The humans of four million years ago were fruitarian rather than omnivore, like present day chimpanzees. So suggest microscopic marks on both the teeth of living species and on fossil teeth, claims David Ryde, once acknowledged as the UK’s least-prescribing GP. His studies and experience had led him to advising changes in diet rather than dishing out drugs.

return to newsletter

In this article we summarise what convinced David that:

• humans were probably originally vegan, even fruitarian, and
• contemporary levels of meat-eating may be a factor in many diseases

Although the move from veganism to omnivore happened over millions of years, it may still have outstripped the ongoing evolution of the human digestive system, he suggests, causing many of the illnesses from which we suffer today.

David’s evidence includes:

• the human stomach needs half as much hydrochloric acid to digest plant protein as it needs to digest animal protein. Even using half as much hydrochloric acid the human stomach digests plant protein in half the time. [1] This may explain why newly-converted vegetarians often note less discomfort digesting a vegetarian meal, and feeling less sleepy than after eating an omnivore meal
• Humans are unlikely to have been naturally omnivorous. Most animals eat a narrow range of food when that food is abundant, only eating outside that range if it becomes scarce. This suggests that omnivore diets are more of a fall-back position than the norm
• From around 24 million to 5 million years ago fruit appears to have been the main (possibly the only) ingredient in the human diet. Humans appear to have begun to include small amounts of (raw) meat around 4.5 million years ago [2] When an ice age and drought turned humans from gatherers to hunter-gatherers during the Pliocene period (3.5 million years ago), the raw meat content of the human diet likely increased
• However, as meat is almost universally cooked in order to make it more palatable and easier to digest, it is unlikely that a great deal of meat was eaten before humans learned how to light and control fire (around 500,000 years ago)
• Natural carnivores have sharp molars like scissors which tear and cut meat vertically. The meat only begins to digest in the stomach. On the other hand, natural herbivores have flatter molars which both swing vertically to tear and swing sideways to crush. Herbivore digestion starts in the mouth. Human teeth resemble those of the primates which eat principally fruit and vegetables
• In herbivores the length of the bowel is usually around fifteen times the length of the trunk. In carnivores the usual proportion is around threefold. The length of the human bowel is typically ten times the length of the trunk, suggesting that humans are nearer herbivores than carnivores
• The appendix is the shrunken remains of a herbivorous bowel and found almost exclusively in the higher primates, rodents and a few lower mammals
• The DNA differences between gorillas, chimpanzees and humans are less than 1%, [3] less than the differences between species of horses
• At a glance it is easy to mistake a gorilla digestive tract for a human one, suggesting that human and gorilla digestive systems may function in a similar way
• The lighter the primate, the higher the meat content of their diet. [4] The diet of the smallest primate studied (65g) was 70% meat. The diets of the two largest primates studied, the orang- utan and the gorilla were 2% and 1% carnivorous respectively. Average human weights fall between the two
• Vegetarians and vegans tend to be slimmer and live a little longer than meat-eaters. They also suffer from fewer digestive tract and degenerative diseases and are less prone to gallstones, kidney stones, late onset type 2 diabetes and stomach complaints. Walker and Cannon [5] also attributed (e.g.) colon cancer, hypertension, strokes, heart disease, diverticulosis (small pouches or sacs branching out from an organ, usually the large intestine) tooth decay, piles, peptic ulcers and varicose veins to the 20th Century diet