Soy: The Way to a Woman's Heart Is through the Stomach

BOSTON, May 29 -- Substituting soy into an otherwise healthy diet may be cardioprotective for postmenopausal women, researchers found.

In a prospective trial, replacing 25 grams of protein with half a cup of soy nuts (dry-roasted soybeans) lowered systolic blood pressure 9.9% and diastolic 6.8% in hypertensive women, said Francine K. Welty, M.D., Ph.D., of Beth Israel Deaconess Medical Center here, and colleagues.

It also dropped low-density lipoprotein cholesterol by 11% and apolipoprotein B by 8%, they reported in the May 28 issue of Archives of Internal Medicine.

While the dietary intervention lasted only eight weeks, long-term intake would likely have substantial benefits, they wrote.

"A 12-mm of mercury decrease in systolic blood pressure for 10 years has been estimated to prevent one death for every 11 patients with stage one hypertension treated," they said.

"Therefore, the average reduction of 15-mm Hg in systolic blood pressure in hypertensive women in the present study could have significant implications for reducing cardiovascular risk and death on a population basis," they continued.

In the randomized crossover study, 60 healthy postmenopausal women-12 of whom were hypertensive-were put on the Therapeutic Lifestyle Changes diet recommended by the Adult Treatment Panel of the National Cholesterol Education Program for lowering heart disease risk.

The diet consists of 30% of energy from total fat (7% or less from saturated fat), 15% from protein, and 55% from carbohydrate with less than 200 mg of cholesterol per day, 1200 mg of calcium, and two meals of fatty fish per week.

During one of two eight-week periods, participants substituted one-half cup of soy nuts a day for 25 g of protein from other sources. The soy nut serving contained 25 g of soy protein and 101 mg of aglycone isoflavones.

Participants could not use lipid-lowering drugs, hormone therapy, osteoporosis medications, or soy products during or in the two months prior to the study.

Among the findings for soy nut supplementation compared with the diet alone, the researchers reported:

• 9.9% lower systolic blood pressure among hypertensive women (137 versus 152 mm Hg, P=0.003).
• 5.2% lower systolic blood pressure among normotensive women (110 versus 116 mm Hg, P<0.001).
• 6.8% lower diastolic blood pressure among hypertensive women (82 versus 88 mm Hg, P=0.001).
• 2.9% lower diastolic blood pressure among normotensive women (67 versus 69 mm Hg, P=0.02)
• 11% lower LDL cholesterol among hypertensive women (146 versus 164 mg/dL, P=0.04) but no effect for normotensive subjects.
• 8% lower apolipoprotein B among hypertensive women (116 versus 126 mg/dL, P=0.04) but no effect for normotensive subjects.

Together, the results "are comparable with those seen with antihypertensive drugs" and suggest important health benefits, Dr. Welty said.

Even the modest diastolic blood pressure reductions are likely to reduce cardiovascular risk, they noted.

In one previous study, a 2-mm Hg reduction similar to that found in Dr. Welty's study yielded a 6% reduction in coronary heart disease and a 15% reduction in stroke.

Exercise and weight loss did not appear to account for the effects since neither differed between diet periods, Dr. Welty said. However, total and saturated fat of the soy diet were significantly lower than in the control diet.

The difference was likely caused by the increased isoflavone content of the soy diet, the researchers noted. But since previous studies have shown that isoflavone supplements by themselves have no effect on blood pressure, whole soy may be the key, they added.

The researchers said the findings are likely to be generalizable to postmenopausal women in clinical practice because the study had women follow the diet at home with instruction from a dietician only initially.

"Therefore, dietary soy may be a practical, safe, and inexpensive modality to reduce blood pressure," they concluded. "If the findings are repeated in a larger group they may have important implications for reducing cardiovascular risk in postmenopausal women on a population basis."