How does soy improve the symptoms of menopause?

Soy decreases hot flushes

Dr. Alice Murkies and colleagues3 from Brighton Medical Clinic in Australia compared the effects of supplementation with soy flour versus wheat flour on the number of hot flushes experienced in a group of post-menopausal women. The number of hot flushes experienced by the women receiving soy flour decreased significantly within 6 weeks. After 12 weeks, the number of hot flushes had significantly decreased by 45% in the women receiving soy flour and by 25% in the women receiving wheat flour.

The effects of a standard diet compared to a phytoestrogen-rich diet on menopausal symptoms was examined by Dr. Amnon Brzezinski at the Hedassah Medical Centre in Israel ⁴ . One quarter of the total daily calorie intake was replaced with phytoestrogen-rich foods (including tofu, soy drink, tempeh and flaxseed). The women consuming both the standard diet and phytoestrogen-rich diet experienced an improvement in their total scores of menopausal symptoms. However, the women consuming the phytoestrogen-rich diet experienced a 55% reduction in the number of hot flushes compared to the women on the standard diet, where the number of hot flushes were significantly decreased by 35%.

Dr. Paola Albertazzi and colleagues ⁵ at the University of Ferrara in Italy reported that symptomatic women (experiencing over seven hot flushes per day) consuming 40 grams per day of soy protein with its naturally occurring isoflavones had significantly fewer hot flushes than those consuming the non-soy (casein ¨C milk protein) control. The number of hot flushes decreased significantly after two weeks on soy treatment. By 12 weeks of treatment, the number of hot flushes had decreased by 45% with soy treatment compared to the start of the study. The women receiving the non-soy control also experienced a significant 30% decrease in the number of hot flushes after 12 weeks reflecting that a strong placebo effect exists with hot flushes, and many tend to go away with time anyway.

In a randomized, crossover trial with healthy postmenopausal women, the effect on hot flushes of a therapeutic lifestyle changes (TLC) diet was tested over eight weeks and compared with the same TLC diet but to which a half cup of soy nuts (roasted whole soybeans) was added, spread over 3-4 occasions during the day. Of note, the TLC diet was a very healthy diet, based on the recommendations by the US Adult Treatment Panel of the National Cholesterol Education Program to lower risk of coronary heart disease. The arm that included soy nuts, adjusted the protein content of their diet accordingly to compensate for the additional 25 grams of protein provided by the soy. The women were also asked to walk for 30 minutes daily, if they were not already adequately active, since exercise is also thought to provide some efficacy for alleviating hot flushes. Compared to the TLC diet alone, the researchers from the Beth Israel Deaconess Medical Center in Boston, Massachusetts, found that the TLC diet plus soy nuts resulted in a 45 % decrease in hot flushes in those women who experienced 4.5 flushes per day or more at the start of the study, and a 41 % reduction in those with a lower number of daily flushes to start of with ⁶ . In addition, when this whole soy food was consumed, there was a significant improvement in various scores measuring quality of life during the menopause. Surprisingly, the amount of exercise had no effect on hot flush reduction. As the study was not 'blinded' (meaning it did not include a control group), the improvement might have been due to a placebo effect. However, even if this were the case, the almost 50 % reduction in hot flushes due to a lifestyle intervention was beneficial to the women.

Dr. Scott Washburn and colleagues ⁷ from Wake Forest University, USA, compared the effects on various menopause symptoms, of consuming a carbohydrate control or 20 grams of soy protein with isoflavones in one daily dose or 20 grams of soy protein with isoflavones split into two daily doses. No differences were observed in the number of hot flushes experienced by the women in either group. However, the researchers observed a significant reduction in the severity of hot flushes in women consuming 20 grams of soy protein with isoflavones in two split doses, compared with women receiving the carbohydrate control and the soy protein in one dose.

It is well known that estrogen replacement therapy is much more powerful, reducing hot flushes by around 77 %, but many women these days are choosing not to undergo hormone therapy. Despite their less potent effects, soy foods may offer some alternative to a drug approach, to ease the symptoms of the menopause.

Soy may improve vaginal dryness

In the study by Dr. Brzezinski ⁴ discussed above, the women who consumed the phytoestrogen rich diet experienced a more significant reduction in the level of vaginal dryness compared to the women consuming the standard diet.

In an Australian study, Dr. Fabian Dalais and colleagues ⁸ at the Monash Medical Centre in Victoria compared the effects of a soy (as soy grits, providing 52mg of isoflavones per day), linseed or wheat diet on various symptoms of menopause. Women consuming the linseed and wheat, but not the soy experienced significant reductions in the number of hot flushes (41% with linseed and 51% with wheat) compared to baseline. However, only the women consuming soy showed a significant improvement in the measure of vaginal cytology. This suggests that the isoflavones in the soy had effects similar to oestrogen, in stimulating the increase of cells that are capable of producing mucus to lubricate the vagina.

Not all studies on soy, soy extracts or isoflavones derived from the soybean or red clover however, found significant benefits for the menopause. Some have reported neutral findings ⁹ ^, ¹⁰ ^, ¹¹ . It has been suggested that the conflicting results in this area of research may be attributed to the great compositional differences of the soy products used (products were not manufactured in a standardized way), the length of the studies and the study designs ¹² .