While abundant food supplies support host immunity, they may also fuel pathogen proliferation, whereas food limitation restricts resources for both host and parasite. The balance between these processes, and the physiological limits to fasting as a protective strategy, remain poorly understood. Here, we tested how the duration and timing of food deprivation relative to pathogen exposure affect resistance to infection, using the oyster Magallana gigas and its pathogen, Ostreid herpesvirus 1. We used a cross-over design with two sequences differing in the timing of starvation relative to infection. We hypothesized that (i) survival would increase with fasting duration until a threshold is reached where energy depletion becomes detrimental, and (ii) fasting would only protect when it immediately precedes infection, because its effect relies on reduced host metabolism. Consistent with these hypotheses, oysters fasted immediately before infection showed increased survival peaking after 14-28 days, followed by a sharp decline, while prior fasting with refeeding provided no benefit. Biochemical analyses revealed that advanced protein catabolism may underlie the tipping point where starvation shifts from protective to detrimental effects on disease resistance.