is a health issue in low doses.

    ” But I think the thyroid doctors distrust their patients to follow a simple supplementation program.” There are reasons for that — 95% of people won’t. Over or underdose.

    Here is a little factoid you might like: I have a cousin in the wholesale organic food business. HE won’t touch the stuff. When I ask why, he says, do you know what they use for pest control — copper. His claim is they overdose everything to keep the bad stuff out, hence his reluctance to eat it. Turn that on its head — perhaps that is some of the benefit of eating organic (or even eating vegetables 50 years ago) — more copper.

  31. Hi Robert,

    Well, low-carb is good for weight control. Exactly how beneficial it is for overall health, in a low-toxin well-nourishing diet, is going to be hard to determine.

    Yes, I’m not saying the doctors are wrong to think that of their patients – just that it leads to inferior recommendations. Luckily our readers are in the 5%, and we can recommend the best strategy.

    That’s very interesting about the organic crops and copper. Maybe I should eat organic more often!

  32. I think plant didn’t hijack sweetness receptor but humans used the receptors for fat craving. There are two reasons —
    1. herbivores can taste sweetness.
    2. Some pure carnivores (Cats) can’t taste sweetness.

    In prehistoric times humans needed fat to fulfill his energy requirement as we can’t burn large volumes of proteins for energy and our diet was not high in carb.

  33. People can acquire a taste for bitter foods such as tea, coffee or certain alcoholic drinks or green vegetables. However they consume it differently than sweets like ice cream. They sip bitter drinls slowly and in small quantities. Except for Popeye no-one has a craving for huge amounts of spinach. I wonder if it is related to the medicinal antipathogen effects. Animals also have been observed seeking out bitter herbs when they are sick.

  34. Amazing article. One personal observation: when I was eating calorie restricted I sometimes became really hungry in the evening and could through rather big amounts of fruit etc unless I really forced myself not to.

    At one point I realised that 10g of Roquefort (a very fat cheese) would also do the trick, and at very little calories….

  35. Although they are all very good, without a doubt, this is one of the best posts yet. I am young (21yrs old) and have not eaten any sugar besides that found in fruit and small amounts of dairy products for the past 8 years. I don’t actually ever crave sweets, and if I do it is for a banana or some a very good orange when I am done exercising or first thing in the morning. Other than that, I never crave sweets.

    However, I have found myself eating more berries lately because of their supposed health benefits, and have noticed that my craving for sweets instantly shot up. I now attribute the berry calories as snacks and the associated increase in sweet taste cravings from the animal fats this snack has displaced. The remedy? Well, it’s either a big egg omelette for dinner, or something with beef and cheese. Haha.

    THis post is dead on. I don’t know how you guys keep doing it, but your nutrition understanding is simply incredible. The best around, for sure.

  36. That’s funny Nelson, because I am also 21 years old and many people think I am weird because I find 90% dark chocolate too sweet. The only stuff I consume is 100%. I had various of my friends on the verge of throwing up when I gave them a piece of the chocolate I was eating.

  37. Ahem: There is a whole pan of dark chocolate gluten-free brownies in my kitchen, and I’ve had no desire for them all day.

    I’m crediting the supplements (I’m on all the PHD recommended supplements save kelp), and I’m particularly thinking copper has made a big difference (I’ve suspected a copper deficiency for some time as I started going gray young). Or perhaps also selenium. (I’m hypothyroid…hoping for some improvement there.)

    In any case, I feel great physically, I’ve not been binge-y or nearly as much as a sweet freak (and I’ve been known to eat an entire bag of caramels in less than an hour, and then head out to the store for more), and I’ve felt mentally stable and pretty happy. Just for what it’s worth.

  38. Hi Mary,

    That’s great!

    I do think proper nutrition makes a tremendous difference. So many people are malnourished … when we wrote Step Three of the book I was amazed at how universal malnutrition was.

    Best, Paul

  39. Great post as usual Paul.
    Interesting you should mention sweet cravings and malnutrition.
    The other day when you said that sleepiness I’ve been experiencing after lunch might be hypoglycemia I did some research and found an article by Dr. Stephen Wangen (whom I found via Jimmi Moore’s podcast) in which he says:
    “one of the primary causes of hypoglycemia is that people are not properly absorbing the nutrients from the food that they eat. These people get hungry within a couple of hours after eating, and they have to eat again, or ingest some candy to get their blood sugar back up. But it never lasts very long. These people have trouble gaining weight, though it’s not a prerequisite for having hypoglycemia. And people often will say that their need to eat is a sign of a high metabolism. This is incorrect. It’s a sign of malabsorption.”
    This description was dead on for me. I have indeed been craving sweets lately more than usual…which is very atypical for me… If what Dr. Wangen says is true then maybe I’m not absorbing fats as well as before due to a lack of gallbladder.
    I guess I should just eat more fats and protein instead of Paleo sweets I’ve been craving.
    Thanks Paul.

  40. Hi Mia,

    What a great insight. Yes, the loss of the gallbladder really does make it hard to be well nourished.

    Let us know how the higher-fatty-meat diet works! Maybe you can take bile-promoting supplements like taurine just before your meal too.

    Best, Paul

  41. Dr. Wangen, via Mia: “People often will say that their need to eat is a sign of a high metabolism. This is incorrect. It’s a sign of malabsorption.”

    This may well be true. Now that I eat high-fat paleo/PHD, I not only have more energy…I’m sure I’m eating less. I’ll frequently get through an active day with one huge meal and a bedtime snack.

    I think we’re talking about the popular perception of ‘hypoglycemia’, though (“I ate recently and now I’m tired”), not clinical hypoglycemia.

