Researchers have explained this pattern by hypothesizing that people living in urban areas eat more unhealthful, highly processed foods and live less physically active lifestyles.
However, a major new study — the results of which appear in the journal Nature — now turns this idea on its head by showing that obesity rates across the world have grown more rapidly in rural areas than in urban areas.
In the study, researchers from the Imperial College London in the United Kingdom led a global team of more than 1,000 specialists. Together, they analyzed the health data of more than 112 million adults from 200 countries and territories, covering a period of 32 years from 1985 to 2017.
The team sourced these data from 2,009 population-based studies that made their participants’ height and weight measurements available. From these two values, it is possible to calculate a person’s body mass index (BMI), which allows healthcare professionals to determine whether or not the individual has obesity.
To make sure that their final results were as reliable and unbiased as possible, the researchers excluded data that participants had self-reported.
The investigators’ extensive analysis revealed that women’s BMI increased by an average of 2.0 kilograms per square meter (kg/m2) over the study period, while men’s BMI rose by 2.2 kg/m2 on average.
However, the increases in BMI were most prominent not in urban areas but in rural ones, according to the researchers. They note that rural areas in low- and middle-income countries actually accounted for more than 80% of the BMI increase.
The team explains that the situation has changed since 1985 when in most countries, people living in urban areas had higher rates of obesity than those in rural areas.
Between 1985 and 2017, the average BMI in rural regions worldwide rose by 2.1 kg/m2 for adults of both sexes, whereas in urban areas, the average BMI of women and men increased by 1.3 kg/m2 and 1.6 kg/m2 respectively.
“The results of this massive global study overturn commonly held perceptions that more people living in cities is the main cause of the global rise in obesity.”
Senior author Prof. Majid Ezzati, Imperial College London
At the same time, the researchers note that the income of a country plays a role in the average BMI increase of its population. In high-income countries, BMIs have grown the most in rural areas, especially in the case of women.
The authors believe that this might be because rural populations in high-income countries typically enjoy fewer benefits than their urban counterparts, having lower incomes, more restricted access to education, and less access to healthful foods due to high costs.
“Discussions around public health tend to focus more on the negative aspects of living in cities,” notes Prof. Ezzati. “In fact, cities provide a wealth of opportunities for better nutrition, more physical exercise and recreation, and overall improved health.”
“These things are often harder to find in rural areas,” he emphasizes.
Rural communities in low- and middle-income countries have grown economically compared with the 1980s. The authors note that the benefits that this has afforded them — such as more modern agricultural tools and access to better infrastructure and means of transport — may actually have had a negative effect on health by decreasing people’s levels of physical activity and introducing more unhealthful foods.
“As countries increase in wealth, the challenge for rural populations changes from affording enough to eat to affording good-quality food,” Prof. Ezzati emphasizes.
The only countries where this pattern did not seem to apply were those of sub-Saharan Africa, where women from urban areas had higher BMI growth rates than women from rural regions.
This finding, the researchers say, could be because the women living in the cities tend to do less physically active work — desk work, for instance — and do not engage in the same physically demanding tasks as their counterparts in rural areas.
All in all, however, the current findings indicate that researchers and policy-makers may need to reassess their understanding of the factors that drive unhealthful weight gain across the world and consider new ways of tailoring approaches to health in different urban and rural communities.
“This means that we need to rethink how we tackle this global health problem,” says the senior author.