Dietary fiber can be considered "any dietary component that reaches the colon without being absorbed in a healthy human gut". Thus "fiber", according to the recent literature, is contemplated any substance other than plant cell-wall material. The latter is a new definition expanding the previous one beyond carbohydrates. In fact, there is evidence that compounds other than cell-wall polysaccharides that are able to evoke similar physiological effects of those stimulated by soluble and insoluble polysaccharides. Moreover, this definition does not presume that the physiological effects of any fiber component are manifested only when fiber reaches the colon. Dietary fiber intake is important from a metabolic view point (lipid and glucose metabolism) or acting as prebiotics on microbiota health, in preventing colonic cancer, in treating bowel diseases and symptoms, on mineral absorption. Fiber intake seems to be important in particular in the elderly to the point that all national dietary guidelines and food guide pyramid for elderly people underline the necessity to increase dietary fiber intake, and therefore fruits and vegetables.