It depends on the baby. I EBF my daughter for 8 months and didn't have to avoid anything because nothing made me sick. You obviously can't go crazy on chocolate and junk foods, limit caffeine, no alcohol and if you do you have to pump and dump for a few hours, no smoking or drugs, etc etc. Some foods will cause baby discomfort, as what you eat pretty much passes into the breastmilk. For example, dairy can make some babies sick, others can't handle broccoli, onions, etc etc.