Is soy a safe alternative to HRT?

11th June 2018

By Diana Chiu

Most women who are going through menopause will have experienced some of the annoying (or, occasionally, debilitating) side effects that come with it. These unpleasant side effects, which can include hot flushes, mood swings, and vaginal dryness, are due to low levels of oestrogen.

A common treatment prescribed for the management of menopausal symptoms is hormone replacement therapy (HRT). This is normally oestrogen alone or combined with another hormone, progestin, given in the form of patches or as tablets.

However, HRT is not suitable for everyone. Women who have a history of breast cancer, heart disease, previous blood clots, stroke, active liver disease, or high risk of endometrial cancer should not have HRT.1 This is because HRT is associated with a higher risk of causing these conditions, or making them worse. As a result, some high risk women may want to consider alternative treatments for managing their symptoms.

Why soy?

Soy contains isoflavones, which are plant-based compounds containing a weak plant oestrogen called phytoestrogen. These phytoestrogens bind to oestrogen receptors in the body and work like a weak form of oestrogen. Many people, therefore, believe that eating soy, and in doing so taking in more phytoestrogen, will provide the same effects as HRT in helping menopausal symptoms.


Everyone absorbs a variable amount of isoflavone from the same soy product, which means the effects of the soy consumed may be different in different women.

But not all soy protein contains the same amount of isoflavone. Depending on how the food is processed, soy protein can contain almost no isoflavone to a few milligrams.2 The structure of the isoflavone is also important because, in its natural form, isoflavone is attached to a sugar molecule which must be removed before it can be absorbed by the gut.

The removal of this sugar molecule is done by intestinal enzymes which vary in quantity between different people. Therefore everyone absorbs a variable amount of isoflavone from the same soy product, which means the effects of the soy consumed may be different in different women.

If you want to increase isoflavone intake it is important to check food labels to see how much isoflavone each product contains. Examples of foods that contain soy include miso soup, tofu, soy milk, and edamame.

Does soy actually help control menopause symptoms?

There haven’t been many studies done to test whether increasing consumption of soy leads to definite health benefits, and the results of the ones that have been done are generally conflicting. At present it is not entirely clear whether soy is a good alternative to HRT or not, in terms of reduction of menopause symptoms.

In one large study of 1106 premenopausal Japanese women it was found that women who consumed more soy and had a higher isoflavone intake experienced fewer hot flushes.3 But in another study of 87 menopausal women who were given one muffin a day containing soy, it was found that there was no difference in frequency or severity of hot flushes between them and women who didn’t consume extra soy.4

Women who have hot flushes and take HRT, however, seems to have improved quality of life.5 There are no studies that compare soy to HRT in how well they treat hot flushes, so we do not know which is more effective.


Some human studies suggest eating too much soy (more than 100 mg soy isoflavones a day) leads to reduced ovarian function, with lower circulating sex hormones.10 In general, diets containing 1-2 servings of soy a day are considered safe.

In another trial of 25 postmenopausal women who supplemented their diet with soy flour, linseed or red clover sprouts, it was found that there was more vaginal hormonal release with soy flour compared to the latter two foodstuffs.6 This suggests that soy may help with menopause-related vaginal dryness. However, this was a very small study, so more research needs to be done.

Is taking soy safe?

In general, soy is well tolerated in most women. Some women may experience minor stomach cramps and bloating because of the starches in the soy products, however. Studies are conflicting about the harmful effects of consuming soy in large quantities. There are animal studies that suggest excessive soy can affect fertility, embryo development, and cause early puberty.8,9

Some human studies suggest eating too much soy (more than 100 mg soy isoflavones a day) leads to reduced ovarian function, with lower circulating sex hormones.10 In general, diets containing 1-2 servings of soy a day are considered safe.

Is soy more beneficial than HRT?

As the effects of soy are variable between different people, it isn’t possible to say whether or not it is better or more effective than HRT for each individual. In general, the effects of soy are deemed weaker than those of HRT, because soy contains weaker oestrogen. Whether or not you personally find soy beneficial, there is no harm in taking it, in moderation, as part of a healthy balanced diet.

If soy does not help with your menopausal symptoms and you are able to take HRT, it may be worthwhile trying HRT. There is less evidence for soy’s benefits compared with HRT for certain menopausal symptoms, which may mean you are at a higher risk of some side effects if soy is your sole alternative to HRT.

