Danni, 39, was handed a shock bowel cancer diagnosis despite being the healthiest she’d EVER been. Now she has a ‘scary’ theory for what caused it – as cases surge globally

At 39, Danni Duncan was the fittest and healthiest she’d ever been – until she was given the worst news imaginable, turning her world upside down.

The mum, from Melbourne, had just given birth to her fourth child in September 2024 when she began experiencing extreme fatigue that made no sense to her.

It began with tiredness and bloating – symptoms she simply put down to having a newborn baby, along with juggling a young family and two businesses.

But the star marathon runner knew something was seriously wrong when she suddenly struggled to get through a workout at the gym. 

The fitness and nutrition coach said she felt ‘life flash before my eyes’ when she was told she had bowel cancer, despite having no family history of the disease.

‘I couldn’t believe it. My first thought was, “No this can’t be happening, I’m supposed to live to 100”. I’ve always been fit and healthy. I’m literally one of the healthiest people I know. How has this happened to me?’ Danni told Daily Mail.

‘I’m a runner so I was training for a marathon at the time and I was really struggling, I couldn’t even finish a set. I was getting dizzy at home and then one day, I almost fainted making breakfast. My husband said “You need to go to the doctor”.’

Danni said her surgeon told her that childhood exposure to ultra-processed foods – like popular supermarket snacks and fast food – and even household cleaning products ‘most probably’ contributed to her cancer diagnosis.

‘That’s pretty scary,’ she explained.

‘The doctor was talking about things like all the ultra-processed foods and chemicals that we were exposed to through the 90s and the early 2000s.

‘We were active kids who grew up on fruits and vegetables but we also had processed ham and cheese with white sandwich bread. In the ’90s, there was this big influx of ultra-processed food because convenience was a thing.

‘It was the ’90s… Parents were busy (they still are) and as long as we had our meat and three veg and some fruit – the mentality was, “We’d burn it off”.

‘At the time, our parents would have thought the processed foods were great – but without understanding the impact of what they were going to do to us.’

Like many ’90s kids growing up in Australia, she remembers her dad using fly spray to get rid of pesky flies and the family putting on sunscreen without checking the ingredients to see what they were actually applying to their skin.

Danni said her surgeon explained that she may have developed cancer after her cells were weakened by stress at some point in her life, following a mutation that had developed over time.

Fighting back tears, Danni said she couldn’t shake the fear that her youngest child might grow up never knowing her as a mum. 

‘I thought “London’s not going to know who I am”,’ she said. 

The biggest challenge she faced was breastfeeding London, who is now 14 months old. 

‘My dream with her was to breastfeed her for 12 months because I wasn’t able to for my other three children,’ she said. 

‘When I had to do chemotherapy, I had to stop breastfeeding her. Stopping that journey when I didn’t want to just felt like such an unnatural thing to do. 

‘I just felt like it was ripped away from us, which was just so unfair. I was so excited when I was able to feed London but having to cut that short was really heartbreaking for me.’

During her chemo treatment, Danni said she’s been ‘pumping and dumping’ her breast milk but hopes she can return to feeding her daughter later this month. 

Before her devastating diagnosis, the mum was training and competing in back-to-back marathons when one day she failed to finish one of the races. 

‘I stopped at 30km, which is not me. I felt awful. Abnormally low energy, despite good fuelling. I blamed broken sleep, four kids and two businesses,’ she explained. 

‘Weeks later I was bloated. People said “peri-menopause,” “four kids,” or “almost 40″… I didn’t buy it. Then came dizziness. I couldn’t finish gym sets, I couldn’t run. One morning in April this year, I almost passed out so I went to see a doctor.’

Her tests showed she was severely anemic, with a haemoglobin level of 77 and iron was 1, so it was concerning that she wasn’t having a period – even though such low levels would typically cause heavy bleeding. 

She was booked for an urgent iron infusion and colonoscopy and gastroscopy so they could figure out where the blood was coming from. 

More than a week later, she discovered a 2.7cm tumor in her bowel.

The only symptoms she experienced was fatigue and bloating. 

‘The unusual fatigue was a big red flag for me because I eat healthy and I’m very active so the fact that I couldn’t even finish a set at the gym was a red flag,’ she said. 

‘But apart from that and bloating, there were no other symptoms.’

In May this year, she was told she had stage 2B bowel cancer, meaning the tumour had gone through the bowel wall but had not yet spread to the lymph nodes.

‘Never did cancer cross my mind,’ Danni said. 

