Leisure-time physical activity and high-risk fat: a longitudinal population-based twin study

Abstract

Background and Objective: 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. Therefore, we studied the effects of a physically inactive vs active lifestyle on high-risk (visceral, liver and intramuscular) fat in twin pairs discordant for leisure-time physical activity habits for over 30 years. Design: A longitudinal population-based twin study. Subjects: Sixteen middle-aged (50-74 years) same-sex twin pairs (seven monozygotic (MZ), nine dizygotic (DZ)) with longterm discordance for physical activity habits were comprehensively identified from the Finnish Twin Cohort (TWINACTIVE study). Discordance was initially defined in 1975 and the same co-twin remained significantly more active during the 32-yearlong follow-up. Main Outcome Measures: Magnetic resonance imaging-assessed visceral, liver and intramuscular fat. Results: 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 cm 2 , 95% confidence interval (CI) 7.0-104.1, P ¼ 0.010). The liver fat score was 170% higher (13.2, 95% CI 3.5-22.8, P ¼ 0.030) and the intramuscular fat area 54% higher (4.9 cm 2 , 95% CI 1.9-7.9, P ¼ 0.002) among the inactive co-twins. All the trends were similar for MZ and DZ pairs. Peak oxygen uptake was inversely associated with visceral (r ¼ À0.46, P ¼ 0.012) and intramuscular fat area (r ¼ À0.48, P ¼ 0.028), with similar trends in intrapair difference correlations (r ¼ À0.57, P ¼ 0.021 and r ¼ À0.50, P ¼ 0.056, respectively). The intrapair difference correlation between visceral and intramuscular fat was also high (r ¼ 0.65, P ¼ 0.009). Conclusion: 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.

Leisure-time physical activity and type 2 diabetes during a 28 year follow-up in twins

“…However, use of BMI as a covariate is problematic as both high muscle mass and high fat mass can contribute to high BMI. Our previous twin studies have shown that despite the lack of statistically significant differences in BMI between physically active and inactive members of twin pairs, physical activity reduces waist [24] and high-risk body fat (ectopic fat stores, liver fat and visceral fat) but maintains skeletal muscle mass and function [33], leading to lowered type 2 diabetes risk independent of BMI. It is also possible that the results from BMI-adjusted analyses are overadjusted, as physical activity may reduce type 2 diabetes by independently reducing BMI.…”

“…More specifically, physical activity or exercise training has been shown to reduce visceral fat [33], improve skeletal muscle insulin sensitivity [37,38] and increase the oxidative capacity of skeletal muscle, which correlates with insulin sensitivity [39], and also leads to increased/modified fat oxidation, which is most likely to prevent lipid-mediated insulin resistance [40].…”

Physically active vs. inactive lifestyle, muscle properties, and glucose homeostasis in middle-aged and older twins

“…Hence, exercise-induced retention of muscle strength rather than that of muscle mass could be the key factor in the maintenance of muscle function to avoid age-related mobility limitations (Hughes et al 2001;Visser et al 2005;Goodpaster et al 2006;Newman et al 2006;Delmonico et al 2009). Furthermore, regular physical activity is an effective way to slow down the age-and/or inactivity-related infiltration of muscle fat Delmonico et al 2009;Leskinen et al 2009b). However, the role of muscle fat infiltration in strength loss, muscle weakness, and mobility limitations needs further study (Visser et al 2005;Goodpaster et al 2008;Delmonico et al 2009).…”

“…As such, the accumulation of ectopic "high-risk" fat and adipocyte function are important mechanisms in mediating the prolonged effects of life-long regular exercise on glucose metabolism (Goodpaster et al 2000;Boule et al 2005;Petersen and Shulman 2006;Dube et al 2008;Leskinen et al 2009b;Taube et al 2009;Rector and Thyfault 2011). Notably, the cotwins did not differ significantly in either body weight or BMI (see Table 1), and there were no differences in their fat intakes (Rintala et al 2011), yet the inactive co-twins had significantly more visceral, intramuscular, and liver fat, as we have reported earlier (Leskinen et al 2009b).…”

Causes and consequences of obesity: the contribution of recent twin studies

“…32 Intensive substudies of these physical activity discordant twins further revealed that although the physically inactive (79.5 ± 18.4 kg) and active twins (72.9 ± 11.9 kg) had only small differences in body weight, the inactive twins had 170% more liver fat and 54% more intramuscular fat than the active twins. 33 Thus, the value of physical activity should not be judged only by its' effects on body weight.…”