Physical activity reduces effect of obesity gene + Hormones drive post diet weight gain: important to prevent obesity

The genetic predisposition to obesity due to the 'fat mass and obesity associated' (FTO) gene can be substantially reduced by living a physically active lifestyle.

Medical Research Council Epidemiology Unit, in Cambridge, UK,

http://www.eurekalert.org/pub_releases/2011-11/plos-par102511.php

People on diets likely to regain weight owing to hormones - Results showed that following initial weight loss of about 13 kgs, the levels of hormones that influence hunger changed in a way which would be expected to increase appetite.

“Ultimately it would be more effective to focus public health efforts in preventing children from becoming obese.” 

http://newsroom.melbourne.edu/news/n-674