Prevalence, Comorbidities, and Mortality of Obesity Classes 4 and 5 in Adults

ABSTRACT Introduction Adult obesity has reached epidemic proportions globally. Although the prevalence and comorbidities of standard obesity classes (classes 1–3, BMI 30–49.9 kg/m 2 ) have been described, the characteristics of obesity classes 4 and 5 (BMI ≥ 50 to < 60 kg/m 2 and BMI ≥ 60 kg/m 2 , respectively), representing the most extreme end of the obesity spectrum, remain poorly defined. Objective The objective of this study was to determine the prevalence of obesity classes 4 and 5, or extremely severe obesity, in adults over time and to investigate the relationship between extremely severe obesity and metabolic comorbidities and mortality. Methods Data from nationally representative samples from National Health and Nutrition Examination Surveys from 2000 through 2023 involving 54,793 adults aged 18–65 years in the US were analyzed, including mortality data from 43,454 adults. Results The prevalence of obesity classes 4 and 5 increased by over 250% from 0.6% in 2000 to 2.2% in 2023 ( p < 0.001). Extremely severe obesity was particularly prevalent among females and non‐Hispanic Blacks. Subjects with obesity classes 4 and 5 had an odds ratio of 6.7–78.7 and 2.1–10.9 of metabolic comorbidities, and a 10‐year mortality hazard ratio of 2.2 (95% CI 1.6–3.0) and 1.8 (95% CI 1.3–2.4) compared with subjects without obesity and with obesity classes 1–3, respectively (all p < 0.001). Conclusions The findings highlight the rise of a so far insufficiently characterized obesity entity, extremely severe obesity, and underline the strong association of extremely severe obesity with severe metabolic complications including death. These results emphasize the need for immediate public health interventions to address obesity, particularly obesity classes 4 and 5.