Plant-Based Diet Cut Hot Flashes 78%: WAVS Study

Kate Johnson

October 27, 2022

Women eating a reduced-fat vegan diet combined with a daily serving of soybeans experienced a 78% reduction in frequency of menopausal hot flashes over 12 weeks, in a small, nonblinded, randomized-controlled trial.

"We do not fully understand yet why this combination works, but it seems that these three elements are key: avoiding animal products, reducing fat, and adding a serving of soybeans," lead researcher Neal Barnard, MD, explained in a press release. "These new results suggest that a diet change should be considered as a first-line treatment for troublesome vasomotor symptoms, including night sweats and hot flashes," added Barnard, who is president of the Physicians Committee for Responsible Medicine, and adjunct professor at George Washington University, Washington.

But, while "the findings from this very small study complement everything we know about the benefits of an excellent diet and the health benefits of soy," they should be interpreted with some caution, commented Susan Reed, MD, president of the North American Menopause Society, and associate program director of the women's reproductive research program at the University of Washington, Seattle.

For the trial, called WAVS (Women's Study for the Alleviation of Vasomotor Symptoms), the researchers randomized 84 postmenopausal women with at least two moderate to severe hot flashes daily to either the intervention or usual diet, with a total of 71 subjects completing the 12-week study, published in Menopause. Criteria for exclusion included any cause of vasomotor symptoms other than natural menopause, current use of a low-fat, vegan diet that includes daily soy products, soy allergy, and body mass index < 18.5 kg/m2.

Participants in the intervention group were asked to avoid animal-derived foods, minimize their use of oils and fatty foods such as nuts and avocados, and include half a cup (86 g) of cooked soybeans daily in their diets. They were also offered 1-hour virtual group meetings each week, in which a registered dietitian or research staff provided information on food preparation and managing common dietary challenges.

Control group participants were asked to continue their usual diets and attend four 1-hour group sessions.

At baseline and then after the 12-week study period, dietary intake was self-recorded for 2 weekdays and 1 weekend day, hot flash frequency and severity was recorded for 1 week using a mobile app, and the effect of menopausal symptoms on quality of life was measured using the vasomotor, psychosocial, physical, and sexual domains of the Menopause-Specific Quality of Life (MENQOL) questionnaire.

Equol production was also assessed in a subset of 15 intervention and 12 control participants who had urinary isoflavone concentrations measured after eating half a cup (86 g) of soybeans twice daily for 3 days. This was based on the theory that diets such as the intervention in this study "seem to foster the growth of gut bacteria capable of converting daidzein to equol," noted the authors. The ability to produce equol is detected more frequently in individuals following vegetarian diets than in omnivores and … has been proposed as a factor in soy's apparent health benefits."

The study found that total hot flash frequency decreased by 78% in the intervention group (P < .001) and 39% (P < .001) in the control group (between-group P = .003), and moderate to severe hot flashes decreased by 88% versus 34%, respectively (from 5.0 to 0.6 per day, P < .001 vs. from 4.4 to 2.9 per day, P < .001; between-group P < .001). Among participants with at least seven moderate to severe hot flashes per day at baseline, moderate to severe hot flashes decreased by 93% (from 10.6 to 0.7 per day) in the intervention group (P < .001) and 36% (from 9.0 to 5.8 per day) in the control group (P = .01, between-group P < .001). The changes in hot flashes were paralleled by changes in the MENQOL findings, with significant between-group differences in the vasomotor (P = 0.004), physical (P = 0.01), and sexual (P = 0.03) domains.

Changes in frequency of severe hot flashes correlated directly with changes in fat intake, and inversely with changes in carbohydrate and fiber intake, such that "the greater the reduction in fat intake and the greater the increases in carbohydrate and fiber consumption, the greater the reduction in severe hot flashes," noted the researchers. Mean body weight also decreased by 3.6 kg in the intervention group and 0.2 kg in the control group (P < .001). "Equol-production status had no apparent effect on hot flashes," they added.

The study is the second phase of WAVS, which comprises two parts, the first of which showed similar results, but was conducted in the fall, raising questions about whether cooler temperatures were partly responsible for the results. Phase 2 of WAVS enrolled participants in the spring "ruling out the effect of outside temperature," noted the authors.

"Eating a healthy diet at midlife is so important for long-term health and a sense of well-being for peri- and postmenopausal women," said Dr Reed, but she urged caution in interpreting the findings. "This was an unblinded study," she told this news organization. "Women were recruited to this study anticipating that they would be in a study on a soy diet. Individuals who sign up for a study are hoping for benefit from the intervention. The controls who don't get the soy diet are often disappointed, so there is no benefit from a nonblinded control arm for their hot flashes. And that is exactly what we saw here. Blinded studies can hide what you are getting, so everyone in the study (intervention and controls) has the same anticipated benefit. But you cannot blind a soy diet."

Reed also noted that, while the biologic mechanism of benefit should be equol production, this was not shown – given that both equol producers and nonproducers in the soy intervention reported marked symptom reduction.

"Only prior studies with estrogen interventions have observed reductions of hot flashes of the amount reported here," she concluded. "Hopefully future large studies will clarify the role of soy diet for decreasing hot flashes."

Barnard writes books and articles and gives lectures related to nutrition and health and has received royalties and honoraria from these sources. Reed has no relevant disclosures.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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