Reconciling the obesity paradox: Obese patients suffer the highest critical illness associated mortality rates

The obesity paradox refers to the observation that obese patients admitted to intensive care units (ICU) have lower case fatality as compared to healthy weight patients. However, selection bias could explain the apparent paradox. Our objective was to assess whether obese people have a different overall burden of critical illness associated mortality. A retrospective population-based cohort study was conducted in North Brisbane ICUs during 2017-2019. Patients were classified as underweight, healthy weight, overweight, and obese according to BMIs <18.5, 18.5-24.9, 25-29.9, and ≥ 30 kg/m², respectively. ICU admission incidence rates were 245.6, 138.2, 178.9, and 421.9 per 100,000 population; 90-day all cause case fatalities were 24.0%, 17.0%, 18.1%, and 16.0%; and critical illness associated mortality rates were 58.8, 23.4, 32.4, and 67.7 per 100,000 population among underweight, healthy weight, overweight, and obese patients, respectively. As compared to patients of healthy weight, those who were underweight (relative risk; RR 2.51; 95% CI, 1.79-3.44), overweight (RR 1.38; 95% CI, 1.16-1.65), and obese (RR 2.89; 2.43-3.43) were each at significantly higher risk for critical illness associated mortality. While obese patients have lower case fatality they are at much higher risk for ICU admission and as result suffer the highest burden of critical illness associated mortality in our region.