For a long time, colorectal cancer — also known as bowel cancer — has been thought of as a disease that mainly affects older adults. And while the risk still increases considerably with age, something important has been changing: colorectal cancer is being diagnosed more frequently in people under 50.

In Australia, early-onset colorectal cancer has shown one of the largest increases among cancers affecting younger adults. Between 2000 and 2025, the incidence rate among Australians aged 20–49 increased from 10.6 to an estimated 17.9 cases per 100,000 people. The increase has been particularly striking among people in their 30s, with rates rising from 6.3 to an estimated 19 cases per 100,000 among those aged 30–39.

It's a trend researchers around the world are paying close attention to. Colorectal cancer is already a significant global health concern — it is the third most common cancer worldwide and the second leading cause of cancer-related death, according to the World Health Organization (WHO). 

So, why are more younger adults being diagnosed? We'll look at what's behind the rise in early-onset colorectal cancer, signs and risk factors to know, and practical steps that may help reduce your risk.

What is colorectal cancer?

Colorectal cancer is cancer that develops in the colon or rectum, which together make up the lower part of the digestive system. You may also hear it referred to as bowel cancer, particularly here in Australia. Cancer that begins in the colon is called colon cancer, while cancer beginning in the rectum is called rectal cancer; the term colorectal cancer covers both.

Many colorectal cancers begin as small growths on the inner lining of the bowel called polyps. Most polyps don't become cancerous, but certain types can gradually develop abnormal changes and become cancer over a period of years. This is one reason screening can be so valuable — some polyps can be identified and removed before they have the opportunity to develop into cancer.

As colorectal cancer develops, abnormal cells can grow into the wall of the bowel and, in more advanced cases, spread to nearby lymph nodes or other parts of the body.

Why are cases rising in people under 50?

At the moment, there isn't one definitive explanation. Cancer Australia describes early-onset cancers as likely resulting from a complex interplay of multiple factors, including changes in lifestyle, diet, obesity rates and environmental exposures. More recent research into early-onset colorectal cancer is also investigating metabolic health, early-life exposures and changes in the gut microbiome.

Importantly, genetics alone can't explain such a rapid change over just a few decades. Instead, researchers are looking closely at how the environments and lifestyles of more recent generations may differ from those that came before them.

Changes in diet and lifestyle

Some of the factors associated with colorectal cancer risk are already familiar. Diets containing large amounts of processed and red meat, lower intake of fibre-rich foods, physical inactivity, smoking and higher alcohol consumption have all been investigated in relation to colorectal cancer.

A 2026 Roadmap published in Nature Reviews Cancer examined what researchers currently know about the factors potentially contributing to colorectal cancer in people under 50. Researchers are particularly interested in how dietary and lifestyle patterns beginning much earlier in life could influence risk over time. Western-style dietary patterns — often characterised by greater consumption of ultra-processed foods, refined carbohydrates and saturated fats — are among the areas currently being investigated.

This doesn't mean that eating a particular food causes colorectal cancer. Cancer develops through a complex combination of factors, and overall dietary patterns and long-term exposures are more useful to consider than blaming individual foods.

Obesity and metabolic health

Another area receiving increasing attention is metabolic health.

A 2025 review published in Nature Reviews Endocrinology examined the potential relationship between metabolic conditions and the increasing incidence of colorectal cancer in adults under 50. The researchers noted that the rise in early-onset colorectal cancer has occurred alongside increasing rates of obesity and type 2 diabetes among younger populations.

While researchers haven't established that these trends fully explain the increase in early-onset colorectal cancer, the review highlights several possible biological connections. Insulin resistance and high insulin levels, chronic low-grade inflammation and changes to the gut microbiome are among the mechanisms being investigated for how metabolic dysfunction could potentially contribute to an environment that favours colorectal cancer development.

Could the gut microbiome play a role?

One particularly interesting area of research involves the gut microbiome — the enormous community of bacteria and other microorganisms living within our digestive system.

Our gut microbiome can be influenced by many things, including diet, medications, lifestyle and environmental exposures. Researchers are investigating whether certain changes in these microbial communities could contribute to an environment that makes colorectal cancer more likely to develop.

Recent research has even begun investigating particular bacterial exposures. For example, scientists are studying whether toxins produced by certain strains of E. coli may damage DNA in cells lining the colon and potentially contribute to colorectal cancer developing earlier in life.

