An exclusion diet is the diet that eliminates foods suspected of causing food allergies or intolerances — the diagnostic and therapeutic tool of allergy dietetics, closely related to the elimination diet. Under professional supervision, the suspect foods are removed completely for a defined period while symptoms are monitored; improvement implicates the excluded foods, and controlled reintroduction confirms the culprit. Common exclusions are milk, egg, wheat, soy, nuts, fish, and shellfish — the major allergens. The diet’s power is its directness — symptoms that resolve on exclusion and return on challenge are strong evidence — but unsupervised exclusion risks nutritional deficiency and needless restriction, especially in children. It remains the practical gold standard where tests are inconclusive: the diet itself as the diagnostic instrument.