Soy's beneficial effects have often been studied in women. Now, a study published in the Journal of the American College of Nutrition has investigated the effects of soy protein and soy isoflavones on blood pressure and cholesterol levels in 61 middle-aged men, at high risk of developing coronary heart disease. For five weeks, half the men consumed diets containing at least 20 grams of soy protein and 80 milligrams of soy isoflavones each day. The effects on their blood pressure, cholesterol levels, and urinary excretion of isoflavones were measured, and then compared to those of the other half of the men who were given a placebo diet containing olive oil.
The men consuming soy in their diet were found to have significant reductions in both diastolic and systolic blood pressure. Not only was their total blood cholesterol significantly lower, but their levels of HDL (good) cholesterol significantly increased. While the control group consuming the soy-free diet containing olive oil also experienced an increase in their HDL cholesterol levels, their blood pressure was not affected, nor did their levels of LDL (potentially harmful) cholesterol drop.
The researchers concluded that daily intake of at least 20 grams of soy protein including 80 mg of isoflavones for a minimum of 5 weeks would be effective in reducing the risk of cardiovascular disease in high-risk, middle-aged men.