The Genetics of Sloth

On Sunday, I listened to Claude Bouchard, Director of the Pennington Biomedical Research Centre, Baton Rouge, LA, presenting the George Bray Award lecture at the 2008 Scientific Meeting of The Obesity Society (former NAASO), Phoenix, Arizona.

In his talk, Bouchard focused on the genetic determinants of physical activity. It turns out that you can actually breed mice that demonstrate high levels of spontaneous activity and mice that sit around all day and do nothing but eat (they’d probably also watch TV if they had one). A number of genetic loci have been found that point to the presence of genes that distinguish these animals.

Similarly in humans, twin studies suggest that genetic transmission is a key determinant of spontaneous physical activity and participation in sports. Several quantitative trait loci have been identified for high spontaneous activity or sedentariness (e.g. on Chromosomes on 2, 7, 10, 18 &19).

According to Bouchard, although the individual genes involved have yet to be identified, the evidence in support of genetic variations accounting for spontaneous physical activity level or sendentariness are strong.

Bouchard also presented extensive evidence for the remarkable genetic variability in response to training and exercise. Thus, whether measured by gain in strength, fitness or muscle mass, there are clear genetic differences between individuals in their response to the same level of exercise.

While factors such as baseline fitness, age, sex, weight, or ethnicity, each explain only around 2-5 % of the variability to exercise response, familial aggregation can explain around 50% of the variability.

Clearly, this has important implication for the risk of weight gain. As one can easily imagine, being “genetically-programmed” for high levels of spontaneous physical activity (e.g. fidgeting) and having genes that allow the body to rapidly adapt to and benefit from regular exercise will make you much less likely to gain weight than if your genetic program reads “sedentariness”.

It is only natural that individuals who are genetically programmed for activity and for whom exercise is a rewarding and beneficial experience are far more likely to take up and persist with an exercise program than individuals who genetically lack these traits.

Tailoring exercise programs to encourage and meet the requirement of those genetically programmed to sedentariness will likely remain challenging.

Phoenix, Arizona