title: Plasma leptin concentrations, basal metabolic rates and respiratory quotients in young and older adults.
abstract: OBJECTIVE
  To-examine the interrelationship of circulating leptin concentrations, basal metabolic rates (BMR) and respiratory quotients (RQ) in young and older adults.
  
  
  METHODS
  Cross sectional study.
  
  
  METHODS
  Seventy-six Australian men and women, 48 young (< 35 y) and 28 older ( > or = 50 y).
  
  
  METHODS
  Fasting plasma leptin concentrations by RIA, BMR and RQ by indirect calorimetry, percentage body fat (BF%), fat mass (FM) and fat-free mass (FFM) from total body water (TBW) based on deuterium dilution, waist and hip circumferences from anthropometry.
  
  
  RESULTS
  Older subjects had significantly higher BF%, FM and waist-to-hip ratio (WHR), but significantly lower FFM and absolute BMR as compared to younger subjects. Absolute leptin concentrations were 60% higher in older subjects but did not achieve statistical significance. There was, however, a significant gender x age group interaction in leptin concentrations. This was reflected in a significant inverse relationship between age group and leptin in women when data was controlled for waist circumference (r = -0.38, P = 0.028), or FM (r = -0.36, P = 0.042). A similar relationship was not observed in men on controlling for BF% or FM. Log transformed plasma leptin was best explained by a model that included BF%, gender, age-group, gender x age-group and WHR r = 0.75, adjusted r2 = 0.56, standard error of estimate (SEE) = 0.73 ng/ml). BMR was best explained by FFM, FM and age group r = 0.94, adjusted r2 = 0.87; SEE = 429 kJ/day). On controlling for BF%, WHR and FFM, leptin was negatively related to RQ only in older men (r = -0.67, P = 0.033). There was no relationship of leptin to BMR in the groups studied.
  
  
  CONCLUSIONS
  The study demonstrates an age-related modification of the gender bias in leptin, and a gender-specific inverse relationship between leptin and RQ in older people. The decline in leptin and the lack of a relationship between RQ and leptin in older women may indicate an increased risk of weight gain relative to older men.
authors: Department of Nutrition, Dietetics and Food Science, School of Public Health, Curtin University of Technology, Perth, WA, Australia. soaresm@health.curtin.edu.au
authors: M J
authors: MJ
authors: Soares
authors: L S
authors: LS
authors: Piers
authors: K
authors: K
authors: O'Dea
authors: G R
authors: GR
authors: Collier
mesh_terms: D000273:Adipose Tissue; D000293:Adolescent; D000328:Adult; D000375:Aging; D001481:Basal Metabolism; D001823:Body Composition; D001824:Body Constitution; D001834:Body Water; D002153:Calorimetry, Indirect; D003903:Deuterium; D005260:Female; D006801:Humans; D007700:Kinetics; D020738:Leptin / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D012727:Sex Characteristics
chemical_list: D020738:Leptin; D003903:Deuterium