Food/behavior journal

After talking with the allergist this morning I have decided to continue my food journal with Grace and watch how her behavior changes based on what she eats. Has anyone else done this or had expirience with this? We had a play date with a friend this morning. She is one of the few people Grace just LOVES so she always has fun playing with her and her kids. At the end as we were getting ready to leave, Grace threw a HUGE fit that lasted until we were home and I had her in bed! Poor Emma was covering her ears the whole way home! I am considering having them share a room again so we can pull all the toys out of one room for when Grace is having a fit she can just be alone in that room instead of trashing the house. I am hoping by using the food journal I will find some more correlations between what she eats and how she behaves! She has come a long way and I am hoping this setback is short lived! What are your expiriences with food/behavior??