Bowel cancer and diet

June is Bowel Cancer Awareness Month, an annual reminder from Cancer Australia of a cancer that touches many lives and cannot only be prevented but also treated when caught in time.

Bowel cancer is the second deadliest cancer in Australia. About 103 people die due to bowel cancer each week (about 5350 people per year).

What is bowel cancer?

“Bowel cancer, also known as colorectal cancer, can affect any part of the colon or rectum; it may also be referred to as colon cancer or rectal cancer, depending on where the cancer is located (1)”.

Bowel cancer risk factors

Like any health conditions, risk factors for bowel cancer can be split in unmodifiable and non-modifiable.

Non-modifiable risk factors include age, family history, genetic factors and some related conditions such as Crohn’s disease and ulcerative colitis.

Modifiable risk factors include diet, body composition, physical activity, smoking and medication use.

Bowel cancer and diet

Dietary choices can alter a person’s risk of developing bowel cancer. The evidence below comes from the 2018 Continuous Update Project Expert Report prepared by the World Cancer Research Fund and American Institute for Cancer Research (2).

Convincing evidence

Alcohol

Consuming 2 or more standard drinks per day increases the risk of bowel cancer.

This could be due to the toxic effects of acetaldehyde, a toxic product of alcohol metabolism, on colonic cells, due to increased oxidative stress, or other mechanisms.

Processed meats

Consuming processed meats is a convincing cause of bowel cancer. Processed meats are those preserved by smoking, curing, salting or addition of chemical preservatives.

The evidence shows the risk increases per 50 grams of cured meats per day.

Processed meats are high in fat and a source of potentially carcinogenic compounds.

Body composition

Convincing evidence supports the fact that being overweight or obese, measured by BMI above 27 kg/m², large waist circumference or large waist-to-hip-ratio, increases the risk of bowel cancer.

A high proportion of body fat is associated with increased insulin levels and systemic inflammation, both of which may increase the risk of bowel cancer.

Probable evidence

Wholegrains

Consumption of wholegrains probably protects against bowel cancer, with the risk decreasing at intakes of 90 grams per day.

Wholegrains are a source of dietary fibre, which may lead to the production of beneficial short-chain fatty acids, reduce transit time of stools in the intestines, and prevent insulin resistance. In addition, wholegrains are a source of several vitamins, minerals and phytochemicals which may have protective effects against cancer.

Dietary fibre

Consumption of foods containing dietary fibre probably protects against colon cancer.

Dietary fibre gets fermented by gut bacteria in the intestines, leading to the production of short-chain fatty acids, which are protective against bowel cancer. In addition, dietary fibre may lead to better toilet habits and reduced insulin resistance.

Dairy products

Consumption of dairy products probably protects against bowel cancer. The risk for bowel cancer is significantly decreased per 400 grams per day.

Broken down by types of dairy foods, the evidence is stronger for milk (with a decreased risk per 200 grams per day) than for cheese.

Studies linking dietary calcium intake with risk of bowel cancer have also shown benefits, suggesting that dairy foods are protective against bowel cancer.

Calcium supplements

There is evidence that taking calcium supplements (anywhere between 200 to 1000mg per day) may protect against bowel cancer.

Red meat

There is some evidence that consumption of red meat may be associated with bowel cancer, however the evidence is not strong and, in cases, not significant. Interestingly, one study showed the opposite effect.

The carcinogenic potential of red meat consumption is related to compounds that are produced when cooking at high temperatures and compounds that can be produced in the body from haem iron.

Limited evidence

There is limited evidence that consumption of the following foods and nutrients may protect against bowel cancer:

• Foods containing vitamin C
• Fish
• Non-starchy vegetables
• Fruits
• Vitamin D
• Multivitamin supplements

Bowel cancer and diet – Summary and recommendations

Besides being physically active and not smoking, eating a healthy diet is likely protective against bowel cancer. Specific recommendations include:

• Drinking less than 2 standard drinks per day, ideally having several alcohol-free days per week or not drinking at all
• Limiting consumption of processed meats such as bacon, salami and many processed sausages, ideally 1-2 portions per week as a maximum
• Maintaining a healthy body composition
• Choosing wholegrains instead of refined grains
• Eating sufficient dietary fibre (at least 25 grams per day for adult women and at least 30 grams per day for adult men)
• Consuming dairy products such as milk and yoghurt, reduced fat if necessary
• Choosing a variety of protein sources, including fish, rather than eating red meat all the time. When eating red meat, using a variety of cooking methods rather than using only high temperature methods (e.g. grilling, frying).
• Eating a variety of non-starchy vegetables and fruits, including those high in vitamin C (e.g. tomatoes, capsicum, broccoli, citrus fruit, strawberries)

References

1. Bowel Cancer Australia. Bowel Cancer Awareness Month. Available at: https://www.bowelcanceraustralia.org/bowel-cancer-awareness-month
2. World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Report 2018. Diet, nutrition, physical activity and colorectal cancer. Available at: http://dietandcancerreport.org

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