Obesity Science & Practice · Published 2026-01-06 · DOI 10.1002/osp4.70108
ABSTRACT Background Fit–Fat Index (FFI), defined as the ratio of cardiorespiratory fitness (CRF) to waist‐to‐height ratio (WHtR), combines measures of fitness and fatness, and may offer a more accurate assessment of cardiometabolic risk than either component alone. The prospective associations of CRF, fatness indices, and mortality were examined. Methods CRF and fatness indices (body mass index [BMI], waist‐to‐hip ratio [WHR], and WHtR) were assessed in 1089 men aged 42–61 years. FFI variants (FFIBMI, FFIWHR, and FFIWHtR) were calculated by dividing CRF by each corresponding fatness measure. Hazard ratios (HRs) with 95% confidence intervals (CIs) and risk prediction metrics were estimated. Results Over a median follow‐up of 31.2 years, 288 CVD deaths and 695 all‐cause deaths were recorded. After multivariable adjustment, the HR (95% CI) for CVD death per 1 SD increase was 0.81 (0.70–0.93) for CRF, 1.09 (0.96–1.23) for BMI, 1.13 (1.02–1.25) for WHR, 1.13 (0.99–1.30) for WHtR, 0.82 (0.71–0.95) for FFIBMI, 0.78 (0.68–0.91) for FFIWHR, and 0.80 (0.69–0.93) for FFIWHtR. Findings were similar for all‐cause mortality. Addition of CRF and FFI variants to a model containing established risk factors significantly improved CVD mortality risk prediction and reclassification (p‐value for all < 0.05). Conclusions Combining aerobic fitness and fatness into FFI measures may provide better risk stratification than either aerobic fitness or fatness alone.
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