Hot flashes, the most common menopause-related symptom, cause many women to seek foods and supplements touted to offer relief despite flimsy evidence.
Now, according to the most comprehensive study to date, eating two servings of soy foods a day may help reduce the frequency and severity of hot flashes.
Experienced by up to 85 per cent of women going through menopause, hot flashes are thought to be triggered by changes in the hypothalamus, the part of the brain that regulates body temperature.
The result is an intense feeling of heat in the face and chest often accompanied by flushing (redness of skin) and sweating. Hot flashes last 30 seconds to a few minutes and can persist for weeks, months, even years.
While diet doesn’t cause hot flashes, it can set them off. Alcohol, caffeine, hot beverages and spicy foods are known triggers for many women.
So, too, is carrying excess body fat. Women who have a body mass index (BMI) greater than 30 are more than twice as likely to have moderate to severe hot flashes than women whose BMI is less than 25.
BMI is calculated by dividing a person’s weight (in kilograms) by height squared (in metres). A BMI value from 18.5 to 24.9 is defined as normal weight; a BMI of 30 or greater is considered obese.
The interest in soy for hot flashes began when researchers noticed only about 10 per cent of Asian women experience menopausal symptoms. It’s been speculated that Asian women are less likely to have hot flashes due to their high soy consumption.
Soy protein contains isoflavones, natural compounds that can bind weakly to certain estrogen receptors in the body.In so doing, soy isoflavones might help compensate for declining estrogen levels that accompany menopause and offer some relief for hot flashes.
Until now, the evidence for soy has been inconclusive, with some studies showing benefit and others finding no effect.
The current report, published online in Menopause: The Journal of the North American Menopause Association, reviewed 19 randomized controlled trials that enrolled more than 1,200 women taking soy isoflavone extracts (not soy foods) or placebos.
When all studies were combined, there was a clear and consistent positive effect for isoflavones. Compared to taking placebos, consuming at least 54 milligrams daily for six weeks to a year reduced hot flash frequency by 20 per cent and the severity by 26 per cent.
Women who took isoflavones for at least 12 weeks experienced a threefold greater reduction in hot flashes than women who consumed isoflavones for a shorter duration.
Isoflavone supplements with higher levels of genistein – one of the two main types of isoflavones in soybeans – were the most effective at easing hot flashes.
Genistein is the primary isoflavone found in soy foods as well as soybeans, suggesting that adding soy to your diet, or using supplements made from whole soybeans, may work better than synthetic isoflavone supplements.
The fact that isoflavones act like a weak form of estrogen in the body concerns some women, particularly those at high risk for breast cancer. That’s because certain risk factors for breast cancer are related to the length of time breast cells are exposed to the body’s own circulating estrogen. It’s thought that estrogen can promote the growth of breast cancer cells.
However, studies suggest that consuming soy reduces breast cancer risk in Asian populations. In Western women, soy has not been shown to increase or decrease risk. (Western women may not consume enough soy isoflavones to lower breast cancer risk.) Recent studies have also linked a higher intake of soy foods such as tofu, soy beverages and soy flour with a lower risk of breast cancer recurrence.
Soybeans are worth adding to your diet even if you don’t have hot flashes. They’re high in protein, low in saturated fat and offer fibre, omega-3 fatty acids, vitamins, minerals and antioxidants.
Leslie Beck, a Toronto-based dietitian, is the national director of nutrition for Body Science Centers, medical clinics focusing on healthy aging (www.BSC5.com).