So if obesity is caused by genes, how come we are having an epidemic of obesity that arose in less than two generations? Maybe there is a clue in the story of the Pima Indians.

The Pima Indians are southwestern Native Americans who are very prone to obesity and its complications. Thirty-five years ago The National Institutes of Health established a medical center in Phoenix devoted to the study and treatment of these people. Pima Indians are famous now for being studied and reported on in hundreds of research papers. This is the front line in the war on obesity and it is a stark reminder that we are losing. Despite lots of studies and treatment plans, these Indians are getting more and more obese. As we have mentioned in our discussion of the epidemic of obesity, the theory is that these people developed a very thrifty metabolism by living marginally for many generations in the desert, always close to drought and starvation and fighting viciously with their neighbors, the Apache Indians. They are paying dearly now for their friendship with the white man who brought clean, safe, cheap, plentiful and tasty Big Macs.

The Pima Indian's rate of obesity is topped by only one group of people in the world, the Nauru Islanders. The Nuaru Islanders live on a tiny island in the West Pacific that is rich in phosphate used for fertilizer and derived from guano deposited over millennia. The Nauru Islanders are very wealthy and leisurely.

So while not proving the mechanism, we see that obesity is both strongly genetic and probably environmental at the same time. Are the Pima Indians better off today than a few generations ago, when they were living harsh marginal lives?