Testing for a Food Allergy Lack of endurance, chronic health problems, or just on average not feeling like yourself are all routine warnings of food intolerances. Intolerance to foods can produce a lot of different indications including irritable bowel syndrome (ibs), headaches, eczema, fatigue and mood swings. Warnings occasionally can happen some time after the food has been eaten so it is complicated to figure out the food that is causing the problem without allergy testing.