‘No blood in stool, no bowel changes, no weight loss. My doctor explained that because of the amount of blood I was losing, I probably did have blood mixed in before passing – so I never saw it.’

After her post-chemo oncology appointment, Danni was given promising news: she’s now ‘cancer free’ but will have routine blood tests every three months, as well as yearly colonoscopies and CT scans. 

By sharing her story, she hopes Australians get checked if they notice any unusual symptoms, no matter how minor they are. 

‘I unfortunately lost a friend recently to bowel cancer. He didn’t know he had bowel cancer. He literally died within five days of finding out because it had spread to his liver and lungs already,’ Danni said. 

‘We just need to do more for early detection and bringing awareness. This is no longer an old person’s disease. It’s not a disease that now 50-year-old men get. It’s a disease that is affecting young, fit, healthy adults.

‘If something feels off for you – advocate for yourself. If I wasn’t as fit and tuned into my body, I might’ve dismissed it as postpartum. This is your reminder: get checked.

‘Bowel cancer is now the second biggest cancer killer for 29 to 45 year olds. Move, strength train, fuel your body – be the healthiest version of you for YOU. Because you never know what’s around the corner.’

For those going through cancer, Danni said: ‘Keep exercising and move your body.’ 

‘I know some days it’s hard and sometimes, even just getting out of bed is a mission, but it literally saved my mental health. It kept me strong. 

‘There’s research to prove that exercise can be just as effective as chemotherapy. So move your body as much as possible, and hopefully, for most people, there’s light at the end of the tunnel. 

‘When you’re in it, it’s horrendous, and you think it’s never ending, but now that I’m out the other side… thank goodness, it just looks like a memory now.’

Weighing in on Danni’s case, colorectal surgeon Dr Graham Newstead said that while lifestyle factors such as diet and exposure to chemicals are often linked to the disease, scientific evidence to support such claims is limited.

‘The onset of bowel cancer in particular is not known,’ the medical director of Bowel Cancer Australia told Daily Mail.

‘I understand a surgeon or a doctor saying, “It might have been your lifestyle”. What he or she is really saying is, “We’re not sure of the cause, yet we are seeing it more in young people”. 

‘Maybe our lifestyle is a factor, but lifestyle is a grab bag of a whole bunch of factors, which we are trying to work out. Lifestyle is not a cause, at least as far as we know, though there is certainly research going on in the laboratory.’

The Associate Professor said increased life expectancy has changed the patterns of bowel cancer occurrence in Australia. 

Historically, most bowel cancers occurred in older people, as the average age of death was between 50 and 55.

‘Now, if you’re pretty fit and not grossly obese, our average age of death has moved into the early 80s so we are living longer and longer. We’re now living long enough to develop bowel cancers at a later age,’ Dr Newstead explained. 

‘On the other end of the spectrum, we used to only see non-genetic bowel cancers occurring from around age 55 onwards. 

‘But now we are seeing 11 per cent – roughly 1,700 of the 17,000 cases diagnosed each year in Australia – occurring in people under 50. 

‘Although they’re most common in people aged 40 to 45, we’re also seeing cases in 30 year olds with no family history.’ 

He said that while the incidence of 1,700 in a population of 26million is ‘not huge’, it’s ‘very relevant because these are young people with young families’. 

‘So we want young people not to be scared, but to be aware – that you do not ignore symptoms of blood,’ Dr Newstead said.

‘Be aware that any of the warning signs of a big polyp or an early cancer, like bleeding, tiredness, or a change in your bowel habit, can occur.’

Bowel cancer, also known as colorectal cancer, is the fourth most commonly diagnosed cancer and the second deadliest in Australia.

If detected early, the chance of successful treatment and long-term survival improves significantly.

Not all bowel cancers show symptoms. But common signs include abdominal pain or bloating, constipation, diarrhoea, unexplained weight loss, tiredness, weakness or breathlessness.

‘The warning signs are obviously blood in the toilet or on the paper. Even if you can feel you have got haemorrhoids – little lumps on the anal margin – that doesn’t mean the blood is coming from them. So if you have got blood, you need a colonoscopy,’ Dr Newstead said.

‘Tiredness can also be a sign because you could be losing blood in tiny amounts but persistently from higher up in the bowel, from a polyp that’s getting larger, or an early cancer. You can become tired without overt blood loss that you can see, but it can still be from minute blood loss.

‘Persistent changes in bowel habits are another warning sign. These changes can include frequency, consistency, or the diameter of your stools, as well as other abdominal symptoms such as bloating, gas, and discomfort.’