對碳水化合物恐懼症

October 7, 2007
Carbophobia By GINA KOLATA
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GOOD CALORIES, BAD CALORIES
Challenging the Conventional Wisdom on Diet, Weight Control, and Disease.
By Gary Taubes.
601 pp. Alfred A. Knopf. $27.95.
Gary Taubes is a brave and bold science journalist who does not accept conventional wisdom. In “Good Calories, Bad Calories,” he says what he wants is a fair hearing and rigorous testing for ideas that might seem shocking.
His thesis, first introduced in a much-debated article in The New York Times Magazine in 2002 challenging the low-fat diet orthodoxy, is that nutrition and public health research and policy have been driven by poor science and a sort of pigheaded insistence on failed hypotheses. As a result, people are confused and misinformed about the relationship between what they eat and their risk of growing fat. He expands that thesis in the new book, arguing that the same confused reasoning and poor science has led to misconceptions about the relation between diet and heart disease, high blood pressure, cancer, dementia, diabetes and, again, obesity. When it comes to determining the ideal diet, he says, we have to “confront the strong possibility that much of what we’ve come to believe is wrong.” The best diet, he argues, is one loaded with protein and fat but very low in carbohydrates.
Taubes spent five years working on the book, which runs to more than 450 pages. The bibliography alone goes on for more than 60 pages. He also says he interviewed more than 600 doctors, researchers and administrators, though he adds that “the appearance of their names in the text ... does not imply that they agree with all or even part of the thesis set forth in this book.” Taubes does not bow to the current fashion for narrative nonfiction, instead building his argument case by case, considering the relationship between dietary fat and heart disease, carbohydrates and disease, diet and obesity. As a result, the book can be hard to read, tedious in many places and repetitious.
Yet much of what Taubes relates will be eye-opening to those who have not closely followed the science, or lack of science, in this area. (Disclosure: At one point he approvingly cites my articles on the lack of evidence that a high-fiber diet protects against colon cancer.) For example, he tells the amazing story of how the idea of a connection between dietary fat, cholesterol and heart disease got going and took on a life of its own, despite the minimal connection between dietary cholesterol and blood cholesterol for most people. He does not mince words. “From the inception of the diet-heart hypothesis in the early 1950s, those who argued that dietary fat caused heart disease accumulated the evidential equivalent of a mythology to support their belief. These myths are still passed on faithfully to the present day.” The story is similar for salt and high blood pressure, and for dietary fiber and cancer.
In fact, Taubes convincingly shows that much of what is believed about nutrition and health is based on the flimsiest science. To cite one minor example, there’s the notion that a tiny bit of extra food, 50 or 100 calories a day — a few bites of a hamburger, say — can gradually make you fat, and that eating a tiny bit less each day, or doing something as simple as walking a mile, can make the weight slowly disappear. This idea is based on a hypothesis put forth in a single scientific paper, published in 2003. And even then it was qualified, Taubes reports, by the statement that it was “theoretical and involves several assumptions” and that it “remains to be empirically tested.” Nonetheless, it has now become the basis for an official federal recommendation for obesity prevention.
But the problem with a book like this one, which goes on and on in great detail about experiments new and old in areas ranging from heart disease to cancer to diabetes, is that it can be hard to know what has been left out. For example, Taubes argues at length that people get fat because carbohydrates in their diet drive up the insulin level in the blood, which in turn encourages the storage of fat. His conclusion: all calories are not alike. A calorie of fat is much less fattening than a calorie of sugar.
It’s known, though, that the body is not so easily fooled. Taubes ignores what diabetes researchers say is a body of published papers documenting a complex system of metabolic controls that, in the end, assure that a calorie is a calorie is a calorie. He also ignores definitive studies done in the 1950s and ’60s by Jules Hirsch of Rockefeller University and Rudolph Leibel of Columbia, which tested whether calories from different sources have different effects. The investigators hospitalized their subjects and gave them controlled diets in which the carbohydrate content varied from zero to 85 percent, and the fat content varied inversely from 85 percent to zero. Protein was held steady at 15 percent. They asked how many calories of what kind were needed to maintain the subjects’ weight. As it turned out, the composition of the diet made no difference.
As I read Taubes’s book, I kept wondering how he would deal with an obvious question. If low-carbohydrate diets are so wonderful, why is anyone fat? Most people who struggle with their weight have tried these diets and nearly all have regained everything they lost, as they do with other diets. What is the problem?
On Page 446, he finally tells us. Carbohydrates, he says, are addictive, and we’ve all gotten hooked. Those who try to break the habit start to crave them, just as an alcoholic craves a drink or a smoker craves a cigarette. But, he adds, if they are addictive, that “implies that the addiction can be overcome with sufficient time, effort and motivation.”
I’m sorry, but I’m not convinced.
Gina Kolata is a medical reporter for The Times and the author of “Rethinking Thin: The New Science of Weight Loss and the Myths and Realities of Dieting.”