What if It’s All Been a Big Fat Lie?
23rd February 2011
Gary Taubes does diet. Somewhat old but still interesting.
America has become weirdly polarized on the subject of weight. On the one hand, we’ve been told with almost religious certainty by everyone from the surgeon general on down, and we have come to believe with almost religious certainty, that obesity is caused by the excessive consumption of fat, and that if we eat less fat we will lose weight and live longer. On the other, we have the ever-resilient message of Atkins and decades’ worth of best-selling diet books, including ”The Zone,” ”Sugar Busters” and ”Protein Power” to name a few. All push some variation of what scientists would call the alternative hypothesis: it’s not the fat that makes us fat, but the carbohydrates, and if we eat less carbohydrates we will lose weight and live longer.
What’s forgotten in the current controversy is that the low-fat dogma itself is only about 25 years old. Until the late 70’s, the accepted wisdom was that fat and protein protected against overeating by making you sated, and that carbohydrates made you fat. In ”The Physiology of Taste,” for instance, an 1825 discourse considered among the most famous books ever written about food, the French gastronome Jean Anthelme Brillat-Savarin says that he could easily identify the causes of obesity after 30 years of listening to one ”stout party” after another proclaiming the joys of bread, rice and (from a ”particularly stout party”) potatoes. Brillat-Savarin described the roots of obesity as a natural predisposition conjuncted with the ”floury and feculent substances which man makes the prime ingredients of his daily nourishment.” He added that the effects of this fecula — i.e., ”potatoes, grain or any kind of flour” — were seen sooner when sugar was added to the diet.
If you work out the numbers, you come to the surreal conclusion that you can eat lard straight from the can and conceivably reduce your risk of heart disease.
David Ludwig, the Harvard endocrinologist, says that it’s the direct effect of insulin on blood sugar that does the trick. He notes that when diabetics get too much insulin, their blood sugar drops and they get ravenously hungry. They gain weight because they eat more, and the insulin promotes fat deposition. The same happens with lab animals. This, he says, is effectively what happens when we eat carbohydrates — in particular sugar and starches like potatoes and rice, or anything made from flour, like a slice of white bread. These are known in the jargon as high-glycemic-index carbohydrates, which means they are absorbed quickly into the blood. As a result, they cause a spike of blood sugar and a surge of insulin within minutes. The resulting rush of insulin stores the blood sugar away and a few hours later, your blood sugar is lower than it was before you ate. As Ludwig explains, your body effectively thinks it has run out of fuel, but the insulin is still high enough to prevent you from burning your own fat. The result is hunger and a craving for more carbohydrates. It’s another vicious circle, and another situation ripe for obesity.