Changes in mood, performance, cortisol, and physiological variables with a month-long energy restricting diet (3.347 MJ/day) were studied in nine overweight (mean mass 71.2 +/- 8 kg; body mass index 26.1 +/- 2.8 kg/m(2)), healthy premenopausal (age 20-36 years) women. Measurements were taken in the 2 weeks before the diet (baseline) and again in the final 2 weeks of the diet to attenuate menstrual cycle differences. A reduction in energy intake and concomitant weight loss (5.80 +/- 1.65 kg) were accompanied by a significant decline in systolic blood pressure (5.4%), heart rate (7.6%), and cortisol concentration (13.6%). Fatigue and vigour on the Profile of Mood States (POMS) questionnaire were adversely affected; however, subjective assessments of mood, concentration, temperature sensitivity, appetite, and sleep quality using visual analogue scales, were not significantly altered during the month-long period of energy restriction. Motor performance, as assessed by hand-eye coordination, improved with both a reduction in mean reaction time and improved accuracy in response to visual stimuli. The very low-energy diet appeared to be neither physiologically nor psychologically stressful. Beneficial effects were evident with a reduction in BMI, reduced risk of cardiovascular stress, improved motor performance, and a decline in physiological stress with dieting success.