The ever-popular low-carbohydrate diets appear to work because they force people to eat more protein, which consequently suppresses the appetite, not because of a lower carbohydrate intake, according to new study findings published in the American Journal of Clinical Nutrition.

These results suggest that it’s not necessary for people to cut back carbohydrates to lose weight, according to Dr. Arne Astrup of the Royal Veterinary and Agricultural University in Copenhagen, who wrote an accompanying editorial.

Protein appears to encourage people to eat fewer calories overall, Astrup noted, so if people simply increase their intake of protein, that should help them lose weight. “You can just eat a little more lean meat and low-fat dairy products,” Astrup recommended.

Lead study author Dr. David S. Weigle of the University of Washington School of Medicine in Seattle and his colleagues note that low-calorie diets rarely work. This has encouraged researchers to consider that changing the ingredients of the diet, but not its calories, makes a difference in people’s waistlines.

Previous research shows that low-carbohydrate diets, typically high in fat and protein - are effective, the authors report, but so are low-fat diets.

Weigle and his team speculated that low-carb diets may work because they encourage people to eat more protein, which decreases people’s appetites and causes them to consume fewer calories.

To investigate, the researchers followed 19 people placed on different diets. As part of the first diet, which was designed to maintain body weight and lasted 2 weeks, people received 15 percent of calories from protein, 35 percent from fat, and 50 percent from carbohydrates.

In the next diet, people followed a calorie-controlled diet for 2 weeks, in which they got 30 percent of calories from protein, 20 percent from fat, and 50 percent from carbohydrates. People then spent another 12 weeks consuming the same percentage of calories from each type of food, but were told they could eat as many calories as they wanted.

People reported feeling less hungry on the calorie-controlled, high-protein diet. When they continued the diet but could eat consume as many calories as they wanted, they took in nearly 450 fewer calories per day and lost almost 5 kilograms (11 pounds).

Astrup explained that protein helps people lose weight because, “calorie for calorie,” protein makes people feel fuller than carbohydrates or fat. The researcher noted that it’s unclear why protein works better at curbing appetite.

SOURCE: American Journal of Clinical Nutrition, July 2005.