A three-fold jump since 1975 in the percentage of adults worldwide who are obese has been driven mainly by a shift in diet and lack of exercise, but genes do play a role as well, according a large-scale study published on Thursday.
For people genetically predisposed to a wider girth, these unhealthy lifestyles compounded the problem, resulting in an even higher rate of weight gain, researchers reported in The BMJ, a peer-reviewed medical journal. The standard measure for obesity, the Body-Mass Index (BMI), is calculated on the basis of weight and height.
A BMI of 25 up to 30 means that one is overweight. Thirty and above corresponds to obesity, a major risk factor for heart attacks, stroke, diabetes and some cancers. About four percent of adults in the mid-1970s had a BMI of 30 or higher. By 2016, that share had risen to 13 percent (11 for men and 15 for women), according to the World Health Organization.
There are currently about two billion people 18 and older - 39 percent of all adults - with a BMI above the "overweight" threshold of 25, and 700 million of them are clinically obese.
The prevalence of excess weight has risen even more dramatically among children, from four percent in 1975 to over 18 percent in 2016.
To tease out the relative impact of environment and genes on obesity, scientists led by Maria Brandkvist at the Norwegian University of Science and Technology combed through data on nearly 120,000 people in Norway whose height and weight were regularly measured between 1963 and 2008. Adults began tipping the scales at significantly higher weights in the 1980s and 1990s, they found. Those born after 1970 were far more likely to have a substantially higher BMI as young adults than earlier generations.
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