title: Energetic cost of protein turnover in healthy elderly humans.
abstract: OBJECTIVE
  Whole body protein turnover (PTO) and resting energy expenditure (REE) are both correlated to fat-free mass (FFM), in young and elderly subjects, and REE is positively correlated to PTO in young adults. Thus, the aim of this study was to compare the energetic cost of PTO in young (n=39, 23.4+/-3.1 y) and elderly (n=41, 67.5+/-3.6 y) healthy volunteers.
  
  
  METHODS
  REE (indirect calorimetry), PTO ((13)C-leucine isotopic dilution) and body composition (bioelectrical impedance analysis with age-specific equations) were measured in the postabsorptive state.
  
  
  RESULTS
  Elderly subjects had a higher fatness (30.5+/-7.1 vs 18.2+/-5.5%, elderly vs young, P<0.001), a similar REE (0.97+/-0.13 vs 1.06+/-0.15 kcal min(-1)), and a lower PTO (1.28+/-0.22 vs 1.44+/-0.18 micromol kg(-1) min(-1), P<0.001). PTO, REE and FFM were significantly correlated and after adjustment for FFM, REE was positively correlated to PTO (r=0.61, P<0.001). The slope of this relationship was the same in both groups, while the adjusted mean REE was lower in elderly subjects (0.97+/-0.09 vs 1.05+/-0.07 kcal min(-1), P<0.01).
  
  
  CONCLUSIONS
  In comparison with young subjects, the energetic cost associated with PTO in elderly subjects is not different, but the proportion of REE not associated with PTO is lower.
authors.affiliation: Laboratoire de Nutrition Humaine, Université Clermont Auvergne, CRNH, Clermont-Ferrand, France. boirie@clemont.inra.fr
authors.forename: Y
authors.initials: Y
authors.lastname: Boirie
authors.forename: B
authors.initials: B
authors.lastname: Beaufrère
authors.forename: P
authors.initials: P
authors.lastname: Ritz
mesh_terms: D000273:Adipose Tissue; D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism*; D001481:Basal Metabolism; D001823:Body Composition; D002153:Calorimetry, Indirect; D002247:Carbon Isotopes; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D007930:Leucine / Q000378:metabolism; D008297:Male; D011506:Proteins / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D011506:Proteins; D007930:Leucine