Overweight people who adhere to a low-calorie diet lose weight regardless of the diet’s fine points, a study finds. Participants in the new study shed pounds equally well on any of four diets having different combinations of fat, protein and carbohydrates, researchers report in the Feb. 26 New England Journal of Medicine.
“It’s really how much people eat that counts,” says study coauthor Frank Sacks, a nutrition researcher and physician at the Harvard School of Public Health and Brigham and Women’s Hospital in Boston. But he acknowledges that most volunteers found it difficult to maintain all the weight loss during the two years of the study.
The results are the latest in a growing body of data emerging from large, multiyear trials in which volunteers are randomly directed to follow a particular diet. But the new findings differ from the most recent study of this kind, published in 2008. In that two-year study, researchers in Israel found that a low-carbohydrate diet allowing unlimited calories resulted in greater weight loss and higher levels of HDL, the good cholesterol, than did a low-fat diet in which calorie intake was restricted (8/16/08, p. 9).
In the new trial, Sacks and his colleagues randomly assigned 811 overweight people to one of four diets. Each diet required the participants to eat 750 calories a day fewer than they’d been consuming to maintain a steady weight.
The four diets varied in composition. As a percentage of calories per day, proteins ranged from 15 to 25 percent, fats from 20 to 40 percent and carbohydrates from 35 to 65 percent.
In the end, the different formulas didn’t matter much. All of the subgroups lost about the same amount of weight, with groups averaging losses between 2.9 and 3.6 kilograms (6.4 to 7.9 pounds) over two years. Waist circumferences shrank about equally in all four groups. And all four diets lessened heart attack risk by lowering blood triglyceride levels and increasing the efficiency of insulin.
Some minor differences did emerge. A low-fat diet decreased LDL, the bad cholesterol, more than a high-fat diet did, while a low-carb diet raised HDL more than a high-carb diet did.
Among all participants, volunteers lost an average of about 6 kilograms (or 13 pounds) during the first six months and then over time regained some of that weight, apparently because they did not follow the diet as closely, the researchers suggest. Only a small minority maintained a weight-loss trend for two years.
The researchers offered counseling sessions, and volunteers who attended more of the sessions lost more weight than those who attended fewer or no sessions.
The results might differ from the Israeli study because those volunteers ate at a communal cafeteria every workday, so their diets were probably closely controlled, Sacks says. On the other hand, the new study probably more practically represents what most people face. Dieters are on their own out there, he says.
The new findings also suggest that weight loss relies more on eating behavior than food choice, and that there are no shortcuts, says biochemist and nutrition researcher Martijn Katan of the VU University in Amsterdam, the Netherlands.
Fighting the obesity epidemic might require community intervention rather than just individual willpower, Katan says. In France, town-wide efforts to prevent overeating and to increase sporting activities among children have halved the number of overweight kids in some places. This community approach “is being rolled out all over Europe,” he says. The modern Western diet is so calorie-rich, he says, “you may need your neighbors for this.”