Eating extra soy for one year doesn’t help postmenopausal women cut their cholesterol levels, new research shows.
The findings support the Food and Drug Administration’s 2007 move to reevaluate its decade-old decision allowing soy product makers to claim heart benefits, Dr. Sara Chelland Campbell of Florida State University in Tallahassee and her colleagues say.
When a woman stops having her period, her estrogen levels plummet, which in turn ups her total cholesterol level and her level of “bad” LDL cholesterol, while reducing her “good” HDL cholesterol levels, Campbell and her team explain in the journal Menopause.
Because soy contains estrogen-like substances called isoflavones, it has been promoted as having health benefits for women after menopause, including cutting cholesterol levels and strengthening bones.
Recent studies investigating soy and cholesterol levels in postmenopausal women have been short, or have only looked at individual soy components, the researchers note. They conducted the current study to investigate the long-term effects of soy protein in food, specifically 25 grams of soy protein and 60 milligrams of isoflavones every day for a year, in women after menopause.
They enrolled 87 postmenopausal, overweight women who were younger than 65, 62 of whom completed the study. Study participants had moderately high total cholesterol levels (236 milligrams per deciliter in the control group, 231 mg/dL in the soy group; less than 200 mg/dL is considered optimal), and were randomly assigned to eat soy products, or comparable products containing the milk protein casein, for a year. The products included a snack bar, drink mix, and cereal.
Total cholesterol and “good” HDL levels showed a small increase in the women given soy products, the researchers found, while soy had no effect on “bad” LDL cholesterol levels or triglyceride levels.
Among control group women, average total cholesterol had risen to 254 mg/dL after a year (an 18-point increase), compared to about 243 mg/dL for the soy group (a 12-point increase). HDL levels increased from 58 mg/dL to 63 mg/dL in the control group, and from 57 mg/dL to 60 mg/dL in the soy group.
Having HDL levels below 50 mg/dL is a “major risk factor for heart disease” in women, according to the American Heart Association (AHA), while 60 mg/dL is believed to help protect the heart.
Since 1999, Campbell and her colleagues note, the FDA has allowed soy product labeling to claim that diets low in saturated fat and cholesterol, along with 25 grams of soy protein daily, “may reduce the risk of heart disease.”
Other recent studies have called this benefit into question, the researchers add, and the AHA in 2000 changed its position to say that the benefit of soy protein or isoflavones is “minimal at best.”
They conclude: “Our results support the large body of literature showing no favorable alterations in the lipid profile as a result of the incorporation of 25 g/day of soy protein in the diet.”
SOURCE: Menopause, online March 3, 2010.