1. Maintain a healthy weight and eat less fat meat
Being overweight increases the overall risk of cancer and belly fat has been linked to an increased risk of colon cancer, regardless of body weight. Does this mean people should eat less meat in general too? For example, would you suggest going meatless one day a week? Is this recommendation only for processed meat? What do you classify as ‘fat meat’?
Overweight or obesity is a condition in which a person has an abnormally high and unhealthy proportion of body fat. Obesity is associated with increased risks of certain cancers, including colorectal (colon and rectum) cancer (CRC). One American study estimated that in 2007 in US, about 34,000 new cases of cancer in men (4%) and 50,500 in women (7%) were due to obesity. In Europe, 11% of CRC cases have been attributed to overweight and obesity.
A number of mechanisms have been proposed to account for the association of obesity with increased colon cancer risk. One hypothesis is that high levels of insulin or insulin-related growth factors in obese people may promote colon cancer development.
Red meat and processed meat are classified by the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) as causes of colorectal cancer. Haem iron (found in red meat) and animal fat are classified by WCRF/AICR as a possible cause of colorectal cancer, based on limited evidence. An estimated 21% of bowel cancers in the UK are linked to eating red and processed meat. In short, the effects of red meat have been examined in many epidemiologic studies; most, though not all, associate an increase in colorectal cancer with greater intake of red meat.
Based on this evidence, one should limit the amount of red meat, especially processed meat intake. Examples of red meats are beef, pork, lamb and liver. Processed meats include hot dogs and some luncheon meats. Generally, the recommended daily intake of red or processed meat is 70gm or 500gm a week.
There are also evidence to show an association between red meat and colorectal cancer might be related to the cooking process. Several studies have found that the risk of colorectal cancer is specifically increased among meat eaters who consume meat with a heavily browned surface (frying) or meat that has been prepared at high temperatures at prolonged durations (grilling). It is believed that prolonged high temperature convert the fats in the meat to mutagenic (cancer causing) chemicals.
2. Be physically active
Regular activity is associated with lower risk of many diseases, including colon cancer. Moderate physical activity ranges from house cleaning to running. Are there any guidelines to follow? Eg. 15mins of moderate activity a day, like brisk walking.
Being physically active is beneficial to our overall health. Researchers have established that regular physical activity can improve health by:
- Helping to control weight
- Maintaining healthy bones, muscles, and joints
- Reducing the risk of developing high blood pressure and diabetes
- Promoting psychological well-being via endorphins released during exercise
- Reducing the risk of death from heart disease
- Shown to be associated with decreased risk of certain cancers including colorectal cancer
Researchers are learning that physical activity can affect the risk of cancer. There is convincing evidence that physical activity is associated with a reduced risk of cancers of the colorectal and breast. Despite these health benefits, recent studies have shown that more than 50% of the population do not engage in enough regular physical activity.
How much physical activity do adults need?
The Centers for Disease Control and Prevention (CDC) recommend that adults “engage in moderate-intensity physical activity for at least 30 minutes on 5 or more days of the week,” or “engage in vigorous-intensity physical activity for at least 20 minutes on 3 or more days of the week”. Examples of moderate-intensity and vigorous-intensity physical activities can be found on the
CDC Physical Activity website.
3. Sufficient intake of Vitamin D
A healthy vitamin D intake reduces the risk of colorectal cancer and increases survival rates for those already affected by colorectal cancer. How does healthy vitamin D levels reduce the risk of colorectal cancer? In general, do women in Singapore lack vitamin D?
In 1980, Garland and Garland proposed that lower levels of vitamin D, resulting from reduced sunlight exposure, could account for the increase in mortality from colon cancer among populations at higher latitudes. Vitamin D could reduce the risk of colorectal cancer through various mechanisms, including reducing cell proliferation, inhibiting angiogenesis, promoting cell differentiation, and stimulating apoptosis.
