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.