Journal
AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM
Volume 289, Issue 3, Pages E446-E455Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpendo.00001.2005
Keywords
energy intake; energy expenditure; leucine flux; exercise; nitrogen balance; lean mass
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The effects of prolonged caloric restriction ( CR) on protein kinetics in lean subjects has not been investigated previously. The purpose of this study was to test the hypotheses that 21 days of CR in lean subjects would 1) result in significant losses of lean mass despite a suppression in leucine turnover and oxidation and 2) negatively impact exercise performance. Nine young, normal- weight men [ 23 +/- 5 y, 78.6 +/- 5.7 kg, peak oxygen consumption ( VO2 (peak)) 45.2 +/- 7.3 ml . kg(-1) . min(-1), mean +/- SD] were underfed by 40% of the calories required to maintain body weight for 21 days and lost 3.8 +/- 0.3 kg body wt and 2.0 +/- 0.4 kg lean mass. Protein intake was kept at 1.2 g . kg(-1) . day(-1). Leucine kinetics were measured using alpha- ketoisocaproic acid reciprocal pool model in the postabsorptive state during rest and 50 min of exercise ( EX) at 50% of VO2 (peak). Body composition, basal metabolic rate ( BMR), and exercise performance were measured throughout the intervention. At rest, leucine flux ( approximate to 131 mu mol . kg(-1) . h(-1)) and oxidation ( R-ox; approximate to 19 mu mol . kg(-1) . h(-1)) did not differ pre- and post- CR. During EX, leucine flux ( 129 +/- 6 vs. 121 +/- 6) and R-ox ( 54 +/- 6 vs. 46 +/- 8) were lower after CR than they were pre- CR. Nitrogen balance was negative throughout the intervention ( approximate to 3.0g N/ day), and BMR declined from 1,898 +/- 262 to 1,670 +/- 203 kcal/ day. Aerobic performance ( VO2 peak, endurance cycling) was not impacted by CR, but arm flexion endurance decreased by 20%. In conclusion, 3 wk of caloric restriction reduced leucine flux and R-ox during exercise in normal- weight young men. However, despite negative nitrogen balance and loss of lean mass, whole body exercise performance was well maintained in response to CR.
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