We compared the effects on blood pressure (BP) of three isocaloric diets with reduced total fat and saturated fatty acid (SAFA) contents but with different proportions of monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA). Diet LF (low fat) provided 20 en% fat (7.9% SAFA, 7.8% MUFA, 3.0% PUFA); diet HP (high PUFA) 26 en% fat (7.5% SAFA, 8.2% MUFA, 8.1% PUFA), and diet HM (high MUFA) 26 en% fat (7.3% SAFA, 14.1% MUFA, 3.2% PUFA). The diets were consumed for 8 weeks (intervention) preceded by 2 weeks and followed by 8 weeks on a habitual diet (baseline/ switchback) with 33-34 en% fat (13-14% SAFA, 12% MUFA, 6% PUFA). Forty-five free-living couples were randomly allocated into the three diet groups, and 43 men and 44 women completed the study. BP was measured weekly with an automatic device. Compliance to diet was monitored by repeated food records, serum