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 ?

82 Comments.

  1. Annie – You are correct.

    Binging is often a sign of an eating disorder like bulimia, anorexia and even cases of people dieting for too long. People who binge can and do eat EVERYTHING when they have an episode, consuming thousands upon thousands of calories in a matter of hours.

  2. I’ve had ‘pudding’ (a savory food) and ‘scrapple’ a few times from different vendors, and each time it tastes very sweet! The ingredients include things like pork skins, pork snout, liver, etc. The vendors i’ve purchased from assure me no sweeteners are added, and none are listed in the ingredients.

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  4. In last few months, with very little carbs, mostly meat and lots of animal fat, I have very little real cravings. I mainly eat when I detect my stomach has been empty for a long time.

    BTW: I avoid grains (gluten), and dairy (casein protein) and any refined sugars.

    I have never felt better. My weight is stable.

  5. You forgot to mention one very important thing – serotonin.

    Perhaps sweet taste is due to serotonin deficiency:

    http://www.ncbi.nlm.nih.gov/pubmed/8697046

  6. Hi majkinetor,

    Emily Deans had a piece on the Wurtman’s theory, apparently it has been debunked: http://evolutionarypsychiatry.blogspot.com/2011/08/do-carbs-keep-you-sane-midmorning-post.html.

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  10. Dr. Jaminet,

    Can you spend on this post from Dr. Simone?

    ARE ALL SUGARS HARMFUL?

    The answer is No. There are scores and scores of different types of sugars each having different properties, metabolic pathways, and functions. The most familiar to you might be glucose, sucrose (table sugar), lactose (in milk), and fructose (fruits and corn). But some people in the media and some scientists lump them all together and use the word sugar inappropriately.

    SUCROSE is composed of 50% glucose and 50% fructose. Sucrose is the sugar that is commonly added to foods for sweetness in biscuits, cookies, cakes, pies, candy, ice cream, sorbets, and beverages. It is a common ingredient in many processed and so-called “junk foods.” Sucrose is broken down and provokes a rapid rise in blood glucose that increases the risk for obesity, cardiovascular disease, cancer, metabolic diseases, renal complications, vision deterioration, and tooth decay. Some cancers have insulin receptors that allow glucose to attach and feed the cancer.

    HIGH-FRUCTOSE Corn Syrup is a misleading term allowed to be used in the US that represents a combination of glucose and fructose, just like sucrose. In this instance glucose is added to fructose to make this combination sweeter. In Great Britain and Canada, it must be called what it is: glucose-fructose.

    FRUCTOSE is the sweetest of all sugars and is found in many plants like fruit and corn. Fructose is absorbed directly into the bloodstream during digestion, then into the liver and not regulated by insulin at all.

    The GLYCEMIC INDEX measures how a particular sugar in a food will raise or lower the blood glucose level. Glucose, the sugar to which all other sugars are compared, is defined as having a glycemic index of 100 and all other sugars have a lower glycemic index. Foods that are digested quickly and release glucose rapidly into the bloodstream have a high glycemic index.

    LOW GLYCEMIC INDEX FOODS: Fruits, vegetables, legumes, nuts, fructose (glycemic index is only 11), kidney beans, chick peas, converted white rice. I chose fructose as the sweetener for Simone Super Energy because it has a very low glycemic index and is not regulated by insulin.

    MODERATE GLYCEMIC INDEX FOODS: Whole wheat products, basmati rice, sweet potato, sucrose, baked potato.

    HIGH GLYCEMIC INDEX FOODS: White Bread, White rice, corn flakes, glucose, maltose, and extruded foods like pastas, many breakfast cereals, Fig Newtons, premade cookie dough, some french fries, certain baby foods, ready-to-eat snacks, Murukku, Sevai, Idiappam, and jalebi. In the extrusion process, raw materials are first ground to the correct particle size, then mixed with sugar or fat or dye, or meat etc.

    For a complete list of 750 foods with their glycemic index
    http://www.ajcn.org/content/76/1/5.full.pdf+html

    Charles B. Simone, M.MS., M.D.

