Diet and Colon Cancer: Opportunities For Prevention

By Dr Yap Chin Kong
MBBS, MMED, MRCP(UK), FAMS, FRCP(Edinburgh)
Senior Consultant Gastroenterologist

Approximately 58-80% of cancers are caused by environmental factors and dietary factors may be involved in 35% of cancers.



Environmental factors act to promote or protect cells from mutations. Environmental factors that are linked to cancer include:

1.Smoking: lung, pancreas, bladder cancer
2.Obesity: breast, endometrium, colon cancer
3.Infection with viruses: Human Papilloma virus for cervical cancer, hepatitis B
and C for liver cancer, Ebstein-Barr virus for nasopharynx cancer.
4.Bacteria: Helicobacter pylori for stomach cancer
5.Radiation: Leukemia, thyroid cancer.

An important component of environmental factors is our diet. Dietary factors that have a protective effect include: high fiber intake, fresh fruits, vegetables; dietary factors that are linked to cancer include: high salt intake, high fat intake, smoked meats, betel nut, excessive alcohol. A lean body weight has a protective effect against cancer. Medications such as hormone replacement therapy can protect against colon cancer but promote breast cancer. Dietary supplement and anti-oxidant are attractive concepts but have not been proven to reduce cancer when used as treatment.

Cancer is the result of uncontrolled growth of cells in an organ, with the capacity to spread outside of the organ. It gradually results in interference with normal function and its consequences. The different cancers are classified according to the organ of origin. In Singapore, the top five common cancers in males are: lung, colon, stomach, liver, nasopharynx; in women: breast, colon, lung, cervix, stomach. The commonest cause of death is due to cancer, followed by heart disease. Throughout life, genetic changes (also called mutations) occur in our cells. These changes occur over time and can be inherited directly from our parents, or acquired due to the aging process and from environmental factors.

The epidemiology of colon cancer in the Asia-Pacific region varies widely. IARC statistics place New Zealand and Australia with the highest incidence rates: 55.3 per 100,000 in New Zealand and 50 per 100,000 in Australia. Some countries in South Asia e.g. Bangladesh and Sri Lanka have among the lowest rates: 1 per 100,000 in Bangladesh and 1.8 per 100,000 in Sri Lanka. In many countries, colon cancer is on the rise. Environmental and life-style factors play a role and urbanization seems to be associated with the increase. In Singapore, the incidence in the Indian race is approximately double that in Madras. Studies from Asia point to an increase in consumption of dietary meat and fat, a reduction in dietary fibre, fresh fruit and a sedentary life-style as associations with colon cancer. These data point to the presence of genetic, environmental (including diet) and life-style influences in the causation of colon cancer.

Colon cancer: detect it early

About one in twenty or 5% of people will develop colon cancer during their life-time. Colon cancer is the commonest cancer in Singapore and has doubled in the last 30 years. The rising trend is worrying and is likely related to dietary factors and an aging population.

Almost all colon cancer arise from polyps. The progression from polyp to cancer takes many years due to the accumulation of genetic mutations. Polyps that are detected and removed by “polypectomy” effectively prevents the development to cancer. If cancer has developed, detection at an early stage I and II, can result in cure in approximately 80%. The chance of cure of more advanced stage cancer (III and IV) falls to 40%. Hence early detection by screening is an attractive concept.

For the “average risk” person, several options for screening are available, starting at age 50 years. These are: stool occult blood test, sigmoidoscopy, combined stool test and sigmoidoscopy, colonoscopy, barium enema and CT colonography. The best studied and scientifically proven method to reduce the chance of dying from colon cancer is the stool occult blood test. There is a 15-30% reduction in the risk of dying from colorectal cancer. A positive test should be followed by colonoscopy. A negative test should be repeated annually. Because of false positive and negative readings, the search is on for better methods to improve on the accuracy of tests to detect early cancer. These include stool cancer markers and CT colonography. Currently, colonoscopy is the preferred method as a screening test because it examines the entire colon is considered the current “gold standard” in the examination of the colon. The benefits in reducing death from colon cancer are potentially greater than stool occult blood screening. Polyps and early cancer that are found can be removed non-surgically using snare polypectomy. If no polyps are found, colonoscopy offers “protection” against cancer for 5-10 years.

For “high risk” persons, only colonoscopy is recommended. “High risk” refers to persons with a personal or family history of colon cancer or polyps, or a personal history of inflammatory bowel disease. “Very high risk” refers to persons who may have inherited a colon cancer gene in rare genetic conditions.

Opportunities for prevention
Environmental and dietary factors are likely to influence the development of cancer over many years or even decades. Immigrants to a country have a risk of cancer that is between their country of origin and the adopted country. It is their children who acquire the cancer risk of their adopted country. Hence, environmental factors may have an effect in the early part of life and explain why adopting healthy dietary and lifestyle habits later in life have little impact on the cancer risk. For these measures to work, they probably have to be adopted for many years, starting early in life.

Logically, the strategy to reduce the problem of colon cancer is two pronged approach. The first approach is to screen “average risk” individuals starting at the age of 45-50 years (with colonoscopy as the preferred test). This approach benefits the immediate large numbers of persons who are at risk. The second approach is to adopt a healthy lifestyle and dietary habit now. This is because a good habit has to be adopted by adults before it can be passed on to our children. Although it may not affect cancer risks in adults now, it has benefits to reduce cardiovascular risk which is a major cause of death. The aim to reduce cancer risk and may not be achieved until the next generation.


Contributed By Yap Chin Kong
MBBS, MMED, MRCP(UK), FAMS, FRCP(Edinburgh)
Senior Consultant Gastroenterologist
Keywords: gastroenterology, polyps, diet, colon, cancer