Top Ten Problems With Applying The Paleolithic Diet Principles: Number 2, Part 1

Eating large amounts of vegetables for putative health benefits

When I wrote The Garden of Eating, I had not yet realized fully that modern hunter-gatherer diets do not represent Paleolithic human diets. Loren Cordain (The Paleo Diet) and Ray Audette (Neanderthin), the two individuals who had the strongest influence on my conception of Paleolithic diets, both presented the paleolithic diet as omnivorous and containing large amounts of fruits and vegetables.

Yet what little direct evidence we have of Paleolithic diets does not support an omnivorous diet as a matter of course. Archaeological digs find human remains on grasslands, where little edible vegetation grows at any time of the year. For at least two million years previous to the invention of agriculture, the earth remained in the grip of the ice ages, which limited the growth of edible plants.

Hence, the environments in which our stone age ancestors roamed and evolved favored the reproductive success of people who could live largely on relatively wild game meat and its associated fat. By looking at the bones of stone age humans living about 12,000 years ago in Britain, scientists have determined that they ate diets containing an amount of meat -- mostly bovines and elk -- similar to that consumed by the arctic fox—in other words, they ate only meat and fat!(1)

If vegetation had provided any significant portion of prehistoric human diets, modern humans should show adaptations to intake of raw vegetation similar to other primates or herbivores. Since the bulk of wild and cultivated vegetal foods consists of fiber, a type of carbohydrate, the key to evolutionary success as an herbivore lies in having a method for extracting energy from fiber.

Gorillas, chimps, and herbivores like sheep have guts specialized for fermentation of fiber with the aid of symbiotic protozoa and bacteria. This fermentation process occurs in the stomach in foregut fementers like sheep, or in the large intestine in hindgut fermenters like chimps and gorillas. Because fermentation of fiber to produce fats—primarily butyric acid, the signature fat in butter—generates most of the energy used by an herbivore, these animals can not live without the organ in which this process takes place.

Humans do not have any significant ability to digest and extract energy from fiber. Moreover, humans can live without a stomach or large intestine, unlike herbivorous animals that depend on one or the other. This clearly indicates that the human gut evolved to handle unrefined foods containing little or no fiber, i.e. animal foods. In other words, humans evolved on and are specifically adapted to a carnivorous diet.

When I mention this to students, they often can’t believe I said it. They have the idea that humans can not live without eating vegetables. If dietitians hear it, they start talking about the “dangers” of a no/low carb diet, which they believe include ketoacidosis, a lack of fiber and beneficial phytochemicals, and an increased risk of cancer.

Well, we can live without vegetables and all those “dangers” amount to a heap of myths. I will discuss them in future posts.

(1) Richards MP, Hedges REM, Jacobi R, Current, A, Stringer C. Focus: Gough’s Cave and Sun Hole Cave human stable isotope values indicate a high animal protein diet in the British Upper Palaeolithic. J Archaeol Sci 2000;27: 1–3.
Richards M P. A brief review of the archaeological evidence for Palaeolithic and Neolithic subsistence. Eur J Clin Nutr, December 2002, Volume 56, Number 12, Pages 1270-1278.