Fat Intake and Colorectal Cancer
Cancer is one of the major causes of death in Western countries, and colorectal cancer ranks as one of the most deadly types of cancer. In Canada for males aged 40-59 the incidence of colorectal cancer is second only to lung cancer; for females aged 40-59 it is third behind breast and lung cancers. For many years there has been a growing amount of epidemiology, experimental and clinical research that have all pointed to the fact that diet can be a major factor in the incidence and prevention of colorectal cancer.
The intestinal wall is folded into deep cavities called crypts. The folding of the intestinal wall increases the surface area of the intestine and allows for efficient absorption of nutrients. The inner lining of the intestine is a dynamic wall between food as it passes down the GI tract and the interior of the body. The cells that line the crypts grow, divide and die. Dead cells are shed into the intestine and are swept down the GI tract.
Colorectal cancer develops over a long time after a genetically altered cell continues to grow and divide in an abnormal way. The cells of the intestinal wall are constantly exposed to carcinogens in food and partially digested food, and therefore, the hypothesis that diet can influence colorectal cancer is an easy one to make.
Dietary fat has been the main focus of most studies looking at diet and colorectal incidence. Both the amount of fat and the type of fat appear to be important. Reports published in the 1960's using Japanese data indicated that it was the amount of dietary fat that increased the risk for colorectal cancer. The link between diet and the population of micro-organisms in the intestinal tract was being established and it was felt that the type of diet changed the population of bacteria residing in the intestines and this, in turn, influenced the susceptibility to cancer. Some enzymes produced by the intestinal bacteria have been shown to be able to detoxify carcinogens as they pass down the GI tract. Some of the bacteria produce short chain fatty acids such as butyrate which has been shown to slow the growth of cancers. Diets high in fat tended to reduce the numbers of beneficial bacteria. Lowering the total amount of fat in the diet has been the recommendation of many advisory bodies.
More recent studies have shown that when one looks at the type of fat that is being consumed, it is saturated or animal fats that may increase the risk of colon cancer. Diets rich in polyunsaturated fatty acids, particularly omega-3 fatty acids, appear to reduce the risk of colon cancer. Initial epidemiological studies done in Europe have been followed by experiments done with animals to demonstrate a mechanism that could be used to explain the benefits of polyunsaturated fatty acids.
We keep hearing that we should be reducing the fat in our diet. It would seem that reducing the risk of colorectal cancer is just one more reason to be taking a look at how much and what type of fat we are consuming.
You can find out more about the latest trends for cancer rates in Canada at the
Public Health Agency of Canada