Body of Evidence Were Humans Meant to Eat Meat?

Cardiologist William C. Roberts hails from the famed cattle state of Texas, but he says this without hesitation: Humans aren’t physiologically designed to eat meat. “I think the evidence is pretty clear. If you look at various characteristics of carnivores versus herbivores, it doesn’t take a genius to see where humans line up,” says Roberts, editor in chief of The American Journal of Cardiology and medical director of the Baylor Heart and Vascular Institute at Baylor University Medical Center in Dallas.

As further evidence, Roberts cites the carnivore’s short intestinal tract, which reaches about three times its body length. An herbivore’s intestines are 12 times its body length, and humans are closer to herbivores, he says. Roberts rattles off other similarities between human beings and herbivores. Both get vitamin C from their diets (carnivores make it internally). Both sip water, not lap it up with their tongues. Both cool their bodies by perspiring (carnivores pant).

Human beings and herbivorous animals have little mouths in relation to their head sizes, unlike carnivores, whose big mouths are all the better for “seizing, killing and dismembering prey,” argues nutrition specialist Dr. Milton R. Mills, associate director of preventive medicine for the Washington, D.C.-based Physicians Committee for Responsible Medicine (PCRM). People and herbivores extensively chew their food, he says, whereas swallowing food whole is the preferred method of carnivores and omnivores.

Got Milk?

Dr. Neal D. Barnard, PCRM’s founder and president, says humans lack the raw abilities to be good hunters. “We are not quick, like cats, hawks or other predators,” he says. “It was not until the advent of arrowheads, hatchets and other implements that killing and capturing prey became possible.”

Milk, another animal product, can also be problematic for people. That’s why, in response to the popular “Got Milk?” ad campaign, Barnard’s organization sponsored billboards this past summer that read, “Got Diarrhea?”

“Dairy foods are definitely not a natural part of our diet,” contends vegetarian dietitian and author Virginia Messina, who fields the public’s nutritional questions at “We only started consuming them about 10,000 years ago, which is very recent in our evolution. Our physiology suggests that we really did not evolve to consume dairy beyond early childhood.”

Three out of 10 adults are lactose intolerant, meaning they can’t digest the sugar in milk. So they likely suffer gas or diarrhea when undigested lactose reaches the large intestine, according to an April report in the Nutrition Action Healthletter.

While celebrities sport milk mustaches in ad campaigns, some research raises questions as to whether milk is a better source of calcium than, say, spinach or collard greens. Echoing the conclusions of research elsewhere, a Harvard University study of more than 75,000 nurses found no evidence that nurses who drank the most milk enjoyed fewer broken bones.

Are We Omnivores?

Milk’s high protein actually could leach calcium from bones, according to Dr. Walter Willett, of the Harvard School of Public Health, speaking on the PBS program HealthWeek.

“Drinking cow milk has been linked to iron-deficiency anemia in infants and children; it has been named as the cause of cramps and diarrhea in much of the world’s population and the cause of multiple forms of allergies as well. The possibility has been raised that it may play a central role in the origins of atherosclerosis and heart attacks,” writes Dr. Frank Oski, former director of the Johns Hopkins University Department of Pediatrics, in his book, Don’t Drink Your Milk!

As intriguing as these arguments may be, the idea that humans are natural vegetarians has “no scientific basis in fact,” argues anatomist and primatologist John McArdle. Alarmed by this growing belief, McArdle, a vegetarian, says the human anatomy proves that people are omnivores.

“We obviously are not carnivores, but we are equally obviously not strict vegetarians, if you carefully examine the anatomical, physiological and fossil evidence,” says McArdle, executive director of the Alternatives Research and Development Foundation in Eden Prairie, Minnesota.

According to a 1999 article in the journal The Ecologist, several of our physiological features “clearly indicate a design” for eating meat, including “our stomach’s production of hydrochloric acid, something not found in herbivores. Furthermore, the human pancreas manufactures a full range of digestive enzymes to handle a wide variety of foods, both animal and vegetable.

“While humans may have longer intestines than animal carnivores, they are not as long as herbivores”; nor do we possess multiple stomachs like many herbivores, nor do we chew cud,” the magazine adds. “Our physiology definitely indicates a mixed feeder.”

If people were designed to be strict vegetarians, McArdle expects we would have a specialized colon, specialized teeth and a stomach that doesn’t have a generalized pH—all the better to handle roughage. Tom Billings, a vegetarian for three decades and site editor of, believes humans are natural omnivores. Helping prove it, he says, is the fact that people have a low synthesis rate of the fatty acid DHA and of taurine, suggesting our early ancestors relied on animal foods to get these nutrients. Vitamin B-12, also, isn’t reliably found in plants. That, Billings says, left “animal foods as the reliable source during evolution.”

History argues in favor of the omnivore argument, considering that humans have eaten meat for 2.5 million years or more, according to fossil evidence. Indeed, when researchers examined the chemical makeup of the teeth of an early African hominid that lived in woodlands three million years ago, they expected to learn that our ancestor lived on fruits and leaves. “But the isotopic clues show that it ate a varied diet, including either grassland plants or animals that themselves fed on grasses,” reported the journal Science in 1999.

So, the question remains: Are humans natural vegetarians? In the end, whether a person lives a vegetarian lifestyle has less to do with esoteric matters of anatomy and more to do with ethics and personal values. The architecture of the human body offers no simple answers.