By stressing the importance of a carbohydrate-based, low-fat diet, current U.S. dietary guidelines may have unexpectedly contributed to the current obesity epidemic, investigators reported.
In accordance with national recommendations, Americans have slightly reduced their fat intake, wrote Dr. Paul Marantz of the Albert Einstein College of Medicine, New York, and his coauthors. But their carbohydrate and total-calorie intakes have increased, along with the rate of national obesity (Am. J. Prev. Med. 2008 Feb. 8 [Epub doi:10.1016/j.amepre.2007.11.017]).
The observation is not enough to establish a causal link, but enough data exist to make at least an inference. "The hypothesis that dietary fat admonitions actually caused the current U.S. obesity epidemic is consistent with the data, logically sound, and plausible on the basis of both behavioral and biological mechanisms," they said.
The recommendation to reduce fat intake, first promulgated in 1980, focused on the association between cardiovascular disease and one risk factor: hypercholesterolemia. But although there was solid evidence that modifying fat intake could reduce cholesterol, there was--and still is--no evidence that governmental guidelines against fat could improve cardiovascular disease outcomes, the investigators said.
Instead, Dr. Marantz and his team argue, data now suggest that these guidelines negatively affected health by contributing to the obesity epidemic and its attendant increase in diabetes. They used statistics from the Centers for Disease Control and Prevention to support that view.
From 1971 to 2001, consistent with national recommendations of a low-fat, carbohydrate-based diet, fat intake decreased by 5% in men and 9% in women. But carbohydrate intake increased by 7% in men and 6% in women, and total daily caloric intake increased by 168 calories in men and 335 calories in women. In fact, even though women decreased their percentage of fat intake, their increase in daily calories translated into an increase in absolute fat intake, from 557 fat calories per day to 616 fat calories per day.
A corresponding increase in obesity ensued in both genders, the authors noted. In 1971, 55% of American men and 41% of women were overweight or obese; by 2001, those numbers had risen to 70% of men and 62% of women.
The relationship between the guidelines and changing dietary habits is probably multifactorial, they said.
Fat may induce satiety--an important inhibitor of excess calorie intake--which would be a biologically plausible rationale for the idea that low-fat diets may lead to higher calorie consumption.
A societal force is probably also at work, they said. …