Rates of obesity worldwide have nearly tripled since 1975, and the prevailing belief is that city living is to blame. But a major study that covers 112 million adults suggests that weight gain in rural areas is responsible for much of this increase.

Members of the NCD Risk Factor Collaboration — an international group of health scientists — analyzed over 2,000 studies of how body mass index (BMI) has changed around the world from 1985 to 2017. (BMI is a height-to-weight ratio that is a popular measure of obesity, though not without its flaws.) The results, published today in the journal Nature, show that during this time period, more than 55 percent of the rise in BMI globally came from rural populations — specifically rural populations in emerging economies, which include many places in Latin America, Asia, and the Middle East. “In the world as a whole, BMI has been going up faster in rural areas than in urban areas,” study co-author Majid Ezzati, an expert in global environmental health at Imperial College London, said in a press briefing.

This directly contradicts the belief that people living in rural areas are less likely to gain weight because they eat healthier, unprocessed foods and do more physical labor. That may have been the case, continued Ezzati, but as rural areas industrialize, life starts to change. People don’t need to walk to fetch water because they have running water. They don’t need to walk to other places because roads are being built and cars are more common. These changes bring a lot of health benefits, added Ezzati, “but they also mean less moving around and less physical labor.”

As rural areas become wealthier, people living there can afford more food and, often, less healthy food. This means they’re eating the same processed foods as their urban counterparts, without the other benefits of city living that make it easier to be physically active. Notably, there are more sports facilities and gyms in urban areas, and far more opportunities to walk. Everything might be further away in the countryside, but that leads to people driving from one place to another. Rural areas also have higher rates of preventable deaths, due to limited access to health care.

The data from today’s study confirms that, in wealthy and industrialized countries, people living in rural areas have long had higher BMI and higher rates of obesity than those living in cities. (This finding holds in the US, according to the Centers for Disease Control and Prevention.) It’s just that we’re starting to see this trend develop in lower-income countries as well. Many global health efforts focus on malnutrition, but perhaps it’s time to shift the focus to getting high-quality calories and moving more.

Sherry Pagoto, a professor of health sciences at the University of Connecticut, says certain disparities can make it harder for rural populations to access this type of education or care. Rural and lower-income areas are less likely to have internet access, for example, which makes it harder to communicate educational information. She would like to see obesity initiatives that are specifically tailored for either rural or urban populations. Groups like the Robert Wood Johnson Foundation are trying to solve problems in rural areas by integrating health education with local institutions, like in churches or community centers, she says. “We have to think outside the box a little,” she says. “How do you leverage what’s there in order to solve that problem more quickly?”