When It Comes to Long-Term Weight Loss, There’s No Magic Bullet
Most diets can help people lose weight, but only moderate-fat, high-carbohydrate regimens seem to keep the pounds off for good, according to the first comprehensive scientific review of popular diets by the federal government.
Any diet that limits food to about 1,500 calories per day produces short-term weight loss, no matter how sound or exotic the regimen, according to the U.S. Department of Agriculture report, which is scheduled to be released Thursday. But only a few have been proved to produce long-term health benefits, such as lowering cholesterol and blood pressure levels, the report concludes.
“This basically tells you that you can lose weight on any of the diets, if you keep your calories down,” said Agriculture Secretary Dan Glickman. “The trick is how you maintain that weight loss.”
The report, the first in an ongoing review of popular diets, casts doubt on newer unorthodox approaches, such as the high-protein Atkins diet, and finds that the least glitzy regimens--traditional programs recommended by groups such as the American Heart Assn. and Weight Watchers--have the best scientific evidence to back up their success rates and health claims.
These programs recommend consuming no more than 30% of calories as fat, limiting protein to about 20% of the diet and consuming more fruits, vegetables and complex carbohydrates to help satisfy hunger with fewer calories. They are the most nutritionally adequate and showed some of the best improvements in blood levels of the most dangerous cholesterol and blood fats and in blood sugar control, the study found.
“Based on the scientific knowledge we have, this seems to be the most efficacious way to go and it is most likely the safest,” said Xavier Pi-Sunyer, director of the obesity research center at St. Luke’s-Roosevelt Hospital in New York and editor of Obesity Research, which will publish the full USDA study in the March/April issue.
The report is part of the government’s attempt to help Americans lose weight. At least half of all adults are considered overweight or obese, putting them at increased risk for a variety of serious health problems. Millions try to trim their waistlines, spending an estimated $33 billion annually on diet books, diet pills and weight loss programs, many of which have never undergone rigorous scientific testing.
The report found that there is also good scientific evidence supporting the effectiveness and healthfulness of very-low-fat, high-carbohydrate diets, such as the Dean Ornish program and the Pritikin diet. These programs also produced good long-term weight loss, for those able to stick with them. But the report also found solid evidence that these diets are deficient in vitamin E, B12 and zinc, requiring supplements.
The fewest number of studies--and the least rigorous scientifically--were on the low-carbohydrate, high-protein weight loss programs, such as the Atkins diet, the report found.
In the short run, these diets produced a greater loss of body water than of fat, which was regained when the diet ended. No controlled, randomized studies exist to support the loss of body fat with long-term use of the diets. Nor was there evidence to suggest that individuals improve blood cholesterol levels or blood sugar with these diets.
“All the statements that they are saying are true,” said Colette Heimowitz, director of education and research at the Atkins Health and Medical Information Services in New York. “In the beginning, short-term weight loss [on the Atkins diet] is water weight. . . . But most people who are overweight have added water anyway.”
However, 40 years of experience has shown Atkins that the program works, she said. “But we are not researchers,” Heimowitz said. “We agree that long-term research needs to be done. It’s something we’ve been fighting for for a long time. . . . It’s a blessing that the USDA has done this report.”
Experts were also quick to acknowledge the limitations of the study. The report did not involve new research, but was based on a review of all existing scientific literature on obesity, weight loss and diet. The effort was designed to evaluate the scientific soundness of various weight loss programs and to determine their effectiveness in trimming pounds and maintaining weight loss for good, as well as measuring their effect on such things as blood pressure, cholesterol levels, lean body mass, hunger and appetite.
“This is a good start,” Pi-Sunyer said. “But we need long-term studies that show compliance, dropout rates, sustainability, effectiveness and safety. We can’t talk about that without having a randomized, clinical study, which we don’t have.”
“What this report shows is that whatever diet you choose, we know that you can take the weight off,” said Judith Stern, professor of nutrition at UC Davis and vice president of the American Obesity Assn. “But if you read the report carefully, we also know that no matter what, after about two months of dieting, you will stop losing weight and plateau and will start regaining unless you exercise regularly, have social support and decrease stress. It is a tremendous effort to keep the weight off.”
