Nutrition: Overeating, Weight Gain and Lean Body Mass—Is Dietary Protein Content the Key?

RESEARCH HIGHLIGHTS Nature Reviews Endocrinology 8, 127 (2012); published online 24 January 2012; doi:10.1038/nrendo.2012.5

NUTRITION Overeating, weight gain and lean body mass—is dietary protein content the key?

hen healthy individuals overeat, During the 8-week overfeeding period, energy stored as fat was >90% for the low- the amount of weight gain is individuals had an energy intake that protein diet but only ~50% for the diets Wreduced if the diet has a low- was approximately 40% above the intake with normal or high protein content. For protein content; however, this diet also calculated as their maintenance energy these last two diets, most of the remaining results in a loss of lean body mass and the requirement during the run-in period. energy was consumed by increased diet- same increase in fat mass as with normal- All participants gained weight but the induced thermogenesis, probably related protein or high-protein diets. These data mean weight gain for the low-protein diet to protein synthesis. were revealed in a new study published group (3.16 kg) was ~50% of that for the “We knew that too little protein in the diet in JAMA. other two diet groups; gains were 6.05 kg during weight-loss diets (undereating) is High food intake contributes to a positive and 6.51 kg with the normal-protein and detrimental for health as it causes excessive energy balance that, over an extended high-protein diets, respectively. Of note, loss of lean body mass from muscle and period, can result in the development the reduced weight gain in the low-protein other vital organs and tissues, but this of obesity. However, the amount of diet group resulted from an incapacity study shows that even during overeating weight gain that results from overeating to increase lean body mass, which did too little protein causes loss of lean tissue is highly individual and the reasons for increase in individuals overfed the other and reduces the rate of metabolism. So, this this individuality remain an enigma. two diets. By contrast, fat mass increases result emphasizes the importance of protein The protein content of food overeaten were not significantly different between in the diet for health and body-weight might affect weight gain—a hypothesis the three groups, although, interestingly, regulation,” comments Arne Astrup of the investigated by Bray et al. in this an average 200 g of excess fat was gained in University of Copenhagen, who was not single-blind, randomized, controlled study. individuals in the low-protein diet group. involved in this study. “A calorie is a calorie—or is it? That was Overeating did not significantly affect “From a public health perspective,” part of the question we tried to answer in resting energy expenditure or total Astrup continues, “the study has, in my this highly controlled study of different energy expenditure if the diet was low in view, little relevance to guide the consumers dietary protein levels during overfeeding in protein. By contrast, both types of energy to select the most healthy diet to prevent healthy men and women who were normal expenditure increased during overfeeding weight gain and cause weight loss because weight or slightly overweight,” explains lead with normal-protein or high-protein diets. the most important property of dietary researcher George Bray of the Pennington This increase occurred despite a lack of protein is its much stronger satiating effect Biomedical Research Center, USA. change in physical activity levels between that, in many studies, has been shown to The researchers randomly allocated baseline and during overeating. The make overeating much more difficult. 25 healthy individuals of 18–35 years of researchers used metabolic calculations to The design of this study was fixed caloric age and with a BMI of 19–30 kg/m2 to be discover why energy expenditure differed overfeeding, so the appetite regulation of overfed a low-protein diet (5% of energy by the protein content of the overfed diet. the participants was put out of play.” from protein), a normal-protein diet They found that the percentage of extra The findings, however, provide food (15%) or a high-protein diet (25%) for for thought. “For fat and carbohydrate a 8 weeks. The percentage of energy content calorie is a calorie, this study showed. from carbohydrate was constant between But protein was different. the different diets (41–42%), whereas that Changing dietary protein over a from fat varied. The group of participants range of 5% to 25% did not affect included both men and women and was fat storage, but it did affect the increase varied in terms of ethnicity. Participants in lean body mass and thermogenesis,” stayed in an inpatient metabolic unit concludes Bray. during the 10 weeks to 12 weeks of the Carol Wilson study, which included a run-in period of 13–25 days during which individuals received an isocaloric diet (15% of Original article Bray, G. A. et al. Effect of dietary protein energy from protein) that had been content on weight gain, energy expenditure, and body calculated to be weight stabilizing by composition during overeating: a randomized controlled trial. JAMA 307, 47–55 (2012) energy expenditure measurements. © Karen Struthers | Dreamstime.com