title: Physical activity energy expenditure predicts changes in body composition in middle-aged healthy whites: effect modification by age.
abstract: BACKGROUND
  It is unclear whether physical activity energy expenditure (PAEE) predicts changes in body composition.
  
  
  OBJECTIVE
  The objective was to describe the independent associations between PAEE and changes in body composition in a population-based cohort.
  
  
  METHODS
  This was a prospective population-based study conducted in 739 (311 men and 428 women) healthy middle-aged (median age: 53.8 y) whites. The median follow-up was 5.6 y. PAEE (MJ/d) was assessed by heart rate monitoring, individually calibrated by using the FLEX heart rate method. Fat mass (FM) and fat-free mass (FFM) were assessed by bioimpedance.
  
  
  RESULTS
  Body weight (BW) at follow-up was significantly related to baseline PAEE (P < 0.05) after adjustment for sex, baseline age, FM, FFM, and follow-up time. A significant interaction between PAEE and age (P = 0.023) was observed. After the subjects were stratified (above and below the median for age), BW increased by a mean (+/-SD) of 1.7 +/- 5.9 kg (P < 0.0001) in the younger cohort. In this group, follow-up FM was significantly associated with baseline PAEE (P = 0.036) after adjustment for confounders. In the older cohort, BW did not change between baseline and follow-up. In this group, in contrast with the younger population, follow-up BW, FM, and FFM were all significantly and positively associated with baseline PAEE (P < 0.01 for all).
  
  
  CONCLUSIONS
  Baseline PAEE predicts a change in FM in younger adults, who as a group gained weight in this study. In contrast, baseline PAEE in older adults--who were on average weight stable--is associated with a gain in BW, which was explained by an increase in FM and FFM.
authors.affiliation: Medical Research Council Epidemiology Unit, Cambridge, United Kingdom. ue202@medschl.cam.ac.uk
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekelund
authors.forename: Søren
authors.initials: S
authors.lastname: Brage
authors.forename: Paul W
authors.initials: PW
authors.lastname: Franks
authors.forename: Susie
authors.initials: S
authors.lastname: Hennings
authors.forename: Sue
authors.initials: S
authors.lastname: Emms
authors.forename: Man-Yu
authors.initials: MY
authors.lastname: Wong
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Wareham
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism*; D000375:Aging / Q000378:metabolism*; D001823:Body Composition; D004734:Energy Metabolism; D015444:Exercise; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies