Extra calories from proteins may lead to weight gain but more muscle than fat: Study

By Dr. Ananya Mandal, MDJan 4 2012

A new study shows that people who eat extra calories will gain the same amount of fat regardless of how much of their daily diet comes from protein. The study is one of the most extensive where researchers look at differences among food types on weight gain.

The results show that people who overeat gain less weight if they avoid protein. According to George Bray, an obesity specialist and the study’s lead researcher, this is not reassuring. Low-protein eaters gained just as much fat, and lost lean body mass, the study in the Journal of the American Medical Association found.

“There is nothing in medicine that would suggest losing lean body mass is a good idea,” said Bray, a professor at Louisiana State University’s Pennington Biomedical Research Center in Baton Rouge. “People on the low protein diet could think they were doing a good thing by gaining less weight, but they gained the same amount of fat and lost lean body mass.”

The results suggest the obesity epidemic may be worse than is currently known because those with lower body weight may have undetected layers of fat that can harm their health, the researchers said. About 65 percent of Americans are overweight, and one-third are considered obese, according to the U.S. Centers for Disease Control and Prevention.

The study followed 25 young adult volunteers (aged between 18 and 35) who agreed to live in a university metabolic unit for three months. Staff members prepared their meals, including an extra 1,000 calories a day, and watched to make sure they ate every bite. Volunteers were divided into three groups getting a low-protein, high- protein or normal protein diet, with the same calories.

At the end of the study they found that those getting just 5 percent of their calories from protein gained significantly less weight than those given more protein, adding 3 kilograms (6.6 pounds), compared with 6 kilograms (13 pounds). Volunteers in the highest protein group increased metabolism levels, though not enough to curb weight gain, and led to more lean body mass. “The calories are the critical factor,” Bray said. “Protein will change the scale weight, but not your fat rate,” he said. “Don’t be fooled by the scale, it may not be your friend.”

“Most people are overeating and for those people who are, they need to pay attention to what they are putting into their mouths,” said study co-author Leanne Redman, an assistant professor of endocrinology at Pennington Biomedical Research Center in Baton Rouge, La. “If you overeat a high-fat, low-protein diet, you may gain weight at a lower rate, but you are gaining more fat and losing more muscle.”

The study shows how low-protein foods with extra sugar and fat are contributing to the obesity epidemic, wrote Zhaoping Li and David Heber, from the University of California, Los Angeles’ Center for Human Nutrition, in an accompanying editorial. “The Western diet tends to be high in fat and carbohydrates and low in protein,” they said.

“Because this diet increases the risks of over-nutrition through fat deposition beyond that detected by body mass index, the method used to assess the current obesity epidemic and the magnitude of the obesity epidemic may have been underestimated.” Dr. David Heber, director of the Center for Human Nutrition at the University of California, Los Angeles added, “Calories count.” He encourages a high-protein, low-fat diet that is rich in colorful fruits and vegetables. “We are talking about lean protein such as white-meat chicken, ocean fish, turkey, egg whites and certain protein powders. Protein is more satiating, and helps reduce appetite,” he explained.

Connie Diekman, director of university nutrition at Washington University in St Louis, said, “This study provides support to the calories-count message as it relates to percent of body fat. I find the conclusion of this study especially helpful in encouraging people to be aware of the calories they consume and to avoid focusing on just where those calories come from.”

“Many people make the mistake of cutting back on protein or skipping meals when they’re trying to lose weight,” said Dr. George Blackburn, chief of the Nutritional/Metabolism Laboratory at Beth Israel Deaconess Medical Center in Boston. “But most of us need about 45 to 55 grams of protein each day spread over three meals to keep the body from losing muscle.”

One eight-ounce glass of milk has 8 grams of protein, while three ounces of lean beef, chicken or fish has about 21 grams; a cup of dry beans has 16 grams, and an eight-ounce container of yogurt has about 11 grams, according to the US Centers for Disease Control and Prevention. Only about half of Americans, Blackburn added, get adequate amounts of protein throughout the day, and as a result of this deficiency it may be harder to retain muscle and fight the mid-life spread.