Colon cancer was uncommon before 1900. It is now the second leading cause of cancer death in men and third in women. This would suggest that colon cancer has less of a genetic influence, and more influence from things such as lifestyle, diet, and possibly toxins and chemicals. While there is definitely a genetic predisposition to colon cancer, it only accounts for an estimated 5-10 percent of all cancers of the colon. Ninety percent of cancers of the colon are of the adenocarcinoma type, and carcinoma of the rectum is classified separately from carcinoma of the colon.
A number of risk factors for the development of colon cancer have been identified.
Obesity is associated with an increased risk of developing cancers of all types, especially cancer of the colon. The type of obesity where the fat distribution is around the abdomen, as opposed to being on the extremities, is referred to as central obesity, and is associated with an especially high risk of colon cancer. One way in which obesity is felt to contribute to the development of cancer is through the stimulation and overproduction of insulin. Insulin has a growth-promoting effect on cells, and chronic overstimulation of this mechanism is though to possibly contribute to the development of malignant transformation. As well, those who are obese often have diets that are high in fat, high in sugar, and high in preservatives and other chemicals, while being low in nutrients such as antioxidants, which are known to be protective against certain cancers.
Red meat is known to contain several substances felt to increase the risk of colon cancer. These include nitrosamines, heterocyclicamines, and iron, all of which have been linked to an increased risk of colon and other cancers.
The consumption of dietary fiber has been associated with a decreased risk of developing colon cancer. This association seems to occur through several different mechanisms. First, undigested dietary fiber is delivered to the colon, where bacteria that are present in the colon act upon it. This process results in the production of a chemical called butyrate. Butyrate is the fuel of choice for the epithelial cells of the colon, so that a steady supply of butyrate allows for a steady source of energy for the cells of the colon, resulting on normal function, healing, and growth. A lack of butyrate interferes with cell function and has been linked to an increased risk of colon cancer. Second, the presence of fiber in the GI tract promotes motility, causing the GI contents to be transported more quickly through the GI tract. The bacteria in the GI tract produce metabolic by-products as they assist in the process of digestion, and a prolonged stay in the GI tract can result in an overproduction of these by-products, some of which are known to be toxic, a process known as putrefaction. As such, as fiber promotes motility, there is less time for putrefaction to occur. Finally, one function of fiber is to bind and eliminate toxins and chemicals from the system, some of which may promote the development of colon and other cancers.
There are two kinds of fiber, soluble and insoluble. Soluble fiber is digested more than is insoluble fiber, so that insoluble fiber is the type that typically ends up in the colon, where it is used by the bacteria to produce butyrate. Insoluble fiber is, therefore, the preferred type of dietary fiber, and is found in fruits and vegetables, where as soluble fiber is found primarily in grains.
A number of other factors have been found to increase the risk of colon cancer, including deficiencies of folic acid, B12, calcium, Vitamin D, methionine, and S.A.M. The mechanism, especially for folic acid and B12 deficiency, is felt to be on the basis of inadequate repair of DNA. This is especially important for cells of the GI tract, which, along with the skin, have the most rapid cell turnover in the body. Smoking and alcohol consumption also contribute to a higher risk of colon cancer, both by depleting the body of folic acid.
A diet rich in fruits and vegetables would contain many of the nutrients needed to lower the risk of colon cancer, including folic acid and insoluble fiber. Cruciferous vegetables (“cross-like,” such as broccoli and cauliflower) are excellent choices due to their fiber and nutrient content, whereas processed foods are typically low in fiber and nutrients, and contain preservatives, dyes, and other chemicals that add to the toxin-elimination burden of the GI tract. Diets high in foods containing Omega-3 fatty acids have been associated with a decrease risk of colon cancer, whereas diets rich in foods containing Omega-6 fatty acids have been associated with an increased risk of colon cancer.