Older lady talking to GP

Bowel cancer – what’s your risk?

Know the symptoms and how to reduce your risk

Reviewed by Valion Health


Australia has one of the highest rates of bowel cancer in the world, with 1 in 15 Australians developing the disease in their lifetime. It also holds the ominous title of being Australia's second deadliest cancer, claiming the lives of 103 Aussies every week. While your risk of developing bowel cancer rises after the age of 50, the number of Australians under age 50 who are diagnosed is on the up. The good news is that almost 99% of bowel cancer cases can be treated successfully if picked up early, so it’s important to know the symptoms and what you can do to reduce your risk.


What is bowel cancer?

Bowel cancer (or colorectal cancer) can affect any part of the colon or rectum. Depending on where the cancer is located, you might also hear it referred to as colon or rectal cancer. Ready for the biology bit? The colon and rectum are parts of the large intestine. The colon is the longest part (the first 1.8m) and its job is to receive almost completely digested food, absorb water and nutrients, and pass waste (stool/faeces/poo) to the rectum. The rectum is the lower part (the last 15cm), and it receives waste from the colon and stores it until it passes out of the body through the anus (the opening at the lower end of the rectum).


What are the symptoms?

There are often no symptoms during the early stages of bowel cancer, which is why screening is so important. As a cancerous tumour grows though, it can narrow and block the bowel which may lead to noticeable changes to the size, shape, and/or colour of poo. This can happen with or without bleeding from the rectum. Cancers in the left side of the colon generally cause constipation alternating with diarrhoea, abdominal pain, nausea and vomiting, while right-sided cancers produce vague, abdominal aching.

If you experience any of these symptoms for more than two weeks you should talk to your GP who can refer you to a specialist for a colonoscopy to investigate the cause:

  • A recent, persistent change in bowel habit (such as looser, more diarrhoea-like poo, constipation, going to the toilet more often, or trying to go)
  • A change in shape or appearance of your poo (like narrower poos than usual or mucus in poo)
  • Blood in your poo or rectal bleeding
  • Frequent gas, pain or cramps
  • A feeling of fullness or bloating in the bowel or rectum
  • Unexplained anaemia (a low red blood count that can cause tiredness, weakness or weight loss)
  • A feeling that the bowel has not emptied completely after going to the toilet
  • Pain or a lump in the anus or rectum
  • Abdominal pain or swelling


Risk factors (and how to reduce your risk)

There are two kinds of risk factors for bowel cancer: modifiable (things that can be changed) and non-modifiable (things that can’t).

Modifiable risks


Your risk of developing bowel cancer increases significantly if you drink two or more alcoholic drinks a day. So if you choose to drink alcohol, try not to overdo it.


Taking aspirin every day for at least 5 years decreases the risk of both developing and dying from bowel cancer. But it’s important to talk to your GP first because other conditions could be made worse by aspirin.

Body fat

The risk of bowel cancer rises with increased body fat. As an adult it’s important to keep your weight within a healthy BMI (body mass index) range and avoid gaining weight or increases to your waist circumference.

Dairy products and calcium supplements

Consuming 400g of dairy products per day, such as low-fat milk, yoghurt and cheese, decreases your risk of bowel cancer by 15%. If you’re lactose intolerant, chat to your GP or nutritionist about a calcium supplement.

Physical activity

Physical activity can reduce colon (not rectal) cancer by 16%, so aim to be physically active (heart rate elevated) for at least 30 minutes a day and try not to sit still for too long (like when you’re watching TV).

Polyp removal

Most bowel cancers start as benign, non-threatening polyps on the wall of the bowel (called “adenomatous” polyps). These are usually harmless, but they can become cancerous and over time develop into a cancerous tumour.

Red and processed meat

Eating too much red meat, especially processed meats, increases your risk of bowel cancer. Eat no more than three portions per week (about 350–500g) and avoid processed meats where possible.


Smoking 40 cigarettes (two packs) per day increases your risk of developing bowel cancer by around 40% and nearly doubles your risk of dying from it. Quit smoking and avoid exposure to tobacco smoke.

Wholegrains and dietary fibre

Eating at least 90g of wholegrains a day can reduce your risk of bowel cancer by 17%. As a guide, your plate should be two-thirds wholegrains, vegetables, fruits, beans, nuts, and one-third poultry or lean red meat.


Non-modifiable risks


As you age your risk of bowel cancer increases, from 1 in 189 before aged 50 to 1 in 15 after (when you’re more likely to grow polyps). But rates are rising in young adults and it’s now the sixth leading cause of death overall for Aussies aged 25–44.

Family history 

In around 30% of all bowel cancer cases diagnosed, there’s a family history present. Generally the more members of a family affected by bowel cancer and the younger they were at diagnosis, the greater the chance. Check your risk.

Genetic inheritance

Genetic mutations have been identified as the cause of inherited cancer risk in some bowel cancer–prone families (around 5–10% of bowel cancer cases overall). Make sure you know your family history and talk to your GP if there’s a strong family history of bowel cancer.

Inflammatory Bowel Disease (IBD)

Crohn's disease and ulcerative colitis (both inflammatory bowel diseases) can cause inflammation of the colon and rectum. People with these conditions have an increased risk of developing bowel cancer and should be monitored regularly.


Screening and surveillance

As well as a healthy diet and lifestyle choices, screening and surveillance can help to reduce your bowel cancer risk. Bowel cancer screening is easy and can even be done at home! If you’re aged 50–74 you can get a free faecal immunochemical test (FIT) in the post every two years through the National Bowel Cancer Screening Program (NBCSP). Screening involves collecting small samples of toilet water or poo on a card or in a container and sending them to a pathology lab for analysis. The results are sent back to you and your GP.

The test can detect blood (one possible symptom of bowel cancer) that can’t be seen with the naked eye. A positive result means blood in poo has been detected (which will then need further investigation by a GP and a referral for colonoscopy within 30 days) while a negative result means blood in poo hasn’t been detected in the samples.

If you’re not eligible for the NBCSP, talk to your GP or pharmacist about BowelScreen Australia, or order a screening test online or by calling Bowel Cancer Australia's Helpline on 1800 555 494. If you’re from a family with a history of bowel cancer, you may need extra testing (like regular colonoscopies) to detect bowel cancer early, before you’re 50. If you think you have a family history of bowel cancer or an inherited gene mutation, talk to your GP.


Remember, you’re not alone

Bowel Cancer Australia provides practical and emotional support to anyone affected by bowel cancer, including information, resources and support. Eligible Teachers Health members can also access support through our Cancer Support Program.


Valion Health support eligible Teachers Health members through the Cancer Support Program.