While younger adults still make up a minority of bowel cancer patients, cases in people aged under 50 have been rising in the UK and worldwide, prompting growing interest and research within the scientific community into why this is happening. This upward trend has been observed since at least the mid-1990s, with a 2009 study estimating annual increases in incidences of about 1.5%–1.6% per 100,000 men and women under 50.

In light of the latest studies showing some clear correlation between ultra-processed foods (UPF), microplastics and bowel cancer, this blog explores what we know so far about the causes and contributory factors, how lifestyle and environment might be involved, and when to seek specialist advice from a Consultant Gastroenterologist or Colorectal Surgeon at New Victoria Hospital.

Early‑onset bowel cancer: what’s changing?

Early‑onset colorectal (bowel) cancer (EOCRC) usually refers to cancer diagnosed before the age of 50, as the most common age group affected are 60–70s. However, over the past few decades, EOCRC rates have climbed steadily, even as bowel cancer in older adults has fallen or stabilised because of screening and better awareness.

Data from UK cancer registries show a significant rise in EOCRC in regions such as South East Scotland and across England and Wales, with the sharpest increases seen in people in their 30s and 40s across socio-economic groups. Studies describe this as a genuine new pattern rather than a simple shift towards diagnosing cancers just before the traditional screening age.

Globally, colorectal cancer has become one of the leading causes of cancer death in adults under 50, with particular concern for men but also a substantial impact on women. Despite this, only a small proportion of all bowel cancers occur in people under 50, so the absolute risk for an individual younger person remains relatively low.

Could UPFs and microplastics be increasing bowel cancer risk in younger adults?

Growing evidence suggests that UPFs and microplastics have a role in increasing the risk for EOCRC. However, it would be inaccurate to point the finger at them as sole culprits. Researchers believe that a complex mix of environmental, lifestyle, and biological factors is driving EOCRC rather than a single cause. Many of these influences may begin in childhood or early adulthood and act over years by affecting the gut lining, immune system, and the community of microbes in the bowel.

Diet and ultra‑processed foods

One of the strongest suspects is the modern “Western‑style” diet, which is typically high in:

• Red and processed meats
• Saturated fat
• Refined carbohydrates and sugary drinks
• Salt and food additives

Reviews of EOCRC research link such diets to inflammation in the bowel, increased production of potentially harmful substances like hydrogen sulphide, and changes in the gut microbiota that may promote tumour formation. Diets lower in fibre, fruit, vegetables and wholegrains reduce the production of protective short‑chain fatty acids in the colon and are associated with higher colorectal cancer risk in general.

Ultra‑processed foods (UPFs), which often contain emulsifiers, synthetic colouring, flavour enhancers and other additives, are attracting particular attention. Experimental and epidemiological work suggests some additives and processing methods may damage the gut barrier or alter the microbiome in ways that could increase cancer risk, although definitive causal proof in humans is still lacking.

Environmental exposures and microplastics

Researchers are starting to explore how wider environmental pollutants might contribute to EOCRC. These include synthetic food dyes, titanium dioxide (a whitening agent used in some foods and cosmetics), residual pesticides and other industrial chemicals.

Microplastics and nanoplastics, now detectable in human blood, stool and even tissues, are emerging as potential players. Laboratory studies suggest these particles can alter gut permeability, disturb the microbiome and provoke inflammation, but human data are still limited and no direct cause‑and‑effect link with bowel cancer has yet been established.

Other factors contributing to EOSCRC risk

Although the UPFs and microplastics are getting increasing attention, other factors need to be considered as equally important when analysing bowel cancer risk.

Sedentary lifestyle and obesity

Physical inactivity is another consistent risk factor for colorectal cancer, with many younger adults now spending long periods sitting at work, commuting or using screens. Sedentary behaviour and excess body weight are associated with insulin resistance, chronic low‑grade inflammation and altered levels of growth factors and hormones, all of which can encourage abnormal cell growth in the bowel.

Obesity in childhood and young adulthood appears particularly important, because it may “set the scene” metabolically and influence the gut microbiome for decades. However, EOCRC also occurs in people with a healthy weight, reinforcing that multiple mechanisms are likely to be involved.

Gut microbiome and antibiotics

The trillions of bacteria, viruses and fungi that live in the colon – collectively the gut microbiome – are now considered central not just to bowel health. These microbes help digest fibre, produce vitamins, regulate the immune response and generate metabolites that can either protect against or promote cancer.

Studies suggest that EOCRC is often associated with an altered microbiome (dysbiosis), including over‑representation of certain bacteria that can damage DNA or drive chronic inflammation. The microbiome is highly sensitive to diet, environmental toxins, infections and medications, which may explain why EOCRC has risen as lifestyles have changed.

