A food intolerance cannot be tested for in the same way as a food allergy. The best way of identifying a food intolerance is to perform an elimination diet.
All possible causes of the intolerance are eliminated from the diet for at least 2 -4 weeks, and then gradually introduced, looking for symptoms. It is recommended that you see a Dietician or Nutritionist in order to perform an elimination diet. They will advise you on the best approach, and ensure that the child’s nutrition is adequate during the process.
It is advisable to use a food diary. This will help you and your Health Care Practitioner to link the symptoms to the triggers. I often think that I will never forget what I ate a few days ago, but you definitely do forget. By keeping the diary you can also try and link delayed reactions.