Twenty-four-hour intermittent fasting extends lifespan at the expense of fecundity in Daphnia

Dietary restriction (DR) is a well-established intervention for extending lifespan, yet the specific efficacy of intermittent fasting (IF) and its associated trade-offs remain under-explored in many Daphnia magna. This study investigated the effects of three IF intervals—2h, 24h, and 48h—on the longevity and fecundity of two clones of Daphnia. We hypothesized that longer fasting intervals would significantly extend lifespan at the cost of reproductive output, consistent with the disposable soma theory of resource allocation.Our results demonstrate that 24h IF significantly increased longevity relative to ad libitum controls, even outperforming caloric restriction(definition) (CR) by reducing late-life mortality. In contrast, 48h IF significantly reduced longevity, suggesting a metabolic tipping point where somatic damage from prolonged fasting outpaces cellular repair. Despite IF cohorts receiving greater total caloric intake than CR cohorts, both IF and CR groups exhibited similarly reduced fecundity. This suggests that reproductive output is governed by a regulatory mechanism that averages nutrient availability rather than responding to immediate food pulses. These findings indicate that IF provides a potent "therapeutic window" for life extension in D. magna, but exceeding optimal fasting durations triggers detrimental cellular stress. This research highlights the critical importance of interval calibration in fasting regimens to balance the trade-off between survival and reproduction.