How ultra-processed foods are linked to cancer, and how experts believe they can cause tumours: Top doctors now blame modern diets for unprecedented spike in cancer rates

It is a disturbing phenomenon that, so far, doctors have been unable fully to explain. Cancer, a disease most often associated with older age, is becoming increasingly common in the under 40s.

This month, a major study found people born in 1990 are three times more likely to develop certain forms of the disease than those over the age of 70. And other types were on the rise in younger age-groups, while rates declined in older people.

So what is fuelling the trend? Numerous theories have been put forward: antibiotic over-use, mobile phone radiation and even invisible particles of plastic in drinking water. But a growing number of experts are pointing to one major cause: ultra-processed foods.

Also known as UPFs, these are ready-made foods – including bread, cereals and even salad dressing – packed with artificial ingredients used to preserve, add flavour and enhance texture.

Some have even gone as far as to say they could be as dangerous as tobacco – and should come with a cigarette-style health warning.

It might sound far fetched. But, increasingly, some of Britain’s top cancer experts believe there is some truth to it.

Ultra-processed foods, also known as UPFs, are ready-made foods – including bread, cereals and even salad dressing – packed with artificial ingredients used to preserve, add flavour and enhance texture

Professor Charles Swanton, oncologist and chief clinician at Cancer Research UK, has raised the alarm over the ‘disturbing’ rise in cancer in young people and linked it to increased consumption of junk food.

Speaking at the American Society of Clinical Oncology, he said a growing body of research suggests that some bowel cancers could be ‘initiated’ by changes in the gut caused by low-fibre, high-sugar diets.

Prostate oncologist and Queen’s University Belfast professor Dr Joe O’Sullivan puts it more simply. ‘The spike in young cancer rates has to be due to something we’re consuming,’ he said.

‘And ultra-processed foods are the biggest lifestyle change in the last 40 years.’

Britain’s foremost commentator on the topic, Dr Chris van Tulleken, whose book Ultra-Processed People was a best-seller last year has ‘no doubt’ that the two are connected.

‘We have more than a dozen good quality studies indicating a link between cancer and ultra-processed foods,’ he told The Mail on Sunday. ‘Governments took action to reduce the number of people who smoke cigarettes based on far less evidence.’

Over the past three decades, cancer rates in the Western world have increased faster for 25- to 29-year-olds than for any other age groups. And the cancers with the sharpest rise among the young have been those of the digestive system – the oesophagus, stomach, pancreas, bile duct, liver, gallbladder and colon.

Data from the University of Washington School of Medicine shows cases of colon cancer have increased by 70 per cent over the past three decades.

Analysis by the US-based Colon Cancer Coalition suggests that 30 per cent of all colorectal cancer cases and 7 per cent of all deaths this year will be in under 55s.

The Princess of Wales, 42, is one of several high-profile cases of early-onset cancer – where diagnosis occurs before 55 – to draw headlines in recent years. The Princess announced that she was having preventative chemotherapy for an unspecified cancer in March, after undergoing abdominal surgery.

The Princess of Wales announced that she was having preventative chemotherapy for an unspecified cancer in March, after undergoing abdominal surgery

Dame Deborah James – known as Bowel Babe – was another, diagnosed with colon cancer at 35 and raising millions for charity in her final days in 2022.

In fact, cancer is now the leading cause of death for young adults in upper-middle income countries. Professor David Cunningham, consultant oncologist at The Royal Marsden, is deeply concerned at the pattern.

‘Although it’s still relatively rare we are seeing more and more young adults with colorectal cancer in various stages,’ he said.

‘It doesn’t seem to be just that we’re diagnosing the condition more effectively. There’s something going on that must be to do with environmental, rather than genetic, factors. It’s disquieting.’

Dr Cunningham says he has a ‘shocking’ number of young patients – some under the age of 25: ‘These are people who don’t have any known genetic predisposition and they’re not overweight. In some it’s been quite striking that they’re quite fit.

‘It’s hard to believe that you can get a cancer at the age of 20 because of environmental factors.

‘But it’s happening. And that’s where diet comes in.’

Doctors have long known that too much alcohol and red meat cause inflammation in the gut. And this may trigger cancer. But what if other food we eat – staples such as sliced bread and breakfast cereal – are doing the same?

This is the central tenet of Dr van Tulleken’s book, which argues that much of our diet now consists of foods that are both ‘nutritionally deficient’ and ‘addictive’.

The term ultra-processed is a relatively recent classification – developed by researchers in Brazil to describe food that has undergone the most manufacturing, in large-scale factories and with sophisticated technology.

But Dr van Tulleken defines it more simply: something wrapped in plastic and with at least one ingredient you wouldn’t find in a home kitchen.

And it’s not just so-called junk food. Seemingly healthy granola bars, packaged whole-wheat loaves, low-sugar jams and even baby food fit within the category of ultra-processed.

According to a 2019 study, ultra-processed foods make up 57 per cent of the average UK diet, with the number rising to 80 per cent for poorer people and children. So what is it about these products that could cause cancer? Dr van Tulleken thinks there are several explanations: ‘We are very sure that ultra-processed foods drive weight gain and obesity – this is backed up by lots of experiments in both animals and people.’

