Organisms require resources for growth, reproduction, and survival. However, due to limited resources, organisms must trade off limited resources among competing processes. They sense and monitor the availability of nutrients using nutrient-sensing pathways, which can initiate physiological changes or modify gene expression. Previous studies have proposed that the mechanistic target of rapamycin (mTOR), a signalling pathway, plays a fundamental role in facilitating adaptive plasticity when individuals face limitations in their energy resources. Despite the fundamental importance of this process in evolutionary biology, how nutritional limitation is regulated through the expression of genes governing this pathway and its consequential effects on fitness remain understudied, particularly in birds. We employed dietary restriction to mimic resource depletion and investigated its impact on body mass, reproduction, and gene expression in Japanese quails (Coturnix japonica). Quails were exposed to feeding at 20%, 30%, and 40%, restriction levels or ad libitum for 2 weeks. All restricted groups had reduced body mass, although decreases in the number and egg mass were only found in severe restrictions.Additionally, restriction reduced the expression of mTOR and insulin-like growth factor-1 (IGF1) genes, whereas the ribosomal protein S6 kinase-1 (RPS6K1) and autophagy-related genes (ATG9A and ATG5) were increased. Proportionally higher reproductive investment was associated with individual variation in mTOR expression. Furthermore, we observed sex-specific responses to body mass and gene expression, indicating that sexes can cope with nutritional deficits differently and emphasise the importance of considering sexual differences in studies of dietary restriction.