A Look at Our Closest Wild Relatives

To answer the question, “What should humans eat?” many researchers look to other primates, such as chimpanzees, monkeys, and gorillas. Nonhuman wild primates are also omnivores or, as often described, herbivores and opportunistic carnivores. They eat mainly fruits and vegetables, but may also eat small animals, lizards, and eggs if given the opportunity. Only 1% and 2%, respectively, of the total calories consumed by gorillas and orangutans are animal foods. The remainder of their diet is from plant foods. Because humans are between the weights of the gorilla and orangutan, it has been suggested that humans are designed to eat around 1.5% of their diet as animal foods.² Most Americans derive well over 50% of their calories from animal foods.

Although most primates eat a considerable amount of fruit, it is critical to point out that the cultivated fruit in American supermarkets is far different from the highly nutritious wild fruits these animals rely on. Wild fruits have slightly higher protein contents and a higher content of certain essential vitamins and minerals, but cultivated fruits tend to be higher in sugars. Cultivated fruits are therefore very tasty to humans, but because they have a higher sugar composition and also lack the fibrous pulp and multiple seeds found in wild fruit that slow down the digestion and absorption of sugars, cultivated fruits raise blood sugar levels much more quickly than their wild counterparts.

Wild primates fill up not only on fruit but also on other highly nutritious plant foods. As a result, wild primates weighing one tenth as much as a typical human ingest nearly 10 times the level of vitamin C and much higher amounts of many other vitamins and minerals. Other differences in the wild primate diet are also important to point out, such as a higher ratio of α-linolenic acid, the essential ω-3 fatty acid, to linoleic acid, the essential ω-6 fatty acid² (Table 44-1).

TABLE 44-1 Estimated Mineral Intakes of Wild Monkeys and Humans

Hunter–Gatherer Diets

Determining what foods are best suited for humans may not be as simple as looking at the diet of wild primates. There are some structural and physiologic differences between humans and apes. The key difference may be a larger, more metabolically active brain. It has been theorized that a shift in dietary intake to more animal foods may have produced the stimulus for brain growth. The shift itself was probably the result of limited food availability that forced early humans to hunt grazing mammals, such as antelope and gazelle. Archeological data supports this association: the brains of humans started to grow and become more developed at about the same time as evidence shows an increase in bones of animals butchered with stone tools at sites of early villages.

Improved dietary quality alone cannot fully explain why human brains grew, but it definitely appears to have played a critical role. With a bigger brain, early humans were able to engage in more complex social behavior, which led to improved foraging and hunting tactics, which in turn led to even higher quality food intake, fostering additional brain evolution.

Data from anthropologists looking at hunter–gatherer cultures provide much insight as to what humans are designed to eat; however, it is very important to point out that these groups were not entirely free to determine their diets. Instead, their diets were molded by what was available to them. For example, the diet of the Inuit Eskimos is far different from that of the Australian aborigines. It may not be appropriate to answer the question, “What should humans eat?” simply by looking at these studies. Nonetheless, it is important to point out that regardless of whether hunter–gatherer communities relied on animal or plant foods, the rate of diseases of civilization, such as heart disease and cancer, is extremely low in such communities.³

It should also be pointed out that the meat that our ancestors consumed was much different from the meat found in supermarkets today. Domesticated animals have always had higher fat levels than their wild counterparts, but the desire for tender meat has led to the breeding of cattle that produce meat with a fat content of 25% to 30% or more, compared with less than 4% for free-living animals and wild game. In addition, the type of fat is considerably different. Domestic beef contains primarily saturated fats and virtually undetectable amounts of ω-3 fatty acids. In contrast, the fat of wild animals contains more than five times more polyunsaturated fat per gram and has a good amount of beneficial ω-3 fatty acids (approximately 4%).⁴

Considerable evidence indicates that a high intake of red or processed meat increases the risk of mortality. For example, in a cohort study of half a million people aged 50 to 71 years at baseline, men and women in the highest versus lowest quintile of red and processed meat intake had elevated risks for overall mortality.⁵

In another prospective cohort study, subjects were followed from 1980 (women) or 1986 (men) until 2006. Low-carbohydrate diets, either animal-based (emphasizing animal sources of fat and protein) or vegetable-based (emphasizing vegetable sources of fat and protein), were computed from several validated food-frequency questionnaires assessed during follow-up.⁶ A low-carbohydrate diet based on animal sources was associated with higher all-cause mortality in both men and women, whereas a vegetable-based, low-carbohydrate diet was associated with lower all-cause and cardiovascular disease mortality rates.

The Importance of a Plant-Based Diet

The evidence supporting diet’s role in chronic degenerative diseases is substantial and overwhelming. There are two basic facts linking the diet–disease connection: (1) a diet rich in plant foods (i.e., whole grains, legumes, fruits, and vegetables) is protective against many diseases that are extremely common in so-called Western society, and (2) a diet providing a low intake of plant foods is a causative factor in the development of these diseases and provides conditions under which other causative factors are more active.

The Pioneering Work of Burkitt and Trowell

Much of the link between diet and chronic disease originated from the work of two medical pioneers, Denis Burkitt, MD, and Hugh Trowell, MD, authors of Western Diseases: Their Emergence and Prevention, first published in 1981.⁷ Although now extremely well-recognized, their work is actually a continuation of the landmark work of Weston A. Price, a dentist and author of Nutrition and Physical Degeneration. In the early 1900s, Dr. Price traveled the world observing changes in teeth and palate (orthodontic) structure as various cultures discarded traditional dietary practices in favor of a more “civilized” diet. Price was able to follow individuals as well as cultures over 20 to 40 years and carefully documented the onset of degenerative diseases as their diets changed. On the basis of extensive studies examining the rate of diseases in various populations (epidemiologic data) and his own observations of primitive cultures, Burkitt formulated the following sequence of events:

Since Burkitt and Trowell’s pioneering research, a virtual landslide of data has continually verified the role of the Western diet as the key factor in virtually every chronic disease, especially obesity and diabetes. Box 44-1 lists diseases with convincing links to a diet low in plant foods. Many of these now common diseases were extremely rare before the twentieth century.