Over time, though, the dieters in both groups tended to rebound somewhat toward their original weights.
James Shikany, the lead author of the study, said the results show that sticking to the Medifast diet makes it harder for dieters to eat more calories than they should.
"It's more of a regimented type of diet, and some people find that's what they need in order to limit their portion intake," said Shikany, who is a professor at the University of Alabama at Birmingham Division of Preventive Medicine.
Dansinger said the weight loss results from the Medifast diet appear to fall in the middle of the pack of other weight loss interventions.
Some approaches, such as weight loss surgery or more extreme diets can have more dramatic results.
But in terms of dietary interventions or FDA-approved weight loss pills, the effect is roughly comparable, he said.
Lisa Davis, the vice president of science and clinical affairs at Medifast, said earlier studies of the diet actually found greater weight reductions.
One explanation she offered is that the current study participants' demographics, such as race, appeared to be different in Shikany's study than in earlier ones.
In particular, Shikany's study included a majority of African Americans whereas other studies had mostly caucasians, Davis said.
"I think that's worth investigating in the future," she told Reuters Health.
Medifast funded the current study, and one of the researchers has been a consultant to Medifast.
Dansinger said that based on this and other studies, he would recommend meal-replacement diets.
"In my opinion, for patients who have had repeated failures with other attempts at sustaining weight loss, the Medifast plan or other similar plans appear to be a good option," he said.
Shikany agreed, but said it's unclear whether cost could be a factor in the diet's appeal.
"If you take (cost) out of the equation, I think it would be a good option for some people, especially for people who need that extra assistance in weight loss efforts as far as determining portions," he said.
SOURCE: http://bit.ly/10seYLw International Journal of Obesity, April 9, 2013.