How does a nutritionist treat food allergies?

Nutritionist: She doesn't. She advises you what foods to avoid or may sometimes put you on a rotation diet. She is a part of a heathcare team with nurses and physicians.

Assists allergist: The nutritionist has 2 major goals in helping you with food allergy: help you identify the food(s) to which you are allergic in processed foods to avoid trace exposure & ensuring that you find alternative nutrients so that elimination of allergenic foods doesn't cause malnutrition. Patients eliminating 3 or more foods for long periods will benefit from working with a clinical nutritionist.