Most foods are absolutely fine and will not decrease your milk supply. There are a few herbs, however, that can decrease supply, and it is best to avoid large quantities of these while you're breastfeeding. These are most commonly mint, sage, and parsley. Small amounts of these will cause no harm, so just don’t overdo them while you’re cooking or choosing herbal tea. And be careful of juicing: Sometimes large amounts of herbs are often used in the juice. Otherwise eating a healthy, balanced diet is all you need to worry about.