National Geographic : 2014 Sep
52 national geographic • september 2014 enzyme lactase, which breaks down the lactose into simple sugars. After humans began herding cattle, it became tremendously advantageous to digest milk, and lactose tolerance evolved inde- pendently among cattle herders in Europe, the Middle East, and Africa. Groups not dependent on cattle, such as the Chinese and Thai, the Pima Indians of the American Southwest, and the Bantu of West Africa, remain lactose intolerant. Humans also vary in their ability to extract sugars from starchy foods as they chew them, depending on how many copies of a certain gene they inherit. Populations that traditionally ate more starchy foods, such as the Hadza, have more copies of the gene than the Yakut meat-eaters of Siberia, and their saliva helps break down starches before the food reaches their stomachs. These examples suggest a twist on “You are what you eat.” More accurately, you are what your ancestors ate. There is tremendous variation in what foods humans can thrive on, depending on genetic inheritance. Traditional diets today in- clude the vegetarian regimen of India’s Jains, the meat-intensive fare of Inuit, and the fish-heavy diet of Malaysia’s Bajau people. The Nochmani of the Nicobar Islands off the coast of India get by on protein from insects. “What makes us human is our ability to find a meal in virtually any environ- ment,” says the Tsimane study co-leader Leonard. Studies suggest that indigenous groups get into trouble when they abandon their tradi- tional diets and active lifestyles for Western living. Diabetes was virtually unknown, for instance, among the Maya of Central America until the 1950s. As they’ve switched to a West- ern diet high in sugars, the rate of diabetes has skyrocketed. Siberian nomads such as the Evenk reindeer herders and the Yakut ate diets heavy in meat, yet they had almost no heart disease until after the fall of the Soviet Union, when many settled in towns and began eating market foods. Today about half the Yakut living in villages are overweight, and almost a third have hyperten- sion, says Leonard. And Tsimane people who eat market foods are more prone to diabetes than those who still rely on hunting and gathering. For those of us whose ancestors were adapted to plant-based diets—and who have desk jobs— it might be best not to eat as much meat as the Yakut. Recent studies confirm older findings that although humans have eaten red meat for two million years, heavy consumption in- creases atherosclerosis and cancer in most populations—and the culprit isn’t just saturated fat or cholesterol. Our gut bacteria digest a nu- trient in meat called L-carnitine. In one mouse study, digestion of L-carnitine boosted artery- clogging plaque. Research also has shown that the human immune system attacks a sugar in red meat that’s called Neu5Gc, causing inflam- mation that’s low level in the young but that eventually could cause cancer. “Red meat is great, if you want to live to 45,” says Ajit Varki of the University of California, San Diego, lead author of the Neu5Gc study. Many paleoanthropologists say that although advocates of the modern Paleolithic diet urge us to stay away from unhealthy processed foods, the diet’s heavy focus on meat doesn’t replicate the diversity of foods that our ancestors ate—or take into account the active lifestyles that protected them from heart disease and diabetes. “What bothers a lot of paleoanthropologists is that we actually didn’t have just one caveman diet,” says Leslie Aiello, president of the Wenner-Gren Foundation for Anthropological Research in New The real hallmark of being human isn’t our taste for meat but our ability to adapt to many habitats and to create many healthy diets.