Children's Health

Nature Trumps Nurture in Child Obesity

Feb. 11, 2008 -- Children's genes are more important than their environment in determining whether they will become overweight, new research shows.

In a study that included more than 5,000 identical and non-identical twin pairs, researchers found heredity to be a much bigger predictor of childhood obesity than lifestyle.

They concluded that three-quarters of a child's risk for becoming overweight is due to genetic influences, while just under a quarter of risk can be attributed to environment.

Researcher Susan Carnell, PhD, says the fact that genes play such an important role in a child's weight was somewhat surprising.

"It was quite striking that even in young children genes seem to be having a really important effect," she tells WebMD.

Genes and Childhood Obesity

The obesity rate among children in the U.S. has more than doubled for preschoolers and teens over the past three decades and more than tripled for children between the ages of 6 and 11, according to the CDC.

Similar increases have been seen across the globe, including in the U.K., where the twin study was conducted.

Carnell and colleagues studied twins in an effort to quantify the impact of genetic and environmental influences.

"Twin studies provide a unique method for disentangling nature and nurture by taking advantage of the fact that (identical) twins share all of their genes, whereas (fraternal) twins on average share half of their segregating genes," they wrote.

A total of 5,092 identical and non-identical twin pairs who were enrolled in the larger ongoing trial took part in the study; the participants were born between 1994 and 1996.

Researchers measured each child's body mass index (BMI) and waist circumference and then compared the findings between the identical and non-identical twins.

Using a standardized genetic modeling analysis, the researchers concluded that the differences in the children's BMI and waist circumferences were 77% attributable to genes.

The study appears in the latest issue of the American Journal of Clinical Nutrition.

Bad Genes Don't Make Obesity Inevitable

The findings do not mean that becoming overweight or obese is inevitable for children who are genetically susceptible, but it does mean that these children may need some extra support, Carnell says.

"It may be that genes influence behavior through appetite or by making it harder for some people to resist food," she says. "So while one child might be perfectly OK living in a home filled with [potato chips] and cakes, another might find it very challenging."

She adds that diet, lifestyle, and other environmental influences play a major role in obesity, especially for genetically predisposed children.

"This type of genetic predisposition could not be expressed if there wasn't so much food around," she says. "We would all be skinny. It is our environment that is allowing our genetic susceptibility to express itself. It would benefit everyone if we did more as a society to encourage activity and healthy eating, but it would be especially beneficial for children who are highly susceptible to their environment."