Since forever we have known that obesity is a highly heritable disease. Genes are important, though not solely determinative. They set the table for obesity, but for the most part, it is the environment that serves it up. That’s because the genetic basis for obesity usually comes from multiple genes, not a single gene. So to get a handle on a person’s genetic risk for obesity, we need a genetic risk score.

Yesterday in Nature Medicine, Ruth Loos and a huge global consortium of scientists published impressive research to describe perhaps the best methods yet for compiling a genetic risk score for obesity. With this method, at age five, this PGS (polygenic score) together with a child’s BMI could accurately predict the BMI of a child at age 18 more than a third of the time.

Why not more often? Because most often, genes do not act alone. The environment triggers this condition in biologically susceptible individuals. That triggering can happen early in life, or sometimes, much later. Taken together, genes plus environment tell the story.

Response to Behavioral Interventions

One interesting aspect of this research is that it shows that genetic risk scores can predict the response to diet and exercise for obesity. People with a high risk score were more likely to lose weight with these interventions. They were also more likely to gain it back later. The authors explain what they found:

“In intensive lifestyle intervention trials, individuals with higher PGSs lost modestly more weight in the first year (0.55 kg per s.d.) but were more likely to regain it.”

Reject the Binary

People want simple answers, but binary thinking in obesity almost never works well. Nature versus nurture or genes versus environment is one of those binary constructs that does not hold up and this study offers a good illustration of that.

Both genes and environment are important for understanding the risk of obesity that most people face. Some people will never gain excessive weight in any set of circumstances. Others are heavy all their life no matter what they do or where they live.

However, most of us live somewhere in between those two extremes. Our genes put us at risk for obesity and our environment serves it up. Our choices are mostly a matter of what we want to do about it.

Click here for this new research in Nature Medicine. For further reporting on it, click here and here.

Hope I (detail), painting by Gustav Klimt / Wikipedia