Diet alters Drosophila melanogaster mate preference and attractiveness Animals decide which potential mate to pair with based on their subjective evaluation of each candidate mate's attractiveness. Attractiveness and its perception are plastic traits, dependent upon genetic and environmental factors. When evaluating mate attractiveness, in some cases animals make predictive judgements of mate reproductive potential, or fitness, based on the mate's condition. Diet, a fluctuating environmental factor, influences health and conditional states. However, how dietary enrichment of individual macronutrients (fat, protein, or sugar) affects behaviour, mate choice, and reproductive outcomes in both sexes is not fully understood. Here we show that a moderate increase in dietary macronutrients alters attractiveness, mate preference, and reproductive output of Drosophila melanogaster. Our results demonstrate that diet is an important factor in determining mating behavior and reproductive output, acting in a sex-specific fashion. These findings provide a framework for exploring the genetic mechanisms that drive changes in mating behaviour, fitness, and, hence, trait evolution.