Foods made from soybeans, including tofu, tempeh, edamame, soy milk, and soy nuts, contain several important nutrients: protein (the only plant food that contains all 8 essential amino acids humans need for health), fiber, iron, calcium, zinc, and B vitamins. Soy foods are also important for what they don’t contain: they don't have any cholesterol and they're low in saturated fat, two items that are known to increase the risk of heart disease. Soy foods are also the most widely-consumed foods that contain a type of healthy phytochemical called isoflavones.
What are Isoflavones?
Isoflavones are phytoestrogens, compounds from plants that have weak estrogenic activity in our body. Legumes, grains and vegetables all contain small amounts of isoflavones, with soybeans as the most concentrated source. The three isoflavones genistein, daidzein, and glycitein and their respective glycosides account for approximately 50%, 40% and 10%, (respectively) of the total isoflavone content of soybeans. Each gram of soy protein in soybeans and traditional soy foods is associated with approximately 3.5 mg of isoflavones.
What are the Health Benefits of Isoflavones?
The research on isoflavones is currently yielding mixed results and because of this lack of consensus, there are no clear research-based recommendations at this time.
Since soy isoflavones are structurally similar to estrogen, a hormone naturally produced by our body, it has been suggested that soy isoflavones might help protect against hormone-associated cancers. People in Asian countries such as Japan and China, where soy foods are part of the everyday diet, have much lower rates of prostate and breast cancers compared to North America where we typically don’t consume soy foods as often. However, there are many different variables to consider in cancer risk, and the research about a possible benefit of consuming soy foods to reduce the risk of cancer are mixed. There do not seem to be any negative health effects of consuming moderate amounts of soy foods.
Decreasing levels of estrogen in women in menopause increases the risk of decreased bone density, which can lead to osteopenia or osteoporosis. Research on the potential benefits of soy foods in maintaining bone density is ongoing, with no clear recommendations.
Are Isoflavones Safe?
Research on the health benefits and risks of soy foods has been going on for 25 years, with thousands of published research studies.
Early scientific studies using animals suggested that the estrogenic activity in soy foods might be harmful for breast cancer survivors, since high levels of estrogen are implicated in some types of breast cancers. However, a consistent body of more recent human research shows that soy foods are safe for everyone, including people diagnosed with cancer. In fact, large population studies that examined the amount of soy foods consumed among breast cancer survivors show that consuming moderate amounts of soy foods does not increase the risk for worse outcomes.
Let's Talk Soy Tips:
Moderate consumption of soy foods is 1 – 2 servings per day of whole soy foods, or 25-50 grams of soy isoflavones per day. The content of isoflavones in soy foods varies widely. Here are a few examples...
- ½ cup miso = 57mg
- ½ cup edamame = 16 mg
- 1 ounce dry-roasted soybeans = 41 mg
- 3 ounces cooked tempeh = 30 mg
- 3 ounces soft tofu = 19 mg
Although diets containing soy foods appear safe and potentially beneficial, the long-term safety of very high supplemental doses of soy isoflavones is not yet known and there is little scientific evidence showing health benefits of using isoflavone supplements.
Our recommendation is to include 1-2 servings of soy foods most days of the week into your food choices and avoid supplements.
Not sure where to start? Try...
- Snacking on soy nuts or dry-roasted soybeans
- Make a vegetable stir-fry with tofu instead of chicken or beef.
- Toss edamame into brown rice pilaf.
- Use soft or silken tofu instead of milk or yogurt in smoothies.
- Drink plain soymilk instead of cow’s milk or other types of non-dairy milks.
- Choose a veggie burger made from soy (be sure to read the ingredient label because veggie burgers are made from a variety of different plant foods) instead of a hamburger.
Many processed foods made from soy (hot dogs, chicken alternatives, and frozen meals made with soy) contain higher amounts of sodium, preservatives and additives. Be sure to read the nutrition facts label so you know exactly what you’re consuming.
Fermented soy foods (miso, natto, soy sauce, tamari, tempeh) contain tyramine, an amino acid that needs to be reduced in people who take MAO inhibitors such as phenelzine or tranylcypromine. Soy milk, edamame, and tofu are not fermented and do not need to be limited.
High intakes of soy protein may interfere with the efficacy of the anticoagulant medication warfarin.
By Lynn Grieger, RDN, CDE, CPT, CHWC
- Eilat-Adar S, Sinai T, Yosefy C, Henkin Y. Nutritional recommendations for cardiovascular disease prevention. Nutrients. 2013;5(9):3646-83. Published 2013 Sep 17. doi:10.3390/nu5093646
- American Institute for Cancer Research. Soy and Cancer Survivorship. http://www.aicr.org/patients-survivors/healthy-or-harmful/soy.html?_ga=2.11276340.1857739609.1545341215-879666975.1542997456 Accessed 1-7-19.
- Oregon State University, Linus Pauling Institute. Soy Isoflavones. https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/soy-isoflavones Reviewed 10-2016. Accessed 1-7-19.
- Messina M. Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature. Nutrients. 2016;8(12):754. Published 2016 Nov 24. doi:10.3390/nu8120754
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.