title: Irisin levels correlate with energy expenditure in a subgroup of humans with energy expenditure greater than predicted by fat free mass.
abstract: OBJECTIVE
  Obesity is a result of chronic overconsumption of calories relative to the amount of energy expended. While fat free mass can account for ~80% of the variance in energy expenditure, there is still considerable variability in energy requirements between individuals that cannot be explained. We hypothesized that responsiveness to the recently discovered myokine, irisin, which has been touted to increase energy expenditure via activation of brown adipocytes in rodents and possibly humans, may explain some of the variability in energy expenditure.
  
  
  METHODS
  Post-menopausal women (n=17) spent 24-h in a whole room indirect calorimeter. During the study day, subjects remained sedentary and consumed meals tailored to their energy requirements. Plasma irisin, leptin and adiponectin were measured in samples taken from each subject.
  
  
  RESULTS
  Our results suggest that in general, irisin levels do not correlate with 24-h energy expenditure, however, for a subpopulation irisin levels and energy expenditure are highly correlative.
  
  
  CONCLUSIONS
  Irisin may help explain some of the observed variability in individual energy requirements that cannot be accounted for by fat free mass. Therefore, interventions designed to increase irisin action may prove to be promising avenues for the treatment of obesity.
authors.affiliation: UNC Nutrition Research Institute, University of North Carolina Chapel Hill, North Carolina Research Campus, Kannapolis, North Carolina, USA. andrew_swick@unc.edu
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Swick
authors.forename: Stephen
authors.initials: S
authors.lastname: Orena
authors.forename: Annalouise
authors.initials: A
authors.lastname: O'Connor
mesh_terms: D015502:Absorptiometry, Photon; D052437:Adipocytes, Brown / Q000378:metabolism; D002001:Adipose Tissue, Brown / Q000378:metabolism; D000368:Aged; D001823:Body Composition / Q000502:physiology*; D002153:Calorimetry, Indirect; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D020738:Leptin / Q000378:metabolism; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism
chemical_list: C577593:FNDC5 protein, human; D005353:Fibronectins; D020738:Leptin
keywords: BAT; BMI; DXA; EE; FFM; FM; FNDC5; Indirect calorimetry; PGC-1α; RQ; VCO(2); VO(2); body mass index; brown adipose tissue; dual x-ray absorptiometry; energy expenditure; fat free mass; fat mass; fibronectin type III domain containing 5; peroxisome proliferator-activated receptor γ coactivator-1α; respiratory quotient; volume CO(2) expired (liters/min); volume oxygen consumed (liters/min)