D.B.: What’s the common explanation?
G.T.: The conventional wisdom is that obesity is a problem of energy imbalance. We eat too much, we’re too sedentary, so we get fatter — and this in turn causes the diabetes, Type 2, which is the common form. I don’t find this energy balance concept meaningful. It’s like saying when somebody gets richer, they make more money than they spend; they accumulate wealth. It’s a tautology; it tells you nothing about why it happens.
Still, it’s this energy balance thinking that leads us to blame the food industry for providing too much tasty food, and the individual who’s afflicted for not being able to eat in moderation and not being suitably active.
D.B.: Can you explain what you call the alternative hypothesis?
G.T.: Simple. Obesity is a hormonal/regulatory disorder just like any other growth defect. And the hormone that primarily drives fat accumulation is insulin, the same hormone that is disregulated in diabetes. Just as growth hormone is the primary driver of skeletal and muscular growth, insulin is the primary driver of our horizontal growth, the expansion of our fat tissue.
We secrete insulin in response to carbohydrates in our diet and there’s a condition called insulin resistance that is the fundamental defect in Type 2 diabetes and is so closely associated with obesity that we can speculate that it might be the cause. The Centers for Disease Control and Prevention estimates that 75 million American are insulin resistant.
D.B.: Can you explain insulin resistance?
G.T.: Insulin is a hormone secreted by the pancreas that can be thought of as orchestrating how the body uses or partitions its fuel. It tells your cells to take up blood sugar and burn that sugar, technically glucose, for fuel. But it also tells your fat tissue to take up fat and inhibits the release of fat; it tells your muscles, your lean tissue, to use protein for rebuilding.
If you’re insulin resistant, your pancreas needs to secrete more insulin to control blood sugar, and that insulin will increase your fat accumulation as a consequence.
Researchers studying insulin resistance believe it begins in the liver, beginning with the accumulation of fat in the liver cells. As it turns out, the fructose constituent of sugar — half of cane or beet sugar, 55 percent of high fructose corn syrup — is metabolized primarily in the liver, and when it is delivered to the liver in high doses, the liver converts it into fat. So that’s what I mean when I say sugar is at the scene of the crime both in populations and biologically, in the body itself.
D.B.: Given the rates of obesity and diabetes in the United States, what do you think is called for today?
G.T.: I’m arguing the reason we’ve failed to curb the obesity and diabetes epidemics is we’ve misunderstood the cause. We blame eating too much and exercising too little, rather than the carbohydrate content of the diet, specifically sugar.
We need better research that asks the correct questions and rigorously, methodically and skeptically identifies the precise dietary causes of these disorders so we know what has to be removed to reverse or stop them. We need studies that can disassociate the physiological or toxic effects of sugar — on body fat, on insulin resistance status — from the calories it contains.
D.B.: Let’s say that happens. Then what?
G.T.: Then we have to get the message right. If we believe that sugar is just empty calories, then it’s reasonable to say eat it in moderation and balance the calories in sugary snacks by exercising more. We don’t have to steal Christmas, in effect, by removing sugar from our diets and our lives.
But I’m arguing that if sugar causes obesity and diabetes, then we should drop the “too much of,” or “overconsumption of,” or “excess of,” and just say sugar causes these diseases. (We could say added sugars, or refined sugars, if we don’t want to implicate fruit). We know that smoking too many cigarettes will cause lung cancer, but we don’t say “too many cigarettes” cause lung cancer; we say “cigarettes cause lung cancer.” The message is fundamentally different.
D.B.: What do you think the sugar industry should do? . . .