    Dr. Jaminet: Thanks for adding me to your blogroll! I’ve added the PHD blog to my list of Recommended Reading here:
    http://www.gnolls.org/1141/eat-like-a-predator-not-like-prey-paleo-in-six-easy-steps-a-motivational-guide/

    JS

  42. Hi JS,

    I noticed that too. Once I got all my micronutrition sorted out, my calorie intake went down dramatically. It doesn’t seem to take much food to satisfy me any more. I can eat one meal a day quite happily, and not a huge meal.

    Thanks for the recommendation!

    Best, Paul

  43. Paul, when you get a chance, re: the above on iodine and Hashimoto’s:

    “3) The ill effects are obvious, immediately detected, and quickly reversed when iodine dose is dropped;”

    What ill effects would one look for? I am diagnosed hypothyroid, with some indication that it might be Hashimoto’s.

    No rush, I hope everyone is having a great weekend!

    PS So fun to see Gnolls here, and PHD over at Gnolls, as I discovered both sites around the same time, and now worlds are colliding, as George Costanza says, but in a good way.

  44. “The dose makes the poison”

    No, it doesn’t. Paracelsus was an alchemyst; that statement was supposedly true of the Panacea (universal medicine) and Philosopher’s Stone – i.e., a tiny bit cured you of all ailments, more could maim you, more than that might kill you.

    In modern understanding of biochemistry, poison is a type, not an amount. A nutrient is something we need in a certain amount; less causes some problems, more causes other problems. a nutrient does not become “poison” from too little, nor from too much. In contrast, there is no amount of strychnine, e.g., that is a nutrient.

    Fructose is therefore a nutrient, not a toxin. The few grams of fructose from eating a couple servings of raw whole fruit per day is not “poisonous.” That’s absurd.

    On a related note, regarding bringing the bf% into the healthy range (the term “weight-loss” is so mis-leading as to be evil): Taubes had a link in his recent blog post to Jenny Brand-Miller et al. That study has me thinking that the answer to the French Paradox (how they can eat all that bread and not get fat) is… the French Paradox (eating healthy natural fats mutes the insulin effect of the carbs).

    So, if a certain amount of protein is minimum, and a certain amount of fat also, and a limit to total cals, then there is a limit to total carbs (but not necessarily keto).

    Since you said you read commenters’ blogs, I’ll plug my post on The Obesity Epidemic at my other (Mano-sphere) blog:
    http://attractionreaction.wordpress.com/2010/11/10/chapter-8-the-obesity-epidemic/

  45. surely fructose is not a nutrient, because it’s not essential/beneficial in any amount?

  46. Hi Mary,

    Thyroid hormones affect all parts of the body so there are many possible symptoms when thyroid hormones are out of whack.

    There are long lists of symptoms, but I like the lists Mary Shomon makes at about.com. This link: http://thyroid.about.com/cs/basics_starthere/a/symptoms.htm has basic lists with longer lists at the “checklist” pages for hypothyroidism and hyperthyroidism.

    When you add iodine, typically you may have a transient hypERthyroidism, sometimes followed by a reactive hypOthyroidism. So you have to watch for symptoms on both lists.

  47. Hi Jeffrey,

    “The dose makes the poison” doesn’t signify that small doses are beneficial, only that they are innocuous. Any toxic effects are inconsequential.

    That’s the case with fructose: its only benefits are its ability to serve as a calorie source after conversion to glycogen or fat. But glucose can do the same, with less toxicity.

    Thanks for the link, I’ll check it out.

    Best, Paul

  48. So what do you think about Ray Peats stance that sucrose is generally a superior metabolic fuel compared to starch, and that natural sources of sucrose such as fruit are generally more nutritious, more easily digestible and have lower toxin loads than natural sources of starch? If so, our taste for sweets needs to no other explanation than that it evolved to direct us to the best and least harmful sources of metabolic fuel.

  49. Hi Collden,

    I assume you mean his discussion here: http://raypeat.com/articles/articles/glycemia.shtml.

    As usual he cites a lot of old or offbeat sources that I haven’t read, and doesn’t link specific statements to sources, so it would take some work to evaluate what he says.

    For example, he cites “The experiments of Bernardo Houssay (1947 Nobel laureate) in the 1940s, in which sugar and coconut oil protected against diabetes,” but coconut oil is going to protect against diabetes in combination with anything. So I would have to look at the source to see if there’s any evidence favoring sugar over starch at all in those experiments.

    He says “Fructose inhibits the stimulation of insulin by glucose,” which I think is misleading, but even if there are circumstances in which it happens, the situation is clearly more complicated, e.g. fructose is insulinogenic when glucose levels are high, http://www.ncbi.nlm.nih.gov/pubmed/3548311.

    I think in low-carb dieters, who have glycogen storage space in their livers, it’s not a big deal to eat fructose in combination with glucose. I said as much at the end of my interview with Jimmy Moore, that it wasn’t a big deal to use sugar sweetened ice cream if you’re low-carb.

    I agree that fruit is generally low in toxins, but so are our “safe starches” after cooking. Safe starches are also easily digestible.

    I agree with Ray’s critique of PUFA, but that argues against fructose and in favor of starches, since PUFA in combination with fructose is much more dangerous than PUFA in combination with glucose.

    Since we evolved not in the forest but in open woodlands where tubers but not fruit were available, I think it’s doubtful that evolution was selecting for a starch vs sugar preference.

    Best, Paul

  50. Re: People reaching for sweets when binging. I don’t agree. Many women typically reach for starchy yet savory things like chips which combine carbs, fat and salt. Others like myself can easily binge on nuts — even low carb nuts like macadamia nuts and cheese.

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