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Thursday, September 15, 2011

Humans Are Starch Eaters

Here’s an interesting talk by Nathaniel Dominy, PhD, an Associate Professor of Anthropology at Dartmouth University. He explains the central role of diet in the amazing worldwide success of the human species. If you can’t find enough to eat, you can’t do any of the other things that you would need to do to help your species survive, such as bear and rear children.

He makes several important points. One is that human beings are behaviorally “plastic.” He uses the term “plastic” in the scientific sense, meaning that something can take any shape. Our behavior is “plastic” because it can easily be reshaped. As he pointed out, human beings can adapt to many different climates because we have learned to make and wear clothes. We can also learn to eat lots of different foods.

One type of food that is available everywhere except the Artic is starchy foods. All of the energy in our diet comes from sunlight, which green plants use to make glucose out of carbon dioxide and water. Plants then store a lot of this glucose in the form of starch, often in their roots or tubers and in their seeds. Unfortunately, starch is hard to digest. To digest it, we use amylase, an enzyme that converts the starch back to glucose.

Dominy suspects that our ancestors’ ability to recognize and use tuber-forming plants opened up a food source unknown to other primates. “It’s kind of a gold mine. All you have to do is dig it up.” 

Dominy points out that, when compared with other primates, human beings have extra copies of the gene for the starch-digesting enzyme amylase. As a result, we have a lot more amylase in our saliva than gorillas or chimpanzees do. People from societies that depend heavily on starchy diets have several more extra copies of the amylase gene and therefore produce a lot more amylase in their saliva. In other words, they have become genetically more efficient at digesting starches. This kind of change can be seen in genetically related populations that have been adapting to different diets for only a few thousand years.

Although humans can and do eat practically anything (we are behaviorally plastic), that doesn’t mean that we are well adapted to a meat-based diet. As he puts it, “Anatomically, we’re not adapted to meat at all…. We simply don’t have the adaptations that you would need to chew meat efficiently. Anyone can look at the teeth of their dog or cat and see what your teeth should look like if you’re going to eat meat. Our teeth don’t match.” Dominy concludes, “The fundamental component of the human diet is a mix of plant foods, with a large amount of starch coming from tubers and seeds.”

In this context, I’d point out that the adaptations to a meaty diet go far beyond the shape of the teeth. Even though dogs often eat a fatty, meaty diet, they generally don’t get high cholesterol or atherosclerosis unless they also have a thyroid disorder that upsets their cholesterol metabolism. In contrast, human beings that eat a fatty, meaty diet are much more susceptible than dogs are to high cholesterol and atherosclerosis. That explains why atherosclerosis is the leading cause of death in the United States but practically nonexistent in societies where people eat a low-fat, plant-based diet.


  1. I disagree. I think humans are predators. We are at the top of the food chain. Starch eaters are pudgy. Cows, hippos, elephants, gorillas are starch eaters. They all have big bellies. They store their energy in white adipose tissue. Everything that eats protein is lean (unless we have put them in a zoo and feed them pellets instead of their regular diet). They store their energy in their muscles.

    I've lost about 50 lbs from avoiding starch and eating primarily meat, beans, and green leafy vegetables. This required no exercise.

    I was obese when I ate lots of pasta, white rice, and bread. When I cut those things out fat melted off, blood sugar normalized (the real cause of diabetes is high blood sugar and insulin resistance), and the real indicator of heart disease risk, VLDL level, dropped significantly.

  2. You may disagree with the world's foremost nutritional epidemiologists if you wish; but to impress me, you'd have to cite a lot of really impressive research that they have inexplicably overlooked.

    Some people do lose weight on Atkins-style diets, simply because they are taking in fewer calories. The effect is due partly to restricted food choices and partly to ketosis-induced appetite suppression. When people do get reduced insulin resistance as a result of such a diet, it's because the beneficial effects of the weight loss outweigh the harmful effects of the high fat consumption on insulin resistance. When compared to a low-fat, plant-based diet, the Atkins-style diets pose a risk of long-term complications: an increased risk of heart disease, cancer, osteoporosis, autoimmune disease, and liver and kidney disease. There are far safer ways to maintain your weight.

  3. What are some examples of edible tubers other than potatoes that one could include in their diet?

    Also, what are the best type of starchy carbs recommended to include other than tubers?

    1. Here's a comprehensive list:

  4. A tuber is a modified stem. Potatoes are technically tubers, not roots. But the difference is of interest only to botanists. For practical purposes, you can classify lots of different things as root vegetables, even if they are technically tubers, roots, or buds. Here's a list of "root vegetables:

  5. Humans and great apes (bonobos, chimpanzees, gorillas, and orangutans) share a common gut anatomy, consisting of a simple stomach, small intestine, small cecum terminating in an appendix, and a hindgut consisting of the large intestine, rectum, and anal canal [1]. Nevertheless, significant differences have been reported in their gut proportions [2-4]. While the large intestine represents the majority of the great ape gut volume, the majority of the modern human gut volume consists of the small intestine [2-4]. Initial surveys have also indicated modern humans have a smaller total gut volume to body mass ratio relative to the great apes [5-7]. However, this could be influenced by primate gut plasticity related to diet and genetic diversity [2,8].

    It has been proposed that gut proportions changed at some point within the human lineage in response to higher quality foods which can be digested in the small intestine [2]. The diets of hominids and/or early human populations improved, in part, due to cooking [9] and the increased abundance of animal products obtained through scavenging, hunting, fishing, and dairy consumption [10-19]. In contrast, great ape species in the wild derive a significant amount of their total daily metabolic energy needs through the fermentation of lower quality plant materials in their hindguts [20-25]. Although hindgut fermentation also occurs in humans [26-28], there is evidence that wild great apes derive greater amount of total daily metabolic energy from this process than do humans on Western diets [20-22]. However, seasonal changes in great ape diets and the limited dietary diversity of the humans studied will influence the interpretation of these data sets.

  6. Gorillas are primarily leaf-eaters. Humans are primarily starch-eaters. That's why human beings are repelled by the very idea of subsisting on nothing but "rabbit food." As one might surmise from studying comparative anatomy, human beings are adapted to a somewhat richer food source than gorillas eat: primarily the underground storage organs of plants, such as roots, tubers, and corms.

    Gorillas do not eat a "diet high in fat, as do all other plant eaters." Gorillas eat a diet high in fiber, which is fermented to produce some short-chain fatty acids, such as butyric acid and propionic acid. If you feed a gorilla a low-fiber diet that is high in triglycerides (fats), the gorilla is likely to suffer from the diseases that strike Western industrialized populations, such as ulcerative colitis and heart disease. Gorillas that eat a leafy diet do not get those diseases.

    The point of the gorilla analogy is to emphasize that plants contain protein, not to argue that leaves are a good source of calories. My book Not Trivial explains how to use an argument by analogy.