Exploring the Possible Link between Diet and Colorectal Cancer

  • 19 Apr 2023
  • 6 mins

Colorectal cancer remains the leading cancer affecting men and women in Singapore across all races1 and by age-standardized incidences, the rate is among the higher levels in the world.2 In addition to the risk factors like age, family history, and ethnicity, is having a poor diet. Dietitian Ms. Wong Chai Ling explains how diet is related to colorectal cancer and how the different food types help to prevent and fight the disease.

Poor Diet Risks

With the urban lifestyle found in Singapore – where both parents in a nuclear family are most likely working – most working adults, youths, and children would likely eat out for convenience. Being busy also means that many lean towards eating easy-to-prepare processed food, which is typically higher in calories.3

Even when work and study were arranged to be conducted at home during the pandemic, it did not curb “eating out.” Food orders increased during the pandemic.4 This suggests more still preferred to “eat out” than to cook at home, though being at home.

Other than the main factor of working and studying mainly from home during this time at play, which may have made it less conducive to cook, there were also the roles of reduced cooking skills5 and a craving for food variety6 to consider. These dietary habits may lead to a poor diet.

“A poor diet can be defined in relation to poor eating habits including undereating or overeating, and not having enough of the healthy balanced nutritious foods we need for our bodies to function well,” Ms. Wong explains.

Eating out correlates with higher calorie and fat intake and may involve the risk of lacking in some nutrients. And we tend to choose foods based on our mood or cravings accordingly instead of making healthy choices along with the likelihood of eating extras found in upsized portions and desserts. Also, if alcohol is taken with a meal, this may encourage us to eat more. There is also no control over cooking methods or ingredients.

“Frequent consumption of excessive amounts of unhealthy food and beverages with low nutritional value, such as sugar-sweetened beverages, highly processed food, along with high saturated fat and salt intake, eating food low in fiber, and alcohol intake will increase the risk of weight gain. It may potentially lead to obesity, if the excess calories are not burnt, chronic diseases and some cancers,” she adds.

A Poor Diet Ups the Risk of Colorectal Cancer

According to the World Cancer Research Fund/American Institute for Cancer Research, a poor diet may increase the risk of colorectal cancer.7

Probable evidence showed that eating more than 18 oz of red meat weekly, which includes beef, pork, and lamb, increases colorectal cancer risk.

Processed meat, such as luncheon meat and ham, is preserved by smoking, curing, salting, or adding preservatives. Consuming 3.5 oz of processed meat daily increases the risk of colorectal cancer by 36% compared to someone who eats no processed meats.

More than 1 oz above recommended alcohol consumption daily also increases the risk of colorectal cancer. Alcohol damages the cells lining the colon and rectum, leading to inflammation and increased cell growth, which can increase the risk of cancer.

In addition, alcohol can impair the body's ability to absorb nutrients, including folate, which is essential for DNA synthesis and repair. This impairment also contributes to cancer risk.

“Everyone is encouraged to eat a rainbow of fruits and vegetables, and balance these with nutrient-dense foods from other food groups to maintain overall health and well-being. It may also potentially reduce the risk of some cancers and chronic diseases,” she advises.

If the severity of the septal deviation is mild, the patient may respond well to medical therapy such as with the use of intranasal steroid sprays or nasal decongestants. 

Surgical intervention can be considered should the patient fail to improve with medical therapy or if he would like a permanent solution without having to rely on medications in the long term. 

Super Fiber

Consuming fiber-rich foods, such as fruits and vegetables, decreases colorectal cancer risks. A high intake of dietary fiber, of at least 22 grams per day, is associated with improved colorectal cancer survival.8

The Singapore Health Promotion Board recommends a daily dietary fiber intake of 20 g for women and 26 g for men. This equates to two servings of fruit and two servings of vegetables daily or a half plate of fruits and vegetables for each meal. Fiber from whole grains, nuts, and seeds also helps to reduce the risk of colorectal cancer.

"The fiber in these foods are fermented by gut bacteria to produce short chain fatty acids during digestion and promote the pH needed in the gut for nutrient absorption and prevent the abnormal differentiation of cancer cells," Ms. Wong explains. “It also helps to reduce insulin resistance and the risk of high blood sugar.”

Any imbalance in the body’s pH required for healthy functions may result in poor absorption of nutrients and digestive health.

Grains tend to be high in fiber, likewise for antioxidant food with Vitamin E, selenium, copper, zinc, and lignans. The examples of foods rich in lignans are flaxseeds, barley, and sesame seeds.

