Irisin levels correlate with energy expenditure in a subgroup of humans with energy expenditure greater than predicted by fat free mass

Objective. Obesity is a result of chronic overconsumption of calories relative to the amount of energy expended. While fat free mass can account for similar to 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. Materials/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. Conclusion. 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. (C) 2013 Elsevier Inc. All rights reserved.