NEW YORK (Reuters Health) - A diet free of animal products and low in fat may help trim the waistline without the task of strict calorie watching, a new study suggests.

Researchers found that of 64 postmenopausal, overweight women, those assigned to follow a low-fat vegan diet for 14 weeks lost an average of 13 pounds, compared with a weight loss of about 8 pounds among women who followed a standard low-cholesterol diet.

The weight loss came despite the fact that the women were given no limits on their portion sizes or daily calories -- and despite the fact that the vegan diet boosted their carbohydrate intake.

"People imagine carbohydrates to be fattening, but they are not," said lead study author Dr. Neal D. Barnard, an adjunct associate professor of medicine at George Washington University in Washington, D.C.

He is also president of Physicians Committee for Responsible Medicine, a nonprofit group that advocates vegetarianism as part of preventive medicine.

The greater weight loss among women on the vegan diet may stem from specific metabolic effects, Barnard told Reuters Health.

He pointed out that the diet improved the women's sensitivity to insulin, a hormone that ushers sugar from the blood and into cells to be used for energy. This was also accompanied by an increase in what's known as the thermic effect of food -- the amount of calories the body expends to process and store food.

The vegan diet improved women's insulin sensitivity to a greater a degree than the comparison diet did -- though the difference was not statistically significant, meaning the finding could be due to chance.

Barnard and his colleagues at George Washington and Georgetown universities report the findings in the American Journal of Medicine.

Vegan diets eschew all animal products, including dairy and eggs, in favor of fruits and vegetables, grains, nuts and beans. Although high-protein weight-loss regimens have painted carbohydrates as the enemy, a number of studies have found that vegetarians and vegans, who tend to eat a lot of fiber- and vitamin-rich carbohydrates, are much less likely to be overweight than meat-eaters.

Women in the current study found the vegan diet easy to follow, according to Barnard, because they were not asked to count calories or keep tabs on portion sizes. They were, however, told to avoid added oils, nuts and seeds to keep their fat intake down.

Women in the comparison group followed a diet based on National Cholesterol Education Program guidelines, which meant restricting fat to less than 30 percent of calories and protein to about 15 percent of calories.

Participants, who ranged in age from 44 to 73, also attended weekly meetings that included nutrition and cooking lessons.

Based on dietary records the women kept, both groups ended up reducing their calorie intake by almost 400 calories per day, on average. But those on the vegan diet lost more weight.

Despite the restrictions of going vegan, Barnard maintained that it's easy to take on the lifestyle. "Just eat fruits, vegetables, beans and whole grains," he said. "Everything you're eating is good for you."

It is wise, he noted, to take a multivitamin, particularly to get enough vitamin B12, which is found naturally only in animal products.

SOURCE: American Journal of Medicine, September 2005.