A cereal is a grass cultivated for the edible components of its grain, composed of the endosperm, germ, and bran. In their natural form (as in whole grain), they are a rich source of vitamins, minerals, carbohydrates, fats, oils, and protein, but when refined the remaining endosperm is mostly carbohydrate.
Pictured here are oats and barley, together with some products made from them.Photograph: Agricultural Research Service, United States Department of Agriculture