Calorie restriction accelerates the catabolism of lean body mass during 2 wk of bed rest.
BACKGROUND
Muscle inactivity and low energy intake commonly occur in persons with acute or chronic disease, in astronauts during space flight, and during aging.


OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Biolo
Gianni
G
Department of Clinical, Technological and Morphological Sciences, Division of Internal Medicine, University of Trieste, Italy. biolo@units.it
Ciocchi
Beniamino
B
Stulle
Manuela
M
Bosutti
Alessandra
A
Barazzoni
Rocco
R
Zanetti
Michela
M
Antonione
Raffaella
R
Lebenstedt
Marion
M
Platen
Petra
P
Heer
Martina
M
Guarnieri
Gianfranco
G
D000328:Adult; D000596:Amino Acids / Q000378:metabolism; D001510:Bed Rest; D001823:Body Composition; D015992:Body Mass Index; D018592:Cross-Over Studies; D004038:Diet, Reducing; D002149:Energy Intake; D004734:Energy Metabolism; D006801:Humans; D007930:Leucine / Q000378:metabolism*; D010084:Oxidation-Reduction; D011506:Proteins / Q000378:metabolism*; D012016:Reference Values; D015431:Weight Loss
D000596:Amino Acids; D011506:Proteins; D007930:Leucine