A new study of global trends in body-mass index (BMI) has found that obesity is rising faster in the world’s rural areas than in cities.

The study found that since 1985, surprisingly the average BMI in rural areas has increased by 2.1 kg/m2 in both women and men, whereas in cities the increase was 1.3 kg/m2 and 1.6 kg/m2 in women and men respectively.

The research, led by Imperial College London and published in Nature, analysed the height and weight data of more than 112 million adults across urban and rural areas of 200 countries and territories between 1985 and 2017.

Overall, from 1985 to 2017 BMI levels rose by an average of 2.0 kg/m2 in women and 2.2 kg/m2 in men globally, equivalent to each person becoming 5-6 kg heavier. More than half of the global rise over these 33 years was due to increases in BMI in rural areas.

The results of the large study “overturn commonly held perceptions that more people living in cities is the main cause of the global rise in obesity,” explains senior author Professor Majid Ezzati of Imperial’s School of Public Health. “This means that we need to rethink how we tackle this global health problem.”

There was also a significant difference between high, middle, and low-income countries, finding that in high-income countries, the study showed that BMI has been generally higher in rural areas since 1985, especially for women. Perhaps due to the disadvantages experienced by those living outside cities: lower income and education, limited availability and higher price of healthy foods, and fewer leisure and sports facilities.

Meanwhile, rural areas in low- and middle-income countries have seen shifts towards higher incomes, better infrastructure, more mechanised agriculture and increased car use, all of which bring numerous health benefits, but also lead to lower energy expenditure and to more spending on food, which can be processed and low-quality when sufficient regulations are not in place. All these factors contribute to faster increase in BMI in rural areas.

“As countries increase in wealth, the challenge for rural populations changes from affording enough to eat, to affording good quality food,” adds Professor Ezzati.

The research was funded by the Wellcome Trust, the Medical Research Council, the Royal Society and the Academy of Medical Sciences.