Obesity Study on 112 Million People Reveals Hidden Roots of Deadly Epidemic

Scientists may have been focusing on the wrong areas all along.

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Obesity, which threatens the lives of billions of people around the world, is often blamed on the rise of city living. Scientists have looked tirelessly in urban areas for a solution to this dire public health issue, but now a new Nature paper reveals they’ve been focusing on the wrong places. Leveraging data on 112 million people from 1985 through 2017, it disproves a major assumption about which lifestyles are driving BMIs to unprecedented levels.

The study was a massive undertaking. By analyzing 2,009 obesity studies, a team of over 1,000 scientists found that the biggest increases in BMI didn’t occur in urban regions but in people living in rural areas around the world. This, said co-author Majid Ezzati, Ph.D., a professor at Imperial College London, is a big change from previous thinking.

“There has been a very widely stated assumption, widely stated by academics, by the media, and by our policy organizations that urbaniztion is the main driver of the obesity epidemic,” said Ezzati on Tuesday. “The bottom line of the paper — the main result — is in the world as a whole, BMI has been going up faster in rural areas than in urban areas.”

Rural areas, says Ezzati, have had higher rates of BMI growth because it's harder to get access to cheap, healthy food options. 

The “Urban Advantage”

City living is linked to obesity because previous research has shown a noticeable overlap in the rise in obesity and the growth of cities. Among the many factors underlying the link are issues of access to and education about good nutrition for the urban poor. Increased air pollution both outside and inside the home takes its toll too, making it harder to exercise even though there are more opportunities to walk and cycle in big cities. The new study doesn’t negate these findings, but it shows that rural living contributes to the obesity crisis even more.

Ezzati and his colleagues report that 55 percent of the global rise in BMI can be attributed to people living in rural areas of the world. Broken down by sex, 60 percent of the rise in BMI in women and 57 percent in men can be attributed to increases in rural areas. Urbanization, or the conversion of rural areas into urban ones, had far smaller effects that they expected. From 1985 to 2017, only 14 percent of the change in BMI in men and 13 percent in women were attributed to urbanization.

This trend can largely be explained by trends in middle- and low-income countries that are just beginning to industrialize, illuminating how societal development paves the path towards enduring obesity, said Esszati. As countries get richer, the people living in rural areas end up with less and less access to good nutrition, and their BMIs pay the price over time. High-income countries, including the United States, ran into this issue years ago, and we are still seeing the consequences.

“For those of you who live in especially larger, high-income countries, places like the United States or Australia the whole idea of rural food deserts may actually be familiar to you,” he says.

In the US at least, food deserts — places that lack access to affordable, healthy food options — are a problem in both rural and urban environments. A 2012 US Department of Agriculture report showed that 15.9 percent of food deserts are in rural regions while 8.2 are found in urban areas.

Poverty is a major contributor to lack of access to healthy food. Cities have what he calls an “urban advantage”: In tightly packed regions, there are more opportunities to get healthy food within a reasonable distance of home. Furthermore, as a result of previous assumptions about the obesity crisis, cities have been the focus on anti-obesity policies, like the creation of running paths or parks to promote active living, as a commentary published with the article points out.

“So the fact is that it’s actually easier to eat healthy in cities because fresh foods are available at lower cost and also there are possibilities for sports and leisure,” said Ezzati.

As middle and low-income countries industrialize, many rural areas seem to fall into a trap. Industrialization causes economies to grow and prices to fall, but for a number of reasons, healthy food remains relatively expensive and becomes even more limited as unhealthy options become increasingly available. In short, the issue of undernutrition (the lack of food) is replaced by problems of malnutrition — an abundance of low-quality calories.

“At the same time, people can afford more food, but those types of food are not necessarily healthy food in rural areas,” Ezzati said.

A New Way of Approaching Food Policy

What analyses like this one emphasize is that obesity is so wide-ranging that it must be tackled holistically, by reshaping policies and infrastructure, rather than only promoting action on the individual level. A key point that Ezzati made clear is that it’s not just about encouraging exercise or limiting the amount of calories people eat. It’s about improving access to good food. “What we really need is getting people not to just eat enough calories, but to eat healthy calories,” he says.

Ezzati argues that we need to think more critically about not only limiting access to unhealthy foods, but providing access to healthy foods for people in rural and urban areas. 

To the authors, the data suggest that it’s time for governments to step in. Some are already using regulation to curb how many calories people consume: For instance. Mexico’s sugar tax has led to decreases in sales of sugar-sweetened beverages, much like the “soda tax” famously rolled out in Berkeley, California. Ezzati, for his part, lauded the strict advertising regulations in Chile that banned cartoon characters and toys associated with sugar-sweetened foods.

The existing policies, however, don’t actually provide healthy alternatives. One potentially powerful idea that’s been floated by some researchers is that prescriptions for healthy food could help offset its high costs. But as of now, says Ezzati, there are no exemplary healthy-food policies anywhere in the world.

“I would actually say that the policy challenge, which in my mind no country is currently addressing to perhaps a positive ending, is: How do we get the food to eat healthy?”

This study, he hopes, will be a wakeup call.

“What we hope the results are going to do is that they’re actually going to try to get both donors and governments to rethink our nutrition policies,” he added.

Abstract: Body-mass index (BMI) has increased steadily in most countries in parallel with a rise in the proportion of the population who live in cities1,2. This has led to a widely reported view that urbanization is one of the most important drivers of the global rise in obesity3–6. Here we use 2,009 population-based studies, with measurements of height and weight in more than 112 million adults, to report national, regional and global trends in mean BMI segregated by place of residence (a rural or urban area) from 1985 to 2017. We show that, contrary to the dominant paradigm, more than 55% of the global rise in mean BMI from 1985 to 2017—and more than 80% in some low- and middle-income regions—was due to increases in BMI in rural areas. This large contribution stems from the fact that, with the exception of women in sub-Saharan Africa, BMI is increasing at the same rate or faster in rural areas than in cities in low- and middle-income regions. These trends have in turn resulted in a closing—and in some countries reversal—of the gap in BMI between urban and rural areas in low- and middle-income countries, especially for women. In high-income and industrialized countries, we noted a persistently higher rural BMI, especially for women. There is an urgent need for an integrated approach to rural nutrition that enhances financial and physical access to healthy foods, to avoid replacing the rural undernutrition disadvantage in poor countries with a more general malnutrition disadvantage that entails excessive consumption of low-quality calories.