The dietary fiber in whole grains comes from its bran layer. Like sugar and starch, fiber is a carbohydrate, but with a twist: the body does not digest and absorb it. So, fiber is essentially calorie-free. That's one reason people lose more weight on high fiber diets: meals are filling on fewer calories (1). And, because it's not digested, fiber is able to improve intestinal tract function.
The "insoluble fiber"- the main type in wheat - helps prevent constipation. Oats and barley are rich in "soluble fiber" which helps lower cholesterol and stabilize blood sugar. And, in the intestinal tract, both types of fiber can be converted into compounds that reduce cholesterol, enhance calcium absorption, and boost immunity (2).
1. Slavin, JL (2005), Dietary fiber and body weight. Nutrition Mar;(3):411-8.
2. Slavin, JL (2003), Why whole grains are protective: biological mechanisms. Proceedings of the Nutrition Society, 62, 129-134.
