Camus et al. examined gene expression in female and male flies given a protein-rich diet (which is optimal for egg production) and a carbohydrate-rich diet (which is optimal for sperm production). Many metabolic genes (‘core genes’) displayed similar responses to diet in both female and male flies (bottom left). A smaller group of genes – including a number of reproductive genes – showed clear-cut differences in expression for each diet depending on sex, with some exhibiting antagonistic behaviors in the two sexes (bottom right). Further analyses revealed that this sex-opposite regulation occurs within the IIS/TOR signaling network.