Comparing Different BMI Categories for Projecting Obesity Trends

Objectives Obesity trends are typically monitored using a single BMI ≥ 30 threshold. This common practice may be inadequate if there are differential changes between levels of obesity, in particular disproportional acceleration of severe (BMI 35–40, class 2), and morbid obesity (BMI over 40, class 3). We study this question for a central European country to identify whether differential changes alter conclusions about future public health burden related to obesity. Study Design Trend analysis using longitudinal survey data. Methods Data from the Czech portion of the Survey of Health, Ageing and Retirement in Europe (SHARE) from 2006–2022 were analyzed. We modeled prevalence trends for obesity thresholds (BMI ≥ 30, ≥ 35, and ≥ 40), using natural cubic splines for the time trend, while controlling for age, sex and education and holding population composition constant for the 2022 demographic structure. Projections were forecasted through 2030, with 10th -90th percentile intervals generated via parametric bootstrap. To estimate the cost impact, projected prevalence rates in mutually exclusive obesity classes were multiplied by published excess healthcare cost estimates for each respective class. Results The prevalence of severe and morbid obesity is increasing at a much more rapid rate than moderate obesity. This trend is the primary driver of projected growth in excess costs. Conclusions Relying solely on general obesity measure (BMI ≥ 30) is insufficient and misleading, causing an underestimation of the trends and impact of the obesity epidemic. Differentiating between obesity classes is essential for effective policymaking.