Background <p>Nutrition during early life often has lasting consequences for adult physiology. However, it remains unclear how developmental diet shapes both the initial energetic state and subsequent change of energy stores. To address this, we systematically varied yeast and sugar concentrations in the developmental diet of <i>Drosophila melanogaster</i> and quantified energy reserves (in joules, derived from fat, glycogen, trehalose, and glucose) at eclosion and after 10&#xa0;days of adulthood on a standardized diet. Comparing these time points allowed estimation of net change in energy reserves. Additionally, we examined how these effects depend on sex, population, and reproductive status.</p> Results <p>Developmental diet strongly influenced initial energy reserves. Higher sugar concentrations increased energy stores at eclosion. However, the subsequent net change in energy was inversely related to these starting conditions. Flies reared on high-sugar larval diets, which emerged with the most energy, exhibited the smallest net change during early adulthood. In contrast, flies from low-sugar diets emerged leaner and subsequently showed the largest net increase. These patterns were modulated by sex and reproductive status. In males, energy stores more closely reflected the larval nutritional background, whereas in females this relationship was weaker—likely due to the energetic demands of oogenesis. Mating was generally associated with lower energy reserves across groups.</p> Conclusions <p>Early-life diet affects both the starting point and early-adult change in energy reserves in <i>Drosophila</i>. These findings outline a framework in which developmental history and adult conditions jointly shape energetic trajectories.</p>