Carbohydrate-rich foods. Clockwise from lower left are: cereal grains and ears, brown bread, dried pasta, potatoes and grains of rice. Cereal grains such as wheat are ground into flour for bread. The pasta is also made from a form of flour. Potatoes are a root vegetable, while rice grains come from a cultivated grass crop. Carbohydrates are a major source of energy in the diet, and one or more of these foods are eaten in most parts of the world.