Updated: Jun 30
Is SOY good or bad for you?
Soy companies advertise it as a health food and suggests it has cardiovascular and other health benefits. However many studies have linked soy to breast cancer, other hormone disorders, impaired thyroid function, digestive disorders and allergies.
Soy contains phytoestrogens, or plant-based estrogens. These are mainly two isoflavones, genistein and daidzein, that act like estrogen, the female sex hormone, within the body. Because estrogen plays a role in everything from breast cancer to sexual reproduction, this is where most of the soy controversy stems.
Soy and babies...
One study of women who were fed soy formula as infants found that this group had somewhat longer and more painful periods than people who were fed cow's milk formula (1).
Another study of infants who were fed soy formula found slight differences in the sizes of their uteruses at 36 weeks compared to those fed cow’s milk formula, suggesting estrogen exposure (2). While these studies may indicate some soy-specific effects, research doesn’t raise concerns about the development of term infants fed soy formula (FYI, soy formula is not recommended or designed for preterm infants) (3).
Should you eat soy?
Soy is increasingly difficult to avoid in the American diet, particularly if you eat any processed food (4). It’s used in infant formula, flour, vegetarian cheese, tofu and many meat replacements (6). It is frequently used as a filler in meat products (6). And soy use is only on the rise: worldwide, consumption has increased 5-6% per year over the last 15 years (5).
The science about soy isn’t absolute. In fact, it’s often contradictory. It’s clear that more research is needed to determine all the positive and negative effects related to eating soy. At the end of the day, eating too much of anything, even if it is nutritionally good for you, can have negative effects. So make your best judgement and if you plan to consume soy, then do so in moderation and try to use organic soy products.
1. Strom BL. Exposure to Soy-Based Formula in Infancy and Endocrinological and Reproductive Outcomes in Young Adulthood. Jama. 2001;286(7):807.
2. Adgent MA, Umbach DM, Zemel BS, Kelly A, Schall JI, Ford EG, et al. A Longitudinal Study of Estrogen-Responsive Tissues and Hormone Concentrations in Infants Fed Soy Formula. The Journal of Clinical Endocrinology & Metabolism. 2018Jan;103(5):1899–909.
3. Bhatia J, Greer F. Use of Soy Protein-Based Formulas in Infant Feeding. PEDIATRICS. 2008;121(5):1062-1068.
4. Messina M. Soybeans and the U.S. Food Supply Internet. Soy Nutrition Institute. 2016 cited 2019Nov11. Available from: https://thesoynutritioninstitute.com/soybeans-and-the-u-s-food-supply/
5. Thoenes P. Soybean International Commodity Profile. Markets and Trade Division Food and Agriculture Organization of the United Nations. 2015
6. Steinman H. “Hidden” allergens in foods. Journal of Allergy and Clinical Immunology. 1996;98(2):241-250.