The research question addressed in this study is whether short-term feeding of a diet high in fat and carbohydrates and low in protein will reduce the impact of mild stressors on stress- prone rats. Stress-prone people are more likely to have a serotonin deficiency. Serotonin levels may decline and disrupt mood during stress (Delbende, 1992; van Praag, 1980). A high carbohydrate, low protein diet may reduce stress by increasing tryptophan and serotonin in the brain (Markus et al., 1998). A diet high in fat may influence stress by affecting corticosteroid ("stress hormone") levels. The rats used in the study were bred for high (HiS) or low (LoS) saccharin consumption. LoS rats tend to be more vulnerable to stress than HiS rats (Dess & Minor, 1996). The rats were given either the experimental diet or the control diet for three days. They then were exposed to three mild stressors and their responses were measured. The results indicated that diet does affect stress response, but not in the manner predicted. The HiS rats and LoS rats on the experimental diet were somewhat jumpier than the control groups in one measure of jumpiness. Diet did not significantly alter behavior in the other two tests. The combination of a high fat diet, high carbohydrates and low protein diet elevated stress response. Thus, future research could examine the diets more closely and discover why the combination aroused the rats, rather than calming them.