Soyfoods can make important contributions to a heart-healthy diet. They are low in saturated fat so that replacing animal foods with soy products can help to lower blood cholesterol levels. Soy protein itself also lowers blood cholesterol directly. This is an effect that was formally acknowledged by the US Food and Drug Administration more than a decade ago.
But elevated cholesterol is just one risk factor for heart disease. Two new studies add to existing evidence that soyfoods potentially reduce risk of heart disease and stroke independent of their effect on cholesterol.
One study, which was conducted in Iran, involved 29 subjects with type 2 diabetes who had kidney disease. Half of the study participants first consumed a diet containing one cup of soymilk and half consumed a diet containing one cup of cow’s milk for four weeks. During a two-week “wash out” period, the subjects consumed neither of these milks before switching to the other type of milk for four weeks. At the end of each four week study period, systolic blood pressure increased in response to cow’s milk whereas it decreased by 4.5 percent when the subjects consumed soymilk. The difference between groups was statistically significant, which means it is unlikely that the findings occurred just by chance.
In addition, earlier studies also show that consuming soy can help to lower blood pressure, although the effect in this study is larger than in many previous studies. Furthermore, the decrease came in response to just one cup of soymilk per day. This means that the benefits can be obtained with practical and easy additions of soyfoods to the diet.
The second study was conducted in Korea. It included 85 postmenopausal women who received either 70 milligrams of isoflavone per day for 12 weeks or placebo capsules daily. Seventy milligrams of isoflavones is the amount found in about three servings of soyfoods. After the 12-week intervention, levels of triglycerides increased by about 7 percent in the placebo group but decreased by about 17 percent in the women who consumed the isoflavones. The difference between groups was statistically significant. Triglycerides are fats that circulate in the blood. Elevated triglyceride levels may be a risk factor for heart disease.
These two studies show that soyfoods lower risk of cardiovascular disease through multiple mechanisms, not simply be lowering blood cholesterol levels.
Miraghajani et al., Journal of Renal Nutrition, 2013; Kim et al., Arch. Pharm. Res., 2013