April 9, 2007 -- If you're trying to lose weight, calories count more than the types of food in your diet, a U.S. Department of Agriculture-Tufts University study shows.
The study shows that after a year, overweight people on a low-carb low-glycemic-index diet lost just as much weight -- 8% of their original weight -- as people on a reduced-fat, high-glycemic-index diet.
"The present results suggest that a broad range of healthy diets can successfully promote weight loss," conclude Sai Krupa Das, PhD, and Susan B. Roberts, PhD, of the USDA's Human Nutrition Center on Aging at Tufts, and colleagues.
"A wide variability in the balance of different dietary macronutrients has little effect on mean long-term weight loss during calorie restriction," Das, Roberts, and colleagues suggest.
The study, funded by the National Institute on Aging, was small but highly sophisticated. The yearlong study enrolled 34 healthy, overweight men and women.
All study participants went on diets designed to cut their calorie counts by 30%.
Half went on a low-glycemic-load diet, a form of low-carb diet that avoids sugary, starchy foods. It's sometimes called a "slow-carb" diet. They got 40% of their calories from carbs, 30% from fats, and 30% from protein.
The other study participants, whose high-glycemic-index diet was matched for taste, attractiveness of appearance, and calorie count, got 60% of their calories from carbs, 20% from fats, and 20% from protein.
Study participants attended weekly behavioral support groups and had regular individual meetings with a dietitian.
Since people in diet studies rarely eat the foods they are supposed to eat, Das and colleagues provided their study participants with foods for the first six months of the study. After giving them shopping and cooking classes, subjects were allowed to buy and prepare their own foods for the second six months of the study.
Energy-intake measures and food diaries showed that people in both groups cheated. But at the end of a year, both groups lost the same amount of weight and the same amount of body fat.
Low-carb diet advocates say people are more likely to stay on these diets because they provide more of the foods people like to eat. The study offers some support for this. During the first three months of the study, when subjects were most compliant with their diets, those in the high-glycemic-index group were less satisfied and had more desire for nondiet foods.
Yet by the end of the year, neither group ate more or less than the other. That may be because the researchers made an effort to ensure that the high-glycemic-index foods were as tasty and attractive as the low-glycemic-index foods.
"However, we did detect a greater tendency for weight and body-fat regain among low-glycemic-diet participants," Das said in a news release. "This finding suggests that reduced caloric intake may be harder to sustain on low-glycemic diets over time."
The findings appear in the April issue of the American Journal of Clinical Nutrition.