Since the 1980s, the worldwide obesity rate has doubled. Across the globe, 40 million children under the age of 5 were overweight or obese in 2011. With more than one-third of American adults classified as obese, it’s clear that obesity is no longer a disease affecting the few. 

But while the common conception of obesity is that it develops after birth through a combination of poor diet, lack of exercise, and an unhealthily lifestyle, the effects of obesity can actually be spread to unborn children.

Researchers from Laval University in Quebec, Canada, have observed the effects of maternal obesity on the genetic makeup of children. Children born after maternal gastric bypass surgery carry a different and less severe set of health risks later in life than children born before their mothers had surgery. 

Maternal obesity can not only cause complications during birth, it actually alters the child's DNA, causing dysfunction in their glucose regulating genes. This puts children at a greater risk of developing obesity themselves, as well as diabetes and cardiovascular disease.

“Maternal obesity is imprinting a type of mark that is put on the DNA of the children and that can then impact their gene expression, increasing the risk of chronic disease,” said study author Marie-Claude Vohl, Ph.D., of the Institute of Nutrition and Functional Foods at Laval Unversity in an interview with Healthline. 

The impact of maternal obesity on offspring has been demonstrated in animals, Vohl said, and her study shows the association also exists in humans. “There is an impact of obesity for the mother, the person that is obese. But there is also an impact on the next generation," Vohl said.

Gene Methylation and Obesity Risk

Researchers observed the offspring of 20 obese mothers, and compared the genetic makeup of siblings born before (BMS) and after (AMS) their mothers had a gastrointestinal bypass or a biliopancreatic bypass, both of which aid in losing weight.  

Between the two groups, BMS and AMS, 5,698 genes were differently methylated, or altered to control their expression. The specific gene methylation pattern pointed toward insulin resistance, a common cause of diabetes. 

This study, though very small, is the first step toward determining which specific genes are altered to allow obesity to be passed from generation to generation. Genetic makeup dictates physical body type, but this study shows that the obesity of the mother is enough to alter the genetic makeup of a child during gestation. 

By identifying the specific genes that are impacted, it’s possible researchers will be able to identify the pathways of obesity and find a way to block the expression of “obese genes.” 

Vohl hopes to see a longitudinal study conducted with a much larger population, as well as the ability to observe BMS and AMS children through middle age to see how often they develop chronic diseases. This study was limited in that regard because the mean age of participants was around 15 years old. 

“It’s to early to do anything, but this study shows that a weight management program is important for a woman that wants to become pregnant,” Vohl says.

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