From the Guidelines
Consuming moderate amounts of soy foods, up to 3 servings daily, is generally safe for most people, including breast cancer survivors, as it is consistent with amounts in a typical Asian diet. This amount can be achieved by having 1 cup of soy milk, 1/2 cup of tofu, tempeh, or edamame, or 1 ounce of soy nuts per serving 1. It is essential to note that higher doses of soy may have estrogenic effects, which could increase the risk of breast cancer progression, and therefore, breast cancer survivors should avoid high doses of soy and soy isoflavones found in concentrated sources such as soy powders and isoflavone supplements 1.
Some key points to consider when consuming soy foods include:
- Soy is nutritionally valuable, providing complete protein, fiber, and various vitamins and minerals while being low in saturated fat
- The concerns about soy's effects on hormones have been largely overstated, as research shows minimal impact on hormone levels in most people
- Individuals with thyroid conditions should consult healthcare providers before significantly increasing soy intake, as soy may interfere with thyroid medication absorption
- Those with hormone-sensitive conditions like certain breast cancers should also seek medical advice before consuming large amounts of soy products or supplements 1.
Overall, a balanced diet that includes moderate amounts of soy foods, along with regular physical activity and a healthy weight, can help reduce the risk of chronic diseases, including heart disease, diabetes, and certain types of cancer 1.
From the Research
Safe Soy Consumption
The amount of soy considered safe for consumption varies depending on individual factors, such as thyroid health and iodine intake.
- Studies have shown that moderate soy consumption is generally safe for healthy individuals with normal thyroid function 2, 3, 4.
- However, individuals with hypothyroidism or compromised thyroid function may need to be cautious with soy consumption, as it may interfere with thyroid hormone absorption or increase the risk of developing clinical hypothyroidism 2, 5.
Thyroid Function and Soy Consumption
Research suggests that soy isoflavones may have a modest effect on thyroid-stimulating hormone (TSH) levels, but the clinical significance of this effect is unclear 3.
- A systematic review and meta-analysis found that soy supplementation had no significant effect on free triiodothyronine (fT3) and free thyroxine (fT4) levels, but slightly elevated TSH levels 3.
- Another study found that isoflavone supplements did not affect thyroid function in iodine-replete postmenopausal women 4.
Special Considerations
Certain individuals may need to limit or avoid soy consumption due to specific health concerns:
- Hypothyroid patients may need to adjust their thyroid hormone dosage if they consume soy foods, as soy can inhibit thyroid hormone absorption 2.
- Individuals with chronic lymphocytic thyroiditis or other thyroid conditions may be more susceptible to the effects of soy isoflavones on thyroid function 5.
- It is essential for soy consumers to ensure adequate iodine intake to minimize the risk of developing hypothyroidism 2.