Research by scientists at the University of Maryland has found that even those individuals with a genetic mutation associated with high body mass index (BMI) may be able to offset their increased risk for obesity through physical activity.

Recent research has suggested there is a strong association between BMI and variants of one gene, known as the fat mass and obesity associated (FTO) gene which are present in about 30 percent of European populations and carrying two copies of the FTO gene significantly increases the chances of becoming obese.

The FTO gene is linked with a 1.75-kilogram increase in body weight and while lifestyle factors such as diet and physical activity are also important contributors to weight gain, but it is unclear exactly how they interact with genetics.

In a study led by Dr. Evadnie Rampersaud, 704 healthy Amish adults, chosen because of that community's relative genetic "purity", with an average age of 43, were recruited from 2003 to 2007.

The recruits underwent a series of physiological tests, including a seven-day measurement of physical activity using an instrument known as an accelerometer, and DNA samples were taken and analysed.

In total 54% of the men and almost 64% of the women were overweight, with 10% of the men and over 30% of the women classed as obese.

The genetic analysis revealed that a 26 single-nucleotide polymorphisms (SNPs, or changes in a single base letter of DNA) in the FTO gene were associated with BMI.

The researchers then divided participants into two groups based on their physical activity levels and assessed the relationship between BMI and the two strongest SNPs.

It was found that both SNPs were associated with BMI only in individuals who had low physical activity scores for their age and sex, and had no effect on those with above-average physical activity scores.

The researchers say activity levels in the 'high-activity' stratum were approximately 900 calories higher than in the 'low-activity' stratum, which, depending on body size, corresponds to about three to four hours of moderately intensive physical activity, such as brisk walking, house cleaning or gardening.

They say the study showed that the FTO gene with its increased BMI and obesity risk is not significant in people who are very physically active and may have important implications in targeting personalized lifestyle recommendations to prevent obesity in genetically susceptible individuals.

Dr. Soren Snitker, who led the research, says the results strongly suggest that the increased risk of obesity due to genetic susceptibility can be blunted through physical activity.

The research is published in the current issue of the Archives of Internal Medicine.