Humans are Herbivores

You may argue that humans are omnivores but it is clear that our anatomy and physiology are those of a herbivore. The following cartoon makes this point:

There is a popular fallacy that humans as a species are well adapted to eating meat and wild plants but little carbohydrate. Also that eating more grains and root vegetables results in chronic diseases such as diabetes. It is difficult to reconcile this theory with the fact that there is least diabetes in the populations who consume the most carbohydrate, and most diabetes in the developed countries where meat, dairy and oil has displaced much of the basic starchy (carbohydrate) food from the diet.

The low carbohydrate enthusiasts claim that we evolved on a meat rich diet. A frequently quoted publication on the Paleolithic diet considered the diets of modern day hunter-gatherers and concluded that their diets were rich in foods of animal origin, leading to the conclusion that the natural human diet is meat based. The first major flaw in this publication was that it relied on old data, which was not collected reliably, and underestimated the amount of plant foods that these people gathered. The other flaw was that the last enclaves of hunter-gatherers were often marginalized into land that was not agriculturally productive and therefore provided limited sources of foods. It is likely that the majority of the Paleolithic humans lived in more productive lands abounding in plant sources of food. There is considerable evidence that early humans had diets that were mainly based on high carbohydrate starchy foods such as grains and root vegetables.

The development of a larger brain was not dependent on eating meat or fish. The mother provides the increased needs for omega-3 fats during the most rapid periods of growth in pregnancy and infancy. After weaning, human growth is incredibly slow and the main extra nutritional cost of a big brain is the energy it consumes, about 20% of resting metabolic rate. The brain runs almost exclusively on carbohydrate: “brain food”?

We don’t know how much meat versus plant our ancestors ate over the last couple of hundred thousand years. The advent of fire and cooking enabled our ancestors to eat things that were poorly digested or hazardous when raw, and greatly increased the range of foods we could eat, both plant and animal. Meat was not an ideal health supporting food for our ancestors, but it was energy dense and in hard times, it was better than hunger and starvation.

Evolution does not seem to have endowed us with a meat eating body or metabolism. We have hands that are suited for picking and collecting the edible parts of plants. We lack claws to attack prey and our skin is soft and vulnerable to laceration should we wrestle with another animal. Neither our hands nor our teeth are suited for tearing the flesh off a carcass. To a paleontologist, our teeth and jaw muscles are those of an herbivore, primarily designed for grinding food rather than tearing and chopping. We lack the large stomach of a carnivore and our intestine is long like an herbivore’s. Our large intestine is adapted to ferment plant foods to extract more energy. And we are vulnerable to disease when we eat more meat. Our cholesterol metabolism, like other herbivores, makes us vulnerable to artery disease when we eat more saturated fat and less fibre.

We are better adapted to eating starchy foods than the great apes who live on fruits and leaves in tropical forests. We have more copies of the gene for the starch digesting enzyme, amylase. Amylase mainly works in the small intestine, but we also have a higher concentration of amylase in our saliva. This adaption enabled us to take advantage of grains and roots of plants that store their energy as starch for the next growth season. Starch granules have been retrieved from surfaces of stone tools in Mozambique, dating back to 105,000yr ago, and from the teeth of our Neanderthal cousins in Europe.

The epidemiology overwhelmingly supports a high starch, predominantly plant based diet as being most health supportive. Cancer, heart disease and diabetes are least common in populations that have the most plant strong diets. Within developed nations, those who consume a more plant-based diet are healthier.

The most effective lifestyle intervention programs for reversing heart disease, diabetes and, most recently, prostate cancer all used a mostly plant-based, low fat diet.

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