Sol, it's kind of more like what haven't I eliminated... I'll give the long-winded account since I have 2 hands free at the moment :)
I ate a pescatarian diet before, kind of like lacto-ovo vegetarian plus fish and seafood. When I had to go on antibiotics the first week after M's birth, I went overboard with yogurt, kefir, etc. to avoid getting thrush and started noticing M getting fussier. Since I had read about milk protein allergy, I went off milk after I finished the antibiotics, although I admit I wasn't vigilant about it at first. Anyway, then M started getting a rash all over. My parents were here at the time and they convinced me it was heat rash, but we ended up going to the pediatrician after they left and he diagnosed it as eczema and suggested that a food sensitivity/allergy to something I'd been consuming could have caused it. So I then decided to do away with soy, peanuts, almonds (I had been drinking almond milk and related items), and seafood (also had been having a good amount of that).Then the next week he started getting a very very small amount of blood in his stools (and his stools had changed from yellow seedy to more green mucousy), so I kept eliminating things: oats and eggs, mainly. The eczema is gone except in a few body creases now, but he still gets blood from time to time. We've since been to a pediatric gastro specialist and he said that he's not concerned with the amount of blood and is very pleased with M's health, so he wants me to keep exclusively breastfeeding. He said he'll grow out of the allergy/sensitivity and he was more concerned with me getting good nutrition than being super strict about my diet based on the amount of blood he was seeing. I've decided I'll reintroduce things slowly once I have a week without any blood.
But, anyway, I think the most interesting side effect of all of this has been noticing how happy and calm M is (and also realizing how far non-dairy/soy, etc. vegan food has come since I was vegan in h.s.).