Genes, of course, but the pandemic of obesity comes mainly from the diet

PARIS – Since 1975, the percentage of obese adults in the world has tripled mainly due to a change in diet and lack of exercise, but genes also play a role, according to a large-scale study released Thursday. .

For people genetically predisposed to a larger circumference, these unhealthy lifestyles have compounded the problem, resulting in an even higher rate of weight gain, researchers have reported in The BMJ, a peer-reviewed medical journal.

The standard measure of obesity, body mbad index (BMI), is calculated on the basis of weight and height.

A BMI of 25 to 30 means that one is overweight. Thirty years or more is obesity, a major risk factor for heart attacks, stroke, diabetes and some cancers.

In the mid-1970s, about 4% of adults had a BMI of 30 or more. In 2016, this proportion had increased to 13% (11 for men and 15 for women), according to the World Health Organization. the health.

There are currently about two billion people aged 18 and over – 39% 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 increased even more dramatically among children, from 4% in 1975 to more than 18% in 2016.

To understand the relative impact of the environment and genes on obesity, scientists at the Norwegian University of Science and Technology led by Maria Brandkvist badyzed data from nearly 120,000 people in Norway, whose height and weight were regularly measured between 1963 and 2008.

Adults began tipping the scales to considerably higher weights in the 1980s and 1990s, they discovered.

People born after 1970 were much more likely to have a significantly higher BMI in young adults than previous generations.

"Obesogenic" environment

Half of the people followed were divided into five groups based on their genetic susceptibility to obesity.

Comparing the two groups to extremes, the researchers found, for example, that 35-year-old men with genetic variants known to promote weight gain were already heavier in the mid-1960s than men of the same age without these inducing genes. of fat.

Four decades later, even as obesity rates increased, this gap almost doubled.

Women showed the same trend, although the increase over time was a little less pronounced.

"In the 1960s, a genetic predisposition would weigh 3.9 kilos more than a 35-year-old man, of average height, higher than his genetically-protected peers," Brandkvist said.

"In Norway today, its vulnerable genes would make it heavier than 6.8 kg."

In addition, he will have gained 7.1 extra pounds "just because he lived in our" obese "environment," she added.

"The 13.9 kg excess weight of this man is mainly caused by the unhealthy lifestyle of today, but also by the interaction of his genes with the l 39; ;environment."

While the correlation between genetic profiles and the degree of obesity was strong, the study – by its nature – can not determine a cause-and-effect relationship, the authors warn.

Only clinical trials can highlight causal relationships, but for many areas of interest, such experiences are not possible with humans, for both practical and ethical reasons.