For decades, bowel cancer has been deemed an ‘old person’s disease’, but experts warn this is no longer true.

people in their 20s, 30s and 40s are being diagnosed with the disease, even though conventional wisdom from doctors says they’re ‘too young’ to worry.

Alarming figures show that the risk of being diagnosed with bowel cancer before the age of 40 has skyrocketed since 2000 – and the Daily Mail has been documenting many heartbreaking cases in recent years.

Melbourne mother-of-two Melissa Dunmore received a stage-three cancer diagnosis a week before her 33rd birthday in early 2024, after surgeons found a 20cm tumour in her colon along with 11 tiny pre-cancerous polyps.

Marlene Sardo-Infirri, 46, lost the love of her life, David, in August 2022, after he was diagnosed with stage-four bowel cancer. He only experienced one symptom – frequent bathroom visits – with no abdominal pain or bleeding.

Many researchers have examined the cause of this surge in cases, often pointing to junk food and ultra-processed diets as likely culprits.

But according to nutrition scientist and lifestyle medicine expert Dr Joanna McMillan, there is another major contributor that is often overlooked: a lack of fibre.

‘We are quick to demonise fats and carbs, while protein has been a golden child. But we’ve completely forgotten about fibre and the important role it plays,’ Dr McMillan tells the Daily Mail.

‘Most people think fibre is just to do with old people and constipation, but it plays multiple roles.’

The 53-year-old, who hails from Scotland but now lives in Sydney, has been researching fibre and its effects on the body for three decades.

Dr McMillan explains that fibre – which she calls a ‘multitasker’ – plays a crucial role in reducing the risk of colorectal (bowel) cancer, particularly by supporting gut health and ensuring that fibre reaches the end of the colon, where many cancers occur.

She emphasises that a diverse intake of fibre types is important for this protective effect.

While most people know about the two different types of fibre – soluble and insoluble – this only scratches the surface of what the body needs.

Dr McMillan says it’s ‘wrong to think’ that the sole purpose of fibre is to keep your bowel movements regular. In fact, it’s far more vital.

Fibre, she explains, plays ‘different roles in pretty much every single part of your gut’, being linked to liver, heart and brain health, as well as mental health, dental health, blood glucose levels, inflammation and more.

‘There are many different types of fibre. Some are completely unfermentable like a broom sweeping through the whole gut,’ she adds.

‘Some fibres can assist with dental health, some fibres play a role in helping your stomach feel full. Once in the small intestine, other fibres swell up with water which slows the attack of our digestive enzymes and helps to lower your blood glucose responses to the meal.

‘Other fibres trap cholesterol that is present and carry it out of the body. When fibres get down to the colon, they help keep you regular, preventing constipation while also making sure your stools aren’t too loose.’

FIBRE AND BOWEL CANCER

When there is a lack of fibre in the colon, unwanted toxins aren’t flushed out, leaving cells susceptible to carcinogens.

However, increasing your daily fibre intake could be the answer to preventing this – in addition to limiting your junk food intake.

Dr McMillan recommends eating a variety of foods from all five plant groups every day to ensure you get the full spectrum of fibre types for optimal health – fruits, vegetables, wholegrains, legumes, and nuts and seeds.

‘Some of these foods have very unique fibres. For example, you get pectin in fruits that you’re not getting a lot of elsewhere,’ she says.

‘Australians are falling short on all five categories. It’s little wonder that almost everybody has a fibre gap because we’re not eating the right foods in terms of diversity of different plant types or total fibre.’

In Australia, the recommended daily fibre intake is between 25-30g. Dr McMillan suggests aiming to consume 30 different plant-based foods across your week.

Dr McMillan adds that fibre supplements, such as Metamucil, can help fill the daily gap, but will never replace a healthy diet.

‘If you take a fibre supplement, you’re only getting that one type of fibre,’ she notes.

While some might think they are eating well by avoiding junk food, processed foods or carbohydrates, that is not necessarily the case.

On one occasion, Dr McMillan had lunch with a friend who thought she was making a healthy choice by having a salad with lettuce, tomato, cucumber and canned tuna.

However, Dr McMillan pointed out that while the meal sounded healthy on paper, it was actually very low in fibre due to the choice of vegetables.

‘She thought she was doing really well because, in her mind, she wasn’t eating any bread,’ Dr McMillan adds.

‘But actually, if she had added a slice of wholegrain sourdough to that meal, she would have had a much more balanced and fibre-rich meal simply by adding that one food, or sprinkling some nuts and seeds through her salad.’

Dr McMillan says foods like bread shouldn’t be demonised as ‘carby’, noting they can be a valuable source of fibre when eaten in proportion to the rest of the meal.

FIBRE AND THE GUT MICROBIOME

Dr McMillan likens the gut to a thriving ecosystem, saying a healthy microbiome is like a rich, biodiverse forest.

‘We can’t talk about the benefits of fibre without mentioning the gut microbiome. Fermentable fibres are food for the good bacteria in the gut, and what is produced benefits us,’ she explains.

‘If you have healthy microbes, it also helps to stop unhealthy microbes, potential pathogens, and keeps the whole ecosystem healthy.

‘The technical name is metabolites, but they are just the products of fermentation within the gut and some are beneficial at reducing the risk of colon cancer because they keep the cells healthy.’

This is used as fuel, specifically butyrate, which is an important component. If there is a lack of butyrate, the colon cells won’t be as healthy.

On the other end of the spectrum, it is possible to have too much fibre which can lead to symptoms such as diarrhoea, bloating or constipation.

Patients with conditions such as IBS or high cholesterol often need to adjust their diet and fibre intake to suit their needs.

‘You’re better off slowly increasing your fibre intake, sometimes even by the spoonful, until your gut can handle it,’ Dr McMillan says.

‘I’m so pleased (fibre is now in the spotlight) because I’ve been looking at this since I was an undergraduate student. It’s something I’ve long talked about.

‘It’s great to see people, especially young people, waking up and realising how important it is.’

To get the recommended amount, an ideal day on a plate would include a variety of fibre-rich foods spread out throughout the day. For example:

• Breakfast: An Aussie favourite – an egg and bacon roll made using Wise Wheat offers an extra hit of fibre with 11.6g per serve
• Lunch: A wholegrain salad with quinoa, chickpeas, spinach, avocado and a lemon-tahini dressing
• Dinner: A hearty vegetable stir-fry with brown rice, broccoli, carrots, capsicum and chicken, drizzled with a sesame-soy sauce
• Snacks: Apple slices with almond butter, or a handful of mixed nuts and seeds

Each of these meals is packed with an array of fibre types, which work together to support digestive health, stabilise blood sugar levels, and keep you feeling full and satisfied.