Research with twins sheds light on predisposition to overweight

11 October 2018

The genetic predisposition to overweight has a greater effect in a living environment that promotes obesity. This was the conclusion of a study conducted at University College London (UCL). Ellen van Jaarsveld was one of the researchers. In an article published on October 1st in JAMA Pediatrics, the researchers emphasized that promoting a healthy living environment is especially important for children with a predisposition to overweight.

Children of overweight parents often become overweight themselves. This predisposition to overweight is in part genetically determined. Researchers at UCL wanted to know whether the heritability of overweight is more pronounced in what they call an ‘obesogenic environment’. Ellen van Jaarsveld from Radboud university medical center contributed to this research: “In such an environment, the extent to which children are exposed at home to factors associated with overweight is important. Take food for example. How much healthy and unhealthy food is available at home and how much are children allowed to eat of these foods? Do parents use food as a reward? Exercise also plays a role: do the parents exercise themselves? Do they walk frequently? Do they have a garden? Are there parks in the area? Finally, we looked at media consumption: how many hours per day are children allowed to watch television? How much do the parents watch television themselves?”
 
Twins
The researchers looked at the genetic predisposition for the Body Mass Index (BMI, a measure of overweight) of more than 1,800 English twins aged four years or younger. They did this in both high and low obesogenic environments. “A third of the group consisted of monozygotic (identical) twins, and two-thirds were dizygotic (fraternal) twins. Twins are well suited for this type of research, because identical twins are genetically identical. Fraternal twins are genetically identical for 50 percent. Because twins grow up under the same circumstances, the degree of difference in BMI between twins can be attributed to genetic predisposition.”
 
Seduction and heritability
The researchers found that in an obesogenic environment the BMIs of the identical twins more closely resembled each other than the BMIs of the fraternal twins. In a low obesogenic environment there was a smaller difference between the two groups. The conclusion is that in obesogenic environments, the heredity of obesity plays a larger role. Van Jaarsveld explains: “If you live in an environment without temptations to overeat, it does not matter if you have a genetic predisposition. Your BMI will remain healthy. But in an environment with many temptations, the hereditary predisposition is expressed more strongly.”
 
Overeating is required for overweight
Children do not automatically become overweight if they have a hereditary predisposition for overweight, says Van Jaarsveld. “That is not how it works. To become overweight, you still need to consume more calories than you metabolize with exercise. However, with a predisposition you have a higher risk of being overweight if you are exposed to more temptations.”
 
The hereditary predisposition to overweight also determines how well children can maintain a healthy weight. People who are genetically predisposed to overweight have more difficulty staying at a healthy weight. This is easier for children without a genetic predisposition, according to Van Jaarsveld: “Some children naturally enjoy exercise, or like to eat healthy food. But if you do not enjoy exercise and you love sweets, it is much more difficult to maintain a healthy weight, especially in an obesogenic environment.”