Mustelin et al 2009 Physical activity reduces the influence of genetic effects on BMI and waist circumference: a study in young adult twins. International Journal of Obesity 33, 29–36;

Obesity and exercise are influenced by genetic and environmental factors. However, whether obesity and physical inactivity share the same genetic versus environmental etiology has not been studied. Mustelin et al analyzed these relationships, and also examined whether physical activity modifies the degree of genetic influence on body mass index (BMI) and waist circumference (WC). The FinnTwin16 Study is a population-based, longitudinal study of five consecutive birth cohorts (1975–1979) of Finnish twins. Data on height, weight, WC and physical activity of 4343 subjects at the average age of 25 (range, 22–27 years) years were obtained by a questionnaire and self-measurement of WC. The overall heritability estimates were 79% in males and 78% in females for BMI, 56 and 71% for WC and 55 and 54% for physical activity, respectively. There was an inverse relationship between physical activity and WC in males and females, and between physical activity and BMI in females. Physical activity significantly modified the heritability of BMI and WC, with a high level of physical activity decreasing the additive genetic component in BMI and WC. Physically active subjects were leaner than sedentary ones, and physical activity reduced the influence of genetic factors to develop high BMI and WC. This suggests that the individuals at greatest genetic risk for obesity would benefit the most from physical activity.
This is a fascinating study as it is not usual to see an environmental or behavioural activty over ride the genetic make up. Furthermore exercise appears to be important in the retention of a normal weight.

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Martin Eastwood

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