Effects of sodium intake and cardiorespiratory fitness on body composition and genetic susceptibility to obesity: results from the Quebec Family Study.

The main aim of this study was to evaluate the effects of sodium intake and cardiorespiratory fitness (CRF) on body composition. The study was also intended to assess whether sodium intake and/or CRF mediate the genetic susceptibility to obesity. Analyses were performed on a sample of 526 adult participants from the Quebec Family Study for whom a complete data set was available for nutrient and energy intake, CRF, and body composition variables. The effects of sodium, CRF, and their interaction were analyzed by comparing sex-specific tertiles using general linear mixed models. In both males and females, we observed a significant effect of sodium intake and CRF on all body composition variables. However, in females only, we found that the effect of sodium intake on body composition variables varies according to CRF level such that high sodium intake was associated with increased body fatness, but only in females with low CRF. This interaction effect remained significant after statistical adjustment for total sugar, fat, and energy intake. Using mediation analysis, we also found sodium intake and CRF to be significant mediators of the relationship between a polygenic risk score of obesity based on >500,000 genetic variants and BMI or waist circumference. In conclusion, this study shows that sodium intake influences body composition via mechanisms that interact with aerobic fitness, especially in females. Furthermore, both sodium intake and CRF seem to be involved in the expression of the genetic susceptibility to obesity.