Twin studies are an elegant method of resolving complex problems, comparing like with like with one variable different.
Exercise is thought to reduce high-risk body fat, but intervention studies are frequently limited by short follow-ups and observational studies by genetic selection. In this elegant study for Finland Leskinen and colleagues studied the effects of a physically inactive or an active lifestyle on high-risk (visceral, liver and intramuscular) fat in twin pairs differerence in leisure-time physical activity habits for over 30 years.
Sixteen middle-aged (50–74 years) same-sex twin pairs (seven monozygotic (MZ), nine dizygotic (DZ)) with long-term difference in physical activity habits during the 32-year-long follow-up.were identified from the Finnish Twin Cohort (TWINACTIVE study).
In within-pair analyses carried out after the adult life-long discordance in physical activity habits, the physically inactive co-twins had 50% greater visceral fat area compared with the active co-twins (mean difference 55.5 cm2. The liver fat score was 170% higher and the intramuscular fat area 54% higher among the inactive co-twins. All the trends were similar for MZ and DZ pairs. Peak oxygen uptake was inversely associated with visceral and intramuscular fat area, with similar trends in intrapair difference correlations. The intrapair difference correlation between visceral and intramuscular fat was also high. The authors concluded that regular physical activity seems to be an important factor in preventing the accumulation of high-risk fat over time, even after controlling for genetic liability and childhood environment. Therefore, the prevention and treatment of obesity should emphasize the role of regular leisure-time physical activity.
Leskinen et al (2009) Leisure-time physical activity and high-risk fat: a longitudinal population-based twin study International Journal of Obesity 33, 1211–1218;