To study the role of diet as a risk factor for coronary heart disease (CHD), 463 adults (25-65 years, 419 males) at risk of or with CHD were assigned to group A (n = 231) receiving a cardiovasoprotective diet or group B (n = 232) receiving a normal diet in a randomized, single-blind fashion. Age, sex, risk factors and incidence of CHD were comparable between the two groups. Group A received a significantly higher percentage of calories in relation to complex carbohydrates, vegetable proteins, polyunsaturated fatty acids, and had a higher polyunsaturated:saturated fatty acid (P:S) ratio compared to control group B, which received more saturated fat and cholesterol. Group A also received more soluble dietary fiber and magnesium (Mg) and was physically more active than group B. Exercise and dietary adherence were tested by a questionnaire. After 12 weeks, results indicated a significant decrease in mean serum total cholesterol (9.0 vs 3.1%), low-density-lipoprotein cholesterol (LDL-C) (9.8 vs 3.8%) and triglyceride (11.1 vs 5.4%), and an increase in serum Mg (8.5%) in the intervention group compared to initial levels. No significant changes in mean levels were noted in the control group. Body weight significantly decreased and physical activity was significantly higher in the intervention group compared to the control group during the 12-week followup on similar intakes of energy. There were insignificant changes in high-density-lipoprotein cholesterol (HDL-C) in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)