Final answer:
Grains, particularly whole grains, contain the highest fiber content among the given options, with grain bran products like crude corn bran and crude wheat bran being especially high in fiber.
Step-by-step explanation:
Among the options provided, grains typically have the highest fiber content, particularly whole grains like crude corn bran and crude wheat bran, which are very high in fiber. Dietary fiber can have significant health benefits, including reducing the risk of coronary heart disease, type 2 diabetes, colon cancer, and it may also contribute to weight management. Fiber does not supply energy but assists in the digestive process by absorbing water and promoting the passage of food through the digestive system. Fruits, vegetables, nuts, and whole grains are all good sources of dietary fiber; however, grain bran products, especially from whole grains, are among the highest in fiber content.