The overweight and obesity transition from the wealthy to the poor in low- and middle-income countries: A survey of household data from 103 countries

Abstract

Background: In high-income countries, obesity prevalence (body mass index greater than or equal to 30 kg/m2) is highest among the poor, while overweight (body mass index greater than or equal to 25 kg/m2) is prevalent across all wealth groups. In contrast, in low-income countries, the prevalence of overweight and obesity is higher among wealthier individuals than among poorer individuals. We characterize the transition of overweight and obesity from wealthier to poorer populations as countries develop, and project the burden of overweight and obesity among the poor for 103 countries.

Methods and findings: Our sample used 182 Demographic and Health Surveys and World Health Surveys (n = 2.24 million respondents) from 1995 to 2016. We created a standard wealth index using household assets common among all surveys and linked national wealth by country and year identifiers. We then estimated the changing probability of overweight and obesity across every wealth decile as countries' per capita gross domestic product (GDP) rises using logistic and linear fixed-effect regression models. We found that obesity rates among the wealthiest decile were relatively stable with increasing national wealth, and the changing gradient was largely due to increasing obesity prevalence among poorer populations (3.5% [95% uncertainty interval: 0.0%-8.3%] to 14.3% [9.7%-19.0%]). Overweight prevalence among the richest (45.0% [35.6%-54.4%]) and the poorest (45.5% [35.9%-55.0%]) were roughly equal in high-income settings. At $8,000 GDP per capita, the adjusted probability of being obese was no longer highest in the richest decile, and the same was true of overweight at $10,000. Above $25,000, individuals in the richest decile were less likely than those in the poorest decile to be obese, and the same was true of overweight at $50,000. We then projected overweight and obesity rates by wealth decile to 2040 for all countries to quantify the expected rise in prevalence in the relatively poor. Our projections indicated that, if past trends continued, the number of people who are poor and overweight will increase in our study countries by a median 84.4% (range 3.54%-383.4%), most prominently in low-income countries. The main limitations of this study included the inclusion of cross-sectional, self-reported data, possible reverse causality of overweight and obesity on wealth, and the lack of physical activity and food price data.

Conclusions: Our findings indicate that as countries develop economically, overweight prevalence increased substantially among the poorest and stayed mostly unchanged among the wealthiest. The relative poor in upper- and lower-middle income countries may have the greatest burden, indicating important planning and targeting needs for national health programs.

Fig 1. Overweight and obesity prevalence rates by economic development and within-survey wealth decile.

Unadjusted overweight (1A) and obesity (1B) prevalence obtained directly from survey data, stratified by GDP per capita and within-survey personal wealth decile. The columns represent GDP per capita categories, and the rows represent deciles of within-country wealth. Within each GDP per capita category, deciles with the lowest prevalence are coded in green, and deciles with the highest prevalence are coded in red. All prevalence estimates were obtained using survey weights. GDP, gross domestic product.

Fig 2. Differential effect of wealth on overweight and obesity by GDP per capita.

Each point represents the probability of being overweight (2A) or obese (2B) relative to the richest decile (90th–100th percentile) at different GDP per capita cutoffs. Each error bar represents robust 95% confidence intervals. The lines are color coded by wealth decile. The wealth-overweight and wealth-obesity transition zones are denoted by the vertical lines. The first line marks where the richest decile was no longer the most likely to be overweight or obese. The second line marks where the richest decile was less likely than the poorest to be overweight or obese. We evaluate the change in the gradient based on where the other percentiles are statistically significantly greater than zero (which means the wealth group has a higher chance of obesity than the 90th–100th percentile personal wealth income group). GDP, gross domestic product.

Fig 3. Change in the wealth distribution of the overweight population between 1995 and 2040.

Each line displays World Bank Income group changes in overweight burden across a wealth decile. Wealth deciles, where 1 is the poorest and 10 is the richest, are displayed on the x-axis. The percent change in each wealth decile's overweight burden share from 1995 to 2040 is on the y-axis.

Fig 4. Overweight inequality projections, 2016 to 2040.

Each map displays country-level projections in overweight prevalence inequality. Map A shows the percent change in overweight prevalence among the relatively poor, defined as individuals in the bottom quintile of the personal wealth distribution. Map B displays the percent change in the share of overweight individuals who are relatively poor. This differs from Map A by quantifying where the reversal of the wealth-overweight gradient will occur the fastest. Map C displays the percent change in the overweight and relatively poor population. The base map was obtained from Natural Earth (https://naturalearthdata.com).