There are two kinds of fiber, insoluble and soluble. Insoluble are the foodstuff that is not dissolved by water or metabolized by bacteria in the large intestine, examples are cellulose, hemicellulose and lignin. Soluble fiber is dissolved in water and metabolized by the bacteria in the large intestine, examples are pectins, gums and mucilages. The soluble fiber is metabolized into short chain fatty acids and gases. These are absorbed into the blood.
Whole grains contain the entire seed of the plant, which includes the bran, germ and endosperm.
Whole grains are an example of insoluble fiber. Since insoluble fiber isn't broken down in the body, it doesn't yield any calories . But since you eat a diet of soluble fiber and insoluble fiber, you cannot conclude that fiber contains no calories. I would continue to encourage people to consume foods high in dietary fiber. These foods help in weight control and reduce the risk of obesity.