According to background information in the article, "Obesity has become a major public health concern with more than 60 percent of adults in the United States categorized as overweight and more than 30 percent as obese." However, which role the composition of a diet plays in response to overeating and energy dissipation remains unclear.
George A. Bray, M.D. and team decided to establish whether the level of dietary protein differentially affected body composition, weight gain, or energy expenditure under tightly controlled conditions. They conducted a randomized controlled trial in 25 healthy, weight-stable American male and female volunteers who were aged between 18 to 35 years with a body mass index between 19 and 30 at an inpatient metabolic unit. The first volunteer was admitted in June 2005 with the last one joining in October 2007.
Following a weight-stabilizing diet, the researchers randomized the participants to receive a diet containing 5% of energy from low protein, 15% from normal protein or 25% on a high protein diet. During the last 8 weeks of their 10- to 12-week stay at the inpatient metabolic unit, the researchers overfed the volunteers. The protein diets provided a raised energy intake of about 40 % translating to 954 calories per day in comparison to the energy intake the volunteers received during their weight stabilization period.
The researchers observed an increase in weight in all participants, irrespective of sex. They established that those in the low protein diet group gained considerably less weight compared with the other two groups, i.e. 6.97 lbs. (3.16 kg) compared with 13.3 lbs (6.05 kg) in volunteers of the normal protein diet group and 14.4 lbs or 6.51 kg in participants in the high protein diet group.
According to the researchers:
"Body fat increased similarly in all 3 protein diet groups and represented 50 percent to more than 90 percent of the excess stored calories. Resting energy expenditure, total energy expenditure, and body protein did not increase during overfeeding with the low protein diet."
The findings showed that the lean body mass (body protein) in the low protein group was lowered by 0.70 kg (1.5 lbs) during the overeating period compared with a gain of 2.87 kg (6.3 lbs) in the normal protein diet group and 3.18 kg (7 lbs) in volunteers in the high protein diet group. In addition, the researchers noted that the resting energy expenditure of 160 calories per day in a normal protein diet and 227 calories per day in a high protein diet increased substantially in the normal and high protein diet groups.
The researchers conclude:
"In summary, weight gain when eating a low protein diet (5 percent of energy from protein) was blunted compared with weight gain when eating a normal protein diet (15 percent of energy from protein) with the same number of extra calories. Calories alone, however, contributed to the increase in body fat. In contrast, protein contributed to the changes in energy expenditure and lean body mass, but not to the increase in body fat. The key finding of this study is that calories are more important than protein while consuming excess amounts of energy with respect to increases in body fat."
Editorial: Overeating and Overweight - Extra Calories Increase Fat Mass While Protein Increases Lean MassDrs. Zhaoping Li, and David Heber, of the University of California in Los Angeles comment in an accompanying editorial, that the results of this study:
"Inform primary care physicians and policy makers about the benefits of protein in weight management. The results suggest that overeating low protein diets may increase fat deposition leading to loss of lean body mass despite lesser increases in body weight. Policy makers and primary care physicians need to understand the role of the Western diet in promoting overweight and obesity.
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. Clinicians should consider assessing a patient's overall fatness rather than simply measuring body weight or body mass index and concentrate on the potential complications of excess fat accumulation. The goals for obesity treatment should involve fat reduction rather than simply weight loss, along with a better understanding of nutrition science."
Written by Petra Rattue