"Obesity is a complex chronic disease in which abnormal or excess body fat (adiposity) impairs health, increases the risk of long-term medical complications and reduces lifespan. Epidemiologic studies define obesity using the body mass index (BMI; weight/height2), which can stratify obesity-related health risks at the population level. Obesity is operationally defined as a BMI exceeding 30 kg/m2 and is subclassified into class 1 (30–34.9), class 2 (35–39.9) and class 3 (≥ 40)."
Source: Wharton S, Lau DCW, Vallis M, Sharma AM, Biertho L, Campbell-Scherer D, et al. Obesity in adults: a clinical practice guideline. CMAJ. 2020 Aug 4;192(31):E875-E891. doi: 10.1503/cmaj.191707. PMID: 32753461.