Gluten is a protein found in grains like wheat. Gluten-intolerant people suffer when they eat this protein, which adversely affects the small intestine. It's important to avoid gluten, which disrupts their metabolism as well causing nutritional problems and abnormal gut flora. This condition is known as Celiac disease, a genetic condition. A gluten free diet can significantly improve health in these cases. Fortunately, not all grains contain gluten, but the traditional Western grains in the wheat, rye, spelt, barley and other classes are problems. Products derived from gluten based foods may also cause similar effects.

Safe, gluten free grains are :

Note: Soy is actually a legume, not a grain, and is considered safe.