title: Differential effects of fatness, fitness and physical activity energy expenditure on whole-body, liver and fat insulin sensitivity.
abstract: OBJECTIVE
  The relative contributions of fitness (maximal oxygen uptake), physical activity energy expenditure (PAEE) and fatness to whole-body, liver and fat insulin sensitivity is uncertain. The aim of this study was to determine whether fitness and PAEE are associated with whole-body, liver and fat insulin sensitivity independently of body fat.
  
  
  METHODS
  We recruited 25 men (mean [SD] age 53 [6] years). Whole-body (M value) and liver (percentage suppression of endogenous glucose output) insulin sensitivity were estimated using a hyperinsulinaemic-euglycaemic clamp. Insulin sensitivity in fat (insulin sensitivity index for NEFA) was estimated during an OGTT. Total and truncal fat were measured by dual-energy X-ray absorptiometry, fitness by treadmill, and PAEE (n = 21) by 3 day heart rate monitoring and Baecke questionnaire.
  
  
  RESULTS
  In univariate analyses, fatness was strongly associated with insulin sensitivity (whole-body, liver and fat). Fitness was associated with whole-body (r = 0.53, p < 0.007) and liver (0.42, p = 0.04) insulin sensitivity, while PAEE was associated with liver insulin sensitivity (r = 0.55, p = 0.01). Regression models were established to describe associations between fatness, fitness and physical activity and measures of insulin sensitivity (whole-body, fat and liver) as outcomes. Only fatness was independently associated with whole-body insulin sensitivity (B coefficient -0.01, p = 0.001). Fitness was not associated with any outcome. Only PAEE was independently associated with liver insulin sensitivity (B coefficient 13.5, p = 0.02).
  
  
  CONCLUSIONS
  Fatness explains most of the variance in whole-body insulin sensitivity. In contrast, PAEE explains most of the variance in liver insulin sensitivity.
authors.affiliation: Endocrinology and Metabolism, DOHaD Division,School of Medicine, University of Southampton, Southampton, UK.
authors.forename: H B
authors.initials: HB
authors.lastname: Holt
authors.forename: S H
authors.initials: SH
authors.lastname: Wild
authors.forename: N
authors.initials: N
authors.lastname: Wareham
authors.forename: U
authors.initials: U
authors.lastname: Ekelund
authors.forename: M
authors.initials: M
authors.lastname: Umpleby
authors.forename: F
authors.initials: F
authors.lastname: Shojaee-Moradie
authors.forename: R I G
authors.initials: RI
authors.lastname: Holt
authors.forename: D I
authors.initials: DI
authors.lastname: Phillips
authors.forename: C D
authors.initials: CD
authors.lastname: Byrne
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000328:Adult; D000704:Analysis of Variance; D001823:Body Composition; D015992:Body Mass Index; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007333:Insulin Resistance; D008099:Liver / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology; D010809:Physical Fitness / Q000502:physiology*; D012044:Regression Analysis