Can Soy and a Low-Fat, Vegan Diet Really Stop Hot Flashes?

Pretty big claim, but how does it hold up?

Drs Producoes/Getty Images

A low-fat, vegan diet + half a cup of soybeans a day = no more hot flashes? That’s the claim from a study and a follow up brief report published in the journal, Menopause. But the science is messier than the headlines, so I’m taking a closer look at the papers and how they fit in with the literature.

The original study claims that not only does a low-fat, vegan diet fortified with ½ cup of soybeans a day almost eliminate hot flashes, but that these results hold even when vegans eat highly processed plant foods. This second paper about the processed foods was published this month and is a secondary analysis of previously published data. If you don’t want the full deep dive, skip to the end section, Can a Low Fat Vegan Diet and/Or Soybeans Reduce Hot Flashes and Night Sweats? If you want the Happy Meal, buckle up.

The original paper is a randomized trial where half the participants were given a low fat, vegan diet and ½ cup of soybeans a day as well as a weekly Zoom meeting with a dietician, and the other half were not told to make any dietary changes but had weekly one hour zoom sessions to maintain engagement. Obviously, speaking with a dietician each week is different than just checking in to maintain engagement. We know support reduces how much people are bothered by hot flashes, so right away this is problematic as it can skew the results.

Unblinded interventions, like only giving one group a diet, can also change other behaviors. A low-fat vegan diet is a pretty dramatic change for most people, so it’s not unreasonable to wonder if it prompted other health-related changes that were not accounted for in the study. For example, the women in the dietary arm could have started walking more or focusing on their sleep. “Recent physical activity’ was recorded, but the methods section does not specify how often. Daily? Once a month?

The original paper also doesn’t explain how the subjects were randomized, which makes me wonder how it got through peer review, although the authors do mention in the second paper that looked at processed foods that the randomization was by computer. There is no power analysis in the original paper, which is how investigators calculate the number of people they need to complete the study to show the results are likely a true effect and not by chance. The authors state, “Because no prior study, to the investigator’s knowledge, had examined the effects of a plant-based diet with soybeans on vasomotor symptoms there was no sound basis for a power analysis.” Basically, this means it’s a pilot study. They actually published preliminary results in 2021, and this new paper includes those 34 original participants and an additional 37 new participants.

Hot flashes were measured for 1 week at the start and the end of the 12 week intervention and people also completed a standard questionnaire, at baseline and at 12 weeks, about the impact of menopause symptoms on quality of life called the MENQOL.

The results seem, well, overly spectacular – an 88% reduction in moderate-to-severe hot flashes for the intervention group versus 34% for the control group. In addition, 50% of those in the intervention had no hot flashes at all. Meaning, this dietary intervention is basically on par with menopause hormone therapy (MHT).

I’m not saying that’s impossible, but spectacular claims require spectacular evidence, and unfortunately, there are other issues. The vegan diet group lost an average of 3.6 kg over the 12 weeks and the control group lost 0.2 kg, and we know that weight loss reduces hot flashes. The sample size is not large enough to separate the intervention from the weight loss.

There are also some issues with the MENQOL scores for vasomotor symptoms. The questionnaire has three questions for vasomotor symptoms, each scored on a scale of 0 to 6, and then the result is the average of the three.

In the initial group that made it to randomization, the mean MENQOL score for hot flashes was 4.5 for the intervention group and 5.7 for the control group, which is statistically different. However, after the drop outs, those numbers were more or less reversed and the intervention group now had a baseline mean MENQOL score of 5.7 and the control group of 4.4 for vasomotor symptoms. The statistics did not take the baseline imbalance with the MENQOL for vasomotor symptoms into account and the authors did not acknowledge the difference in baseline scores in their limitations.

The intervention group went from an average of 5 moderate-to-severe hot flashes a day to 0.6 (this is the 88% reduction) and the control group from 4.4 to 2.9 (the 34% reduction). That’s a big difference and makes it look like the diet plus soybeans is really effective. And yet, at week 12, the intervention group that reported an average of 0.6 moderate-to-severe hot flashes a day the mean MENQOL score for hot flashes of 3.7, which is the exact same score as those in the control group who had an average of 2.9 moderate-to-severe hot flashes a day. It’s a little strange that a group with an average of 0.6 moderate-to-severe hot flashes a day is reporting the exact same bother score as those having 2.9 a day. This is not explained or discussed in the limitations.

