Keeping a long term food diary with frequent notations on everything you eat, how you feel, your activities during the day and any other allergens or chemicals you might have been exposed is a useful aid in identifying complex patterns of food sensitivity.  Upon examination of a detailed diary, patterns sometimes emerge that were not obvious at the time the notations were being made.  In addition, it is useful to also keep track in your food diary of factors other than those mentioned above, such as season, weather changes, menstrual cycle, infections, medications, exercise, alcohol, and amount and quality of sleep.   These factors can also contribute to whether an adverse food reaction occurs and how severe it is.