Caloric content alone contributes to the increase in body fat among overeaters on diets with varying protein levels, while protein content seems to impact lean body mass, according to a study published in Wednesday's edition of The Journal of the American Medical Association.
Although all 25 participants gained weight during the study, which provided almost 1,000 extra calories daily, the group in the low protein diet gained at a significantly lower rate than the normal and high protein diets. However, participants in this group also experienced a decrease in lean body mass, or body protein, while those in the normal and high protein diet group saw increases.
In the study, 25 healthy individuals between the ages of 18 and 35 were admitted to an inpatient metabolic unit for 10 to 12 weeks. During the last eight weeks of their stay, after a weight-stabilizing diet, the participants were overfed on diets deriving 5, 15 or 25 percent of their energy from protein.
All participants saw similar increases in body fat, but the low protein group did not see increases in resting energy expenditure or total energy expenditure.
"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," the team of researchers led by George Bray of the Pennington Biomedical Research Center in Baton Rouge wrote.
"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," Zhaoping Li and David Heber of the University of California, Los Angeles, wrote in an accompanying editorial.