Fish Meal Supplementation and Ambulatory Blood Pressure in Patients With Hypertension: Relevance of Baseline Membrane Fatty Acid Composition

BACKGROUND: Studies on fish oil effects on ambulatory blood pressure (ABP) are inconclusive. We evaluated fish effects on fatty acid composition of red blood cell (RBC) membrane and ABP values and tested the hypothesis that the starting membrane fatty acid composition affects the ability to incorporate additional polyunsaturated fatty acids (PUFA) and decrease blood pressure. METHODS: In 55 hypertensive patients, we measured RBC membrane fatty acid by gas chromatography and performed ABP monitoring. Patients received nutritional counseling and 3 weekly meals of trout rich in PUFA. In 42 patients, RBC membrane fatty acid and ABP were reassessed after 6 months. RESULTS: At baseline, the PUFA/saturated fatty acid (SFA) ratio of RBC membrane (PUFA/SFA) was inversely related to 24-hour, daytime, and nighttime systolic and pulse pressure, a relationship that was independent of covariables. At follow-up, the PUFA/SFA ratio increased in 20 (48%) of 42 patients. Patients with increased PUFA/SFA ratio at follow-up had lower baseline PUFA/SFA ratio than patients without such increase. Fish meal supplementation decreased 24-hour systolic and diastolic pressure only in patients who had increased PUFA/SFA ratio, a change that was more prominent during the nighttime. The change in PUFA/SFA was inversely and independently related to the change in 24-hour systolic and pulse pressure, and a logistic regression analysis indicated low baseline PUFA/SFA ratio as the only independent predictor of PUFA/SFA increase and blood pressure decrease. CONCLUSIONS: The ability of fish meals to increase membrane PUFA content and decrease blood pressure in hypertensive patients depends upon the starting membrane fatty acid composition.