When is soy bad for you

Results are conflicting, potentially due to variation in the types of soy preparations used, the quantities given, and for how long they are used. In some tissues and in some people, they may block the action of estrogen.

Studies so far have not provided a clear answer. Some have shown a benefit with soy consumption and breast cancer while others show no association. In animal and cell studies, high dosages of isoflavone or isolated soy protein extracts tend to stimulate breast cancer growth. Women from Asian countries appear to receive greater protective benefit from breast cancer with high soy intakes than American and European women, but this may simply be a difference in the amount of soy consumed.

The Breast Cancer Family Registry was a prospective study following 6, women diagnosed with breast cancer and living in the U. Another prospective study followed 1, American women who were breast cancer survivors for six years.

The incidence of prostate cancer is highest in Western countries and lowest in Asian countries, where soy foods are a regular part of the daily diet.

In addition, observational studies have found an increased risk of prostate cancer in Chinese and Japanese men who move to Western countries and adopt a Western diet, but not in those who continue eating a traditional diet. In a meta-analysis of 30 case-control and cohort studies from the U.

A review of eight randomized controlled trials examined the effects of soy in men with or at risk of developing prostate cancer. Two of these studies found that isoflavone supplements or dietary soy protein reduced the risk of prostate cancer in men at high risk of developing the disease.

However, none of the studies found a significant effect on prostate specific antigen PSA levels. PSA is a protein produced by the prostate gland that is used to detect prostate cancer. There were no adverse effects reported with soy supplementation. The authors discussed limitations of the review including the small number of participants, the short duration of studies less than one year , and variation in dosages and types of soy given.

Menopause has been linked with changes in mood and memory impairment. Thus, research has raised the possibility that eating soy foods might help prevent age-related memory loss or decline in thinking skills.

Trials have yielded contradictory results, with some showing a benefit with soy isoflavone supplementation [28, 29] and others showing no benefit. However the results overall were mixed, with other studies not demonstrating a benefit. This may have been due to differing dosages given or the types of cognition tests used.

One large study in men found a detrimental effect on cognitive function. In a prospective cohort study of more than 3, Japanese-American men living in Hawaii, the highest intakes of tofu eaten almost daily at midlife ages were significantly associated with greater cognitive impairment and brain atrophy in late life compared with men with the lowest tofu intakes almost never eaten.

Because of this, the researchers stated that the findings were too preliminary to make recommendations. Soy may interfere with thyroid hormone medication used to treat hypothyroidism. In one randomized double-blinded trial, 60 patients with a mild form of hypothyroidism called subclinical hypothyroidism were given low or high-dose phytoestrogen supplements both also contained 30 grams of soy protein , the amount that might be obtained from a vegetarian diet.

The authors suggested that female vegetarian patients with subclinical hypothyroidism may need more careful monitoring of thyroid function. However, the authors also found a benefit on of reduced cardiovascular risk factors in the high phytoestrogen group, with a significant reduction in insulin resistance, inflammatory markers, and blood pressure.

The effect of soy on thyroid function needs further examination. The contents of this website are for educational purposes and are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. The Nutrition Source does not recommend or endorse any products.

Skip to content The Nutrition Source. Harvard T. The Nutrition Source Menu. Search for:. The Takeaway: Soy is a unique food that is widely studied for its estrogenic and anti-estrogenic effects on the body. Studies may seem to present conflicting conclusions about soy, but this is largely due to the wide variation in how soy is studied. Results of recent population studies suggest that soy has either a beneficial or neutral effect on various health conditions.

Soy is a nutrient-dense source of protein that can safely be consumed several times a week, and is likely to provide health benefits—especially when eaten as an alternative to red and processed meat. Heart Disease Soy protein took center stage after research showed that it might lower levels of harmful cholesterol.

Hot Flashes Hormone replacement therapy has traditionally been used as an effective treatment for hot flashes and other unpleasant symptoms that accompany menopause, but its long-term use carries concerns of an increased risk of some diseases including breast cancer and stroke. Of all ethnicities, Asian American women tended to have the highest isoflavone intakes at about 6 mg. The authors noted that American women appeared to benefit from eating smaller amounts of soy.

The most frequent sources of soy foods were not whole or minimally processed soy foods, but rather soy sauce, breakfast or diet drinks, tofu, diet bars, and soy protein isolate powder.

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