Work

The Obesity Paradox in Chronic Kidney Disease: Cardiorespiratory Fitness Is Associated With Mortality Independent of Body Mass Index

Year: 2026

Type: article

Abstract: Rationale & Objective: The obesity paradox, in which a higher body mass index (BMI) is associated with better survival, has been observed in chronic disease populations. However, the interaction between BMI, cardiorespiratory fitness (CRF), and mortality in chronic kidney disease (CKD) remains incompletely understood. We examined the association between BMI, age-adjusted CRF, and all-cause mortality in a large CKD cohort. Study Design: Retrospective cohort study. Setting & Participants: 13,521 predominantly male US veterans (97.4% male) with CKD from the Exercise Testing and Health Outcomes Study within the Veterans Affairs health care system. Predictors: ) and age-adjusted CRF quartiles based on metabolic equivalents achieved during maximal exercise tolerance testing using the Bruce protocol. The index date was the date of exercise testing. Outcome: All-cause mortality. Analytical Approach: Cox proportional hazards models adjusted for age, sex, diabetes mellitus, hypertension, and cardiovascular disease assessed mortality risk across BMI-fitness combinations, with normal BMI and least fit as references. Results: During a mean follow-up period of 7.4 years, 5,144 (38.0%) deaths occurred. A higher BMI was associated with a lower mortality risk: overweight (HR 0.82, 95% CI 0.70-0.95) and obese (HR 0.71, 95% CI 0.61-0.82) versus normal BMI. Higher CRF was associated with progressively lower mortality: moderate fit (HR 0.61, 95% CI 0.50-0.74) and most fit (HR 0.49, 95% CI 0.40-0.60) versus least fit. The combination of obese BMI and highest fitness was associated with a 64% lower mortality risk (HR 0.36, 95% CI 0.25-0.51). Limitations: Predominantly male veteran population; single baseline BMI and fitness measurements; observational design precludes causal inference. Conclusions: In this predominantly male veteran CKD cohort, a higher BMI was associated with lower all-cause mortality across all fitness levels. Age-adjusted CRF demonstrated a strong, graded inverse association with mortality independent of BMI. These observational findings support integrating fitness assessment into CKD management.

Source: Kidney Medicine

DOI: 10.1016/j.xkme.2026.101471

Authors: Swathi Balantrapu, Peter Kokkinos, Immanuel B.H. Samuel, Andreas Pittaras, Charles Faselis, Jonathan Myers