“Besides being rich in fiber, the antioxidant foods provide anti-tumorigenic agents which help to capture free radicals and regulate any abnormal changes that could be happening in body cells,” she adds.

Most types of berries, especially raspberries, have antioxidants. Studies support that raspberries protect the body from cell damage that could lead to cancer.9

Legumes, which include soybeans, peas, beans, and lentils, are another super fiber food. Legumes have anti-carcinogens and studies show legumes’ protective effects against cancer. In addition, legumes are good dietary protein sources and also contain Vitamin E, Vitamin B, selenium, Vitamin B6, and lignans, all of which may also possess potential cancer-preventive effects.10

In addition, legumes are rich in dietary fiber, which may increase stool bulk, decrease bowel transit time, and dilute potential carcinogens in the gastrointestinal tract. "When increasing fiber in your diet, do it gradually and drink plenty of water," Ms. Wong says.

Eat Meat in Moderation

Animal foods are good sources of protein and Vitamin B12 and red meat provides iron, zinc, and B vitamins.

Though there is a probable link between red meat and colorectal cancer, the results of research have not reached high significance.11 However, Ms. Wong advises that meat consumption daily should be limited and balanced with a fiber-based diet.

“Limit eating cooked lean meats to not more than 18 oz per week and schedule meat consumption to once or twice a week or use meat as a treat rather than the star ingredient. For instance, 30-60 g of red meat can be mixed with beans, legumes, lentils, and other vegetables," Ms. Wong advises.

However, suppose the meat is processed by smoking, curing, salting, or adding preservatives before consumption; in this case, there is convincing evidence that increased processed meat consumption may lead to a higher risk of colorectal cancer. Hence, eating any processed meat, including fish here, could put you at risk.

Fish is a good source of polyunsaturated fatty acids (PUFAs). According to research, PUFAs are promising immune-nutrition agents for improving total postoperative infectious complications and anti-inflammation of colorectal cancer patients. In addition, PUFAs may be associated with an improved immune status.12

“In addition, fish is a good source of protein and, unlike fatty meat products, it is not high in saturated fat. Fatty fish is also a good source of omega-3 fatty acids. Research has shown that omega-3 fatty acids help to reduce heart disease and stroke risks," she adds.

However, more research is still needed to ensure more conclusive results on whether fish consumption helps to reduce the risk of colorectal cancer.

Add Calcium to the Diet

"You are also encouraged to include good animal-based protein sources and both low-fat and non-fat dairy products for adequate daily calcium intake in your diet. For instance, eggs are good animal protein sources," Ms. Wong suggests.

Epidemiological studies of people over a certain time suggest the presence of a protective role of high calcium intakes, whether from food or supplements, from colorectal cancer.13

"Low levels of dietary calcium are associated with increased colorectal cancer risks in these studies," she adds.

However, because of the possible increased risk of prostate cancer in men with a high calcium or dairy product intake, the American Cancer Society has no specific recommendations regarding dairy food consumption for cancer prevention.

Calcium and Vitamin D might work together to reduce colorectal cancer risk, as Vitamin D aids in the body's calcium absorption. But not all of the associated studies have found that supplements of these nutrients reduce risk.

In addition to milk and other dairy foods, calcium is available in soya bean products (e.g. tofu, tau huay), small fishes (eaten with bones), and green leafy vegetables. However, calcium from vegetables may not be well absorbed.

Nuts about Food

Generally, nuts are key components of healthy dietary patterns being are good sources of protein, healthy fat, and dietary fiber. According to a study, higher intake of total nuts and tree nuts is associated with a lower risk of cancer. And tree nuts showed the most protective effects among the different types of nuts. Tree nuts include walnuts, pistachios, macadamia, pecans, cashews, almonds, hazelnuts, and Brazil nuts.14

Cooking Method Matters

In addition, cooking red meat at high temperatures above 149oC produces carcinogenic compounds that are risk factors for cancer formation.

To reduce carcinogenic compounds during cooking, Ms. Wong offers the following tips:

  • Avoid exposing the meat to an open flame or a hot metal surface.
  • Avoid prolonged cooking times.
  • Use a microwave oven to cook the meat before exposure to high temperatures.
  • Continuously turn the meat over on a high-heat surface.
  • Remove charred portions of meat.
  • Refrain from using meat drippings to make gravy.

