Energy-restricted diets with standard or high protein levels were equally effective for reducing body weight and boost body composition, says a new study.
Low-fat diets containing either 17 or 35% protein were both associated with a 9% reduction in body weight and a 4% decrease in fat-free mass, according to results of a 12 week study published in theEuropean Journal of Nutrition.
“Altering the carbohydrate-to-protein ratio of an energy-restricted, low-fat diet that achieved similar weight loss and reductions in fat-free mass had similar effects on strength and aerobic capacity in sedentary, overweight and obese men,” wrote the researchers, led by Grant Brinkworth from Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO).
“However, these results are limited to middle-aged men and whether these similar effects occur in younger or older individuals and/or in women and are maintained over the longer-term remains unknown and warrants investigation.”
The study fails to support the hypothesis that a low-fat diet, higher in protein and lower in carbohydrate, is superior to a conventional standard-protein, higher-carbohydrate, low-fat diet for weight loss.
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The Australia-based scientists recruited 56 men with an average age of 45.5 and average BMI of 33.6 kg/m2 to participate in their 12 week study. The men were randomly assigned to consume a low-fat, energy-restricted diet with either standard or high protein levels.
Results showed that both groups experienced similar weight loss (9 kg). There were also no differences between the groups for relative peak oxygen uptake, knee extensor strength and peak handgrip strength.
Brinkworth and his co-workers did observed a trend for a greater reduction in fat mass in the high protein group, but this did not reach statistical significance.
“The primary objective of this study was to compare between group changes,” explained the researchers. “The lack of any apparent effects suggests macronutrient composition, at least during energy restriction with low-fat diets differing in the protein/carbohydrate ratio, does not appear to alter aerobic capacity.”
Source: European Journal of Nutrition
Published online ahead of print, Online First, doi: 10.1007/s00394-012-0338-0
“Comparison of the effects of weight loss from a high-protein versus standard-protein energy-restricted diet on strength and aerobic capacity in overweight and obese men”
Authors: T.P. Wycherley, J.D. Buckley, M. Noakes, P.M. Clifton, G.D. Brinkworth