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.
Department of Clinical, Technological and Morphological Sciences, Division of Internal Medicine, University of Trieste, Italy. biolo@units.it
Gianni
G
Biolo
Beniamino
B
Ciocchi
Manuela
M
Stulle
Alessandra
A
Bosutti
Rocco
R
Barazzoni
Michela
M
Zanetti
Raffaella
R
Antonione
Marion
M
Lebenstedt
Petra
P
Platen
Martina
M
Heer
Gianfranco
G
Guarnieri
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