Little Benefit from Organic Food–based Diet and Vitamins

Generally, organic foods are less likely to contain pesticide residues than conventional foods. While a study has concluded a positive association between a higher frequency of organic food consumption and a reduced risk of cancer, the results are not specific to reducing colorectal cancer.15

“Research also shows relatively small differences in polyphenol compounds and vitamin content when comparing organic and inorganic foods. These differences have yet to show a change in patient outcomes,” she elaborates.

Polyphenols are known for their antioxidant properties. They help protect the body's tissues from damage and reduce inflammation and risks of diseases including cancer. Common sources of polyphenols are berries and green tea.

Most studies have also found no significant benefit from taking multivitamins or mineral supplements daily to protect against or prevent cancer. Research has shown that Vitamin D does not seem to have a role in preventing colorectal cancer, but the benefits are significant for individuals with severe Vitamin D deficiency.16

Likewise, for Vitamin B9 (folate), B6, and B2, research is inconclusive that these help to lower colorectal cancer risk.17

“Research does not contain concrete evidence to show that antioxidant supplements, alone, help to prevent cancer. However, the use of antioxidants supplements, along with a healthy lifestyle and well-balanced diet, can help to lower the chances of developing certain cancers,” she says.

Colorectal Cancer: A Diet Plan

Foods may taste differently, and side effects from treatment like mouth sores or cold sensitivity might make eating challenging. Understandably, a patient’s appetite will be affected. However, nutrition requirements must increase during cancer treatment and there is no "magic bullet" diet that will give the body all of the nutrients required.

Ms. Wong advises to balance the intake of the following food and food groups to receive proper nutrients and combat unwanted weight loss and inflammation.

1. For adequate protein and calorie intake

Good protein sources

  • Animal-based protein from e.g. fish, poultry, meat, eggs, milk, milk products.
  • Plant-based protein from e.g. soya milk, soya products including bean curd, nuts, seeds, legumes.

Calorie-dense foods

  • Whole milk, cheese, yogurt, ice cream, cream, butter, avocado, nuts, seeds, oil, jam, dried fruits.
  • If eating is difficult and/or weight loss occurs during treatment, including total fat and sugars in the diet is acceptable. The main goal is to assist a patient in undergoing treatment during the difficult period.

2. For adequate fluid intake

If eating is difficult and/or weight loss occurs, focus on consuming fluids with calories and protein rather than water e.g. milk, milkshakes, smoothies, soup (made with milk, chicken, fish, meat, legumes), and nutritional supplements.

3. For intake of other nutrients – vitamins and minerals

Get vitamins and minerals from vegetables, whole grains, legumes, and fruits.

If a patient is not eating well and is undergoing treatment, it is advisable for him to check with his doctor before taking any multivitamins.

“Supplementing with large doses of antioxidants by using Vitamins A, C, and E, selenium, and zinc, is not recommended during treatment,” Ms. Wong cautions.

Studies have shown taking antioxidant supplements may interfere with chemotherapy and radiation therapy. While protecting the healthy cells, antioxidants may also protect the tumor cells. This may result in reduced treatment effectiveness. As no two people with the same cancer are the same, it is unclear as to the effect antioxidants have on cancer treatment.18 Hence, checking and clarifying with the oncologist before taking supplements is essential.

"If you are not eating so well during treatment, but would like to cook, you may consider cooking and prepare your food in advance and freezing what you have prepared in small portions. You may steam your food or boil selected ingredients to make a soup; such methods can help to retain most of the nutrients," Ms. Wong outlines.

She also recommends using My Healthy Plate as a guide to help set the right proportions of food groups for a well-balanced meal. Essentially, this means filling a quarter of a plate with whole grains, another quarter with good protein sources, and the balance with fruit and vegetables.

"If you cannot find a meal that fits the quarter, quarter and half proportions, you can make up what is missing in your next meal," she suggests.

Keep Up Good Eating Habits Post-treatment

“You are encouraged ideally, prior to treatment, to eat healthily and once the treatments are completed, and you are moving beyond your treatments, you should resume your healthy eating practices,” Ms. Wong says.

Indeed, our diet has a role in preventing and fighting colorectal cancer. Whether red meat is the leading cause or having more fiber in our diet is the primary prevention, various studies have shown how our diet and colorectal cancer can be related.

Ultimately, making appropriate choices across food groups, particularly regarding fruit, vegetables, and fiber, is critical to healthy eating.

