Among freshwater species intensively used in ecotoxicology, Gammarus fossarum is a relevant test species. Many sub-individual and individual responses are studied in gammarids in order to monitor and predict effects of chemical water quality on aquatic life. In this framework, energetic metabolism variations appear to be a good predictive tool to detect physiological disturbance of organisms linked to ecosystem quality. Among biological processes involving energy uptake, digestive enzymes play a key role. Some papers clearly demonstrated that the activity of these enzymes may be disturbed by pollutants. Consequently digestive enzymes can be proposed as relevant indicators of health organisms. In this way, the monitoring of digestive responses was recently successfully applied with caged organisms for the diagnosis of aquatic system. However, confounding factors may highly influence activity levels of these enzymes, consequently the impact of these parameters should be known and taken into account for an accurate interpretation of activity levels in term of toxicity. The use of control organisms for experiments allows preventing the impact of these biotic factors. However, some other factors as the amount of available food or the food eaten by organisms cannot be easily controlled. The present study aimed to show the influence of food availability on digestive enzyme activities (amylase and trypsin) on both gender of the freshwater amphipod Gammarus fossarum, throughout their reproductive cycle. Organisms were exposed to 3 levels of food available. First data showed a decrease of amylase activity correlated with the food availability. In contrast, for trypsin no effect of starvation was observed on enzyme activity for the both gender. In female, an interaction effect between moult cycle and level food available was also observed on digestive enzyme activities. So male appears as a better biological matrix for using digestive enzymes in biomonitoring survey. Moreover results indicated in starved female a delay in reproductive cycle compared to ad libitum fed organisms which demonstrated the diet stress effect on physiological responses. The digestive capacity inhibition may induce changes in energy allocation. These results concerning digestive capacities (both gender) and reproductive cycle (female) will be discussed in regard to energy reserve measurements and reproductive outcomes (fertility and fecundity).