Today the country's leading medical journal published the first long-term comparison of the top three weight loss diets. And the winner is:

low-carb.

The study in The New England Journal of Medicine is also free on-line and is well worth reading. It compares weight loss on low-carbohydrate, Mediterranean, and low-fat diets.

In this two-year trial the researchers randomly assigned 322 moderately obese participants to these three diets. Those assigned to the low-carb diet weren't restricted to how much they ate. But those on the Mediterranean and low-fat diets were.

In this Israeli study, the Direct Intervention Randomized Controlled Trial (DIRECT), the participants worked in an isolated nuclear research facility. Dr. Meir Stampfer is the study's senior author and a professor of epidemiology and nutrition at the Harvard School of Public Health.

The participants got their main meal of the day, which in Israel is lunch, at a central cafeteria. They filled out questionnaires on what they ate for breakfast and dinner, following professional advice about how to stick to their diet for those meals.

In this controlled environment the people on the low-carb diet lost an average of 10.3 pounds. Those on the Mediterranean diet fared second best with an average weight loss of 9.7 pounds. Those on the low-fat diet did worst, losing only 6.4 pounds.

The typical participant stuck to the assigned diet. The overall rate of adherence at 24 months was 85 percent.

Probably to no one's surprise, those on a low-carb diet had the lowest adherence rate, 78 percent. But this was close to that of those on the Mediterranean diet, 85 percent, and the low-fat diet, 90 percent.

The study was well-designed with many strengths. Not only was this a long-term study with a large group of participants who had a high rate of adherence to their assigned diets, but all the participants started at the same time.

None of the three diets was an extreme version of these choices. This was to keep participants on the diet for long term as a way of life.

The low-carb diet started with a two-month induction phase limiting those participants to 20 grams of carbohydrate per day (and right after religious holidays). It gradually increased to 120 grams per day. They didn't limit total calories, protein, or fat.

If this sounds like the Atkins diet, it is. The leading very low-carb diet for people with diabetes is that of Dr. Richard K. Bernstein, which sets much stricter limits of 6 grams of carbohydrate for breakfast and 12 grams each for lunch and dinner.

The low-fat diet aimed at 1500 calories per day for women and 1800 for men with 30 percent from fat, 10 percent from saturated fat, and 300 mg of cholesterol per day. This follows the guidelines of the American Heart Association.

The Mediterranean diet is moderate-fat, rich in vegetables, and low in red meat. Like the low-fat diet, the study restricted women to 1500 calories per day and men to 1800. No more than 35 percent of calories came from fat, mostly olive oil and nuts. The study designers based it on recommendations in the book, Eat, Drink, and Be Healthy, by Walter C. Willett, M.D. (Simon & Schuster, 2001).