A registered nutritionist can help to identify the specific foods which are causing your reactions, through the use of a food diary where the patient logs their daily food intake and monitors their reactions.
Together you will work out how specific foods affect you using carefully staged elimination diets, where foods suspected of causing intolerance are eliminated for a period of time and the impact measured. A registered nutritionist will be able to monitor and assess how a patient is doing on an elimination diet to confirm suspected intolerances, to then start reintroducing foods and find appropriate substitutes where relevant.
It is important that this process is guided by a registered nutritionist, as prolonged elimination diets can cause nutritional deficiencies. Reintroducing foods can also be tricky, but a professional can establish the right order to reintroduce different foods and spot signs of intolerance. A nutritionist might also recommend digestive enzymes if necessary and suggest tests to confirm some suspected intolerances and/or rule out food allergies.