Category Archives: Eating Disorders

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.


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?


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

[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.

Around the Web; Eating Disorders and Hypothyroidism

Items that caught my eye this week:

(1) Would You Be My Meatheart?: I wasn’t clever enough to give this to Shou-Ching for Valentine’s Day, but would have known to use genuine hearts from the Asian market. Wait till next year honey!

(2) By the way: Who knew Manolo has a food blog?

(3) Ronaldo Forced Out of Soccer for Lack of Thyroid Hormone. Famed soccer star Ronaldo is retiring because he has hypothyroidism and he says soccer authorities consider treatment to be doping – so he has to retire to fix his health.

Absurd! Mary Shomon agrees.

(4) Ronaldo may play the “beautiful game,” but we Americans play the crazy game. This running back plays football like I used to:

(5) Startling if True: Paleo Pepper abridges a talk by Dr. Flechas at claiming that thyroid hormone replacement may actually increase risk of breast cancer among hypothyroid women – what is needed is high-dose iodine:

A women with hypothyroidism has a 6% chance of developing breast cancer. Once she starts taking thyroid hormone, it doubles her chances. Once she’s been on thyroid hormone replacement for 15 years, it more than triples it – she now has a 19.6% chance of developing breast cancer.

I have not seen such statistics before and would have to check these claims. We recommend iodine and selenium as the first steps in dealing with hypothyroidism, but generally support thyroid hormone replacement.

(6) Burying the Lede: Is “strengthens pelvic floor muscles” really the number one benefit?

(7) Another Perfect Health breakfast idea: Emily suggests cream of rice with cream, butter, and apricot applesauce.

(8) Paleolithic Dairy?: Ravi at Daia Sol Gaia argues that dogs may have been domesticated and goats tamed and used for milk as early as 35,000 years ago – the start of the Upper Paleolithic. Is goat milk a Paleo food?

(9) The authentic way to drink Paleo goat milk: Paleolithic settlers at Gough Cave in England, c. 13,000 to 10,000 BC, ate human bone marrow and brain and used the skulls as drinking chalices:

Via Dienekes. Apparently drinking from human skulls is a widely attested practice, both in Paleolithic and historical times – see e.g. the Krum and Herodotus’s Scythians.

Reference: Bello SM et al. Earliest Directly-Dated Human Skull-Cups. PLoS ONE 6(2): e17026. doi:10.1371/journal.pone.0017026. Link.

(10) Avoid vegetable oils if you want a baby: Chris Highcock found a paper showing that infertile women eat 23% more polyunsaturated fat, and 17% less saturated fat, than fertile women. Infertile men eat 20% more polyunsaturated fat than fertile men.

Reference: Revonta M et al. Health and life style among infertile men and women. Sex Reprod Healthc. 2010 Aug;1(3):91-8.

(11) Never give up:

“I had the head doctor of surgical I.C.U. say, ‘Miracles happen.’

(Via Craig Newmark)

(12) Which Machine for the Hippo? I thought this was a cool picture:

(From NPR via John Durant)

(13) Finally, our video: We’ve had a bit of discussion of eating disorders this week, in the comments to the “Therapy AND Life” post. That reminded me of this CBS News interview of a “Biggest Loser” contestant who said she developed an eating disorder during the show:

Therapy AND Life

UPDATE: The Daily Mail article cited below was not only silly, it appears to have been dishonest. I’ve received the following email:

There is an article on your website about me (17/2/2011). Yes, I’m Judith Fine and that article was in the Daily Mail. Firstly, they completely twisted everything that I said so that it makes it look as if I have severe eating problems. Most of that article was a complete pack of lies, neither is it me in the photograph. Could you please, immediately remove it from you website as I am in the process of picking this up with the Daily Mail.

I’ve edited the post to remove content related to Judith. — PAJ

“Orthorexia” has been in the news recently, for instance in this Valentine’s Day article by Diana Appleyard in the Daily Mail:

We all know the type. They never let wheat, yeast or dairy pass their lips. They’ve cut out alcohol and caffeine. They’re obsessed with healthy eating — yet every day, they look more unwell and unhappier.

These are the symptoms of a condition called ‘orthorexia’ by dieticians….

Orthorexia was coined in 1997 by Californian doctor Steven Bratman in his book Health Food Junkies, and means ‘correct appetite’ (from the Greek orthos for right and orexis for appetite). It is a fixation with eating ‘pure’ food that, far from doing you good, can become so extreme that it leads to malnutrition, chronic ill health and depression.

