How could something as bad for us as insulin resistance become so common? Diabetes researchers have proposed several theories about the role of insulin resistance in the eating patterns of several cultures.
A 1962 article in the American Journal of Human Genetics kicked off the debate with the hypothesis about a certain gene. The author, genetics professor James Neel, proposed that people with type 2 diabetes have a "thrifty" gene (actually a set of genes) to cope with cycles of feast and famine. This thrifty gene makes as much use as possible of the minimal amount of food available. In this way it protects the body from starvation by storing fat during times when food is scarce. But during prolonged periods of ample food intake, like today in the United States, the body ends up storing too much fat. An example of a group of people who seem to carry this thrifty gene is the Pima Indians, who live in Arizona.
In a 1998 article in the New Yorker magazine, the author states that the Pima are the most obese people in the world and that half of them over the age of 35 have diabetes. While the traditional Pima diet once consisted of 15% to 20% fat, by the mid-twentieth century they had begun to eat like other Americans with a diet close to 40% fat. And while the author of the New Yorker article doesn't mention it, the Pima had, according to other sources, become much less physically active. Their traditional foods, such as cactus and tepary beans (which are high in fiber and low in fat), kept obesity and diabetes—but probably not insulin resistance—at bay. Their thrifty genes, according to the hypothesis, had made the Pima insulin resistant, but only with the change in lifestyle did the insulin resistance result in obesity and eventually diabetes.
In the New Yorker article, the author states, “Famine, which had long been a recurrent condition, gave way to permanent plenty, and so the Pima's ‘thrifty' genes, once an advantage, were now a liability.” In other words, the same gene that protected the Pima from starvation by storing fat during times of famine, is now, paradoxically, increasing their chances of dying during a time of plenty.
But why should Westernization, like that affecting the Pima, lead to an explosion of diabetes? In spite of being no less subject to repeated famines than other people, Europeans have the lowest rates of diabetes.
Writing in Diabetologia in 1994 and the World Review of Nutrition and Dietetics last year, Australian researchers Jennie Brand-Miller and Stephen Colagiuri proposed what they call a &uot;carnivore connection": insulin resistance evolved to provide advantages to populations that adapted to a diet high in meat and low in plant foods (low carbohydrates). With this diet, insulin resistance would not have caused high levels of circulating insulin. A diet like this that minimizes high glycemic carbohydrates stimulates only modest increases in plasma insulin.
Europeans and Agriculture
Both human and animal studies indicate that insulin resistance is the mechanism for coping with a shortage of dietary glucose, which was the human condition during the two million years of the Ice Ages that ended about 10,000 years ago. At about this time, Europeans were among the first to adopt agricultural practices. This allowed them to consume a diet high in carbohydrate. Brand-Miller and Colagiuri believe the long-standing carbohydrate diet is the reason that Europeans have low rates of diabetes.
Which Diet Is Best to Reduce Insulin Resistance?
No one knows for sure which kind of diet is best to reduce insulin resistance. And to demonstrate just how confusing the many dietary recommendations can be, Brand-Miller supports one theory in her book The Glucose Revolution but hesitates to offer concrete suggestions when asked her opinion recently. In her book, she supports a high-carbohydrate eating plan, but when I asked her to reconcile what appeared to be differing conclusions among the nutrition experts, she replied, “The trouble is we don't have much to go on yet. We need to see a lot more studies in both diabetic and non-diabetic subjects of all ethnic persuasions before we can recommend low-carbohydrate/high-protein diets.”
Clearly, the diet experts have not reached any conclusions about the connection between carbohydrate intake and insulin resistance.
Dietary choices should not be based on theories. Be sure to talk with your healthcare provider before making major changes in your diet.
This article originally appeared at MyDiabetes.com, August 2000.
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