Two new studies highlight the potential of soy to reduce hot flashes, although both suffer from design limitations.
In many respects, the potential alleviation of menopausal hot flashes by consuming soy is the benefit — more than any other — that first caused a lot of women to take a look at soy. Talk about this benefit, along with the claim that soyfoods may prevent breast cancer, arose at about the same time – the early 1990s.1-3 From a public health perspective, breast cancer prevention is the bigger story. But the idea that soyfoods could quickly improve the quality of life for those suffering from hot flashes certainly resonated with a lot of women.
In 1992, Herman Adlercreutz and colleagues first proposed that soyfoods alleviate hot flashes.3 Dr. Adlercreutz was a true pioneering researcher in the soy and isoflavone field. Three years later, the first clinical trial evaluating the efficacy of soy was published. So, it is fair to say the impact of soy on hot flashes has been studied for three decades. As the two studies discussed below show, this relationship continues to be investigated.
In a study published in the journal Menopause, researchers from the Physician’s Committee for Responsible Medicine (PCRM) examined the effect of a low-fat vegan diet that included ½ cup cooked soybeans daily on hot flash alleviation.4 The results were quite striking, although there is an important caveat about the study design. Total hot flash frequency decreased by 79% in the vegan diet group and by 49% in the control group, which was instructed to continue to consume their usual diet. Furthermore, there was an 84% reduction in moderate/severe hot flashes in the vegan group versus only a 42% decrease the control group. For both comparisons, the results were statistically significant.
The soybeans consumed by the study participants contained approximately 55-60mg isoflavones. That is the amount shown to lower hot flashes in a meta-analysis published nearly a decade ago.5 However, the design of this PCRM study prevents the results from being attributed to any specific component of the experimental diet. More troublesome, is that because hot flashes are subjectively determined, that is, the women record the number of hot flashes they experience, it is crucial that study participants are blinded to whether they are in the control or active group.
Not only did the participants know they were consuming a low-fat vegan diet, something that was pretty much unavoidable, but the women in the control group knew they were not in the active group. Therefore, while the study results are consistent with the literature, they are only suggestive. The researchers could have at least partially addressed the design limitations by having the control group consume ½ cup of cooked non-soy legumes daily.
In the other study, short-term intake of a botanical combination improved the global quality of life of Spanish menopausal women, according to the Cervantes Scale.6 The Cervantes Scale is a specific health-related quality of life questionnaire that was originally developed in Spanish to be used in Spain for women through and beyond menopause. In this 8-week study, women were randomly allocated to either the placebo group or a group receiving a combination of soybean isoflavones (~40mg/day) and seed extracts of Aframomum melegueta and Punica granatum.
In contrast to the PCRM study, participants were unaware as to whether they were in the active or control group. But again, because isoflavones were combined with other bioactive ingredients, it is not possible to specifically attribute the benefits to these soybean components. Having said that, it is notable that in their discussion of Aframomum melegueta and Punica granatum, the study authors did not cite one clinical study demonstrating the efficacy of either botanical for alleviating hot flashes.
In conclusion, two newly published studies involving isoflavones report improvements in menopausal symptoms and quality of life. Although the results of both are consistent with the existing literature, which attests to the efficacy of isoflavones, design issues limit the informative value of this new research.
- Messina M, Barnes S. The role of soy products in reducing risk of cancer. J Natl Cancer Inst. 1991;83:541-6.
- Messina M, Messina V. Increasing use of soyfoods and their potential role in cancer prevention. J Am Diet Assoc. 1991;91:836-40.
- Adlercreutz H, Hamalainen E, Gorbach S, et al. Dietary phyto-oestrogens and the menopause in Japan. Lancet. 1992;339:1233.
- Barnard ND, Kahleova H, Holtz DN, et al. The Women’s Study for the Alleviation of Vasomotor Symptoms (WAVS): a randomized, controlled trial of a plant-based diet and whole soybeans for postmenopausal women. Menopause. 2021.
- Taku K, Melby MK, Kronenberg F, et al. Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials. Menopause. 2012;19:776-90.
- Lopez-Rios L, Barber MA, Wiebe J, et al. Influence of a new botanical combination on quality of life in menopausal Spanish women: Results of a randomized, placebo-controlled pilot study. PloS one. 2021;16:e0255015.
This blog sponsored by the Soy Nutrition Institute and the United Soybean Board.