  11. I posted the Dr. SImone thing. My question is, the man is villifying glucose and saying fructose is good. It was his sweetener of choice for a product he made. I understand fructose to basically be a poison. How is he supporting it?

  12. Hi Scott,

    I certainly disagree with vilifying glucose. We went over a lot of the issues in the safe starches debate, see my post “How to Avoid Hyperglycemic Toxicity”, http://perfecthealthdiet.com/?p=4937.

    Even at low doses fructose has minimal benefits and it fairly quickly becomes harmful. Its low glycemic nature is actually an indication of its toxicity — it’s not allowed to circulate freely in the blood.

    I don’t know why Dr Simone would support fructose.

    Best, Paul

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  15. Dr. Jaminet,

    I also agree with your point that food cravings are driven by nutritional deficiencies, but how does that explain some of the research findings that show reduced food cravings after exercise? I don’t think exercise satisfies any nutritional deficiencies. These research findings rather support the hypothesis that food cravings may also be some form of “self-medication,” because sweets and carbohydrates spur release of serotonin and other feel-good brain chemicals, and so does exercise.

    But those researches might be flawed, I haven’t even read them myself because I don’t know where to find them. I just read about it in a few articles on the internet.

  16. Thanks for the interesting reads.
    I like the hypothesis you place, linking sweet craving in humans with a diet that started to include animal proteins/fats.
    Although very intersting, I would argue it may be omitting certain other facts. I think it passes too much on the possibility that a sweet taste evolved already long before humans evolved, and humans were simnple successors of the sweet taste. Of course, we see many animals enjoying the taste of sweet fruit. In very ancient times, when plants had just evolved from non-flowering/fruiting to flowering and fruiting species, hypotheses suggest that plants suffered from animals drawn to eat the fruits, while not distinguishing unripe from ripe fruits, not allowing seeds to mature and putting pressure on the plant species’ survival. It is suggested that fruiting plant species started to evolve color and sweetness as a message to the animals eating the fruits, in an intricate, interdependent evolution between those plants and their ‘clients’.

  17. Hi Paul!

    I have a question for you. I have just begun the diet a few weeks ago. My supplement schedule is almost complete, but my iodine has not come in yet so I have not begun that one. I have suspected I am hypothyroid for several years now, but I have no health insurance and so have never been tested. When I was taking my basal temp. about 6 years ago, though, it was consistently very low. I also have had irregular and extremely painful menstruation, fatigue (not crippling, but unpleasant), PMS, intermittent mild depression, constipation, diminished sex drive, and dry skin. Strangely, some of these symptoms worsened after I had my son 2 years ago, while others improved.

    The main question I have here is about sugar craving and binge eating. I have had on and off problems with binge eating that began over 10 years ago when I went on a calorie restricted, low-carb, low fat diet. At the time, I lost a tone of weight, my bodyfat got below 10%, and I stopped menstruating. This horrible diet was suggested and encouraged by my martial arts instructor at the time! Anyway, I went through a 2 year severe binge period after that. This was mostly cured when I began a diet based on “Nourishing Traditions”, which I maintained throughout my pregnancy.

    Currently, I have been following a rather erratic diet for the past few years. My son had severe colic, and I tried numerous restrictive diets in order to help him when I was breastfeeding, and life has been so hectic since then, I am just now getting around to addressing my health and diet more fully again. I am under pretty severe stress right now. I split with my husband two months ago, moved into my father’s house, started a new job, and am in school as well. I am raising my son mostly by myself. I’m sure all of this stress is not helping my health much, but I am doing my best to optimize diet, sleep, and exercise to be able to handle all of this with some degree of grace!

    Since I began your diet, my sugar cravings and desire to have persisted. I know that the desire to eat, say, a quart of ice cream each evening, is fueled by my stress levels. I am hoping that, with more time trying my best to maintain your diet (excepting the excess fructose consumption, of course), that the desire to overeat will begin to pass? I did manage to stop the sugar indulgences for about a week, but another stressful day brought them back. My energy/will power to resist is at an unusual low these days. Any advice?

    I am within a healthy weight range for my size, BTW, if a littel on the heavy side of that range.

