Relaxed natural selection contributes to global obesity increase more in males than in females due to more environmental modifications in female body mass

Abstract

Objective

Relaxed natural selection, measured by Biological State Index (I _bs), results in unfavourable genes/mutations accumulation in population. Obesity is partly heritable. We aim to examine and compare the effects of relaxed natural selection on male and female obesity prevalence.

Methods

Data for 191 countries of the world were captured for this ecological study. Curvilinear regressions, bivariate and partial correlations, linear mixed models and multivariate linear regression analyses were used to examine the relationship between I _bs and sex-specific obesity prevalence. Per capita GDP, urbanization and caloric intake were controlled for as the confounding factors. Fisher r-to-z transformation, R ² increment in multivariate regression and F-test were used to compare the correlations.

Results

Curvilinear regressions, bivariate and partial correlations (controlled for GDP, urbanization and calories) revealed that I _bs was significantly correlated to obesity prevalence of both sexes, but significantly stronger to male than to female obesity prevalence. Curvilinear regression models also showed strong correlations. Mixed linear models, with effects of GDP, urbanisation and caloric intake controlled for, showed that male and female average obesity prevalence rates were significantly higher in countries with greater I _bs value than their equivalents in countries with lower I _bs. Between higher and lower I _bs countries, the gap of male obesity prevalence is 60% greater than the gap of female obesity prevalence. Stepwise multiple regression identified that I _bs was a significant predictor of obesity prevalence of both sexes. Multivariate regression showed that, adding I _bs as an obesity predictor, R ² increment in male model was significantly greater than in female model.

Conclusions

Relaxed natural selection may drive males and females to accumulate metabolic faulty genes equally. Probably due to greater environmental, personal intervention in regulating female body mass, relaxed natural selection shows less contributing effects to female obesity prevalence than to male obesity prevalence. Gene therapy to prevent obesity may need to be also taken into account.