Diet and Your Risk of Bowel Cancer

Know which foods increase or decrease your chances of this common cancer
By Suzanne Mahady, Monash University
September 23, 2019 Updated: September 24, 2019

Australia has one of the highest rates of bowel cancer in the world, though the United States is high as well. In 2017, bowel cancer was the second-most-common cancer in Australia and rates are increasing in people under 50.

The World Health Organization puts the cumulative risk of developing collector cancer at 4.1 percent in Australia and New Zealand, compared to 2.96 percent in North America, which is still comparatively high in international rankings.

Up to 35 percent of cancers worldwide might be caused by lifestyle factors such as diet and smoking. So how can we go about reducing our risk of bowel cancer?

What to Eat

Based on current evidence, a high-fiber diet is important to reduce bowel cancer risk. Fiber can be divided into two types: insoluble fiber, which creates a bulky stool that can be easily passed along the bowel; and soluble fiber, which draws in water to keep the stool soft.

Fiber from cereal and whole grains is an ideal fiber source. Australian guidelines suggest aiming for 30 grams of fiber per day for adults, but fewer than 20 percent of Australian adults meet that target. In the United States, as few as 5 percent are eating recommended levels of fiber daily.

Wheat bran is one of the richest sources of fiber, and in an Australian trial in people at high risk of bowel cancer, 25 grams of wheat bran reduced precancerous growths. Wheat bran can be added to cooking, smoothies, and your usual cereal.

It’s not clear how fiber may reduce bowel cancer risk, but possible mechanisms include reducing the time it takes food to pass through the gut (and therefore exposure to potential carcinogens), or through a beneficial effect on gut bacteria.

Once bowel cancer is diagnosed, a high-fiber diet has also been associated with improved survival.

Milk and dairy products are also thought to reduce bowel cancer risk. The evidence for milk is graded as “probably protective” in current Australian bowel cancer guidelines, with the benefit increasing with higher amounts.

Oily fish may also have some protective elements. In people with hereditary conditions that make them prone to developing lots of precancerous growths (polyps) in the bowel, a trial where one group received a daily supplement of an omega 3 polyunsaturated fatty acid (found in fish oil) and one group received a placebo, found that this supplement was associated with reduced polyp growth. Whether this is also true for people at average risk of bowel cancer, which is most of the population, is unknown.

And while only an observational study (meaning it only shows a correlation, and not that one caused the other), a study of bowel cancer patients showed improved survival was associated with daily consumption of coffee.

What to Avoid

It’s best to avoid large quantities of meat. International cancer authorities affirm there is convincing evidence for a relationship between high meat intake and bowel cancer. This includes red meat, derived from mammalian muscle such as beef, veal, lamb, pork, and goat, and processed meat such as ham, bacon, and sausages.

Processed meats have undergone a preservation technique such as smoking, salting, or the addition of chemical preservatives that are associated with the production of compounds that may be carcinogenic.

Evidence also suggests a “dose-response” relationship, with cancer risk rising with increasing meat intake, particularly processed meats. Current American and Australian guidelines both suggest minimizing intake of processed meats as much as possible and eating only moderate amounts of red meat.

What Else Can I Do to Reduce Risk of Bowel Cancer?

The key to reducing cancer risk is leading an overall healthy lifestyle. Adequate physical activity and avoiding excess fat around the tummy area are important. Other unhealthy lifestyle behaviors such as eating lots of processed foods have been associated with increased cancer risk.

Health authorities in Australia and the United States recommend people over 50 get screened for bowel cancer. Australians can participate in the National Bowel Cancer Screening program.

Screening is one of the most effective, and evidence-based ways, to reduce your risk.

 is a gastroenterologist & clinical epidemiologist and senior lecturer at Monash University in Australia. This article was first published on The Conversation.

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