New data show that consuming more calories accounts for increases in body fat, regardless of dietary composition.

“As obesity develops, a number of metabolic changes occur, which may not completely reverse when weight is lost,” George A. Bray, MD, of the Pennington Biomedical Research Center in Baton Rouge, La., and colleagues wrote in the Journal of the American Medical Association. “These differences may reflect differences in the way individuals handle the food they eat each day both during weight gain and weight loss.”

Between 2005 and 2007, Bray and colleagues randomly assigned 25 men and women aged 18 to 35 years with BMIs ranging from 19 to 30 to a diet containing 5% protein (low protein), 15% protein (normal protein) or 25% protein (high protein). During the last 8 weeks of the participants’ 10- to 12-week stay in an inpatient metabolic unit, the researchers increased participants’ caloric intake by approximately 40%, corresponding to an extra 954 kcal per day (95% CI, 884-1,022).

At 3.16 kg (95% CI, 1.88-4.44), weight gain in the low-protein group was approximately half that of the normal-protein (6.05 kg; 95% CI, 4.84-7.26) and high-protein groups (6.51 kg; 95% CI, 5.23-7.79), according to study results. Further, the rate of weight gain was significantly less for participants on the low-protein diet (P<.001). However, increases in body fat, which represented from 50% to more than 90% of excess stored calories, were similar among all diet groups.

During the overeating period, participants in the low-protein group experienced a 0.7-kg decrease in lean body mass, whereas the normal-protein and high-protein groups experienced increases of 2.87 kg and 3.18 kg, respectively. Similarly, resting energy expenditure increased significantly in the normal- and high-protein groups when compared with the low-protein group (P<.001) — outcomes that were strongly associated with protein intake, the researchers said.

“Weight gain when eating a low protein diet (5% of energy from protein) was blunted compared with weight gain when eating a normal protein diet (15% of energy from protein) with the same number of extra calories,” the researchers wrote. “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 fat.”

In an accompanying editorial, Zhaoping Li, MD, PhD, and David Heber, MD, PhD, of the David Geffen School of Medicine at the University of California, Los Angeles, highlighted the potential implications of these findings, especially in light of the low-protein aspect of the Western diet.

“Policymakers and primary care physicians need to understand the role of the Western diet in promoting overweight and obesity,” Li and Heber wrote. “Because this diet increases the risks of overnutrition through fat deposition beyond that detected by BMI, 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 BMI and concentrate on the potential complications of excess fat accumulation.”

Source:Endocrine Today.