It's an exciting area of research, but one where it's important not to get ahead of the evidence. We don't yet know that an altered microbiome is the cause of the increase, nor is there currently a particular probiotic, supplement or “gut health” product proven to prevent early-onset colorectal cancer.

Environmental and early-life exposures are also being investigated

Researchers are increasingly looking beyond what someone is doing today and asking whether exposures beginning during childhood, adolescence or early adulthood could help explain why colorectal cancer is appearing earlier.

Potential areas of investigation include environmental contaminants, antibiotic exposure, dietary patterns and other factors capable of influencing metabolism, inflammation, the microbiome or cellular health over many years.

This may also help explain what's sometimes described as a “birth cohort effect” — where people born in more recent generations appear to have different patterns of colorectal cancer risk than generations before them.

There probably isn't one single cause

Ultimately, researchers aren't expecting to discover one food, chemical, bacterium or lifestyle habit responsible for the entire trend.

The latest evidence instead points towards a potentially complicated interaction between diet, physical activity, metabolic health, environmental exposures, genetics, the gut microbiome and factors experienced throughout life. Many of those relationships still need considerably more research before scientists can establish exactly what's driving the increase.

What we do know is that the increase is real. And while understanding why this is happening is important, there's another message that's immediately useful: younger age doesn't mean colorectal cancer symptoms should be ignored.

What are the signs and symptoms to look out for?

One of the challenges with colorectal cancer is that it doesn't always cause obvious symptoms in its early stages. When symptoms do appear, they can also overlap with much more common digestive problems, such as haemorrhoids, irritable bowel syndrome (IBS) or changes in diet.

That doesn't mean every change in your bowel habits should immediately make you think of cancer. But it does mean it's important to know what's normal for you and pay attention when something changes and doesn't settle — regardless of your age.

Here are the symptoms to look out for:

1. Blood in your stool or rectal bleeding

Blood in or on your stool, on toilet paper or in the toilet bowl is one of the signs that should be investigated. Blood may appear bright red, while bleeding higher in the digestive tract can sometimes make stools appear very dark or black.

There are many possible causes of rectal bleeding, including haemorrhoids and anal fissures, but it shouldn't automatically be assumed to be one of these. If you notice blood, particularly if it recurs, speak with your doctor.

2. A persistent change in your bowel habits

Everyone experiences an occasional change in their bowel habits. What matters more is a change that is new, unexplained or persistent.

This might include:

• Diarrhoea or looser stools
• Constipation
• Going to the toilet more frequently than usual
• Smaller or narrower stools
• Mucus in the stool
• Feeling as though your bowel hasn't completely emptied after going to the toilet.

3. Abdominal pain, cramping or bloating

Persistent abdominal pain, swelling, cramping, gas or bloating can also occur with colorectal cancer. Some people may experience an ongoing feeling of fullness or discomfort in the abdomen or rectum.

Again, these are extremely common symptoms and can have many causes. The important distinction is whether they're unusual for you, persistent, worsening or occurring alongside other symptoms.

4. Unexplained tiredness or anaemia

Sometimes the signs aren't obviously related to your bowel at all.

Slow, ongoing bleeding from the bowel can contribute to iron deficiency anaemia, which may leave you feeling unusually tired or weak. Other symptoms of anaemia can include dizziness or shortness of breath.

If blood tests show unexplained iron deficiency anaemia, particularly alongside bowel symptoms, your doctor may recommend further investigation.

5. Unexplained weight loss or loss of appetite

Losing weight without deliberately trying can be another potential warning sign. Some people may also experience an unexplained loss of appetite.

Weight naturally fluctuates, so a small change isn't necessarily concerning. However, significant or continuing unexplained weight loss is something worth discussing with your doctor.

6. Pain or a lump in the anus or rectum

Another possible symptom is pain or a noticeable lump in or around the anus or rectum. This can have many other causes — including haemorrhoids and anal fissures — so experiencing it doesn't necessarily mean you have colorectal cancer.

However, a new or unexplained lump, persistent rectal pain or discomfort that doesn't resolve should be discussed with your GP, particularly if it occurs alongside other changes such as rectal bleeding or altered bowel habits.

Can you reduce your risk of colorectal cancer?

