How diet, nutrition and physical activity affect colorectal (bowel) cancer risk. In total, it has been found that there are more than 29 million adults and over 247,000 cases of colorectal cancer from around the world. The colon is the lower part of the intestinal tract. It extends from the caecum to the rectum. In the colon, water and salts are absorbed from undigested foods, and muscles move the waste products towards the rectum.
The colon contains a vast population of many types of bacteria, which have potentially important functions. These include the fermentation of unabsorbed carbohydrate (non-starch polysaccharides and resistant starch) to release energy and short-chain fatty acids that influence the health of the colonic mucosa. The colon is lined with mucous membranes and contains lymphoid cells that form part of the body’s immune defences.
What causes colorectal cancer?
Our Expert Dr. Ram Chandra Soni has reviewed the evidence on diet, weight, physical activity and the risk of colorectal cancer.
There is strong evidence that:
- Being physically active DECREASES the risk of colon cancer.
- Consuming wholegrains DECREASES the risk of colorectal cancer.
- Consuming foods containing dietary fibre DECREASES the risk of colorectal cancer.
- Consuming dairy products DECREASES the risk of colorectal cancer.
- Taking calcium supplements DECREASES the risk of colorectal cancer.
- Consuming red meat INCREASES the risk of colorectal cancer.
- Consuming processed meat INCREASES the risk of colorectal cancer.
- Consuming alcoholic drinks INCREASES the risk of colorectal cancer.
- Being overweight or obese INCREASES the risk of colorectal cancer.
- Being tall INCREASES the risk of colorectal cancer.
There is some evidence that:
- Consuming foods containing vitamin C might decrease the risk of colon cancer.
- Consuming fish might decrease the risk of colorectal cancer.
- Vitamin D might decrease the risk of colorectal cancer.
- Consuming multivitamin supplements might decrease the risk of colorectal cancer.
- Low consumption of non-starchy vegetables might increase the risk of colorectal cancer.
- Low consumption of fruit might increase the risk of colorectal cancer.
- Consumption of foods containing haem iron might increase the risk of colorectal cancer.
Other causes of colorectal cancer
In addition to the findings on diet, nutrition and physical activity outlined above, other established causes of colorectal cancer include:
Smoking
Smoking 40 cigarettes (two packs) per day increases risk of colorectal cancer by about 40% and nearly doubles the risk of colorectal cancer death.
Other diseases
Inflammatory bowel disease (Crohn’s disease and ulcerative colitis) increases the risk of colon cancer.
Medication
Long-term use (five years or more) of at least 75 mg per day of the non-steroidal antiinflammatory drug aspirin can reduce the risk of colorectal cancer. Hormone therapy in postmenopausal women decreases colorectal cancer risk.
How does colorectal cancer develop?
Approximately 95 per cent of colorectal cancers are adenocarcinomas. Other types of cancer that can occur include mucinous carcinomas and adenosquamous carcinomas.
Carcinogens can interact directly with the cells that line the colon and rectum. Between five and 10 per cent of colorectal cancers are a consequence of recognised hereditary conditions.
