Trends in general and abdominal obesity in South African adults, 1998 - 2017: A joint analysis of nine population surveys

Background. Obesity, a health condition characterised by abnormal accumulation of body fat, is a major public health problem, with the number of affected individuals forecasted to rise sharply worldwide. Local epidemiological data are needed to understand the epidemic’s specific characteristics and to implement effective evidence-based prevention strategies. Objective. To provide insight into the South African (SA) obesity epidemic by analysing trends in the prevalence of general and abdominal obesity between 1998 and 2017. Methods. Harmonised data on 134 029 adults (aged ≥18 years) from nine population surveys were analysed. For each survey dataset, the population distribution of body mass index (BMI), waist circumference (WC) and waist-to-height ratio (WHtR) was estimated, along with the prevalence of obesity and abdominal obesity according to standard epidemiological definitions. Metaregression models were fitted to estimate and compare the average rates of change of the multiple obesity indicators during the study period, for the whole population and by sex, population group, province of residence and geographical type (urban v. rural). Results. Among women, the distribution of BMI, WC and WHtR showed a significant rightward shift between 1998 and 2017, with increases in median values of 1.38 (95% confidence interval (CI) 0.91 - 1.84) kg/m2/decade for BMI, 4.04 (1.27 - 6.82) cm/decade for WC and 0.03 (0.01 - 0.04) units/decade for WHtR. The prevalence of obesity rose sharply, from 29.5% (28.1 - 30.8%) in 1998 to 42.7% (41.0 - 44.4%) in 2017. The prevalence of WC-defined and WHtR-defined abdominal obesity increased from 60.0% (58.6 - 61.3%) to 77.2% (76.0 - 78.4%), and from 62.8% (61.4 - 64.2%) to 78.7% (77.4 - 80.0%), respectively. Among men, changes in the distribution were modest and median trends not statistically significant, at 0.1 (–0.27 - 0.47) kg/m2/decade for BMI, 1.19 (–0.48 - 2.87) cm/decade for WC and 0.01 (–0.01 - 0.02) units/decade for WHtR. Obesity prevalence rose from 10.1% (8.9 - 11.3%) in 1998 to 12.1% (10.7 - 13.4%) in 2017, WC-defined abdominal obesity from 21.6% (19.8 - 23.4%) to 26.4% (24.3 - 28.4%) and WHtR-defined abdominal obesity from 39.7% (37.8 - 41.7%) to 42.8% (40.6% - 45.0%). The prevalence of both general and abdominal obesity also differed across geographical type, province and population group, with a disproportionately rapid increase among groups and areas that initially exhibited lower prevalence. Conclusion. Between 1998 and 2017, the prevalence of both general and abdominal obesity in the SA adult population rose substantially. Evidence-based prevention efforts and policy strategies are urgently needed to curb the growing burden, especially among women.