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 research, which included expertise from LJMU’s Dr Lynne Boddy, was published in Nature. It 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.
Height and weight can be used to calculate BMI, an internationally recognised scale which tells us whether an individual has a healthy weight for their height.
‘Dr Boddy, who leads the Physical Activity Exchange within LJMU’s School of Sport and Exercise Sciences commented: “This is a major new study that challenges commonly-held beliefs that obesity is more of a concern in urban areas. The rapid changes in BMI and obesity prevalence in rural environments, in both developed and developing nations is extremely concerning. These new insights will help focus our efforts to reduce the prevalence of obesity globally.”
The study, led by Imperial College London, involved a network of more than 1000 researchers across the world. They 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 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. In some low- and middle-income countries, rural areas were responsible for over 80 per cent of the increase.
The team found 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 had a higher BMI than their rural counterparts. Over time, 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.
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.
The main exception to the global trend was sub-Saharan Africa where women gained weight more rapidly in cities, possibly because of more low-energy work (such as office work), less need for physical domestic tasks such as collecting firewood and fetching water, shorter commutes and greater access to processed foods.
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 in adults” by NCD Risk Factor Collaboration (NCD-RisC) is published in the journal Nature.
Visualisations of the data are available at: http://www.ncdrisc.org/