title: Three weeks of caloric restriction alters protein metabolism in normal-weight, young men.
abstract: 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 (approximately 131 micromol.kg(-1).h(-1)) and oxidation (R(ox); approximately 19 micromol.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 ( approximately 3.0 g 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.
authors.affiliation: Geriatric Research Education and Clinical Center and Research and Medical Services, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304, USA. friedlan@stanford.edu
authors.forename: Anne L
authors.initials: AL
authors.lastname: Friedlander
authors.forename: Barry
authors.initials: B
authors.lastname: Braun
authors.forename: Margaret
authors.initials: M
authors.lastname: Pollack
authors.forename: Jay R
authors.initials: JR
authors.lastname: MacDonald
authors.forename: Charles S
authors.initials: CS
authors.lastname: Fulco
authors.forename: Steve R
authors.initials: SR
authors.lastname: Muza
authors.forename: Paul B
authors.initials: PB
authors.lastname: Rock
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Henderson
authors.forename: Michael A
authors.initials: MA
authors.lastname: Horning
authors.forename: George A
authors.initials: GA
authors.lastname: Brooks
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Hoffman
authors.forename: Allen
authors.initials: A
authors.lastname: Cymerman
mesh_terms: D000293:Adolescent; D000328:Adult; D001823:Body Composition; D001835:Body Weight; D031204:Caloric Restriction; D002151:Calorimetry; D002247:Carbon Isotopes; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007328:Insulin / Q000097:blood; D007930:Leucine / Q000378:metabolism; D008297:Male; D009584:Nitrogen / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D007328:Insulin; D011506:Proteins; D007930:Leucine; D009584:Nitrogen