Medical screening for early signs of disease are becoming increasingly common. These procedures come in a variety of forms – the simple measurement of blood pressure at a doctor’s visit to screen for cardiovascular disease; for females, a Pap smear looking for abnormal cells that might suggest cervical cancer or undergoing a mammography to look for any signs of the development of breast cancer; and for males, a much-dreaded rectal exam searching for lumps that could be prostate cancer. (1) Many such procedures are over quickly and cause little concern for the person being tested but others are not. A case in point is one of the screening methods for colorectal cancer (cancer occurring in the colon (aka the large intestine, the last section of the intestine) or in the rectum.)
Screening for colorectal cancer can take a few different forms. Until a few years ago, colonoscopy was the method of choice. But now, simpler methods are utilized first such as a FOBT (Fecal Occult Blood Test), a check for blood hiding within a stool sample, or an examination of the lower colon and rectum using flexible sigmoidoscopy (the insertion of a thin, flexible tube with a camera on its tip into the rectum and up through the last two feet of the colon until it encounters the 90° bend where the colon changes direction). (2,3).
In contrast, a colonoscopy allows observation of the whole length of the colon as well as the rectum. It offers the opportunity to remove any polyps or other abnormal tissue found there during the test and to sample this suspect tissue to see if it is showing signs of cancer. Because of this, a colonoscopy can prevent colorectal cancer from developing and, if cancer is detected during a colonoscopy, it is often in its early stages and curable. (4,5) However, a colonoscopy is an invasive process that requires an anaesthetic and, though very rare, comes with risks. The procedure can cause intestinal perforations, tiny tears in the wall of the colon or rectum; bleeding; infection; and adverse reactions to the anaesthetic. (6) Nowadays colonoscopies are generally reserved for those with a higher risk of colorectal cancer due to a strong family history or whose FOBT or sigmoidoscopy have revealed some issues that require further follow-up (7).
One other disadvantage of a colonoscopy is that it necessitates a fair amount of preparation beforehand that can interfere with normal living for several days. Eating plant-based adds an extra layer of complexity to the steps that need to be taken before the test is done and the information provided to a colonoscopy patient does not take into consideration the type of diet the person may be eating. Clearing up this confusion is the purpose of this article.
Prepping for a colonoscopy if you’re Eating a Standard Western Diet
Colonoscopy preparation is extensive because, in order to examine the inside walls of the colon, those walls must be clean. Many foods, especially those high in fiber, leave residues along the colon walls that make them difficult to see.
Common recommendations for cleaning out a bowel go something like this (8,9,4);
- Starting five days before the colonoscopy appointment, the intake of some foods, especially those containing fiber, will be restricted.
- Instructions will state that you must avoid whole grain bread, cereals, and pasta; brown or wild rice; oatmeal; raw fruits or berries of any kind; raw vegetables; nuts and seeds; food containing any nuts or seeds; popcorn.
- Suggested foods that you can eat during this time are white bread or toast; white rice; white pasta; dairy products (yogurt, milk, cheese); eggs; chicken; beef; pork; fish; cooked steamed vegetables; canned fruits
- By two days before the colonoscopy appointment, no fiber-containing food should be eaten.
- One day before the exam, no food is to be consumed. You can drink but only clear liquids (plain water, black tea, black coffee, broth, clear carbonated beverages). Avoid red liquids (red-coloured drinks, beets or beet juice) because they can be mistaken for blood during a colonoscopy.
- Take the laxative preparation recommended by your medical practitioner. At this point you’ll want to stay near a bathroom as the need to defecate will become urgent and frequent.
But what if you’re a plant-based eater and everything you eat is full of fiber? Most of the foods on the suggested foods to eat before a colonoscopy list are foods that you never eat and never intend to eat. Read on to find out how to handle this situation.
Prepping for a Colonoscopy if You’re Eating a Plant-Based Diet (10,11)
When told to start a low-fiber diet a few days before your exam, you might feel overwhelmed and wonder how you’re going to get through those pre-colonoscopy days. Rest assured, there is a way to succeed. It might help to remember that this screening test is only a temporary situation and avoiding high fiber foods for a few days is only a very short time. In addition, there are quite a number of plant-based foods that you can enjoy at this time.
Foods you can eat during the five or six days preceding your colonoscopy;
- Fruits: Ripe bananas; ripe and peeled apricots and peaches; ripe cantaloupe and honeydew melon; ripe papaya; ripe avocado
- Vegetables: Well-cooked asparagus tips; peeled carrots cooked until soft; well-cooked mushrooms; white potatoes, peeled and cooked until soft
- Grains: White rice; white pasta; cream of wheat; cornflakes; puffed rice; breads made with refined white flour (including rolls, muffins, bagels)
- Plant-based milks, tea, coffee, juices
Food to avoid during the five or six days preceding your colonoscopy;
Raw plant foods
- Fruits with skins; dried fruits
- Vegetables with skins; legumes; corn
- Multigrain breads and cereals, oatmeal
- Nuts and seeds
On the day before your colonoscopy;
At this point you will be on a clear liquid diet. This means you can’t consume anything except liquids that you can see through. These include plain water; tea or coffee without milk; vegetable broth; clear carbonated water; and pulp-free juices (if they are not red in colour). Technically, you won’t be able to see through your coffee but for these purposes it is classed as a clear liquid.
