title: The effect of gender and body composition method on the apparent decline in lean mass-adjusted resting metabolic rate with age.
abstract: BACKGROUND
  Declining resting energy expenditure (REE) is a hallmark of normal aging, but the cause of this decline remains controversial. Some, but not all, studies have shown that the decline in REE with age is eliminated after adjustment for fat-free mass (FFM).
  
  
  METHODS
  We examined the effect of four body composition methods used to assess FFM (underwater weighing [UWW], bioimpedance analysis [BIA], tritium dilution, and total body potassium [TBK]) on the relationship between REE and age in 30 healthy men and 101 healthy women aged 18 to 87 years.
  
  
  RESULTS
  The decline in REE with age was significant in women (-80.3 kJ/d/y, p < .004) but not in men (-46.9 kJ/d/y, p = .328). After adjustment for FFM, the decline in REE with age persisted when FFM was measured by BIA, UWW, or tritium dilution, but no decline was seen when TBK was used to adjust for FFM. In both women and men, fat mass was significantly associated with REE after adjusting for age and FFM.
  
  
  CONCLUSIONS
  It is the decline in cell mass with age, detectable by TBK but not by other methods, rather than any metabolic alteration, that explains the decline in FFM-adjusted REE with age.
authors: The Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111, USA. roubenoff@hnrc.tufts.edu
authors: R
authors: R
authors: Roubenoff
authors: V A
authors: VA
authors: Hughes
authors: G E
authors: GE
authors: Dallal
authors: M E
authors: ME
authors: Nelson
authors: C
authors: C
authors: Morganti
authors: J J
authors: JJ
authors: Kehayias
authors: M A
authors: MA
authors: Singh
authors: S
authors: S
authors: Roberts
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism*; D001823:Body Composition; D017097:Electric Impedance; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012146:Rest; D012727:Sex Characteristics; D013851:Thinness