Dietary Fiber
Modern food industries have been able to process seeds and vegetables so as to extract the fat and sugar or, in the case of grains, to mill off the outer branny layers to yield white rice or white wheat flour.
The public, in general, prefers sweet foods that “slip down” easily because of their fat content and contain nothing “scratchy in the mouth.” The fibrous residues from the processing of foods of this type have been used to feed farm animals. Ruminants, in particular, are able to ferment and utilize cellulose.In the past it was thought that, because “roughage” apparently passed through the gut unchanged, the fiber had no significance as long as people had just enough not to become constipated. But in recent years, a lower incidence of cancer of the colon among communities isolated from sophisticated Western food products has prompted the suggestion that these people are protected by the higher fiber content of their diets. Perhaps the greater volume of material in the colon dilutes any carcinogenic compounds present. It is thought that gut bacteria may produce such carcinogens by acting on bile acids.
Of course, differences among communities in the incidence of colon cancer can be explained by things other than diet. However, genetics does not appear to be one of them, because, in general, after two generations, emigrant groups seem to have a disease pattern similar to that of their hosts. Moreover, some studies have confirmed the importance of diet in colon cancer; there tend to be fewer cases among vegetarians than among other groups. Vegetarians obviously have a lower intake of fat and animal protein than do others, and they consume more vegetables and more fiber.
Vegetables are extremely complex mixtures of natural, “organic” chemicals. Some believe that, rather than fiber, the green and yellow vegetables that are the principal sources of carotenoids in our diet may provide protection against colon cancer.
The protective factors could also be other chemicals found in some vegetables more than others. For example, there is a class of compounds, including pectins and gums, that are not digested in the small intestine along with starch, but are rapidly fermented by bacteria when they reach the colon. They are now subsumed within the overall term dietary fiber, though they may in some respects produce effects that differ from those of the largely unfermented cellulose.Research in the field of nutrition is inevitably slow. Diseases appearing mainly in middle-aged humans cannot be modeled with certainty in short-term animal trials. In the meantime, nutritionists’ most common advice, after the admonition to get more exercise and stop smoking, is to consume a “prudent” diet modeled on the traditional Mediterranean peasant diet, with a predominance of cereals, vegetables, and fruit, a sparing amount of meat, preference being given to fish and chicken, and a moderate amount of dairy products that are low in fat.