Well, I don’t eat wheat; I didn’t even know yeast was a food; and though dairy is a big part of my diet, alcohol and caffeine modest parts, I recognize that milk proteins, alcohol, and caffeine can be problematic.

Given that none of these foods are necessary for good health, it’s not obvious to me why excluding them would lead to malnutrition, chronic ill health and depression.

But from the rest of the article, it looks like the real trouble with orthorexia is not the fixation with healthy eating, but faulty ideas of what constitutes a healthy diet. The article’s leading example of an unhealthy “orthorexic” diet is one that excludes fat.

Any fat-less diet is bound to be malnourishing. Perhaps the trouble is not orthorexia, but mistaken ideas about nutrition. Diets people think are therapeutic are, in fact, damaging.

Therapy versus Life … sometimes

Which brings me to a recent essay by Kurt Harris, “Therapy versus Life.”

It’s almost impossible to excerpt, so I’ll just assume you’ve read it. It’s strongly worded, but the ideas are familiar:  I suspect at least 90% of medical doctors would agree.

Doctors are healers, God bless ’em; but every day they have to face patients they cannot heal. This breeds a certain mental toughness.

As I often say, malnutrition, food toxins, and chronic infections are the primary causes of ill health. In some cases, like Judith Fine’s inability to have periods, it’s easy to recognize malnourishment as a likely cause. But the causes of most patients’ impaired health are much less obvious.

Unfortunately, doctors generally cannot diagnose or treat either bad diets or chronic infections. Doctors are great at treating acute disease, and can mitigate many symptoms that chronic diseases generate, but most are helpless to remedy mild, chronic ill health.

Doctors may believe that a patient’s declining health is simply natural aging; or that genuine health impairments may be undiagnosable, untreatable, or incurable. Kurt says it in his forum:

[T]he healthy should not assume they are sick and even the sick may be wasting their time trying to fix what can’t be fixed.

When patients learn that doctors can’t help them, they often turn to experimental self-treatment.

99% of the time, this works out badly. As Kurt’s car metaphor shows, there are many more ways to damage your body than to heal it.

And the 1% of the time it works, the patient doesn’t go tell the doctor. But when it backfires, the patient goes back to the doctor worse than ever. So the doctors see this method fail 100% of the time.

This reinforces the doctors’ consensus: Be prudent. Try to live normally – as healthy people do. Eat like healthy people, live like healthy people, and bear with your incurable maladies as best you can. Thrashing and groping for cures will only do harm.

Therapy – experimental self-therapies – are damaging to life. Choose life, not therapy.

But Diet Is Therapy

But that’s not all there is to it … because the right diet can fix many health problems.

Kurt says this himself:

[T]here is a dietary metabolic milieu that we are adapted to, and the best chance we have of optimizing our health is to try and emulate it …

The human body often can [fix itself] if we just stop ruining it.

We agree. The Perfect Health Diet is, in essentials, identical to Kurt’s PaNu. And when people in ill health eat this way, they commonly get better.

So the right diet is therapy. Choose this diet as therapy, and you’ll have a better life.

What If Your Life is Malady-Inducing?

I chose life over therapy for decades. I rarely went to the doctor. I focused all my energy on life. But I ate a lousy diet.

This isn’t the place to tell my story – that’s coming – but a lousy diet and a focus on life, not therapy, gave me a disabling chronic disease.

And a therapeutic diet gave me my life back. The Four Steps of our book are essentially the steps I took to cure a disabling neurodegenerative condition. With antibiotics, they worked.

So when Kurt asks,

Do you think every problem in your life can be fixed by changing your diet?

I can honestly say: every health problem was fixed!

Therapy for Life

If the Ewald hypothesis and Jaminet corollary are right, then we all stand in need of dietary therapy. As we age, our infectious burden increases and our immune system gets less effective. Sooner or later, infectious diseases threaten us all.

Our rescue is not from medicine, which does not yet know how to treat chronic infections. Our best chance for a long, healthy life lies in diet, nutrition, and immunity-enhancing behaviors like fasting.

Fortunately, the scientific evidence is accumulating to tell us what the right diet is. Specialist professionals still can’t see the forest for the trees, the elephant for its parts; but generalists, aided by respect for ancestral/traditional diets and for evolutionary selection, have blazed the trail. Kurt lists some reliable guides.


Diet is the best therapy. A good diet is life-giving. Good diet and nutrition may cost a few extra minutes a day, but can add decades of happiness.

So I say: choose therapy AND life. We can be healthy centenarians together. Let’s do it!