Can Healthy Diet Prevent Colorectal Cancer?

Colorectal cancer is the most common cancer in Singapore. The average population risk for developing colorectal cancer in Singapore is among the highest in the world. However this is a preventable cancer. Screening for colorectal cancer is proven to save lives. In the United States and northern European countries, colorectal cancer mortality has been falling, and this has been attributed to screening, early detection, prevention by polypectomy, and improved treatment.

Diet has long been thought to have a role in the etiology of colorectal cancer, particularly when a poor diet is combined with excess calorie intake and weight gain, physical inactivity, and unhealthy practices, such as smoking and consuming a great deal of alcohol. Since colorectal cancer, of all the major cancers, seems to have the closest links to diet, multiple studies have been looking into ways in which the cancer might be prevented through changing what and how much we eat.

DIET

Fruit, Vegetables, and Fibre: Fibre has been proposed to dilute or absorb fecal carcinogens and improve transit time in the colon. Clinical studies have shown that a high intake of vegetables or fibre was associated with an approximate 40 percent to 50 percent reduction in risk for colon cancer.

Red Meat, Fat, and Carbohydrates The results of US and European clinical studies found that consumption of red meat or processed meats more than five times a week _increased a risk of colon cancer three-times compared to those who consume red meat less than a month. Several studies have found that risk of colon cancer is specifically increased among meat eaters who consume meat with a heavily browned surface or meat that has been prepared at high temperatures at prolonged durations.

Calcium and Vitamin D Large clinical studies have consistently shown a significant inverse association between calcium intake and colorectal cancer risk. Vitamin D could reduce risk of colorectal cancer through various molecular and cell mechanisms, including its anti-inflammatory properties. It is important to achieve a level of vitamin D at least 30 ng/mL, since this dose has been shown to be optimal also for other health conditions.

B Vitamins B vitamins, particularly low dietary folate has also been specifically associated with increased risk of colorectal cancers. In 1998 USA introduced mandatory folate fortification of flour and breakfast cereals.

Antioxidants and Other Micronutrients Several other dietary micronutrients, including selenium, beta carotene, and vitamins A, C, and E are believed to have anti-carcinogenic effects, based on their anti-oxidant or anti-inflammatory properties. However the clinical studies showed that they do not appear to prevent colorectal cancer.

LIFESTYLE

Alcohol The relationship between alcohol and cancer has been controversial, but most evidence indicates that high intake of alcohol increases risk of colorectal cancer. Men who drink more than two glasses of alcohol per day had a two-fold higher risk of colon cancer compared to men who drank less than 0.25 glass per day.

Tobacco Studies in the U.S. have estimated that approximately 15 percent to 20 percent of colorectal cancers can be attributed to smoking. Tobacco use has been consistently associated with a two-fold increased risk of colorectal polyp-adenoma.

Body Mass and Fat Distribution Men in the highest quintile of BMI having nearly a two-fold higher risk of colon cancer compared with men in the lowest quintile. Women with a BMI >29 kg/m2 had a 1.5-fold increased risk of colon cancer and two-fold increased risk of large (≥ 1cm) adenoma. Fat distribution is also an important factor. Colon cancer risk increased with increasing waist circumference.

Physical Activity An association between greater levels of physical activity and decreased risk of colon cancer has been one of the most consistently observed. Physically active individuals had a 20 percent to 30 percent lower risk of colon cancer compared to less active individuals.

Prevention is better than cure. Cutting down intake of red and processed meats, high-fat dairy products, highly refined grains and starches, and sugars and replacing them with poultry, fish and plant sources as the primary source of protein can help reduce the risk. Improving the understanding of diet and healthy lifestyle might add further benefit and reduce risk of colorectal cancer.