Soy in any form should never be given to infants. Just plain soy milk is devoid of the vitamins, minerals, essential fatty acids and amino acids that an infant needs. Soy formulas, which are required by law to be heavily supplemented with essential nutrients, have been implicated in ADD/ADHD and brain damage. Soy also suppresses thyroid hormone and has a powerful estrogenic effect, just like giving your baby birth control pills. If you must supplement your breast milk for whatever reason, I recommend using a fortified goat milk based formula.