New statistical model shows obesity rising faster in rural areas

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Obesity is increasing more rapidly in the world’s rural areas than in cities, according to a new study of global trends in body-mass index (BMI).

The University’s Dr James Bentham worked with Imperial College London and other researchers to analyse data on the height and weight of more than 112 million adults across urban and rural areas of 200 countries and territories between 1985 and 2017. Their findings are now published in the journal Nature.

Dr Bentham, of Kent’s School of Mathematics, Statistics and Actuarial Science (SMSAS), said they were interested in how BMI and obesity vary between urban and rural areas around the world but there were gaps in the data required for accurate estimates.

The study, involving a network of more than 1,000 researchers across the world, found that from 1985 to 2017, BMI rose by an average of 2.0 kg/m2 in women and 2.2 kg/m2 in men globally, equivalent to an average person becoming 5-6 kg heavier. Overall, more than half of the global rise over this period was due to increases in BMI in rural areas. Furthermore, in some low- and middle-income countries, rural areas were responsible for over 80% of the increase.

Overall the data shows that since 1985 average BMI in rural areas has increased by 2.1 kg/m2 in both women and men. But in cities, the increase was 1.3 kg/m2 and 1.6 kg/m2 in women and men respectively.

These trends have led to striking changes in the geography of BMI over the three decades. In 1985, urban men and women in over three quarters of the countries surveyed had a higher BMI than their rural counterparts. Over time, though, the gap between urban and rural BMI in many of these countries shrank or even reversed.

The team found important differences between high-, middle-, and low-income countries. In high-income countries the study showed that BMI has been generally higher in rural areas since 1985, especially for women. The researchers suggest this is 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.

The authors state that there is an urgent need for rural nutrition to be improved, so that people in rural areas have access to affordable, healthy foods. Otherwise, as people in these areas around the world become wealthier, undernutrition will be replaced by poor nutrition and excess BMI.

Dr Bentham said: ‘We developed a complex and realistic statistical model that allowed us to make estimates of BMI for every combination of country, year, age and sex. We then checked carefully that our model makes predictions that are consistent with our data and have made our computer code available, so that other scientists can fit similar models.’

The research was funded by the Wellcome Trust, the Medical Research Council, the Royal Society and the Academy of Medical Sciences. Rising rural body-mass index is the main driver of the global obesity epidemic by NCD Risk Factor Collaboration (NCD-RisC) is published in the journal Nature.