The Effect of Soy Nut Consumption on Hot Flashes in Postmenopausal Women

Half of the world’s population consists of women, and according to published statistics, nearly 90% of them reach the age of 65, meaning they spend about one-third of their lives in menopause. Menopause refers to the permanent cessation of menstruation, during which FSH levels increase (above 40 units per liter), while estrogen and progesterone hormone secretion decreases. This leads to various changes, including hot flashes, genital atrophy, osteoporosis, and cardiovascular problems in postmenopausal women.

In this article, we aim to examine the effect of soy nut consumption on hot flashes in postmenopausal women. The classic symptom caused by estrogen deficiency is hot flashes, which occur as recurrent and temporary episodes. Symptoms include:

• Flushing
• Sweating and a sensation of heat
• Heart palpitations
• Feelings of anxiety
• Sometimes accompanied by chills

This common and distressing symptom in postmenopausal women, especially at night, can cause sleep disturbances, leading to chronic fatigue, irritability, poor concentration, and memory problems. Hormone replacement therapy (HRT) has been shown to improve hot flashes in most women within a few days. However, evidence suggests that long-term HRT increases the risk of uterine and breast cancer. Additionally, acceptance of this treatment among Iranian women is low, and only a small percentage use hormone replacement therapy.

Prevalence of Hot Flash Symptoms

The prevalence of hot flashes varies across different countries. Studies report a 70–80% prevalence in postmenopausal women in Europe and North America, while in Chinese and Japanese women, it is 18% and 14%, respectively. This difference seems to be related to dietary habits, particularly the consumption of phytoestrogen-rich foods in these populations.

Research Methodology

This was a clinical trial conducted on postmenopausal women who attended healthcare centers in Yazd, Iran. Participants were selected through convenience sampling until the required sample size was achieved. Based on similar studies, the total sample size was calculated to be 30 participants, but considering possible dropouts, 35 women were initially enrolled. During the study, four participants were excluded for reasons such as gastrointestinal issues, irregular consumption, and lack of cooperation, leaving 31 women who completed the intervention.

Eligible women completed an initial questionnaire and provided blood samples for hormone measurement. They were then given soy nuts for 10 days, along with a measuring cup containing 60 grams of soy nuts (daily dose: 60 grams). Participants were instructed on how to consume them.

Inclusion and Exclusion Criteria

Inclusion criteria:

• At least 12 months since their last menstrual period
• Experiencing at least 5 hot flashes per day
• Willingness to participate in the study
• No history of soy allergy
• No hormone replacement therapy
• No unexplained vaginal bleeding
• No active liver or kidney disease
• No history of cancer or thromboembolism

Exclusion criteria:

• Vaginal bleeding
• Soy allergy development
• Unwillingness to continue the study
• Need for medication use

Measurements

Demographic variables, such as age, number of pregnancies, number of births, and age of menopause, were recorded at the beginning of the study. Participants’ weight, height, and systolic and diastolic blood pressure were measured before and after the three-month intervention.

A 5cc blood sample was taken from each participant at the beginning and end of the three months to measure estradiol, FSH, and LH hormone levels. Participants were given a form to record each hot flash episode, allowing researchers to calculate the average frequency of hot flashes per month.

Characteristics of the Soy Nuts Used

The soy nuts used in this study were prepared by Toos Soy Company, with each 100 grams containing 123 mg of isoflavones. Participants consumed 60 grams of soy nuts daily, divided into morning and afternoon snacks.

The results showed that soy nut consumption reduced the frequency of hot flashes, although the exact mechanism remains unknown.

Reasons for Estrogen Reduction

Researchers believe that estrogen reduction is related to changes in metabolism due to soy consumption rather than interactions with FSH and LH hormones. Soy intake did not affect levels of Steroid Hormone Binding Globulin, FSH, or LH.

Another hypothesis is that the isoflavones in soy affect estrogen receptors. Phytoestrogens in soy may compete with endogenous estrogen for binding to sex hormone-binding globulins. Additionally, isoflavones have antioxidant properties, and genistein, a type of isoflavone, is known to inhibit tyrosine protein kinase, which influences endothelial function and may help reduce hot flashes.

Benefits of Soy Nut Consumption

Researchers suggest that soy acts selectively on estrogen receptors and can have agonistic, antagonistic, or neutral effects. Once ingested, phytoestrogens may be excreted, absorbed, or broken down into stronger phytoestrogens. Unlike synthetic estrogens, phytoestrogens are easily metabolized, do not accumulate in tissues, and have a short duration in the body, making them a safe and beneficial dietary option when consumed as part of a normal diet.

One limitation of this study was the lack of a control group, as finding a placebo alternative for natural soy was not feasible. However, consuming natural soy nuts has advantages such as accessibility, psychological acceptance, and nutritional value.

To further clarify the effects of soy nuts, future studies should examine different doses of soy nuts to determine the minimum effective amount for hot flash control and assess its long-term safety.

Conclusion

Since hot flashes are the most common complaint during menopause and hormone replacement therapy is neither widely accepted nor risk-free, a low-cost, low-risk, and beneficial dietary intervention is desirable.

Consuming 60 grams of soy nuts daily as a nutritious and accessible snack is recommended for postmenopausal women to help manage hot flashes effectively.