I am a bf counsellor and generally say to mums that you do not need to modify your diet when bf. And this was true for me for my first two babies.
My third baby is now 7 weeks old and seems especially sensitive to what I eat. He developed very bad colic around 3 weeks of age that was resolved by cuting dairy from my diet. He then had a really bad reaction to egg that I ate - so that is now off the menu.
Today he reacted to something I ate at lunch time. (He seems to react within two hours of me eating with severe screaming in pain as well as bringing up partially digested milk). The only thing I ate that was different was some chutney which contained dried fruit. It has been suggested to me that dried fruit can be problematic. A cranial osteopath I saw today (prior to the reaction to my lunch) said it felt like he was still reacting to something I was eating. One possibility is the orange juice I have each morning for breakfast.
So, I am looking for other people's experience of this as well as some empathy! It is so hard having to keep evaluating my diet and knowing that things I am eating are upsetting him.