Two of the largest studies on the effect of vitamin D are from the NHS and the Women’s Health Initiative (WHI), a randomised placebo-controlled trial of 400 IU vitamin D plus 1,000 mg/day of calcium in 36,282 post-menopausal women. The NHS study showed, based on 193 incident cases of colorectal cancer, that the relative risk of colorectal cancer decreased linearly across quintiles of plasma 25-(OH) vitamin D concentration, with a 47% risk reduction for the highest compared to the lowest quintile. Similarly, in the WHI study, an inverse association was observed between baseline levels of 25-(OH) vitamin D and colorectal cancer risk. In laymen terms, high levels of vitamin D concentration (at least 30ng/mL) is associated with reduced risk of colorectal cancer.
Women in general do not lack vitamin D, which can be obtain from both diet and exposure to sunlight. However, to achieve a vitamin D concentration of at least 30ng/mL in the blood, most women would need to take more than 1,000mg of vitamin D a day. This may be achievable only for some women, particularly in vegetarians.
4. Limit consumption of red meat, especially processed meat
Eating too much red meat increases the risk of colon cancer and processed meats raise risk even more. Try to eat no more than 3 servings – Less is better.
As mentioned above, the recommended daily intake of red meat is about 70gm per day or about 500gm per week. The way of cooking is also important. Avoid prolonged high temperature methods of cooking the red meats, like frying and grilling.
5. Aspirin – Studies have shown that the long-term use of aspirin can lower the risk of colon cancer.
Is this a recommendation to eat more aspirin? Can aspirin be taken as a supplement?
There are risks and benefits to regular aspirin use. Low dose aspirin is given routinely to patients with increased cardiovascular and ischemia stroke risk to prevent heart attacks and strokes.
Aspirin has been shown to reduce colorectal cancer risk. This benefit is observe in observational studies. There have certain flaws in these studies and not all studies have shown this benefit. The best study would be a new randomised trial where tens of thousands of people are randomly assigned to take aspirin or a placebo pill daily for at least 10 years. However, a large long-term study like this would be expensive, and no such study has yet been started.
There are risks and adverse effects from taking aspirin regularly over a long period, such as bleeding in the gastro-intestine tract (eg. stomach) and brain.
Presently, their routine use is not recommended for prevention of colorectal cancer in the general population due to concern about their associated toxicities. The U.S. Preventive Services Task Force recently published a similar recommendation, discouraging routine use of aspirin for colorectal cancer prevention. However, there are specific populations in which the potential benefit associated with their use may outweigh the risks.
6. Go heavy on garlic
Evidence suggests that a diet rich in garlic reduces the risk of colon cancer. How much garlic should one eat? If someone doesn't like the taste of garlic, will taking garlic pills work as well?
Garlic is a vegetable (allium sativum) that belongs to the allium class of bulb-shaped plants, which also includes onions, chives, leeks, and scallions. Garlic is used for flavouring in cooking and is unique because of its high sulphur content. In addition to sulphur, garlic also contains arginine, oligosaccharides, flavonoids, and selenium, all of which may be beneficial to health.
Several population studies show an association between increased intake of garlic and reduced risk of certain cancers, including colorectal cancer. However, these studies use different preparation and dosage of garlic. A recent updated meta-analysis of prospective studies on consumption of garlic and risk of colorectal cancer states that ‘consumption of raw and cooked garlic or garlic supplements is not significantly associated with reduced colorectal cancer risk’.
The National Cancer Institute, part of the National Institutes of Health, does not recommend any dietary supplement for the prevention of cancer, but recognises garlic as one of several vegetables with potential anticancer properties. Because all garlic preparations are not the same, it is difficult to determine the exact amount of garlic that may be needed to reduce cancer risk. Furthermore, the active compounds present in garlic may lose their effectiveness with time, handling and processing. The World Health Organisation’s (WHO) guidelines for general health promotion for adults is a daily dose of 2 – 5g of fresh garlic (approximately 1 clove), 0.4 – 1.2g of dried garlic powder, 2 – 5mg of garlic oil, 300 – 1,000 mg of garlic extract, or other formulations that are equal to 2 – 5 mg of allicin.
Article contributed by Dr Dennis Koh, General Surgeon, Mount Elizabeth Hospital. Dr Koh has special interests in colorectal surgery using minimally invasive techniques.
This article was first published in Shape magazine.
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