Role of Fitness in the Metabolically Healthy but Obese Phenotype: A Review and Update

Despite the strong and consistent evidence supporting that a high physical fitness (PF) level at any age is a major predictor of a healthier metabolic profile, major studies focused on the metabolically healthy but obese (MHO) phenotype have ignored the role of PF when examining this phenotype and its prognosis. Particularly, the role of its main health-related components such as higher cardiorespiratory fitness (CRF) and muscular fitness in the MHO phenotype needs to be reviewed in depth. The present review aimed to: 1) contribute to the characterization of the MHO phenotype by examining whether MHO individuals are fitter than metabolically abnormal obese (MAO) individuals in terms of CRF and other PF components; 2) review the role of CRF and other PF components in the prognosis of MHO. The studies reviewed suggest that a higher CRF level should be considered a characteristic of the MHO phenotype. Likewise, CRF seems to play a key role in the prognosis of the MHO individuals, yet this statement is based on a single study and future studies need to confirm or contrast these findings. Comparability of studies is difficult due to the different definitions used for MHO; consequently, the present review makes a proposal for harmonizing this definition in adults and in youth. Obesity is still related to an important number of comorbidities; therefore, the public health message remains to fight against both obesity and low CRF in both adult and pediatric populations.