Editor’s Note: Dr. Frank M. Sacks was the lead author of one of the largest and longest studies ever to compare the effectiveness of different kinds of diets on weight loss. His study was published in the Feb. 26, 2009 issue of The New England Journal of Medicine.

Arthritis Today: Can you tell us a little bit about the significance of this weight loss study?

Dr. Sacks: The question of what type of diet that can facilitate weight loss is really old and hotly debated, and there are loads of divergent findings in the scientific literature. In other words, there are some findings that favor a low-fat, high carbohydrate diet, some findings that favor the total opposite kind of diet, and there are often problems with many of those kinds of studies.

What we wanted to do was to really test a big range of dietary fat, carbohydrate and protein intakes in a large number of people, 811, and extend it through two years with continual support, with behavior and nutritional sessions in groups and individually.

And we also wanted to make clear that all the diets we’re testing are healthy to prevent heart disease or to prevent diabetes, and some experts would feature one versus another.

We created a really neutral atmosphere. We didn’t want people to go in with a bias that one diet would work better than another.

The results, in a way, surprised us. We thought that the higher protein diet would be more satiating and lead to better weight loss long run, but we didn’t find that at all. We found that protein content really didn’t matter.

What really counted was people’s engagement in the program. Maintaining their commitment and what diet they were assigned to really didn’t have any influence at all.

Arthritis Today: In your paper, you admit that people had a hard time sticking to the diets that were most different from the way they ate before they started the study.

Dr. Sacks: Yes. That’s one of the problems with one of the more extreme popular diets.

For example, take this very low carbohydrate Atkins Diet. What the Atkins studies show is that after the first couple of months, people don’t get down to those very low carbohydrate levels. If they did initially, they can’t maintain that. We didn’t want to test a very low carbohydrate intake. We wanted to study a very large range of carbs, but the lowest carbs, 35 percent, we thought would be possible to go for. What we found was that over time people kind of gravitated back to what their usual carbohydrate, fat and protein intake was. And all in all, their weight loss didn’t suffer from that. What really counted was their engagement in the program.