Women who follow a high-protein, low-carbohydrate diet may lose more weight and body fat, particularly when they engage in regular exercise, than those whose diets are low in protein and high in carbohydrates, a team of Illinois researchers reports.

“A protein-rich diet, restricting carbohydrates, is a very good way to lose weight,” said study author Dr. Donald K. Layman. “It definitely enhances the benefits of doing exercise.”

Yet, both a high-protein and a high-carbohydrate diet are effective for women who desire to reduce their cholesterol level or otherwise improve their blood lipid profile, the report indicates.

A growing body of research points to the benefits of low-calorie diets that are low in carbohydrates and high in protein. Regular exercise is also known to be both a necessary component of any effective weight loss strategy and key to the maintenance of that weight loss. Yet, few researchers have examined the combined role of a high-protein, low-carbohydrate diet and exercise in weight loss and body composition.

To investigate, Layman, a nutrition professor at the University of Illinois, in Urbana, and his team studied 48 women, aged 40 - 56 years. The women were randomly assigned to one of four groups: a high-protein diet group, a high-protein diet group that exercised, a high-carbohydrate group and a high-carbohydrate group that exercised.

The diets were equal in total energy, and were both “nutritionally sound,” the researcher noted, allowing the women to consume recommended amounts of fruits, vegetables and dairy products, while controlling their servings of protein and carbohydrates, respectively.

Those who exercised were required to walk for at least 30 minutes a day for five days a week and to participate in a resistance training program twice a week, using weight machines.

At the end of the 16-week study period, women in all four groups lost a significant amount of weight, lost body fat and reduced their calorie intake, Layman and his team report in the Journal of Nutrition.

However, those who consumed the high-protein diet lost more body weight and total fat and less lean muscle mass than did those on the high-carbohydrate diet, the report indicates. Further, the addition of exercise, particularly to the high-protein diet, allowed women to lose even more body fat and preserve lean mass.

For example, women that consumed a high protein diet and exercised reduced their body fat by 21.4 percent, while those on the high-carbohydrate diet that did not exercise experienced a 12.8 percent drop in body fat, study findings show.

Both the high-protein and the high-carbohydrate diets improved the women’s levels of blood fats, but the effect varied according to the specific diet, the researchers note.

The high-carbohydrate group experienced greater drops in their total cholesterol level and their level of the “bad” LDL cholesterol, while the high-protein group experienced greater drops in their level of triacylglycerol and maintained higher levels of the “good” HDL cholesterol.

Both diets “improved (the women’s) profile but they were a little different in how they improved it,” Layman noted. Thus, in answering the question of which diet works best, Layman emphasized that it “depends on who you are.”

Women with high levels of triglycerides and low levels of HDL cholesterol, such as those with the pre-diabetes metabolic syndrome, may gain the most benefit from a high-protein diet, for example, while those with High cholesterol may gain more benefit from the high-carbohydrate diet, the report indicates.

The research was funded by the Illinois Council on Food and Agricultural Research, the National Cattlemen’s Beef Association, the Beef Board and Kraft Foods.

SOURCE: Journal of Nutrition, August 2005.