A landmark study published today calls into question the U.S. government's official dietary guidelines, enshrined in the food pyramid. For a decade, the government has advised Americans to stay away from fat and eat a diet based largely on carbohydrates. But as NPR's Richard Knox reports, a study published in the American Journal of Clinical Nutrition shows the pyramid and other official guidelines are most likely obsolete.
The Food Guide Pyramid is an American icon. At the base are breads, cereal and pasta -- up to 11 servings a day. Veggies and fruits are next, with two-to-five servings. As the pyramid narrows, it suggests eating fewer dairy products, eggs and meat servings. At the tip are fats and sweets -- to be used "sparingly." As sensible as it may sound, Walter Willett of the Harvard School of Public Health says the food pyramid is "a license to overeat."
"I think the pyramid is so out of sync with scientific evidence that it almost has to be totally dismantled and rebuilt from the ground up," says Willett.
To Willett, the pyramid's problem is that it assumes that only fat calories can make people fat. "And the reality is, it's too many calories from whatever the source, whether they be from carbohydrates or from fat," Willett says.
Willett and his colleague Marjorie McCullough decided to look at heart disease and cancer among people whose diets matched the official government advice. They compared these people to others who ate a Harvard-designed diet containing fewer carbohydrates and more fats. Not just any fat, but foods, such as nuts and vegetable oils, that don't contain harmful trans-fatty acids.
The study found that those who ate the Harvard diet had a significantly reduced risk for major chronic disease. "The benefit we've seen -- for example, a reduction in heart disease by approximately 40 percent in men and 30 percent in women -- is actually quite large," says Willett. "What we've seen is that the impact of diet can be just as powerful as the best cholesterol-lowering drug in terms of prevention."
When it came to cancer, researchers saw no benefit from the lower-carbohydrate Harvard diet. The relationship between diet and cancer is more complicated. Still, the study suggests that official advice to minimize fat is obsolete. Alice Lichtenstein of Tufts University agrees. She was on a federal panel that updated the official guidelines less than two years ago. Lichtenstein says the new Harvard study confirms what most nutritionists believe: The 2000 guidelines are already out-of-date.
But she says the food pyramid and official guidelines alone are not to blame for American obesity.
"I think we're giving the pyramid too much credit, that people are actually following it to the letter and that's why we're getting fatter," she says. "I think there are a lot of reasons why we're getting fatter. I also think a whole industry was spawned on low-fat food, so people could consume fat-free brownies, fat-free ice cream, fat-free cookies, and that really has contributed to the increased caloric intake, the increased carbohydrates and the increase in obesity."
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