I ran across a 1991 New York Times article by Jane Brody discussing the benefits to Pima Indians of returning to their ancestral diet. The Pima have major problems with obesity and diabetes. (I frequently treat Pima Indians in the hospital.) Some quotes:
Studies strongly indicate that people who evolved in these arid lands are metabolically best suited to the feast-and-famine cycles of their forebears who survived on the desert’s unpredictable bounty, both wild and cultivated.
By contrast, the modern North American diet is making them sick. With rich food perpetually available, weights in the high 200′s and 300′s are not uncommon among these once-lean people. As many as half the Pima and Tohono O’odham (formerly Papago) Indians now develop diabetes by the age of 35, an incidence 15 times higher than for Americans as a whole. Yet before World War II, diabetes was rare in this population.
Pima Indians traditionally ate a diet of tepary beans, mesquite seeds, corn, grains, greens, and other high-fiber/low-fat foods. The switch to a diet high in sugar, refined grains, and other highly processed convenience foods may well be responsible for the current high rates of obesity and diabetes. Australian aborigines have the same problem.