Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating: A Randomized Controlled Trial

Study Questions:

What are the relative effects of overconsumption of low, normal, and high protein diets on weight gain, energy expenditure, and body composition?


A single-blind, randomized, controlled trial was conducted in 25 US healthy, weight-stable male and female volunteers, ages 18-35 years, with a body mass index between 19 and 30 kg/m2. After consuming a weight-stabilizing diet for 13-25 days, participants were randomized to diets containing 5% of energy from protein (low protein), 15% (normal protein), or 25% (high protein), which they were overfed during the last 8 weeks of their 10- to 12-week stay in the inpatient metabolic unit. Compared with energy intake during the weight stabilization period, the protein diets provided approximately 40% more energy intake, which corresponds to an average of 954 kcal/d. Body composition was measured by dual-energy x-ray absorptiometry biweekly, resting energy expenditure was measured weekly by ventilated hood, and total energy expenditure by doubly labeled water prior to the overeating and weight stabilization periods and at weeks 7-8.


Overeating produced significantly less weight gain in the low protein diet group (3.16 kg) compared with the normal protein diet group (6.05 kg) or the high protein diet group (6.51 kg) (p = 0.002). Body fat increased similarly in all three protein diet groups and represented 50% to more than 90% of the excess stored calories. Resting energy expenditure, total energy expenditure, and body protein did not increase during overfeeding with the low protein diet. In contrast, resting energy expenditure and body protein (lean body mass) increased significantly with the normal and high protein diets.


The authors concluded that among persons living in a controlled setting, calories alone account for the increase in fat; protein affected energy expenditure and storage of lean body mass, but not body fat storage.


Weight gain when eating a low protein diet was blunted compared with weight gain when eating a normal protein diet with the same number of extra calories, and protein contributed to the changes in energy expenditure and lean body mass, but not to the increase in body fat. The findings are interesting, but not generalizable. Participants were in their 20s and predominantly black males. To what degree age and gender affect the impact of low or high dietary protein on body fat and lean muscle mass will be an important extension of these observations.

Clinical Topics: Diabetes and Cardiometabolic Disease, Prevention, Diet

Keywords: Body Mass Index, Eating, Dietary Proteins, Vascular Diseases, Body Weight, Diet, Protein-Restricted, Energy Intake, Weight Gain, Single-Blind Method, Hyperphagia, Pregnancy

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