1 https://gco.iarc.fr/today/data/factsheets/populations/702-singapore-fact-sheets.pdf
2 https://www.healthhub.sg/live-healthy/106/screening_colorectal_cancer_nuhs
3 https://www.healthxchange.sg/news/singaporeans-eating-more-due-to-busy-lifestyles-food-variety
4 https://www.straitstimes.com/singapore/consumer/habitual-use-of-food-delivery-platforms-likely-to-last-past-pandemic-say-consumers-and-observers
5 https://www.statista.com/statistics/1148008/singapore-reasons-using-food-delivery-apps-more-during-covid-19/
6 https://www.healthxchange.sg/news/singaporeans-eating-more-due-to-busy-lifestyles-food-variety
7 https://www.wcrf.org/wp-content/uploads/2021/02/Colorectal-cancer-report.pdf
8 Zhao J, Zhu Y, Du M, Wang Y, Vallis J, Parfrey PS, Mclaughlin JR, Qi X, Wang PP. Association between Dietary Fiber Intake and Mortality among Colorectal Cancer Survivors: Results from the Newfoundland Familial Colorectal Cancer Cohort Study and a Meta-Analysis of Prospective Studies. Cancers (Basel). 2022 Aug 4;14(15):3801. doi: 10.3390/cancers14153801. PMID: 35954465; PMCID: PMC9367345.
9 https://www.aicr.org/cancer-prevention/food-facts/raspberries/
10 Zhu B, Sun Y, Qi L, Zhong R, Miao X. Dietary legume consumption reduces risk of colorectal cancer: evidence from a meta-analysis of cohort studies. Sci Rep. 2015 Mar 5;5:8797. doi: 10.1038/srep08797. PMID: 25739376; PMCID: PMC4350074.
11 https://www.wcrf.org/wp-content/uploads/2021/02/Colorectal-cancer-report.pdf 12 Li L, Wang D, He N, Dai S, Tu L, Fu R, Chen P. Effects of Polyunsaturated Fatty Acids on Colorectal Cancer Patients: A Meta-Analysis of Randomized Controlled Trials. Nutr Cancer. 2023;75(2):627-639. doi: 10.1080/01635581.2022.2145319. Epub 2022 Nov 13. PMID: 36372063.
13 https://www.wcrf.org/wp-content/uploads/2021/02/Colorectal-cancer-report.pdf
14 Naghshi S, Sadeghian M, Nasiri M, Mobarak S, Asadi M, Sadeghi O. Association of Total Nut, Tree Nut, Peanut, and Peanut Butter Consumption with Cancer Incidence and Mortality: A Comprehensive Systematic Review and Dose-Response Meta-Analysis of Observational Studies. Adv Nutr. 2021 Jun 1;12(3):793-808. doi: 10.1093/advances/nmaa152. PMID: 33307550; PMCID: PMC8166551.
15 Baudry J, Assmann KE, Touvier M, Allès B, Seconda L, Latino-Martel P, Ezzedine K, Galan P, Hercberg S, Lairon D, Kesse-Guyot E. Association of Frequency of Organic Food Consumption With Cancer Risk: Findings From the NutriNet-Santé Prospective Cohort Study. JAMA Intern Med. 2018 Dec 1;178(12):1597-1606. doi: 10.1001/jamainternmed.2018.4357. Erratum in: JAMA Intern Med. 2018 Dec 1;178(12):1732. PMID: 30422212; PMCID: PMC6583612. 16 Emmanouilidou G, Kalopitas G, Bakaloudi DR, Karanika E, Theocharidou E, Germanidis G, Chourdakis M. Vitamin D as a chemopreventive agent in colorectal neoplasms. A systematic review and meta-analysis of randomized controlled trials. Pharmacol Ther. 2022 Sep;237:108252. doi: 10.1016/j.pharmthera.2022.108252. Epub 2022 Aug 1. PMID: 35926664

17 Liu Y, Yu Q, Zhu Z, Zhang J, Chen M, Tang P, Li K. Vitamin and multiple-vitamin supplement intake and incidence of colorectal cancer: a meta-analysis of cohort studies. Med Oncol. 2015 Jan;32(1):434. doi: 10.1007/s12032-014-0434-5. Epub 2014 Dec 10. PMID: 25491145.
18 https://www.oncologynutrition.org/erfc/eating-well-when-unwell/antioxidant-supplements-safe-during-therapy

Contributed by

Ms. Wong Chai Ling
Farrer Park Hospital