A new study in Norway of nearly 120,000 people suggests that while increased obesity is linked to unhealthy lifestyles, genes also play an important role.
In France, it is estimated that obesity affects 15.8% of men and 15.6% of women, or 7 million people. Globally, more than 1.9 billion adults were overweight in 2016. Of these, 650 million are obese.
Researchers are unanimous that the number of cases of obesity has almost tripled since 1975. However, the origins of this explosion are not always clear.
Among the factors favoring obesity is first and foremost dietary changes, which are fatter, sweeter, more salty, and made from ultra-processed foods. A more sedentary lifestyle and changes in the biological environment, such as toxins and gut microbiota, may also contribute to obesity.
A factor is, however, often minimized in the explosion of cases of obesity worldwide: genetics.
Excess weight of 13.9 kg linked to genetics
In an article published in the British Medical Journal, researchers at the Norwegian University of Science and Technology (NTNU) in Trondheim, Norway, have just highlighted the role of genetic heritage in the development of obesity: these genetic differences could make some people more sensitive than others to an obesogenic environment.
"Although previous research has suggested that genetic vulnerability has more important consequences after the onset of the obesity epidemic than before, our dataset provides compelling results, with a large sample size and range. years of assessment and age, "explains Maria Brandkvist, PhD student in the Department of Public Health and Nursing at NTNU and co-author of the study.
To understand to what extent the environment and genes had an impact on obesity, researchers analyzed data from nearly 120,000 people between 1963 and 2008. Their size and weight were regularly recorded to develop and analyze their data. body mass index (BMI).
Half of the people followed were then divided into 5 groups based on their genetic susceptibility to obesity. The results were surprising.
Researchers have found that, on average, in the 1960s, a genetic predisposition made a 35-year-old man of average height 3.9 kg heavier than his genetically protected peers. But if that same 35-year-old man was living in Norway today, his vulnerable genes would make him heavier than 6.8 kg.
"In addition, he and his peers would have gained an extra 7.1 kg just because they lived in our obesogenic environment," says Maria Brandkvist. "This man's 13.9 kg excess weight is caused primarily by today's unhealthy lifestyle, but also by how his genes interact with the environment."
Fight against prejudices about obesity
Although the correlation between genetic profiles and the degree of obesity is strong, the study, by its nature, can not determine a causal relationship with direct effect, acknowledge the authors. However, stresses Maria Brandkvist, these results should make us think about the way in which obese people are perceived in our society.
"Obese people are often stigmatized because they have unhealthy lifestyle choices." Recognizing the importance of the obesogenic environment and its amplification due to our genetic differences can help de-stigmatize obesity. to move away from the individual and focus on a healthier society. "