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19-03-2012 | Genetics | Article

Exercise trumps genetic impact on bodyweight


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MedWire News: Regular exercise can reduce the effects of having a genetic predisposition to obesity, research suggests.

But watching too much television has the opposite effect, the researchers reported at the American Heart Association's Epidemiology and Prevention/Nutrition, Physical Activity and Metabolism Scientific Sessions in San Diego, California, USA.

Qibin Qi (Harvard School of Public Health, Boston, Massachusetts, USA) and colleagues studied data from 7740 women and 4564 men participating in the prospective Nurses' Health Study and Health Professionals Follow-up Study.

The team calculated a genetic predisposition score for each participant based on 32 variants that are known to influence body mass index (BMI), giving minimum and maximum scores of 13 and 43, respectively. "These genes were just identified in the past 5 years and the exact functions of the genetic variants are still unknown," noted Qi, in a press statement. "Future studies will be needed to uncover the underlying mechanisms."

Overall, each additional BMI-associated allele that a participant carried was associated with an increase of 0.13 kg/m2 in BMI. However, the size of the genetic effect on BMI was significantly smaller in participants in the highest quintile of physical activity than it was in those in the lowest quintile, at a BMI increase of 0.08 versus 0.15 kg/m2 per allele.

Data on physical activity and television-watching habits (as a surrogate for sedentary behavior) were collected 2 years before the participants' BMIs were measured.

Each 4 metabolic equivalent/day increase in physical activity, which is equivalent to 1 hour/day of brisk walking, was associated with a 0.06 kg/m2 reduction in BMI - in other words, it approximately halved the effect of one extra BMI-increasing allele.

Watching television had the reverse effect, with the influence of the genetic effect on BMI largest in participants who watched the most television (>40 hours/week), at 0.34 kg/m2 per allele versus 0.08 kg/m2 per allele among those who watched the least (0-1 hours/week).

Each 2 hour/day increase in time spent watching television was associated with a 0.03 kg/m2 increase in BMI, or about 23% of the effect of one extra BMI-increasing allele.

Qi et al said that, based on their findings, the difference in BMI between people with the maximum and minimum genetic predisposition scores, which was about 4 kg/m2, could be halved by undertaking 1 hour of brisk walking every day.

By Eleanor McDermid

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