For those of us who have resolved to eat healthier and lose weight in the new year, that goal may have just gotten tougher to achieve. If you were already confused about what to eat, a study published on Jan. 4, 2012, in the Journal of the American Medical Association most likely set you in a tailspin. Researchers led by Dr. George A. Bray of the Pennington Biomedical Research Center in Baton Rouge, Louisiana, conducted a study to determine whether a person's level of dietary protein independently affects body composition, weight gain or energy expenditure under highly regulated conditions. The trial was carried out according to the highest scientific standards and included 25 healthy American adults. After the subjects followed matching, calorie-controlled diets for two to four weeks, they were randomized to receive diets that contained an additional 40 percent energy (954 calories) as either 5 percent of energy from protein (low protein), 15 percent (normal protein), or 25 percent (high protein) for another eight weeks.
People who consumed the low-protein diet gained less weight (6.97 lbs) than those who consumed a normal-protein diet (13.3 lbs) or high-protein diet (14.4 lbs). Lean body mass decreased during the overeating period by 1.5 lbs (0.70 kg) in the low-protein diet group, compared with a gain of 6.3 lbs (2.87 kg) in the normal-protein diet group and of 7 lbs (3.18 kg) in the high-protein diet group.
Here is my take on the researchers' findings: In this study, calories alone, and not protein, appeared to contribute to an increase in body fat. In other words, overeating leads to weight gain and increased body fat -- plain and simple. But not so fast! Diets higher in protein lead to more lean muscle mass. The higher a person's protein intake, the more lean body weight they gain. Likewise, the higher a person's protein intake, the higher their energy expenditure, because they gain more metabolically active, fat-burning muscle mass. This means that, if you are healthy and active, eating more protein than fat or carbohydrates is more likely to help you gain more muscle mass. Putting on more muscle mass is far healthier than putting on body fat -- but only if you are also physically active.
In the study by Bray and colleagues, the low-protein group didn't gain as much weight as the other groups, but this isn't necessarily a benefit. In fact, they lost 1.5 lbs of muscle mass while gaining weight as fat. The diet in the low-protein group was similar to the Standard American Diet (SAD), which is low in protein and high in unhealthy saturated fats.
The highest-protein diet might have added some muscle mass, but unfortunately it also added the highest amount (7 lbs) of non-lean body weight and 14 lbs total in only eight weeks, which is very unhealthy! The highest-protein diet in this study by Bray et al was also similar to the eating plan promoted by the French physician Dr. Pierre Dukan in his best-selling book The Dukan Diet. The Dukan diet is a low-carbohydrate, high-protein diet that promotes rapid weight loss by forcing the body to burn fat instead of carbohydrates. Many nutrition experts have warned about its potential hazards. For starters, the book warns that dieters may suffer from bad breath, constipation, dry mouth and fatigue -- all consequences of low carbohydrate-high protein diets. High-protein diets can stress your kidneys and, over the long term, lead to kidney damage, osteoporosis, gallstones and ketoacidosis, an unhealthy buildup of ketone bodies in the bloodstream. And remember, not all proteins are healthy. For example, red and processed meats are high in protein but are laden with saturated fats that are associated with a higher risk of several malignancies, such as colorectal and pancreatic cancer. Finally, a recent report by U.S. News and World Report ranked the Dukan Diet at the bottom of 25 top diets.
So, although the high-protein diet helped people in the study add muscle mass, it may not have done so in a healthy way. And, while people on the low-protein diet didn't gain as much weight as those in the other diet groups, they followed an eating plan that replicated many of the unhealthy food choices found in the SAD. This study was grounded in good scientific principles, but its results may only serve to further muddy the advice we give to people who need to lose weight and keep it off. And -- with nearly 35 percent of adults in the United States categorized as overweight, and an additional 33.9 percent as obese -- that's a problem. In fact, reports indicate that 41 percent of Americans are on a diet at any point in time for weight control. It's no wonder that so many of them struggle to find and understand dietary advice.
My own recommendation to those in search of the optimal diet is to consume about 15 percent of your total calories as protein (the same amount of protein found in the study's "normal-protein" diet), which should help you gain muscle mass without gaining significant amounts of weight overall, and without stressing your kidneys. When you do find yourself overeating (at a party or holiday celebration, for example), try to choose foods that are higher in lean protein, such as turkey and wild-caught fish, rather than those that are high in unhealthy fats, like dips and potato chips. (For more information on healthy food choices, see my New Year's blog.)
Weight management is an everyday struggle for many Americans and there is an abundance of quick-fix gimmicky diets on the market. When in doubt, seek consultation with a certified nutritionist, and consider programs and weight management centers that offer a personalized approach to your weight control. Finally, in addition to dietary changes, I recommend seeking out alternative therapies that have demonstrated benefit for weight control, such as behavioral therapy, dietary supplements such as green tea, acupuncture and mindfulness.
Yours in good health.
Gerard E. Mullin MD
 George A. Bray, et. al. "Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating: A Randomized Controlled Trial." JAMA. 2012; 307(1): 47-55.
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