After this study drove me crazy for several days, I decided to phone a friend who is an expert in nutrition, and he was not impressed.

Also, five of the study authors are members of Physicians Committee for Responsible Medicine and this group also funded the study. What I have gleaned from the website is they believe being vegan as being the only safe and ethical dietary option. This means they are invested in a specific outcome the way a pharmaceutical company might be invested in an outcome. It’s just important to note that bias up front, as we would with a Pharma study. Here’s a not scary at all screen shot from their webpage.

So…what can we say from this study? Not much. It’s a pilot study at best. The women enrolled lost weight, which is a significant confounder, and there seem to be issues with the statistics and some results that don’t make sense without further elaboration. Is there any harm in trying a low fat vegan diet with ½ cups of soybeans a day for hot flashes? No, and if this appeals to you, then go for it, but I would not say that these two papers offer anything scientifically robust about this diet. But hey, if it’s a good as they claim, show me with a large, randomized trial. I’m always willing to follow good science.

What Do Other Studies Show?

The dietary arm of the Women’s Health Initiative evaluated the impact of a low fat diet high in fruit, vegetables, and whole grains on weight loss and hot flashes/night sweats. There were 17,473 postmenopausal women aged 50–79 at baseline not taking menopausal hormone therapy in the dietary. The dietary intervention had a modest impact n hot flashes/night sweats. Controlling for weight loss, those following the intervention were 14% more likely to eliminate their symptoms than the controls, although the diet has the greatest benefit for those with mild symptoms. Women who lost 10 or more kg were more than twice as likely to eliminate moderate or severe symptoms compared to those who maintained weight within 5 kg. A weight loss of 10% or more was even more likely to be associated with eliminating moderate-to-severe hot flashes and night sweats.

Most studies for planet-based therapies or soy for hot flashes and night sweats have relatively small numbers of participants or have issues, like the study we reviewed above, so conclusions aren’t really possible. One small, double-blind study evaluated the impact of soy for women with breast cancer using a soybean beverage as the treatment and a rice beverage as placebo. I like this study because the only intervention is the soy, so no others differences in diet or in counseling. In addition, the beverage contained the phytoestrogen content of a traditional Asian diet. Those who had the soy beverage had a 30% reduction in their 24-hour hot flash score and the reduction was 40% with placebo (a difference which is not statistically significant). However, another small, randomized double-blind trial of a drink with 60 mg if isoflavones from soy versus a placebo drink saw a reduction in hot flashes, but not sweating with the drink. Another study randomized women to receive muffins made with soy (25 g of soy flour) or wheat as placebo (there was also flaxseed arm). No difference in hot flashes were seen (31 women had soy muffins and 28 the wheat placebo).

In the last Cochrane review on isoflavones and symptoms of menopause there were 13 trials that evaluated dietary isoflavones (soy flour, powder or beverages), and the conclusion was there was no good data to support a reduction in hot flashes/night sweats, but again, most studies are small and not conclusive.

I’ve not included observational studies, because they are all over the place, and of course, they are not clinical trials.

Can a Low Fat Vegan Diet and/Or Soybeans Reduce Hot Flashes and Night Sweats?

Right now we have no quality data to support this specific dietary intervention for vasomotor symptoms, but for many people this can be a very healthy diet.

Studying diets for hot flashes and night sweats is challenging for many reasons, so unless a study is really well done, firm conclusions will be challenging. It’s especially important to control for weight loss and also make the interventions as equitable as possible. For example, if one group needs to be in contact with a dietician, then both do.

A low fat vegan diet with soybeans seems to result in weight loss, and that can be beneficial for hot flashes, although data from the WHI suggests at least 10% weight loss is needed and that wasn’t achieved in this 12-week study, so hard to know how the weight loss fits in with the findings. There is no data to say losing weight with this diet offers a specific advantage for hot flashes over weight loss from other diets.

