Lean mass predicts asthma better than fat mass among females.

The obesity phenotype associated with asthma is not known. Our objective was to define the relative contribution of various distributions of fat and lean mass to asthma prevalence. Data were obtained from 2,525 participants (including 1,422 females) who underwent dual-energy X-ray absorptiometry (DEXA) at the year 20 examination in the Coronary Artery Risk Development in Young Adults (CARDIA) cohort. Total, truncal, arm and leg distributions of fat and lean mass were adjusted to the person's height. Self-reported asthma was the outcome. Asthma among females was associated with greater total fat mass, arm fat mass, total lean mass, truncal lean mass and arm lean mass. Among males, none of these mass measures were significantly associated with asthma. Among females, the association with asthma was stronger for total lean mass than for total fat mass. Further, among various regional distributions of lean and fat mass in females, truncal lean mass was the strongest predictor. Total lean mass is more strongly associated with asthma than total fat mass among females. These findings are contrary to the popular perception that excess physiological fat drives the obesity-asthma association. Rather, we hypothesise that ectopic fat within the "lean" tissues drives this association among females.