For example, the evidence for soy’s use in preventing osteoporosis is limited, and it is still unclear whether or not it is helpful in preventing bone thinning.11 There is good evidence, however, that HRT helps reducing hip fractures,12 so a danger of substituting soy for HRT is that it could potentially leave you are higher risk of bone thinning.

If HRT is not a suitable option, there are other therapies available, and soy is not the only alternative. Lifestyle measures such as taking regular exercise, maintaining a balanced diet, cutting down on spicy foods, alcohol, and coffee, stopping smoking, and reducing stress levels may help with mood.

Vaginal lubricants or moisturisers can help with vaginal dryness, and prescription medications such as tibolone and clonidine may help with symptoms of hot flushes. Finally, antidepressants may be helpful if you are experiencing low mood and are unable to take HRT. It is worth discussing your options with your GP and they will be able to help you decide which treatment is best for you.

Featured image show two women in a kitchen pouring a pot of yoghurt or milk into a blender full of fruit. The image is cropped so you can only see their torsos.

References

  1. E.M. Kupferer et al., ‘Complementary and alternative medicine use for vasomotor symptoms among women who have discontinued hormone therapy’, J Obstet Gynecol Neonatal Nurs, Vol. 38, No. 1, 2009, pp. 50–9.
  2. S. Bhagwat et al., USDA Database for the Isoflavone Content of Selected Foods, U.S Department of Agriculture, [website], 2008, http://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/isoflav/Isoflav_R2.pdf, (accessed 8 June 2018).
  3. C. Nagata et al., ‘Soy product intake and hot flashes in Japanese women: results from a community-based prospective study’, Am J Epidemiol, Vol. 153, No. 8, 2001, pp. 790–3.
  4. J. E. Lewis et al., ‘A randomized controlled trial of the effect of dietary soy and flaxseed muffins on quality of life and hot flashes during menopause’, Menopause, Vol. 13, No. 4, 2006, pp. 631–42.
  5. A. Maclennan et al., ‘Oral estrogen replacement therapy versus placebo for hot flushes: a systematic review’, Climacteric, Vol. 4, No. 1, 2001, p. 58.
  6. N. F. Col et al., ‘Short-term menopausal hormone therapy for symptom relief: an updated decision model’, Arch Intern Med, Vol. 164, No. 15, 2004, p. 1634.
  7. G. Wilcox et al., ‘Oestrogenic effects of plant foods in postmenopausal women’, BMJ, Vol. 301, No. 6757, 2000, pp. 905–6.
  8. H. W. Bennetts and E.J. Underwood, ‘The oestrogenic effects of subterranean clover (trifolium subterraneum); uterine maintenance in the ovariectomised ewe on clover grazing’, Aust J Exp Biol Med Sci, Vol. 29, No. 4, 1951, pp. 249–53.
  9. H. Hearnshaw et al., ‘Endocrinological and histopathological aspects of the infertility in the ewe caused by oestrogenic clover’, J Reprod Fertil., Vol. 28, 1972, pp. 160–1.
  10. W. N. Jefferson, ‘Adult ovarian function can be affected by high levels of soy’, Journal of nutrition, Vol. 140, No. 12, 2010, pp. 2322S-2325S.
  11. A. J. Lanou, ‘Soy foods: are they useful for optimal bone health?’ Ther Adv Musculoskelet Dis, Vol. 3, No. 6, 2011, pp. 293-300.
  12. J. E. Rossouw et al., ‘Risks and benefits of estrogen and progestin in healthy postmenopausal women: principal results from the Women’s Health Initiative randomized controlled trial’, JAMA, Vol. 288, No. 3, 2002, p. 321.
TwitterFacebook

Dr. Diana Chiu
MBChB (Hons), MRCP, PGCERT (Med Ed), PhD

Diana received her medical degree, with honours, from the University of Manchester. She then went on to receive basic and specialist medical training within the north west of England. She carried out in-depth research in medicine and was awarded a PhD in 2016. Currently, she is finishing her medical training at a large teaching hospital, and one of her greatest interests is medical education. She is an advanced life support instructor and writes regularly for post-graduate examination websites, and also holds a PGCERT in medical education with distinction.