Vegetables are good for you, and in North America we eat too much saturated fat, so a vegan diet or even getting more protein from vegetable sources can benefit many people. Any heart healthy diet could theoretically have some benefit for vasomotor symptoms, because when something is good for your heart it’s often good for many other things. However, a low fat vegan diet with soybeans is not the only heart healthy diet.

The studies looking at soy for hot flashes are overall of lower quality and no conclusions are possible, but in general, it seems there is no benefit. Keep in mind these are generally pilot trials, so a larger, more robust study with longer follow up might give us different results.

I know many people have questions about soy and isoflavone supplements, so I’m going to do a couple of follow-up posts, so stay tuned.

But right now the claims from this paper about a low fat vegan diet with soybeans being a specific intervention for hot flashes are just too good to be tofu (#SorryNotSorry).

References

Kahleova H, Znayenko-Miller, Jayaraman A, et al. Processed foods in the context of a vegan diet, and changes in body weight and severe hot flashes in postmenopausal women: a secondary analysis of a randomized clinical trial. Menopause 2025; 32:000-000.

Barnard ND, Kahleova H, Holtz DN, Znayenko-Miller T, Sutton M, Holubkov R, Zhao X, Galandi S, Setchell KDR. A dietary intervention for vasomotor symptoms of menopause: a randomized, controlled trial. Menopause. 2023 Jan 1;30(1):80-87. doi: 10.1097/GME.0000000000002080. Epub 2022 Oct 16. PMID: 36253903; PMCID:

Kroenke CH, Caan BJ, Stefanick ML, Anderson G, Brzyski R, Johnson KC, LeBlanc E, Lee C, La Croix AZ, Park HL, Sims ST, Vitolins M, Wallace R. Effects of a dietary intervention and weight change on vasomotor symptoms in the Women's Health Initiative. Menopause. 2012 Sep;19(9):980-8. doi: 10.1097/gme.0b013e31824f606e. PMID: 22781782; PMCID: PMC3428489.

Franco OH, Chowdhury R, Troup J, Voortman T, Kunutsor S, Kavousi M, Oliver-Williams C, Muka T. Use of Plant-Based Therapies and Menopausal Symptoms: A Systematic Review and Meta-analysis. JAMA. 2016 Jun 21;315(23):2554-63. doi: 10.1001/jama.2016.8012. PMID: 27327802.

Lethaby A, Marjoribanks J, Kronenberg F, Roberts H, Eden J, Brown J. Phytoestrogens for menopausal vasomotor symptoms. Cochrane Database Syst Rev. 2013 Dec 10;2013(12):CD001395. doi: 10.1002/14651858.CD001395.pub4. PMID: 24323914; PMCID: PMC10247921.

Newton KM. Isoflavones hold limited promise for the treatment of menopausal vasomotor symptoms. Evid Based Med. 2014 Oct;19(5):178. doi: 10.1136/ebmed-2014-110000. Epub 2014 Jun 17. PMID: 24939922.

Lewis JE, Nickell LA, Thompson LU, Szalai JP, Kiss A, Hilditch JR. A randomized controlled trial of the effect of dietary soy and flaxseed muffins on quality of life and hot flashes during menopause. Menopause. 2006 Jul-Aug;13(4):631-42. doi: 10.1097/01.gme.0000191882.59799.67. PMID: 16837885.

Cheng G, Wilczek B, Warner M, Gustafsson JA, Landgren BM. Isoflavone treatment for acute menopausal symptoms. Menopause. 2007 May-Jun;14(3 Pt 1):468-73. doi: 10.1097/GME.0b013e31802cc7d0. PMID: 17290160.

Dorjgochoo T, Gu K, Zheng Y, Kallianpur A, Chen Z, Zheng W, Lu W, Shu XO. Soy intake in association with menopausal symptoms during the first 6 and 36 months after breast cancer diagnosis. Breast Cancer Res Treat. 2011 Dec;130(3):879-89. doi: 10.1007/s10549-010-1096-4. Epub 2010 Aug 12. Erratum in: Breast Cancer Res Treat. 2011 Dec;130(3):891-6. PMID: 20703939; PMCID: PMC3092014.