A: In general, there are only two foods breastfeeding women should avoid or consume in very small amounts: alcohol and fish. Alcohol can be passed from mom to baby in breast milk and affect neurologic development. One drink or less per day is generally accepted as being "safe." Fish (including canned tuna) should be avoided or eaten in moderation, no more than 2 servings a week. Fish contain mercury that can also negatively affect the baby's neurologic development.
Plus, any foods that someone in the family has an allergy to should be avoided; the most common ones are eggs, peanuts, soy, wheat, corn, and milk. Certain foods may also cause irritation, discomfort, gas, or intestinal irritation in babies and they should be avoided if your baby shows negative reactions to them: caffeine (coffee, tea, and chocolate), citrus fruits, spicy peppers, broccoli, and garlic. Some herbs, such as peppermint and parsley, can decrease milk supply if ocnsumed in large amounts. (But other supplements, like Fen-U-Greek, can increase your milk supply.)
Your baby will let you know if something is disagreeing with his system. One thing to keep in mind: it can take up to 14 days of cutting a food group completely out of your diet before it is no longer excreted into the breast milk, so don't decide after only 24 hours if a change is making a difference in your child.