Antibiotics are of particular interest because they can profoundly disrupt gut microbial communities, especially when given repeatedly or early in life. Observational studies link prior antibiotic exposure – including in childhood – with an increased risk of later colorectal cancer, although not all antibiotics have the same effect and more research is needed to separate correlation from causation.

Stress, sleep and the wider exposome

The concept of the “exposome” – the totality of environmental exposures across a lifetime – is increasingly used to frame EOCRC research. Chronic stress, poor sleep, disrupted circadian rhythms, and socioeconomic factors that limit access to healthy food and physical activity may all contribute indirectly through hormonal and immune pathways.

Researchers emphasise that EOCRC likely arises from the cumulative impact of many small risks over time, interacting with individual genetics and the microbiome. Most younger adults with bowel cancer do not have a strong family history, but inherited syndromes such as Lynch syndrome or familial adenomatous polyposis still account for a meaningful minority of cases and require specialist assessment.

What symptoms should prompt medical advice?

Many EOCRC patients are diagnosed at a later stage, often after being referred routinely rather than urgently, which can affect outcomes. Recognising symptoms and acting promptly can make a real difference, even in younger adults who might not see themselves as being at risk.

Key symptoms that should prompt medical review include:

• Blood in your stool or bleeding from the back passage.
• A persistent change in bowel habit (for example, ongoing diarrhoea, constipation or a change in stool consistency) that is not normal for you.
• Needing to open your bowels more or less often than usual or feeling you have not fully emptied your bowels.
• Unexplained weight loss.
• Ongoing abdominal pain, discomfort, bloating or a feeling of a lump in the abdomen.
• Unexplained tiredness, shortness of breath or signs of anaemia.

Having these symptoms does not necessarily mean you have bowel cancer, and conditions such as haemorrhoids, irritable bowel syndrome and infections are much more common. However, persistent, unusual or worrying symptoms should never be ignored, whatever your age, and it is sensible to seek specialist assessment if they continue.

How New Victoria Hospital can help

At New Victoria Hospital, Consultant Gastroenterologists and Colorectal Surgeons assess and investigate bowel symptoms in adults of all ages, including those under 50. They can offer a tailored evaluation that may include blood tests, stool tests such as faecal immunochemical testing (FIT), endoscopic procedures, such as colonoscopy or sigmoidoscopy, and imaging as appropriate.

“As more younger people are being affected, it is vital they feel listened to and their symptoms taken seriously, rather than being told they are ‘too young’ to worry. Advanced colonoscopy is the most effective way to thoroughly investigate symptoms and detect bowel cancer at an early, more treatable stage, and our JAG‑accredited endoscopy service means we can offer a high‑quality, detailed assessment. If something is wrong, we can move swiftly to plan the right surgical treatment.” Mr Pasha Nisar, MA MBBCHIR DM FRCS(GenSurg), Consultant Colorectal Surgeon at New Victoria Hospital

A specialist opinion can help distinguish between common benign conditions and signs that need urgent attention, reducing the risk of delayed diagnosis. Early specialist input can provide reassurance, clarify the need for further tests, and ensure that any serious problem is identified and treated as promptly as possible.

Key take‑home messages

• Bowel cancer in people under 50 is still relatively uncommon, but rates are rising in the UK and internationally, especially in those in their 30s and 40s.
• This trend is unlikely to be explained solely by better detection and is thought to involve a combination of dietary patterns, ultra‑processed foods, sedentary lifestyles, obesity, antibiotic exposure, microbiome changes, and environmental pollutants, acting over many years.
• No studies have proved that UPFs and microplastics can cause early-onset bowel cancer; however, they suggest stronger evidence for association.
• Higher UPF intake is linked to higher colorectal cancer risk, and microplastics are being investigated as a possible contributing environmental factor.
• Many younger adults with bowel cancer do not have a strong family history, so awareness of symptoms is crucial even if you consider yourself otherwise healthy.
• Persistent changes in bowel habit, rectal bleeding, unexplained weight loss, abdominal pain or unexplained tiredness should always be discussed with a doctor and may warrant specialist assessment.
• Consultant Gastroenterologists and Colorectal Surgeons at New Victoria Hospital are available to review symptoms, arrange appropriate investigations and guide personalised management, helping to improve outcomes for this growing group of younger patients.

If you are experiencing any of the symptoms described, or have concerns about your risk of bowel cancer, you can arrange an appointment with our Consultant Gastroenterologists or Colorectal Surgeons without needing to wait for routine pathways by calling 020 8949 9020 or filling in our online contact form.

Reviewed by Mr Pasha Nisar, Consultant General and Colorectal Surgeon, New Victoria Hospital.
This article is for general information only and does not replace individual medical advice. Please consult a healthcare professional for personalised recommendations.