Fiber in cancer prevention

| Diets high in fiber can lower the risk of breast and prostate cancer by absorbing and inactivating estrogenic and androgenic carcinogenic "stimulants" in food, which are eventually eliminated in the feces.

Various epidemiological studies observe a protective effect of fiber on cancer development, mainly in cancer of colon and rectum, at breast and in that of prostate, but also in that of lung. In all the studies, only the total fiber ingested in the diet is considered, regardless of its components (soluble or insoluble fiber) or from which foods it comes. In addition, these studies do not allow us to know if the protective effect is due only to fiber or to other nutrients inherent in foods rich in fiber, such as fruits and vegetables.

Effects on cancer

Fiber prevention mechanisms in colon and rectal cancer are thought to be local:

• Fiber dilutes possible carcinogens that is in the digestive tract.
• Reduces the contact time of carcinogens with the intestinal mucosa.
• Eliminates metabolites of carcinogens produced by the liver through the circulation between the liver and the digestive tract.
• It prevents or hinders the contact time of the bacteria with the food bolus, preventing bacteria, acting on this bolus, from producing free radicals that damage the genetic material of the cells of the intestinal wall and cause cancer cells to appear.

However, the clear association between fiber and cancer has not been confirmed in other recent studies, which has led, together, to conflicting results. Perhaps we should consider, for cancer to appear, not only a low fiber intake but also an intake rich in animal fats, which would act as an enhancer. Thus, the high fat intake would increase the level of bile acids in the intestine which, in turn, will modify and favor the presence of intestinal bacteria that would cause carcinogens to appear in the digestive tract; the bile acids themselves would contain carcinogens or cancer promoters.

In addition, a low-fiber diet would decrease the volume of stool and slow down the transit time, thus exposing the mucosa for longer to possible carcinogens. On the other hand, the lack of fiber would prevent the binding of carcinogens and thus protect the intestinal wall against the attack of carcinogens.