**Background:** Dietary restriction (DR) is a well-established intervention that delays aging and extends lifespan across diverse species, from yeasts to primates. While the direct effects of DR on individuals are extensively documented, less is known about how parental DR influences offspring fitness, particularly when applied during the pre-reproductive adult stage rather than during gestation or lactation. Most prior work has focused on maternal effects during pregnancy in rodents or on fasting-induced DR in invertebrates, and studies examining both maternal and paternal contributions in a single experimental design remain limited. This study aimed to investigate the intergenerational effects of parental DR (without fasting) on lifespan, stress resistance, development, fecundity, body weight, and feeding behavior in Drosophila melanogaster offspring.
**Methods:** Wild-type Canton-S flies were used. Parental (F0) flies were fed either a full diet (FD; 16% yeast extract) or a restricted diet (DR; 4% yeast extract, 25% of the full diet protein level) for 7–10 days after eclosion. Four parental cross-combinations were established: FD male × FD female, DR male × FD female, FD male × DR female, and DR male × DR female. Offspring (F1) were reared on standard CSY medium. Lifespan was measured in demography cages (100 males and 100 females per cage) with three replicates per group, and four independent trials were conducted. Stress resistance was assessed by exposing 7–10-day-old offspring to heat shock (39.5°C), oxidative stress (18 mM paraquat), or starvation (agar-only medium). Developmental viability and timing were evaluated by transferring 10 eggs per vial and monitoring pupation and eclosion every 12 hours. Fecundity was measured by counting eggs laid daily for 10 days from 1 female with 2 males. Feeding rate was quantified using FD&C blue No. 1 dye incorporation measured at 595 nm. Body weight was measured at 1 day and 7 days of age. Statistical analyses included Kaplan–Meier survival estimation, log-rank tests, Student’s t-tests, and Wilcoxon rank sum tests.
**Key Results:** Parental DR significantly extended offspring lifespan when both parents were on DR: male offspring lived 13.5% longer (63.42 ± 0.88 vs. 55.87 ± 0.89 days, p < 0.0001) and female offspring lived 12.8% longer (63.20 ± 1.03 vs. 56.04 ± 0.78 days, p < 0.0001) compared to offspring from FD parents. Cross-combination analyses revealed that female offspring lifespan was primarily influenced by maternal diet (Mother DR: 64.35 ± 0.69 days, 10.4% increase, p < 0.0001; Father DR: 61.85 ± 0.64 days, 1.6% increase, p = 0.3783), while male offspring lifespan increased when either parent was on DR (Father DR: 60.78 ± 0.63 days, 6.0% increase, p < 0.0001; Mother DR: 61.10 ± 0.62 days, 7.1% increase, p < 0.0001). Stress resistance was significantly enhanced: heat shock resistance increased by 24% in males and 37% in females (both p < 0.0001); oxidative stress resistance increased by 18% in males (p < 0.01) and 17% in females (p < 0.05); starvation resistance increased by 23% in females (p < 0.0001) but not in males (p = 0.316). Developmental viability (egg-to-pupa, p = 0.124; pupa-to-adult, p = 0.164) and timing (emergence to pupa, p = 0.361; emergence to adult, p = 0.401) were unaffected by parental diet. Fecundity showed no difference between groups (p = 0.382). Parental DR decreased feeding rate in male offspring (p < 0.0001) but not in females (p = 0.733). Offspring from DR-fed parents were heavier at 1 day of age (males, p < 0.05; females, p < 0.05), but this difference disappeared by day 7 (males, p = 0.366; females, p = 0.289). Notably, offspring from DR-fed parents showed a decrease in body weight over 7 days (males: 9.37% decrease; females: 14.92% increase) compared to offspring from FD-fed parents (males: 0.37% decrease; females: 16.68% increase).
**Clinical Implications:** This study demonstrates that short-term parental dietary restriction can produce beneficial intergenerational effects on offspring longevity and stress resistance without requiring continued dietary restriction in the offspring. The findings support the concept of adaptive parental effects and the thrifty phenotype hypothesis, suggesting that environmental cues experienced by parents can shape offspring physiology in ways that may enhance survival under challenging conditions. The sex-specific effects observed—particularly the stronger maternal influence on female offspring lifespan and the paternal contribution to male offspring lifespan—highlight the complexity of transgenerational epigenetic programming. While direct clinical translation is premature, these results underscore the potential importance of parental nutrition prior to conception in influencing offspring health trajectories. The observation that parental DR increased offspring body weight at birth but not at 7 days, along with reduced feeding rate in male offspring, suggests that parental diet may influence offspring energy metabolism and obesity risk. Future research should investigate the epigenetic mechanisms—such as DNA methylation and histone modification—underlying these intergenerational effects, as well as their applicability to mammalian systems and potential relevance to human health and aging.