Revisiting the Obesity Paradox: Stroke Subtype-Specific Associations of BMI and WHR With Functional Outcome

Abstract Background: While obesity is a known risk factor for ischemic stroke, its prognostic value remains uncertain. We examined the independent and combined effects of body mass index (BMI) and waist-to-hip ratio (WHR) on early stroke outcomes across subtypes. Methods: In this prospective cohort study, 714 patients with acute ischemic stroke or TIA were enrolled over six months. BMI and WHR were assessed on admission. Stroke severity (NIHSS) and functional outcome at discharge (modified Rankin Scale, mRS) were recorded. Stroke aetiology was classified using TOAST and ESUS criteria. Multivariable regression and restricted cubic spline models were applied. Results: A U-shaped association emerged between BMI and both stroke severity and recovery, with overweight patients (BMI 25.0–29.9 kg/m²) showing the lowest NIHSS and highest independence rate (mRS 0–1: 65%). Underweight and obese patients had significantly worse outcomes (p 0.001). WHR was an independent predictor of higher stroke severity (β = +2.8; 95% CI: 2.1–3.5) and poor outcome (OR = 0.70; 95% CI: 0.52–0.94), and showed additive prognostic value when combined with BMI. A sex-specific interaction suggested a greater benefit from overweight in women (OR = 1.72; p = 0.02). Subtype analysis revealed a U-shaped BMI association in cardioembolic stroke (p = 0.014), but not in ESUS. Conclusions: BMI and WHR show distinct, nonlinear, and sex- and subtype-specific associations with stroke severity and outcome. WHR outperforms BMI and enhances prognostication when combined. These findings challenge the obesity paradox and support integrating adiposity phenotypes into individualized stroke risk models. Keywords: Body mass index (BMI), waist-to-hip ratio (WHR), obesity paradox, stroke severity, functional outcome, sex differences, ischemic stroke, restricted cubic splines, ESUS