In a tightly controlled dieting experiment, obese people lost an average of just 6 to 10 pounds over two years.
The study, published Thursday in The New England Journal of Medicine, was supposed to determine which of three types of diets works best. Instead, the results highlight the difficulty of weight loss and the fact that most diets do not work well.
The researchers followed 322 dieters, 277 men and 45 women. The dieters were assigned to follow one of three types of diets — a diet with about 30 percent fat, based on American Heart Association guidelines; a Mediterranean diet; and a low-carbohydrate diet based on the Atkins diet plan. The study was partly financed by the Atkins Research Foundation.
The trial was conducted at the Nuclear Research Center in Dimona, Israel, an isolated workplace that has its own medical department.
In addition to regular meetings and telephone calls with dietitians for the participants, the plan included nutrition counseling for spouses and a revamping of the food served in the center’s cafeteria.
Because the center is in an isolated area, the dieters consistently ate lunch, the largest meal of the day, in the company cafeteria, where food was color-coded to help dieters comply with their eating plan.
The biggest weight loss happened in the first five months of the diet — low-fat and Mediterranean dieters lost about 10 pounds, and low-carbohydrate dieters lost 14 pounds.
By the end of two years, all the dieters had regained some, but not all, of the lost weight. The low-fat dieters showed a net loss of six pounds, and the Mediterranean and low-carbohydrate dieters both lost about 10 pounds.
Researchers said the results sound modest, but they said the small weight loss had resulted in improvements in cholesterol and other health markers.
“In order to keep participants on the diet for long term as a way of life, we did not impose extreme diet protocols,” said Iris Shai, the study’s lead author and a registered dietitian at Ben-Gurion University of the Negev at the S. Daniel Abraham International Center for Health and Nutrition. “More dramatic diet protocols could probably reduce more weight for the short term, but participants would have dropped out.”
There were subtle differences in the three diets studied. Men did better on the low-carbohydrate diets, losing 11 pounds compared with about 9 pounds for the Mediterranean diet.
Women fared best on the Mediterranean diet, losing about 14 pounds compared with about 5 pounds on the low-carbohydrate plan.
For all dieters, there were improvements in the ratios of good to bad cholesterol.
“This suggests that healthy diet has beneficial effects beyond weight loss,” Ms. Shai said.