Brewer's yeast comes from a one-celled fungus and is a byproduct of beer making, though it can also be grown as a nutritional supplement. A good source of iron, chromium and selenium, brewer's yeast also contains several B vitamins, though not B-12. Brewer's yeast has a history of use as a galactagogue, which is a food, herb or medication that increases milk supply in nursing mothers.
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Safe for Nursing Women
According to international board certified lactation consultant Anne Smith, writing for BreastfeedingBasics.com, brewer's yeast is one of several galactagogue herbs usually considered safe for breastfeeding mothers. She warns there is no scientific evidence supporting the claims that it will boost breast milk production, but you might notice a modest increase in supply.
Kathleen Huggins, author of "The Nursing Mother's Companion," cautions some babies have experienced fussiness after their mothers took brewer's yeast. Breastfeeding-problems.com states brewer's yeast has few side effects, but advises women with recurrent yeast problems or yeast infections to avoid using the supplement.