Eat less saturated fat: that has been the take-home message from the U.S. government for the past 30 years. But while Americans have dutifully reduced the percentage of daily calories from saturated fat since 1970, the obesity rate during that time has more than doubled, diabetes has tripled, and heart disease is still the country’s biggest killer. Now a spate of new research, including a meta-analysis of nearly two dozen studies, suggests a reason why: investigators may have picked the wrong culprit. Processed carbohydrates, which many Americans eat today in place of fat, may increase the risk of obesity, diabetes and heart disease more than fat does – a finding that has serious implications for new dietary guidelines expected this year.
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In March the American Journal of Clinical Nutrition published a meta-analysis – which combines data from several studies – that compared the reported daily food intake of nearly 350,000 people against their risk of developing cardiovascular disease over a period of five to 23 years. The analysis, overseen by Ronald M. Krauss, director of atherosclerosis research at the Children’s Hospital Oakland Research Institute, found no association between the amount of saturated fat consumed and the risk of heart disease.
The finding joins other conclusions of the past few years that run counter to the conventional wisdom that saturated fat is bad for the heart because it increases total cholesterol levels. That idea is “based in large measure on extrapolations, which are not supported by the data,” Krauss says.
One problem with the old logic is that “total cholesterol is not a great predictor of risk,” says Meir Stampfer, a professor of nutrition and epidemiology at the Harvard School of Public Health. Although saturated fat boosts blood levels of “bad” LDL cholesterol, it also increases “good” HDL cholesterol. In 2008 Stampfer co-authored a study in the New England Journal of Medicine that followed 322 moderately obese individuals for two years as they adopted one of three diets: a low-fat, calorie-restricted diet based on American Heart Association guidelines; a Mediterranean, restricted-calorie diet rich in vegetables and low in red meat; and a low-carbohydrate, nonrestricted-calorie diet. Although the subjects on the low-carb diet ate the most saturated fat, they ended up with the healthiest ratio of HDL to LDL cholesterol and lost twice as much weight as their low-fat-eating counterparts.
April 29, 2010
