OBJECTIVES: A diet rich in n-3 fatty acids (fish oils) is associated with reduced risks of cardiovascular and metabolic diseases, but the mechanisms remain incompletely understood. Sympathoadrenal activation is postulated to be involved in the pathogenesis of these diseases, and may be inhibited by n-3 fatty acids. We therefore evaluated the effects of a diet supplemented with n-3 fatty acids on the stimulation of the sympathetic nervous system and of stress hormones elicited by a mental stress. METHODS: Seven human volunteers were studied on two occasions, before and after 3 weeks of supplementation with 7.2 g/day fish oil. On each occasion, the concentrations of plasma cortisol, and catecholamines, energy expenditure (indirect calorimetry), and adipose tissue lipolysis (plasma non esterified fatty acid concentrations) were monitored in basal conditions followed by a 30 min mental stress (mental arithmetics and Stroop's test) and a 30 min recovery period. RESULTS: In control conditions, mental stress significantly increased heart rate, mean blood pressure, and energy expenditure. It increased plasma epinephrine from 60.9 +/- 6.2 to 89.3 +/- 16.1 pg/ml (p<0.05), plasma cortisol from 291 +/- 32 to 372 +/- 37 micromol/l (p<0.05) and plasma non esterified fatty acids from 409 +/- 113 to 544 +/- 89 micromol/l (p<0.05). After 3 weeks of a diet supplemented with n-3 fatty acids, the stimulation by mental stress of plasma epinephrine, cortisol, energy expenditure, and plasma non esterified fatty acids concentrations, were all significantly blunted. CONCLUSION: Supplementation with n-3 fatty acids inhibits the adrenal activation elicited by a mental stress, presumably through effects exerted at the level of the central nervous system.Delarue J, Matzinger O, Binnert C, Schneiter P, Chiolero R, Tappy L. Diabetes Metab. 2003 Jun;29(3):289-95.