SG: The Pima were first contacted in 1539 by the Spanish, who apparently found them to be lean and healthy. At the time, they were eating a high-carbohydrate, low-fat diet based on corn, beans, starchy squash, and a modest amount of gathered animal and plant foods from the forest and rivers in the area. In 1869, the Gila river went dry for the first time, and 1886 was the last year water flowed onto their land, due to upstream river diversion by settlers. They suffered famine, and were rescued by government rations consisting of white flour, sugar, lard, canned meats, salt and other canned and processed goods. They subsequently became obese. Their diet consisted mostly of bread cooked in lard, sweetened beverages and canned goods, and they also suddenly had salt. I don't see why that's incompatible with the food reward hypothesis. It is, however, difficult to reconcile with the carbohydrate hypothesis.
I've known about the Pima story for a long time, mainly through the work of Gary Nabhan, who wrote Why Some Like it Hot and several other excellent books. Why Some Like it Hot is particularly relevant here because it posits that certain cultures are uniquely adapted to the foods of their own locality and history. That's a far stretch from the typical paleo proposition that we are all adapted to the same foods we ate 40,000 years ago.
It is interesting to note that at around the same time that flour was making the Pima overweight and diabetic, processed foods were harming other populations in other ways. Nutrition and Physical Degeneration has plenty of pictures of toothless children suffering from TB, but almost none of them are fat. Obesity came to places like Scotland only after the advent of processed foods 2.0, the hyperpalatable junk food engineered in laboratories. Why did the Pima get fat so quickly and before these foods were in the marketplace?
The tragedy of the Pima has been a boon for research into the genetics of diabetes and obesity since they tend towards genetic homogeneity. Through this research, several genes have been identified that are linked to their conditions. These include variants in interleukin 6, uncoupling protein, mannose binding lectin, and the leptin receptor gene, to name but a very few of the promising candidates.
So do these genes doom the Pima? Obviously not. There are a few prominent bloggers who say that whether or not you have diabetes is genetically determined and you cannot eat yourself diabetic. This is nonsense.
The Mexican Pima still live as traditional farmers and ranchers, so they are much more active. They are not skinny, but they are not obese either. What is their diet like? Beans, wheat flour (OMG), corn tortillas, and potatoes are the main staple. They eat much less fat than the US Pima. It was only recently that roads came to their area, so needless to say, they don't eat fast food (at least at the time that paper was written).
I have little doubt that their diet was probably much healthier in the past. Pictures of the Pima in the past show them as being svelte. Staples of this older diet included more unusual desert foods such as tepary beans, mesquite pods, acorns, and heritage varieties of corn. One main point of Nabhan's book is that not all plants of the same species or type are made alike. Different beans have different nutritional properties and phytochemicals. The ancient Pima ate both wild and domesticated legumes. Their diet was around 70% carbohydrates.
Even those Indians who still rely heavily on beans and corn are today consuming varieties that have little or none of the nutritive advantages found in the staples of their historic diet. For example, the sweet corn familiar to Americans contains rapidly digested starches and sugars, which raise sugar levels in the blood, while the hominy-type corn of the traditional Indian diet has little sugar and mostly starch that is slowly digested.
Similarly, the pinto beans that the Federal Government now gives to the Indians (along with lard, refined wheat flour, sugar, coffee and processed cereals) are far more rapidly digested than the tepary beans the Tohono O'odham once depended upon. Indeed, their former tribal name is a distorted version of the Indian word meaning "the Bean People."
When Earl Ray, a Pima Indian who lives near Phoenix, switched to a more traditional native diet of mesquite meal, tepary beans, cholla buds and chaparral tea, he dropped from 239 pounds to less than 150 and brought his severe diabetes under control without medication. In a federally financed study of 11 Indian volunteers predisposed to diabetes, a diet of native food rich in fiber and complex carbohydrates kept blood sugar levels on an even keel and increased the effectiveness of insulin. When he switched back to a low-fiber "convenience-market diet" containing the same number of calories, the volunteers' blood sensitivity to insulin declined.
An overlooked aspect here might be social effects. Obesity in the Pima has been tied to the use of formula. It has been also seen that "non-working" Pima women are more likely to consume traditional foods and feed them to their family than "working" Pima women. I put working in quotation marks because I am referring to work in the extractive capitalist sense. It's clear that Pima women have always worked as gatherers and farmers, I'm talking about work that provides only money to the home, rather than providing income of a more holistic sort.
What is fascinating to me is that the Pima have a lower than expected incidence of heart disease. It's clear to me that the Pima are a genetically distinct population with unique adaptations to their ancient diet and lifestyle. They don't show that carbohydrates per-se cause obesity. They do provide an example of the synergistic effects of genes, diet, and lifestyle. If I were Pima, I would be inclined to eating a low-fat high-fiber diet rich in these traditional foods.
But I'm not.