Purpose: The main aim of the present study (FITFATTWIN) was to investigate how physical activity level is associated with body composition, glucose homeostasis, and brain morphology in young adult male monozygotic (MZ) twin pairs discordant for physical activity.
Methods: From a population-based twin cohort, we systematically selected 10 young adult male MZ twin pairs (age range 32-36 y) discordant for leisure-time physical activity during the past 3 years. Based on interviews, we calculated a mean sum index for leisure-time and commuting activity during the past 3 years (3-y LTMET index expressed as MET-h/d). We conducted extensive measurements on body composition (including fat% measured by dual-energy X-ray absorptiometry), glucose homeostasis including HOMA index and insulin sensitivity index (Matsuda index, calculated from glucose and insulin values from an oral glucose tolerance test), and whole brain magnetic resonance imaging for regional volumetric analyses.
Results: According to pairwise analysis, the active twins had lower body fat% (P = 0.029) and HOMA index (P = 0.031), and higher Matsuda index (P = 0.021) compared to their inactive co-twins. Striatal and prefrontal cortex (sub-gyral and inferior frontal gyrus) brain gray matter volumes were larger in the non-dominant hemisphere in active twins compared to inactive co-twins with a statistical threshold of P < 0.001.
Conclusions: Among healthy adult male twins in their mid-thirties, a greater level of physical activity is associated with improved glucose homeostasis and modulation of striatum and prefrontal cortex gray matter volume independent of genetic background. The findings may contribute to later reduced risk of type 2 diabetes and mobility limitations.
(C) 2014 American College of Sports Medicine