Genetic and Environmental Effects on Fat Distribution: The Healthy Twin Study

Abstract

People commonly think that individuals have different fat distribution and this characteristic was inherited. Also, there are a variety of methods on managing regional fat. However, most fat distribution studies are actually not about regional fat but about abdominal fat. In the case of abdominal obesity, this is the leading cause of obesity-related diseases. As a result, abdominal fat researches have mainly studied and studies of fat distribution on other areas are very poor. The twin cohort study in Korea consists of 3461 individuals including 689 families, 550 pairs of identical twins, and 124 pairs of dizygotic twins. Among 3461 people, 3435 people measured by dual-energy X-ray absorptiometry (DXA) were included in this study. And, fat regions of participants used in this study are arms, legs, head, and trunk. To investigate the correlation with fat mass and obesity indices, we used spearman correlation analysis. The association with regional fat distribution and several environmental factor was analyzed using multiple regression with mixed model. And, genetic factor which has effects on regional fat distribution was analyzed by two method

intraclass correlation coefficients(ICC) and heritability analysis using variance component model. According to results of this study, correlation between fat distribution and waist hip ratio, which is an important indicator of abdominal obesity, was little and portion that environment has effects on regional fat distribution was small. However, although several environmental factors were not associated with regional fat, genetic factor has strong association with regional fat. This could be confirmed by ICC analysis and heritability analysis. Especially, because total fat was correlated with 4 regional fat, this explained a large portion of regional fat in heritability analysis. But, after the effects of total fat were excluded, additive genetic effects still accounted for the remaining effects on fat distribution. This means that genetic factor among several factors have significant effects on regional fat distribution and common idea that there is genetic predisposition on gaining fat by region could be proved to be the truth to some extent. Until now, although the research on central obesity have been done mainly, results on regional fat distribution in this study could help us to understand more overall fat distribution among Koreans. According to these results, there is strong genetic effects on regional fat distribution. This could make us more investigate further study such as association between fat distribution and hormones or genome-wide association study on regional fat distribution. Therefore, these follow-up studies will be able to provide some directions on managing regional fat.