Britain’s foremost commentator on the topic, Dr Chris van Tulleken, has ‘no doubt’ that UPFs and the onset of cancer are connected

‘And we know that obesity is independently linked to a number of different cancers. So even if all ultra-processed food did was drive obesity, then it would also drive cancer.’

Second, he explained, is the nutrient content of the food itself. Typically energy-dense and high in sugars and unhealthy fats, ultra-processed food is low in fibre and real, whole ingredients.

‘They typically have a high-glycaemic index, meaning they release sugar into the blood very quickly – which is linked to insulin resistance, which is itself also linked to certain cancers.’

UPFs may be also damaging the gut microbiome – the thousands of bugs in our digestive system that form a vital part of our immune system and help regulate many bodily functions.

According to Dr Fang Fang Zhang, cancer epidemiologist and chair of the nutrition division at Tufts University in Boston, in the US, major ongoing trials suggest some ingredients in UPFs change the balance of bacteria in the gut.

‘They can reduce the good bacteria and add bad bacteria, damaging the innermost lining of the colon and causing tumours to grow there,’ she said. Of particular concern are a group of additives known as emulsifiers, found in foods such as salad dressings and ice cream.

Designed to bind fats and water – which naturally tend to separate – these chemicals may break down the layer of mucus that lines the gut, allowing bacteria direct contact with the gut wall. ‘We think that this process could be linked to bowel cancer,’ explained microbiome scientist and gut specialist Dr Alasdair Scott. ‘Studies done on animals that confirm this, but not yet on people – in humans it can be much more difficult to prove why exactly a tumour has formed.’

Experts have a similar theory for the rising number of Crohn’s disease and ulceritis colitis cases in recent years, with studies linking the inflammatory bowel conditions to a Western-style diet rich in meat and processed foods.

Both conditions increase the risk of colorectal cancer by causing chronic inflammation in the colon. Evidence is also growing that nitrates and nitrites – preservatives added to processed meats like salami and ham to extend their shelf life and improve their colour and taste – increase the risk of bowel cancer.

A 2015 study revealed that people who eat red and processed meat every day are 40 per cent more likely to develop the disease than those who eat it once a week or less. And in 2022, France’s food regulatory body advised limiting consumption of delicatessen meats due to harmful nitrite additives.

‘The dangers of these additives aren’t specific to young people,’ explained Dr Scott. ‘But young people now are being fed ultra-processed food from birth.’

Experts say regulating UPFs is critical to curbing the surge of early-onset cancers.

‘If we can reduce ultra-processed food consumption, we will see a reduction in cancer cases. Governments need to pay attention to it,’ adds Dr Zhang.

Other doctors, however, are wary to place all the blame on ultra-processed foods – arguing that fit, young people with a balanced diet, are getting sick.

Former BBC Radio 4 producer Molly Guinness, 39, is one of these unexpected patients, commenting on X, formerly known as Twitter, that she’s amongst five other young, slim and healthy people she knows diagnosed with colon cancer in the last year. ‘I look around the waiting room at the colorectal clinic – everyone I see there has a healthy BMI,’ she wrote.

Carla Mitchell was just 36 and in very good shape when she was told she had stage three bowel cancer (see panel, left).

But Dr van Tulleken says: ‘We know that the emulsifiers, sweeteners and the lack of fibre in ultra-processed food changes the microbiome and inflames the gut. The younger you are, the bigger your risk of eating ultra-processed foods. And the more of your life you’ve been eating it, and the more vulnerable you are to its harmful effects.’

Instead, he argues, the UK needs to take the lead of countries like Belgium and Brazil and regulate the sugar, fat and salt content of food better.

After all, ultra-processed food is also linked to other heath problems – cardiovascular disease, diabetes, depression, dementia and irritable bowel syndrome (IBS) to name a few.

‘If we work to help people have a more sustainable diet by fixing the food system to produce more local, whole food at an affordable price, all these risks are lowered,’ Dr van Tulleken added. ‘The only people that poses a risk to is the food industry.’

My bowel cancer fight at 36

Carla Mitchell was told she was ‘too young for anything like cancer’ when she went to the doctor complaining of exhaustion aged 36.

The customer marketing specialist from Kent had noticed a change in her energy levels during the Covid-19 lockdown.

Previously always on her feet, Carla suddenly found herself out of breath and having heart palpitations after simply walking up the stairs.

Carla Mitchell was told she was ‘too young for anything like cancer’ when she went to the doctor complaining of exhaustion aged 36, but was soon diagnosed with stage 3 bowel cancer

‘I’m usually an active person so I knew something wasn’t right,’ she said.

After initially chalking it up to very early menopause symptoms, Carla eventually went to her GP, where she was sent for blood tests.

After further investigations – including a stool sample – Carla was told she had stage three bowel cancer.

‘I thought it could be a thousand different things but cancer wasn’t on my mind at all,’ she said. ‘I knew it could be an option but I just never imagined I would hear those words.’

Carla’s doctors were equally shocked, but swung into action.

After undergoing surgery and three months of chemotherapy, Carla has now been cancer-free for three years.

‘I was extremely lucky to have a doctor who was supportive and fought to find out was the issue was,’ she added.