That news comes from a new study published in the Archives of Internal Medicine.
Half of the participants got meals that were high in plant-based protein (soy, gluten, and nuts) and low in carbohydrates. Oats and barley, which are high in fiber, were allowed in limited amounts, but common starchy foods -- like bread, baked goods, and rice -- weren't included.
For comparison, the other half of the group got a high carbohydrate, low-fat, lacto-ovo vegetarian diet, meaning it included low-fat or skim dairy products and egg whites or egg substitutes.
At the end of the month, both groups had the same average weight loss -- about 9 pounds.
However, it's not clear whether the protein made the difference. Fiber could also have been important, note the researchers, who included David Jenkins, MD, of Canada's University of Toronto and St. Michael's Hospital.
Larger, longer studies are needed to see which diet works best in the long run, especially when people have to prepare their own foods, notes an editorial published with the study.
Jenkins' study was partly funded by soy foods maker Solae and Canadian food distributor Loblaw Companies. In the journal, Jenkins discloses his ties to Solae, Unilever, the California Strawberry Commission, the Almond Board of California, and other companies.
The editorialists, who included Katherine Tuttle, MD, of the Providence Medical Research Center at the University of Washington School of Medicine in Spokes, Wash., note no financial disclosures.