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Am J Clin Nutr. 2007 Aug;86(2):366-72.

Calorie restriction accelerates the catabolism of lean body mass during 2 wk of bed rest.

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Department of Clinical, Technological and Morphological Sciences, Division of Internal Medicine, University of Trieste, Italy.



Muscle inactivity and low energy intake commonly occur in persons with acute or chronic disease, in astronauts during space flight, and during aging.


We used a crossover design to investigate the effects of the interactions of inactivity and calorie restriction on whole-body composition and protein kinetic regulation in 9 healthy volunteers.


Lean body mass (LBM) was measured by using dual-energy X-ray absorptionmetry before and at the end of 14-d periods of bed rest (B) and controlled ambulation (A) in patients receiving eucaloric (E) or hypocaloric (H) (approximately 80% of total energy expenditure) diets. Whole-body leucine kinetics were determined at the end of the 4 study periods by using a standard stable-isotope technique in the postabsorptive state and during a 3-h infusion of a 0.13 g x kg LBM(-1) x h(-1) amino acid mixture.


In the postabsorptive state, we found a significant (P = 0.04) bed rest x hypocaloric diet interaction for the rate of leucine oxidation, an index of net protein catabolism (A+E: 0.23 +/- 0.01; B+E: 25 +/- 0.01; A+H: 0.23 +/- 0.01; B+H: 0.28 +/- 0.01 micromol x min(-1) x kg LBM(-1)). Bed rest significantly (P < 0.01) decreased amino acid-mediated stimulation of nonoxidative leucine disappearance, an index of protein synthesis (A+E: 35 +/- 2%; B+E: 30 +/- 2%; A+H: 41 +/- 3%; B+H: 32 +/- 2%). B+H decreased LBM by 1.10 +/- 0.1 kg, which is significantly (P < 0.01) greater than the decrease seen with A+E, A+H, or B+E.


Calorie restriction enhanced the catabolic response to inactivity by combining greater protein catabolism in the postabsorptive state with an impaired postprandial anabolic utilization of free amino acids.

[Indexed for MEDLINE]

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