Dietary fiber generally refers to parts of fruits, vegetables, grains, nuts and legumes that can't be digested by humans. Meats and dairy products do not contain fiber. Studies indicate that high-fiber diets can reduce the risks of heart disease and certain types of cancer. There are two basic types of fiber - insoluble and soluble. Soluble fiber in cereals, oatmeal, beans and other foods has been found to lower blood cholesterol. Insoluble fiber in cauliflower, cabbage and other vegetables and fruits helps move foods through the stomach and intestine, thereby decreasing the risk of cancers of the colon and rectum.