Impact of fitness versus obesity on routinely measured cardiometabolic risk in young, healthy adults

Obesity demonstrates a direct relation with cardiovascular risk and all-cause mortality, while cardiorespiratory fitness demonstrates an inverse relation. In clinical practice, several cardiometabolic (CM) risk factors are commonly measured to gauge cardiovascular risk, but the interaction between fitness and obesity with regard to CM risk has not been fully explored. In this study, 2,634 Brazilian adults referred for employer-sponsored heath exams were assessed. Obesity was defined as body mass index >30 kg/m² or waist circumference >102 cm in men or >88 cm in women when body mass index was 25 to 30 kg/m². Fitness was quantified by stage achieved on an Ellestad treadmill stress test, with those completing stage 4 considered fit. Hepatic steatosis was determined by ultrasound. CM risk factors were compared after stratifying patients into 4 groups: fit and normal weight, fit and obese, unfit and normal weight, and unfit and obese. Approximately 22% of patients were obese; 12% were unfit. Fitness and obesity were moderately correlated (ρ = 0.38 to 0.50). The sample included 6.5% unfit and normal-weight subjects and 16% fit and obese subjects. In overweight and obese patients, fitness was negatively associated with CM risk (p <0.01 for all values). In fit patients, increasing body mass index was positively associated with CM risk (p <0.01 for all values). In instances of discordance between fitness and obesity, obesity was the stronger determinant of CM risk. In conclusion, fitness and obesity are independently associated with CM risk. The effects of fitness and obesity are additive, but obesity is more strongly associated with CM risk when fitness and obesity are discordant. These findings underscore the need for weight loss in obese patients and suggest an unmeasured benefit of fitness.