    • Dear Carmelita,

      I see your post is a few months old so you may have moved on and won’t see this but thought I would take a shot at some suggestions for you in case you check back here. For your thyroid health and adrenal/ overall metabolism I would encourage you first of all not to fixate on weight ever again or diet ever again, but rather to focus on health. You really damage your health by adopting a end justifies the means attitude about dieting to try and force your body to be thin. Dieting and starvation are major causes of stress that damage the glandular system and metabolism. I don’t mean necessarily short occaisional 24 hour or less fasts, but prolonged calorie and food group restriction such as where carbs are cut out. Your period of doing this I’m sure had a lot to do with your present problems. Some people however can’t do short fasts without suffering sleep problems because of weakening themselves from previous starvation. Next iodine and selenium might help. Also have your ferritin checked, not just hemoglobin and hematocrit. It should be seventy or higher. Menstruating women often don’t have enough iron in storage for optimal thyroid function. You can learn more about this at stopthethyroidmadness.com. Lastly, if you do feel you need to try thyroid supplementation and can’t do it through a doctor due to lack of funds for al the doctors fees and testing costs due to lack of insurance or because of inability to find a doctor that will treat based on clinical evaluation rather than tests, you can treat yourself. You can learn at the previously mentioned site and at realthyroidhelp.com or org can’t remember which.

  18. The taste for sweets could be a craving for potassium. I think you sort of say this in the latest edition of your book. One of the dangers of these candida diets is not getting enough potassium, and then later consuming higher potassium containing foods almost gives a deceptive ‘flare up’ type reaction.

  19. Dear Dr. Jamite. I’ve just finished to read your Book, my best compliment for the work done.

    I don’t agree about fructose. I agree in high amount is very toxic, but I think that in low amount especially during fasting or a low carb diet,it’s a very powerfull anti-catabolic sugar.

    In the liver there is an amount more or less of 100 grams of glucose (sorry I don’t know in pounds how much it is). Now if I usually havea low-carb and low-cal diet, for example for two days at week, with intermittent caloric restriction (that it means more powerfull than intermittent fasting and caloric restriction) can fructose help to safe catabolism of proteins?

    Gluconeogenesis uses proteines and other means to create glucose, and it’s in the liver that everything happens. Now Is it possible that fructose help to avoid to use proteins to do that?

    I read that in lots sports a mix of fructose and glucose help to recover fast that only uses of glucose. This must mean something, do you think so?

    what’s your opinion about?

    Thanks for your attention, bye.

  20. Maybe, as Freud said, “A cigar is just a cigar.” No phallic homosexual implications, it’s just a smoke.

    Maybe evolution didn’t have a “purpose” in making sweet so appealing. Certainly there are few natural hyper-sweet foods, and if there are, limited seasonal availability.

    I think it rather anthropocentric to assume that our bodies were thought out like making a car. We carry a lot of DNA without purpose, but there it is.

  21. I believe that at one time, we were able to synthesize Vitamin C, but that we can no longer do so. Is this current state of our biology the result of our eating fruit, as an early species? If we think about this in anthropological terms, maybe our reaching up for fruit, was one of the reasons we began to walk upright.

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  23. Hi Paul,

    I am having some difficulty drinking my coffee without sugar… I tried rice syrup and don’t really care for it… I thought about buying granulated dextrose (that would be safe right?) then I found unrefined organic coconut sugar. It tastes amazing (like brown sugar)! I’m afraid it’s too good to be true. I assumed if coconut oil is safe then… maybe… coconut sugar would be too. Thoughts?

  24. Hi Paul,

    I wonder if there is a way to actually use my cravings to find out what I am deficient in. Let’s say I have a bad craving, but for nothing special in particular. I could eat a bit of red meat and wait for 30 minutes and see if the craving is still there. If so, I could go ahead and take some vitamin C and wait for another 30 minutes, and so on. Could you please tell me which foods or supplements I should eat in which order and in which amounts in order to zoom in on the nutrient that’s lacking? How long should I wait in between? To tell from my symptoms (eczema, headaches, brain fog) I am probably histamine intolerant).

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