Eating less fat does not magically melt flab away, as some had hoped, but it does not necessarily lead to weight gain either – as some diet promoters had claimed – according to the first study to follow a large number of people who cut their daily fat intake over a long period.
The study of more than 48,000 women who were followed for about seven years found that those who adopted a lower-fat diet initially lost about 5 pounds but gained back all but about 2 pounds. A comparison group that did not change their diet stayed about the same.
Proponents of a reduced-fat diet said the findings show that lowering fat intake, which is being tested as a way to reduce the risk of heart disease and some forms of cancer, also can help people avoid gaining weight in middle-age.
“The take-home message is that lower-fat diets don’t cause weight gain, and for weight maintenance this is a reasonable diet for people to follow,” said Barbara Howard of the MedStar Research Institute in suburban Hyattsville, Md., who led the study being published in today’s issue of the Journal of the American Medical Association. “If we could just get people to maintain their weight, we’d be halfway there on this nation’s obesity epidemic.”
Because the women in the diet replaced their fat calories with calories from carbohydrates, mostly in the form of fruits, vegetables and whole grains, the study also undermines the idea that cutting carbohydrates is the key to weight loss – an idea that’s been promoted in the Atkins diet and other popular regimens, she said.
“Some of these fad diets promote the idea that if you suddenly cut carbs it’s going to miraculously make you lose weight,” Howard said. “This shows that’s probably unfounded.”
But proponents of the low-carb approach disputed that claim, saying the research did not examine what happens when people cut carbs.
“I don’t think this study negates the benefits of a properly done low-carbohydrate diet,” said Abby Bloch of the Dr. Robert C. Atkins Foundation.
Other researchers said the findings undermine the dominant public health message that cutting fat is the key to losing weight.
“This does very strongly refute the dominant view in the 1990s that reducing the amount of fat in the diet would spontaneously lead to weight loss,” said Walter Willett of the Harvard School of Public Health. “What’s happened to the American diet during this low-fat period is people were given the idea that if they reduced calories from fat, weight would go down. Clearly, that has not happened.”
The study involved 48,835 women ages 50 to 79 participating in the Women’s Health Initiative, a federally funded project designed to study a variety of health issues. This part of the study was designed to determine whether adopting a low-fat diet might reduce the risk of heart disease and certain forms of cancer.
Half the women lowered the amount of calories they were getting from fat to about 30 percent by eating less fat and increasing the amount of carbohydrates. The other half did not change their diet significantly.
While the study was not designed to determine whether such a diet could help the women lose weight, the researchers analyzed the impact on weight because of concerns that low-fat diets were contributing to the obesity epidemic. The effects on cancer and heart disease will be reported later this year.
“There have been all these claims that a low-fat, high-carbohydrate diet is the main fuel for the obesity epidemic,” said JoAnn Manson of Harvard’s Brigham and Women’s Hospital in Boston, who helped conduct the study. “This shows there is no tendency towards weight gain.”