In the final part of my series on soy (see Part 1 right here and Part 2 here) and the natural hormones (isoflavones) it contains, I’ll address the evidence on diabetes and blood pressure.
Preliminary evidence shows that soy can be beneficial for patients with diabetes. One study on 77 type 2 patients looked at a soy-based meal plan and compared it to an individual diet plan. The results:
— Significant loss of weight in the soy group
— Fasting blood sugar levels were lower in the soy group (126 milligrams/deciliter [mg/dL]) compared to the others (152 mg/dl)
— The soy group had greater circulation of oxygen in the blood
— The soy group had a lower need for diabetes medications
In another study, researchers randomly tested 32 type 2 diabetes patients on phytoestrogen supplements versus placebo. The supplements provided 30 grams (g) of soy protein and 132 mg of isoflavones a day. The phytoestrogens lowered insulin resistance and LDL (“bad”) cholesterol levels. Then, in a study of 30 postmenopausal women, patients received either 100 mg of isoflavones or 0.625 mg of conjugated estrogen a day. In this head-to-head trial, the isoflavones had comparable reductions in fasting blood sugars and insulin levels.
As well, many smaller trials show that soy proteins could help kidney function in both type 1 and 2 diabetes. Though promising, they were small.
Early evidence shows that soy may keep blood pressure levels safe. In a good-quality study in Scotland, researchers put 61 men with hypertension and/or high cholesterol levels on a diet with at least 20 g of soy and 80 mg of isoflavones or a placebo diet. It lasted five weeks. They found that blood pressure, total cholesterol. and LDL cholesterol all significantly fell — but only in the soy diet group.
In another study, 213 healthy adults (50 to 75 years old) took either soy protein isolate (40 g of soy protein, 118 mg of isoflavones) or placebo for three months. Compared to placebo, the soy group had significant reductions in blood pressure. Elsewhere, researchers did a crossover trial of isoflavone supplements from red clover (50 mg/day) versus placebo for a month in 16 type 2 diabetic patients. Blood pressure fell significantly for those on isoflavone treatment. There, are, however, at least three good studies that failed to find this link.
In both cases, larger studies are needed to evaluate the diabetes and the blood pressure connections with soy. While this is true, also in both cases, it still can’t hurt to try getting more soy in the diet. If you’re on hormone replacement therapy, check with your doctor before upping your soy intake.