Gluten mainly exists in wheat, rye, barley and their hybrids. Various foods produced and processed with these grains, such as bread, cakes, biscuits, beer, etc., generally contain gluten. Gluten is a mixture of a series of protein, which consists of about 50% gliadin and about 50% glutenin, among which gliadin is the chief culprit of human allergy. Glutenin is called gluten in wheat, rye essence in rye and barley gliadin in barley.

Gluten-free food: food that has not been processed by wheat (all wheat plants, such as durum wheat, spelt wheat and Cam wheat), rye, barley or their hybrid varieties, and the gluten content does not exceed 20 mg/kg, can be called "gluten-free food"; Foods processed with wheat (all wheat plants, such as durum wheat, spelt wheat and Cam wheat), rye, barley or their hybrid varieties can also be called "gluten-free food" if the gluten content in the food does not exceed 20 mg/kg by certain food processing technology; If the gluten content of food is 20 ~ 100 mg/kg after the gluten component is removed, it cannot be called "gluten-free food".

Gluten-free diet: refers to foods completely free of gluten, such as gluten-free bread, pizza, some fast food and other staple foods. Gluten-free diet is mainly used to treat patients with celiac disease and gluten allergy, but it is also eaten by some stars and athletes as weight loss and fitness food. A gluten-free diet is a completely gluten-free food. Eating gluten-free diet means strictly abstaining from foods containing wheat bran, such as pasta, pizza, beer, cheese, sandwiches, and even exquisite foods such as sauces, cakes, bread, biscuits and cakes, and buying foods marked gluten-free instead of potatoes, corn, vegetables, meat, beans, nuts, preserved eggs, seafood and rice.