Leisure Time Physical Activity And Body Fat: A Twin Study

Exercise is thought to reduce body fat, but intervention studies are frequently limited by short follow-ups and observational studies by genetic selection. To tackle these problems, we carried out within-pair analyses in twin pairs identified on the basis of their long-term physical activity discordance. By studying both monozygotic and dizygotic twin pairs, we were able to control for childhood environment and partially for genetic liability as monozygotic co-twins share all and dizygotic co-twins on average half of their segregating genes. PURPOSE: To study the effects of a physically inactive vs. active lifestyle on body fat in twin pairs discordant for physical activity for 32 years. METHODS: Sixteen middle-aged (50-74 yrs) same-sex twin pairs (seven monozygotic, nine dizygotic) discordant for physical activity habits were comprehensively identified from the Finnish Twin Cohort (N=5663 baseline healthy pairs). Discordance was initially defined in 1975 and the same co-twin remained significantly more active during most of the follow-up. At the end of the follow-up in 2007 a series of body composition measurements, including bioimpedance measurement of whole body fat and specific MR imaging, was carried out. RESULTS: At the end of the follow-up the inactive co-twins weighed 6.5 kg more (P=0.12) and had 6.0 kg more fat mass (P=0.015) than their active co-twins, but no differences in fat-free masses were found. Visceral fat area was 50 % (P=0.010), liver fat score 170 % (P=0.030) and midthigh intramuscular fat area 48 % (P=0.034) greater among the inactive co-twins. Similar trends were seen among both monozygotic and dizygotic pairs. The intrapair difference correlation between visceral and intramuscular fat was high (r=0.648, P=0.009). CONCLUSION: Long-term habitual physical activity seems to protect from the accumulation of total, visceral and ectopic fat, even after partly controlling for genetic liability and childhood environment. Therefore the prevention of obesity should emphasize the role of regular leisure time activity.