What substance can a patient with celiac disease not tolerate?

A patient with celiac disease cannot tolerate gluten, which is a protein found in wheat, barley, and rye. When individuals with this autoimmune condition ingest gluten, it triggers an immune response that damages the lining of the small intestine. This damage affects nutrient absorption and can lead to a variety of gastrointestinal and systemic symptoms, such as diarrhea, abdominal pain, bloating, and fatigue.

In the context of celiac disease, gluten avoidance is crucial for managing symptoms and preventing further intestinal damage. Patients are advised to adhere strictly to a gluten-free diet, eliminating foods that contain wheat, barley, and rye, along with any processed foods that may have gluten as an additive.

The other substances listed—milk, sugar, and nuts—are not inherently problematic for individuals with celiac disease. While some people may have lactose intolerance or specific allergies to nuts, these conditions are separate from celiac disease and do not directly relate to gluten intolerance.