Not every colorectal cancer risk factor is within your control. You can't change your age, genetics or family history, for example. However, there are several lifestyle factors associated with colorectal cancer risk that you can influence.

According to the World Health Organization, maintaining a healthy lifestyle — including eating a balanced diet, staying physically active, avoiding tobacco and limiting alcohol — may help reduce the risk of colorectal cancer.

1. Eat plenty of fibre

Fibre is particularly important when talking about bowel health. It adds bulk to stools and helps waste move through the digestive system, while certain types of fibre are also fermented by bacteria in the colon.

Importantly, higher dietary fibre intake has been associated with a lower risk of colorectal cancer, particularly fibre obtained from whole grains and other plant foods.

Good sources include wholegrain breads and cereals, oats, brown rice, beans, chickpeas, lentils, vegetables, fruit, nuts and seeds. 

2. Limit processed meat and moderate red meat

There is strong evidence linking higher consumption of processed meat with colorectal cancer risk, while high consumption of red meat has also been associated with increased risk.

Processed meats include foods such as bacon, ham, salami and some sausages, which have been preserved through methods such as curing, smoking, salting or the addition of preservatives. 

This doesn't mean eating a steak occasionally will cause bowel cancer. As with most dietary risk factors, it's more useful to consider how frequently and how much you eat over time.

Cancer Council Australia recommends limiting red meat to no more than 700 grams raw weight (about 455 grams cooked) per week and avoiding processed meat where possible.

You can also vary your protein sources by including foods such as fish, poultry, eggs, legumes and tofu throughout the week.

3. Stay physically active

Regular physical activity isn't only beneficial for your heart, muscles and general fitness — physical activity is also associated with a lower risk of colorectal cancer.

You don't necessarily need to think of exercise as structured gym sessions either. Walking, cycling, swimming, recreational sport and other activities that get you moving can all contribute towards your overall activity levels.

Australian physical activity guidelines recommend adults accumulate 150–300 minutes of moderate-intensity physical activity or 75–150 minutes of vigorous activity each week, or an equivalent combination, alongside muscle-strengthening activities on at least two days per week.

4. Aim to maintain a healthy weight

Being overweight or living with obesity is associated with a higher risk of colorectal cancer. As we discussed earlier, researchers are also investigating how metabolic health, insulin resistance and chronic inflammation may be involved in the development of early-onset colorectal cancer.

Rather than focusing solely on a number on the scales, think about the habits that support long-term health: eating a balanced diet, staying active, getting adequate nutrition and working towards a weight that's appropriate for you.

If weight management is something you're concerned about, a GP or Accredited Practising Dietitian can provide individual guidance rather than relying on restrictive diets or rapid weight-loss approaches.

5. Limit alcohol and don't smoke

Both alcohol consumption and tobacco smoking are associated with an increased risk of colorectal cancer.

For alcohol, less is better when it comes to cancer risk. Australia's NHMRC guidelines recommend that healthy adults drink no more than 10 standard drinks per week and no more than four standard drinks on any one day to reduce the risk of alcohol-related harm. It's important to recognise, however, that these limits aren't a threshold below which alcohol has no cancer risk.

If you smoke, quitting provides health benefits well beyond colorectal cancer risk and is one of the most significant changes you can make for your overall health.

Looking after your bowel health starts with awareness

The rise in colorectal cancer among younger adults is an important reminder that bowel cancer isn't something we should only start thinking about later in life. Researchers are continuing to explore the complex relationship between diet, lifestyle, metabolic health, environmental exposures and the gut microbiome.

There are also factors we can influence. Eating a fibre-rich, balanced diet, limiting processed meat, staying physically active, maintaining a healthy weight, avoiding smoking and limiting alcohol can all form part of an overall lifestyle that helps reduce colorectal cancer risk. None of these measures can guarantee prevention, but together they address several established, modifiable risk factors.

And don't forget about bowel cancer screening. In Australia, eligible people can access free bowel screening through the National Bowel Cancer Screening Program, which is designed to detect signs of bowel cancer before symptoms develop. If you have symptoms, however, don't wait for your next screening test — speak with your GP about them directly.

Ultimately, the growing rates of early-onset colorectal cancer aren't a reason to panic, but they are a reason to pay attention. Understanding your risk factors, making healthier choices where you can, participating in screening when appropriate and getting persistent symptoms investigated can all help put you in a better position to look after your bowel health.

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