Keeping a food diary is a useful way to record how you feel after eating different types of foods and will help your healthcare provider diagnose the cause of your symptoms. They’ll likely also want to find out more about your medical history, so if possible make a note of any food allergies that run in your family.
When testing is inconclusive, your healthcare provider may try other approaches to find out what is making you feel unwell.
For example, they may suggest an elimination diet. During an elimination diet, the suspected trigger food is removed and slowly reintroduced. This is typically used to detect intolerances. However, to diagnose lactose intolerance they would typically use breath and blood tests instead.
Non-IgE-mediated allergies are harder to diagnose. Here, your healthcare provider may suggest an oral food challenge. In an oral food challenge you’ll eat small amounts of the problem food, which gradually increase until you experience a mild reaction. If symptoms develop, you’re possibly allergic to that food.
Depending on your medical history they may also want to look at your digestive tract with a camera. This procedure is called an endoscopy.