The effects of a reduced energy content of two meals on hunger motivation, physiological variables and reactions to emotional stress were investigated. Healthy normal-weight male students received breakfast and lunch in the laboratory. Half of the subjects (n = 28) received meals with normal energy content (1700 kcal), and half received meals with reduced energy content (260 kcal). Psychological and physiological variables were obtained for 8 h from morning to afternoon, including during a period of emotional stress in the afternoon. Psychophysical state was altered by the reduction of energy in food (e.g. increased subjective motivation to eat, decreased systolic blood pressure). Noise decrease feelings of relaxation in subjects who had received low-energy meals, but not in subjects who had received high-energy meals. This enhanced emotional reactivity after low-energy intake is interpreted as a biologically meaningful consequence of the heightened hunger motivation. Furthermore, subjective hunger motivation was potentiated by stress when energy intake in the preceding hours was low. The latter result may be due to increased emotional reactions and/or an augmentation of deprivation-induced physiological changes by noise-induced emotional stress.