When I first visited Ghana in the early 1990’s, there was a very noticeable relationship between BMI and wealth. Rich people were far more likely to be overweight and obese than poor people. That visit took place about ten years after the 1982-1984 famine. Some of the roots of the famine lay in natural causes resulting in crop failure and some lay in local and regional politics, and it was small children that bore the brunt of it. Less than ten years after the famine it was perhaps unsurprising to see that (on average) the thinnest were the poorest, and the fattest were the richest.
Working in Australia in the early 2000s, however, there appeared to be exactly the opposite relationship. It appeared that the poorest were more likely to be overweight or obese and the wealthiest, normal weight. This observation was certainly borne out at an ecological level when my colleagues and I found an unmistakable relationship between area level, socioeconomic disadvantage, and obesogenic environments — fast food chain “restaurants” were more likely to be found in poorer areas.
So which is it? Are the poor more likely to be overweight and obese, or is it the rich? One of the challenges in working out this relationship is that it appears to be different in different countries. Neuman and colleagues conducted a multi-level study of low-and middle-income countries (LMICs) looking at this very problem using DHS Survey data. They found an interaction between country-level wealth, individual-level wealth, and BMI. Unfortunately, the study was limited to LMICs because the DHS surveys do not operate in high-income countries. While it would be tempting to extrapolate the interaction into high-income countries, without the data, it would just be a guess.
We don’t have the definitive answer, but a recent paper by Mohd Masood and me, based on his PhD research, provides some nice insights into the issue. We were able to bring together data from 206,266 individuals in 70 low-, middle- and high-income countries using 2003 World Health Survey (WHS) data. The WHS data are now getting a little old, but it is the only dataset we knew of that provided BMI and wealth measures from a sample of all countries, using a consistent methodology, all measured over a similar period of time.
The analysis showed that as country-level wealth increased, mean BMI increased in all wealth groups, except the very wealthiest group. The mean BMI of the wealthiest 20% of the population declined steadily as the wealth of the country increased. In the wealthiest countries, the mean BMI converged for the poorest 80% of the population around a BMI of 24.5 (i.e., near the WHO cut-off for overweight of 25). The wealthiest 20% had a mean BMI comfortably below that, around 22.5.
It is obviously not inevitable that as the economic position of countries improves, everyone except the very richest put on weight. There are thin, poor people and fat, rich people living in the wealthiest of countries. Nonetheless, the data do point to structural drivers creating obesogenic environments. My colleagues and I had argued, at least in the context of Malaysia, that the increasing prevalence of obesity was an ineluctable consequence of development. The development agenda pursued by the government of the day decreased physical activity, promoted a sedentary lifestyle, and did nothing to moderate the traditional fat rich, simple carbohydrate diet associated with the historically rural lifestyle of intensive agriculture.
We really need more data points (i.e., a repeat of the WHS) to try and tease out the effect of economic development on obesity in the poorest to the richest quintiles of the population. I would suspect, however, that countries need to think more deeply about what it is they pursue (for their population) when they pursue national wealth.