January 5th, 2012

Diets Differ in Effect on Weight Gain and Fat and Lean Mass

A new study published in JAMA demonstrates the various effects of overeating of three diets that differed mainly in protein composition.

George Bray and colleagues randomized 25 healthy volunteers to participate in an inpatient study to consume low-, normal-, or high-protein diets that provided 40% more calories than required to maintain one’s normal weight. After 8 weeks, there was less weight gain in the low-protein group than in the other groups (p=0.002).

Weight gain:

  • low-protein group: 3.16 kg
  • normal-protein group: 6.05 kg
  • high-protein diet group: 6.51 kg

However, there was no difference across the groups in the increase in body fat, and the low-protein diet caused no increase in energy expenditure or lean body mass. By contrast, energy expenditure and lean body mass increased with the normal- and high-protein diets.

Lean body mass:

  • low-protein group: -0.70 kg
  • normal-protein group: +2.87 kg
  • high-protein diet group: +3.18 kg

For the low-protein diet, more than 90% of the extra calories were stored as fat, while for the normal- and high-protein diets, only 50% of the excess calories were stored as fat.

In an accompanying editorial, Zhaoping Li and David Heber write that the study showed that “body fat increased in proportion to excess calories but overall weight gain was less with low protein relative to normal or high protein diets.” Because Western diets are high in fat and carbohydrates, they note, the results “suggest that body weight may underestimate the true hazards of overnutrition.” They point out that in free-living populations, high-protein diets “may contribute to more successful weight loss in the long-term due to the effects on resting energy expenditure observed in this study.”

The editorialists offer the following advice to physicians:

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.

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