Do Obesity Classifications Create the Obesity Paradox? A Scoping Review of Obesity Definitions Applied in Sepsis Research

ABSTRACT Obesity appears to be associated with improved health outcomes in patients with sepsis, a phenomenon termed the obesity paradox. However, the potential influence of varying operational definitions of obesity on clinical outcomes within this paradox remains inadequately characterised. This scoping review aimed to identify, analyse, and synthesise the methodological approaches to obesity definition employed in sepsis research. A systematic literature search was conducted in August 2023 across MEDLINE, Embase, CINAHL, and CENTRAL databases. This review included original articles, systematic reviews, and meta‐analyses reporting on adult patients with both obesity and sepsis. After removing 60 duplicates, 430 citations were screened, and 68 met the inclusion criteria. Among studies on the obesity paradox, 90.5% supporting and 88.6% refuting it employed body mass index‐based definitions, with approximately three‐quarters using retrospective designs. Studies supporting the obesity paradox identified patients with obesity as younger, predominantly female, and with higher comorbidity rates. In contrast, studies refuting the paradox reported more diverse age and sex distributions, yet consistently noted elevated chronic disease prevalence in patients with obesity. Both groups found similar or higher illness severity scores among patients with obesity. The lack of methodological rigour in obesity definitions within clinical research may contribute to the obesity paradox. Future studies should critically evaluate measurement methods and definitional variability to clarify their impact on clinical outcomes.