Another common approach today is to accept the chronic elevation of insulin, and so IGF, as a likely cause of chronic disease, but then assume that the hyperinsulinemia is caused by insulin resistance, which in turn is induced by a combination of high-fat, energy-dense, high-calorie diets, physical inactivity, and excess weight. By this logic, any research that implicates increased insulin activity in disease only confirms that too much food and too little exercise are the true banes of our existence. This approach is the one employed by those clinicians and public-health authorities who now acknowledge that hyperinsulinemia, insulin resistance, and the associated physiological abnormalities of metabolic syndrome are important risk factors for heart disease, but then blame the syndrome itself on excess weight or, if the patient happens to be lean, on physical inactivity. The guidelines from the National Cholesterol Education Program manage to merge both of the latter two approaches, by first enumerating the causes of metabolic syndrome as overweight, physical inactivity, and an “atherogenic diet”—defined as a diet high in saturated fat and calories—and then suggesting that “pharmacological modification of the associated risk factors” is the most effective treatment.

In this approach, high-calorie, high-fat diets and sedentary lifestyles are seen as the causes of all the diseases of civilization. The causal link in this chain from diet and lifestyle to disease is excess weight. “Weight sits like a spider at the center of an intricate, tangled web of health and disease,” as the Harvard epidemiologist Walter Willett has described it in Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating. Or, as Jeremiah Stamler suggested back in 1961, about heart disease in particular, “Excess weight and the common American pattern of gain in weight from young adulthood into middle age are highly prevalent and serious risk factors…. The problem is not the severe, marked, huge, circus-type-of obesity, but rather the 25 or 40 pounds put on gradually over the years—the moderate, creeping obesity so common among middle-aged American men.”

That excess weight is accompanied by an elevated risk of chronic disease is a given. The questionable assumption is that it is an excess of calories of all types, and the dense calories of dietary fat in particular, combined with a relative lack of physical activity, that causes weight gain. In the prevailing wisdom, a simple caloric imbalance is the culprit: we get fat because we consume more calories than we expend.