The adherence to a reduced-calorie diet has more effect on long-term weight loss than any particular emphasis on protein, fat, or carbohydrate content, according to a 2-year study published in The New England Journal of Medicine.

“Diets that are successful in causing weight loss can emphasize a range of fat, protein, and carbohydrate compositions that have beneficial effects on risk factors for cardiovascular disease and diabetes,” the study authors conclude.

Similar studies have been small, of short duration, with few men, notes the research team, headed by Dr. Frank M. Sacks at the Harvard School of Public Health in Boston.

Their study included 811 subjects (36 percent male, ages 30-70 years, who ranged from being overweight to morbidly obese, and were “sufficiently motivated.” The subjects were offered 72 training sessions throughout the trial, instructed to reduce their daily intake by 750 calories, and were randomly assigned to one of these four diets:

- Low fat, average protein: 20 percent fat, 15 percent protein, 65 percent carbohydrates

- Low-fat, high protein: 20 percent fat, 25 percent protein, 55 percent carbohydrates

- High fat, average protein: 40 percent fat, 15 percent protein, 45 percent carbohydrates

- High fat, high protein: 40 percent fat, 25 percent protein, 35 percent carbohydrates

After 6 months, the participants had lost, on average, 7 percent of their initial weight, but most began to regain weight after 12 months.

At 2 years, there was no significant difference among the diets in the amount of weight lost. About one third had lost at least 5 percent of their initial body weight, while one in six lost at least 10 percent. From 2 percent to 4 percent lost 44 pounds or more.

The authors note that the subjects’ “craving, fullness, and hunger and diet-satisfaction scores were similar at 6 months and at 2 years among the diets.”

Attendance at training sessions, on the other hand, had a strong association with weight loss, which the authors view as “a proxy for commitment to achieving weight loss and for engagement in the program.” The findings, they note, suggest that “behavioral factors” are more important than the percentage of nutrients in the diet and are the main influence on weight loss.

Dr. Martijn B. Katan, at VU University in Amsterdam, sees the results as discouraging. “Even these highly motivated, intelligent participants who were coached by expert professionals could not achieve the weight loss needed to reverse the obesity epidemic,” he writes in an editorial.

“We do not need another diet trial,” Katan declares. “We need a change of paradigm.”

That new paradigm, he maintains, will require “a total-environment approach that involves and activates entire neighborhoods and communities,” from various branches of government to schoolteachers, doctors, restaurant owners, sports associations, and the media, encouraging people to eat better and get more exercise.

Otherwise, Katan concludes, “the only effective alternative that we have at present for halting the obesity epidemic is large-scale gastric surgery.”

SOURCE: The New England Journal of Medicine, February 26, 2009.