Soy can cause some mild stomach and intestinal side effects such as constipation, bloating, and nausea. It can also cause allergic reactions involving rash, itching, and anaphylaxis in some people. Some people might experience tiredness. Soy might also affect thyroid function. However, this seems to occur primarily in people who are iodine deficient.
Reuters Health) - Plant-derived estrogens, such as those from soy and red clover, might contribute to unwanted weight gain in some postmenopausal women, according to a new review of previous clinical trials.
Known as phytoestrogens, these natural compounds mimic the effects of estrogen in the body. Women entering menopause have a sharp drop in estrogen levels that can lead to hot flashes, night sweats and other unpleasant symptoms.
While hormone replacement therapy remains the most effective treatment for these symptoms, many women choose to take phytoestrogens instead, said lead author Dr. Marija Glisic of University Medical Center Rotterdam in the Netherlands.
“Currently, the European Menopause and Andropause Society suggests non-hormonal treatment as a realistic option in women who do not wish to take hormonal therapy or in whom hormonal therapy is contraindicated,” Glisic said in an email.
However, it remains unclear whether phytoestrogens help or hurt with regard to the weight gain and other body changes that typically accompany menopause, the study team writes in Maturitas.
To investigate, Glisic and her colleagues reviewed 23 randomized controlled trials involving a total of 1,880 postmenopausal women. All the trials compared women assigned to take phytoestrogens or a placebo, who were at least four years past menopause, and who were consuming a regular diet, not seeking to lose weight. Trials took place in Asia, Europe and North and South America.
Overall, Glisic’s team found no associations between taking phytoestrogen supplements and weight gain or loss, or any other changes in measurements of body composition like waist-to-hip ratio. When they looked at certain subgroups of women, however, there were some slight but statistically meaningful differences.
Thus, collectively the findings provide little evidence that in euthyroid, iodine-replete individuals, soy foods, or isoflavones adversely affect thyroid function. In contrast, some evidence suggests that soy foods, by inhibiting absorption, may increase the dose of thyroid hormone required by hypothyroid patients. However, hypothyroid adults need not avoid soy foods. In addition, there remains a theoretical concern based on in vitro and animal data that in individuals with compromised thyroid function and/or whose iodine intake is marginal soy foods may increase risk of developing clinical hypothyroidism. Therefore, it is important for soy food consumers to make sure their intake of iodine is adequate.
So where did the idea come from that soy increases breast cancer risk? Isoflavones, which are found in soy, are plant estrogens. High levels of estrogen have been linked to an increased risk of breast cancer. However, food sources of soy don't contain high enough levels of isoflavones to increase the risk of breast cancer.
Soy or isoflavone supplements, on the other hand, generally contain higher levels of isoflavones. Some studies have suggested a link between soy or isoflavone supplements and an increased risk of breast cancer in women who have a family or personal history of breast cancer or thyroid problems.
Soy isoflavone supplementation could reduce body weight and improve glucose metabolism in non-Asian postmenopausal women--a meta-analysis.
Typically, supplements provide 25–100 mg total isoflavones if consumed according to package directions . Yet, due to the increasing variety of soy foods in the marketplace, consumers can easily consume 100 mg or more of total isoflavones each day from the diet alone.
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