How does nutrition affect the expression of phenotype

Genes are important for determining function, but nutrition modifies the extent to which different genes are expressed and thereby modulates whether individuals achieve the potential determined by their genetic background. Nutrition modifies both physical and cognitive aspects of performance.

Explanation:

which means it determines (firmly decide) on how much you exercise and what you eat, for an example if you eat unhealthy all the time like alot of dessert or sweets and ssalty foods then it gives you a unhealthy genetic backround (in which each gene functions).