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 you and your children survive.

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.

How Low Should Your Cholesterol Levels Be?

Ideally, your total cholesterol should be below 150 mg/dL. According to William Castelli, who was the medical director of the Framingham Heart Study for many years, people with a total cholesterol value of less than 150 mg/dL simply don’t get heart attacks. And once someone’s total cholesterol is that low, the ratio between the “good” and “bad” cholesterol simply doesn’t matter.

The total cholesterol value is the single most important clue to a person’s risk of heart attack. Once the cholesterol levels in the blood rise to, say, the mid-160s, then the ratio of good versus bad cholesterol (HDL versus LDL) really starts to matter.

William Castelli once explained, “Four out of five people on this earth can’t get their cholesterol over 150; they don’t get heart attacks. One out of five people can’t get their cholesterol down to 150. They do get heart attacks. And almost all of them live in affluent countries.” The “four out of five people” Castelli meant live in societies that eat a low-fat, high-fiber, largely plant-based diet. That kind of diet keeps blood cholesterol levels naturally low.

To see how cholesterol values relate to the risk of heart attack, look at the graphs on this page: http://heartriskonline.com/CholesterolChart.htm