After Your Colonoscopy, Go Back to Enjoying Your High Fiber Foods
Right after your colonoscopy, try to eat lighter portions of food than usual for the first couple of days. Include a small amount of higher fiber foods in your first meal post-colonoscopy but choose a gentle, easy-to-digest fiber such as well-cooked black beans in a stew or soup rather than harder-to-digest raw vegetables or salad. Also, avoid processed foods and junk food. After that first post-colonoscopy meal, you can return to your regular high fiber diet as quickly as you see fit.
To Sum Up…
Many scientific studies illustrate that the more fiber you eat, the less likely it is that you’ll develop colorectal cancer. Part of this effect may be due to the prevention of obesity linked with the ingestion of high-fiber foods because they keep a person feeling full and satiated. Obesity is related to increased risk of colorectal cancer. Fiber also moves waste efficiently through the gastrointestinal tract which lowers the exposure of the colon to any cancer-causing agents which might have been in the food. In addition, protective factors have been found in certain ways of eating, and especially in plants, that are associated with a decrease in the incidence of colorectal cancer. These include diets rich in fruits and vegetables, high-fiber diets, folate-rich diets, vitamin D, vitamin B6, garlic and calcium to name a few. Regular physical activity is also related to lower risk of colorectal cancer. (12,13,14,15)
A recent meta-analysis looked at the relationship of colorectal cancer incidence with inflammatory foods. Inflammation is a normal part of the body’s response to tissue injury. However, when inflammation becomes chronic, the destruction of tissue and its repair occurs simultaneously and continually, involving unceasing recruitment of pro-inflammatory cytokines. Increased levels of cytokines are linked to colorectal cancer. The study concluded that persons eating the highest amount of pro-inflammatory foods had a 40% increased risk of colorectal cancer compared to individuals consuming the lowest amount. Anti-inflammatory food components include a slew of compounds, many of which are found exclusively in plant-based foods – fiber, zinc, magnesium, selenium, monounsaturated fatty acids, polyunsaturated fatty acids, omega-3 fatty acids, omega-6 fatty acids, niacin, thiamin, riboflavin, vitamin B6, vitamin B12, vitamin A, vitamin C, vitamin D, vitamin E, folic acid, beta-carotene, anthocyanidins, flavan-3-ols, flavolols, flavanones, flavones, isoflavones, garlic, ginger, onions, thyme, oregano, saffron, turmeric, rosemary, caffeine and tea. Pro-inflammatory food components include sugars, refined carbohydrates, proteins, total fat, trans-fat, cholesterol, saturated fatty acids and iron, constituents of animal-sourced foods and processed foods. (16)
Components of diets can be related to colorectal cancer through other mechanisms too. For instance, consuming red and processed meat increases levels of heme iron; the processing of meat generates damaging N-nitroso compounds; and the cooking of meat induces the formation of polycyclic aromatic hydrocarbons and heterocyclic aromatic amines; all of which are associated with increased risk of colorectal cancer.
The message here is that you will make it through the colonoscopy process even if you eat only plants. But, even more importantly, eating more foods sourced from plants will provide protection from the development of cancer of the colon and rectum, the very cancer that a colonoscopy is used to detect.
12 Vulcan, A., Ericson, U., Manjer, J., Ohlsson, B. A colorectal cancer diet quality index is inversely associated with colorectal cancer in the Malmö diet and cancer study. Eur J Cancer Prev. 2019 Nov; 28(6): 463-471. Doi: 10.1097/CEJ.0000000000000486. PMID: 30422929.
13 Slattery, M.L. Diet, lifestyle, and colon cancer. Semin Gastrointest Dis. 2000 Jul; 11(3): 142-146. PMID: 10950460.
14 Thanikachalam, K., Khan, G. Colorectal Cancer and Nutrition. Nutrients. 2019 Jan 14;11(1):164.Doi: 10.3390/nu11010164. PMID: 30646512; PMCID: PMC6357054.
15 Song, M., Chan, A.T. Diet, Gut Microbiota, and Colorectal Cancer Prevention: A Review of Potential Mechanisms and Promising Targets for Future Research. Curr Colorectal Cancer Rep. 2017 Dec; 13(6): 429-439. Doi: 10.1007/s11888-017-0389-y. Epub 2017 Sep 4. PMID: 29333111; PMCID: PMC5761320.
16 Shivappa, N., Godos, J., Hébert, J.R., Wirth, M.D., Piuri, G., Speciani, A.F., Grosso, G. Dietary Inflammatory Index and Colorectal Cancer Risk-A Meta-Analysis. Nutrients. 2017 Sep 20; 9(9): 1043. Doi: 10.3390/nu9091043. PMID: 28930191; PMCID: PMC5622803.
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