Soy contains substances called isoflavones (specifically genistein and daidzein) that are similar to the hormone called estrogen. These “phyto-estrogens” (meaning “plant-based estrogens”) are much weaker than the actual hormone – in fact, they have only about 0.1% the activity. Soy has been used for years as an alternative therapy for menopausal hot flashes – so there does seem to be a mild hormonal effect in people that already have an estrogen imbalance. But in babies taking soy, I rarely ever see any signs of hormonal imbalance. For older children and adults, I believe the health benefits (decreased risk of certain cancers, heart disease, etc.) of soy far outweigh the potential risks. I use soy myself and for my kids. Populations that eat a lot of soy seem to be healthier than Americans. The only time I don’t like to use soy is in young babies as their only source of protein, unless they have a documented milk allergy. Many babies are on soy formulas that probably don’t need to be. There are several reasons for this, click here for full discussion of soy formula.
Dr. Jim