Excess calories rather than protein increase body fat
MedWire News: Findings from a US study suggest that increasing the calorie content, but not the protein content, of a diet results in increased body fat.
The researchers found that protein consumption affected the storage of energy and lean body mass and was associated with weight but not body fat gain.
The link between overeating and obesity is well known, but the influence of diet make-up on degree of weight gain and change in body composition in people who overeat is less clear.
To investigate further, George Bray (Pennington Biomedical Research Center, Baton Rouge, Louisiana) and colleagues recruited 25 healthy men (n=16) and women (n=9) with a stable weight and a body mass index (BMI) between 19 and 30 kg/m2 to take part in a study evaluating the effects of overeating on body composition.
Following a 13-25 day period consuming a weight-stabilizing diet, the volunteers were assigned to one of three diets for 8 weeks providing 39.4% (954 kcal/day) more energy than the recommended daily gender-specific amount. The diets all provided the same amount of energy, but low (n=8; 5%), normal (n=9; 15%), or high (n=8; 25%) amounts of protein.
At study completion, participants in the low protein group had gained significantly less weight than those in the normal or high protein groups, at 3.16 kg versus 6.05 and 6.51 kg, respectively.
However, body fat increased similarly in all three groups, by a mean of 3.51 kg, and seemed to be related to total calorie intake rather than amount of protein consumed.
Protein consumption did influence lean body mass, which decreased by 0.70 kg in the low protein group and increased significantly by 2.87 and 3.18 kg in the normal and high protein groups, respectively, at study completion.
Resting energy expenditure was unchanged in the low protein group over the study period, but increased significantly by 160 and 227 kcal/day in the normal and high protein groups, respectively.
"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," write the authors in JAMA.
In an accompanying editorial, Zhaoping Li and David Heber (University of California, Los Angeles) 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 overnutrition 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."
They conclude: "The goals for obesity treatment should involve fat reduction rather than simply weight loss, along with a better understanding of nutrition science."
By Helen Albert