Fiber. It's one of those words we associate with a healthy diet. But do you have any idea why dietary fiber—those starchy substances found in fruits, vegetables, and grains that can't be digested in the human body—is so good for you? Fiber as Calorie-Blocker Adding fiber to the meals you eat may help you get fewer of the calories you gobble down. Since fiber takes up more room in your stomach than other foods, you feel fuller faster—and thus consume less. And according to the USDA, fiber may block some of our body's ability to absorb calories from the foods that we eat…