Here’s an interesting article about the Pima Indians of Arizona.
For about 2000 years, the Pima had been growing corn, beans, and squash on irrigated land in Arizona. As a result, their traditional diet was high in starch and fiber and low in fat (~15% by calorie). After white settlers diverted the Pima’s irrigation water, the Pima had to fall back on the lard, sugar, and white flour supplied to them by the U.S. government. After World War II, the Pima adopted a diet that closely resembles the standard American diet. It is low in fiber and gets about 40% of its calories from fat. As a result, they have horrifically high rates of obesity and type 2 diabetes. In contrast, their blood relatives in Mexico who have kept more or less to their traditional diet have relatively low rates of obesity and diabetes.
Some low-carb gurus have tried to twist the Pima’s story into a justification for eating less carbohydrate and more fat. In reality, it provides strong encouragement for people to eat more starch and fiber and a lot less fat.