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We would like to thank Krachler et al for their letter regarding our study “The Impact of Cardiorespiratory Fitness on the Obesity Paradox in Heart Failure.” 1 Clark A.L. Fonarow G.C. Horwich T.B. Impact of cardiorespiratory fitness on the obesity paradox in patients with systolic heart failure. Am J Cardiol. 2015; 115: 209-213 Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar Our original study demonstrated that the “obesity paradox” in heart failure was significant only in patients with poor cardiorespiratory fitness, as defined by peak oxygen consumption on cardiopulmonary exercise testing of ≤14.0 mg/kg/m2. Krachler et al astutely point out that our measure of fitness relies on adjustment by total body weight, which may underestimate fitness levels; adjustment for lean body mass rather than total body weight has been shown to be a better predictor of outcomes in heart failure. 2 Osman A.F. Mehra M.R. Lavie C.J. Nunez E. Milani R.V. The incremental prognostic importance of body fat adjusted peak oxygen consumption in chronic heart failure. J Am Coll Cardiol. 2000; 36: 2126-2131 Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar We do not have measurements of body composition such as skin fold thickness or dual x-ray absorptiometry recorded in our heart failure cohort and, thus, are happy to learn of the article by Krachler et al, which outlines a method for estimating lean mass based on weight, height, and gender. 3 Krachler B. Volgyi E. Savonen K. Tylavsky F.A. Alen M. Cheng S. BMI and an anthropometry-based estimate of fat mass percentage are both valid discriminators of cardiometabolic risk: a comparison with DXA and bioimpedance. J Obes. 2013; 2013: 862514 Crossref PubMed Scopus (15) Google Scholar We hope to use this method in future studies of obesity, cardiorespiratory fitness, and outcomes in patients with heart failure. Cardiorespiratory Fitness as a Prognostic Factor in Heart Failure Needs to be Standardized for Body CompositionAmerican Journal of CardiologyVol. 116Issue 1PreviewWe read the recently published study by Clark et al1 of obesity as a positive prognostic factor in patients with advanced systolic heart failure (obesity paradox). The investigators observed the obesity paradox only in patients with lower cardiorespiratory fitness. Cardiorespiratory fitness was assessed as peak oxygen uptake (PKVO2) divided by total body weight (ml/min/kg). This measure has been shown to systematically underestimate cardiorespiratory fitness in not only healthy populations2,3 but also subjects with heart failure. Full-Text PDF