Exercise will keep you slim, even if your genes 'are fat'

High levels of physical exercise can override a genetic predisposition to being overweight, according to a new study by American scientists. In a report published in the journal Archives of Internal Medicine, researchers found that the increased risk of obesity associated with carrying a particular gene variant was counteracted by leading an active lifestyle.

More than half of all people of European descent carry either one or two copies of a gene variant known as the fat mass and obesity gene, or FTO. FTO has been linked to obesity and increased body mass index (BMI), and individuals that have two copies of FTO are on average seven pounds heavier and 67 per cent more likely to be obese than those who don't carry it. However, new research by a team from the University of Maryland has found that the negative effects of carrying FTO are not seen in individuals that lead highly-active lives. Professor Soren Snitker, who led the work, explained: 'our study shows that a high level of physical activity can 'level the playing field', equalising the risk of obesity between those who have copies of the FTO gene variant and those who don't'.

The researchers examined 704 Amish men and women, and compared their weight and BMI, their daily activity levels, and whether they carried one or more copies of FTO. The Amish community is useful for this type of genetic study, as they are descended from a small group of European settlers. They therefore have similar genetic backgrounds, making it easier to assess the effects of a single gene variant than in a more genetically mixed population. In the group as a whole, the researchers saw the same association between FTO and increased body weight as has been previously described. But when they divided the study subjects in to two groups based on their daily levels of physical activity, they found that in those with active lifestyles there was no link between carrying FTO and the risk of obesity. 'This provides evidence that the negative effects of the FTO variants on increasing body weight can be moderated by physical activity', said Dr Evadnie Rampersaud, another member of the research team.

Activity levels were measured over a one-week period by a device attached to the hip. Amish society rejects modern technology, so many of their daily activities such as agricultural work or domestic chores are relatively labour-intensive. The 'high activity' group expended, on average, 900 calories per day more than the 'low activity' group - the equivalent of three to four hours of an activity such as manual labour, brisk walking or gardening. The authors concluded that their study emphasises 'the important role of physical activity in public health efforts to combat obesity, particularly in genetically susceptible individuals'.