The dangers of high-protein, low carbohydrate diets for weight loss have been highlighted by the media in recent months but new research seeks to explain the benefits of protein for people trying to lose weight.
Two studies in this month's Journal of Nutrition suggest that eating more high quality protein will increase the amount of leucine, an amino acid, in the diet, helping a person maintain muscle mass and reduce body fat during weight loss. Maintaining muscle during weight loss efforts is essential because it helps the body burn more calories, according to study author Donald K. Layman, professor of nutrition at the University of Illinois at Urbana-Champaign.
Layman's research challenges the conventional wisdom about the role of low-fat foods in weight loss, according to the researcher. High protein diets tend to cause concern because of the consumption of saturated fat and cholesterol in protein-rich foods. However, researchers found that this diet brought more stable blood glucose levels, reductions in total cholesterol and weight loss.
For the study, 24 middle-aged overweight women consumed 1,700 calories a day for 10 weeks. Physical activity of the participants remained constant.
The control group ate according to the USDA Food Guide Pyramid, consuming approximately 0.36 grams of protein and 1.3 grams of carbohydrates per pound of body weight per day.
Study group participants increased the amount of protein they ate daily to about 0.73 grams per pound of body weight and reduced their intake of carbohydrates to 0.95 grams per pound of body weight.
Proteins selected for the study provided optimal levels of leucine, shown to be a regulator of muscle, which is important to maintain when losing weight. The body does not produce leucine, so people need to consume foods rich in the amino acid, such as beef, dairy products, poultry, fish and eggs.
The study group's daily diet consisted of nine to 10 ounces of meat, including at least seven beef meals per week, three servings of low-fat milk or cheese, and a minimum of five servings of vegetables. They also included two servings of fruit and four servings of grains, pasta and rice, and they ate in accordance with the National Cholesterol Education Program's Step 1 heart-healthy guidelines.
Most of the public debate about diet continues to focus on the extremes of very high (Atkins' Plan) or very low (Ornish Plan) levels of proteins. Layman's plan falls within the protein range recently recommended by the National Academy of Sciences Food and Nutrition Board. The USDA Food Guide Pyramid falls at the low end of the accepted protein range.
In Layman's study, both diet groups lost a similar amount of weight, about 16 pounds, but the study group lost two pounds more body fat and one pound less muscle mass than the control group.
"Traditionally, people have built a diet around low-fat foods, instead of high quality protein foods. Study participants following the moderately high protein plan, (termed the 'Sensible Solution') were twice as effective in maintaining lean muscle mass," he said.
"The group following my diet lost fat, maintained muscle and had an improvement in total blood cholesterol level. Subjects found the eating plan easy to follow, allowing them to enjoy foods from all the food groups."
Additional findings showed that women in the study group were less hungry between meals than were those following the traditional diet. The study group also experienced more stable blood glucose levels and reduced insulin response following meals, according to the research. Both groups had reductions in total blood cholesterol, but the study group also had decreased triglyceride levels.
Layman is currently planning a long-term study of his 'Sensible Solution' diet to further investigate the role of leucine in metabolic control.
The study was funded by America's beef producers through their $1-per-head checkoff, Kraft Foods, US Department of Agriculture and the Illinois Council on Food and Agricultural Research.