I’ve spent years studying bowel cancer. This is the truth behind the rise in young people being diagnosed, how SITTING increases your risk, and the changes I’ve made to protect myself: DR YIN CAO

As a cancer scientist, I spend my days studying why more young adults are developing bowel cancer.

As a mother of two young children, based on the evidence I’ve seen I’ve changed how I live, from banning fizzy drinks at home to insisting we walk to school, because I’m convinced that small, daily habits could help prevent this devastating disease.

For a long time, bowel cancer was seen as something that affected older people. But that is no longer the case. Rates among people under 50 are rising sharply, and I believe we urgently need to understand why.

In England, diagnoses in 25 to 49-year-olds have increased by more than 50 per cent since the early 1990s. In the US, where I live and work, bowel cancer is projected to become the most common cancer in people under 50 by the year 2030.

As the co-lead of the PROSPECT (Post-genomics Risk-stratified Observational Study of Early-onset Colorectal Cancer) study, a major UK-US research collaboration, my team is working to understand what is behind this alarming trend.

PROSPECT is funded by Cancer Research UK and the US National Cancer Institute. It brings together experts in cancer biology, genomics, nutrition, lifestyle, and environmental science to study thousands of people under 50 with bowel cancer.

Our goal is to identify patterns in their genetics, lifestyles, gut microbiomes (the community of microbes in the gut) and environmental exposures – to uncover what is driving the disease in younger people and, more importantly, how we can stop it.

Some answers are already emerging.

From my own research and those of others worldwide, the evidence points to diets high in ultra-processed foods, sugary drinks, red and processed meats, and low in fibre as contributing to the rising rates of bowel cancer in younger adults.

High rates of obesity and type 2 diabetes may also increase the risk, particularly when combined with other lifestyle and environmental factors such as prolonged sitting, lack of physical activity, alcohol use (especially on an empty stomach), and possibly air pollution or microplastics.

One striking finding that surprised me is that regular exercise doesn’t reduce the harmful effects of sitting for long periods of time.

Young people now spend more time indoors, sitting for longer stretches than in the past.

The change in behaviour is associated with an increase in early-onset bowel cancer.

One review in 2014 found that for every extra two hours of sitting per day, the risk of colon cancer increased by 8 per cent, even among people who regularly exercised.

The finding about prolonged sitting made me change how I live. I now use a standing desk and break up my work with stretches or short walks. I often suggest to colleagues that we walk and talk rather than sit in a meeting room.

At home, my children, aged ten and six, are not allowed sugary fizzy drinks. They’re kept for special occasions only, because I’ve seen the research linking high-sugar drinks, especially in adolescence, to a higher risk of bowel cancer in young people.

Cutting them out is one of the simplest changes families can make.

Scientists believe the link may come from frequent spikes in blood sugar and insulin that promote abnormal cell growth and inflammation in the gut.

There’s also evidence that cancer cells can use fructose – the sugar found in very high levels in corn syrup and added to many drinks and foods – as a direct fuel source.

High-sugar diets may also disrupt the gut microbiome, promoting harmful bacterial strains while starving protective ones, weakening the gut’s barrier and triggering the kind of inflammation that is known to play a role in cancer.

In our home we also save sweet treats – such as cakes and biscuits – for special occasions and focus on drinking water and eating fruit and other fibre-rich foods.

I also make sure we are all moving throughout the day, whether it is walking to school, playing outside or going to the park at the weekend.

Processed meats such as bacon are off the table in our house – and although my children are still young, I plan to be just as firm when it comes to smoking, vaping (which has been linked to cell damage) and under-age drinking. Early habits matter, and they tend to stick for life.

I drink less alcohol now and never on an empty stomach. That is another simple change people can make.

Drinking without food means alcohol reaches the bloodstream faster, producing higher levels of acetaldehyde, a toxic by-product that can damage the gut lining, cause inflammation, and has been linked to an increased risk of gastrointestinal cancers, including rectal cancer.

Through our research, we are beginning to understand how Western diets, high in red meat and processed foods – and low in fibre – may alter the gut.

These eating patterns encourage sulphur-metabolising bacteria, which can produce hydrogen sulphide.

In excess, this may harm the bowel lining, which in turn may cause cells to mutate.

At the same time, low fibre intake starves the protective bacteria that help keep the gut healthy.

We are also exploring whether very early life factors play a role.

Swedish research suggests babies born by caesarean may be at higher risk of bowel cancer later in life – possibly because they miss exposure to the mother’s vaginal and gut bacteria, affecting microbiome and immune development.

We are also studying whether parents being very overweight before conception could increase the risk in their children (parental obesity may alter sperm and egg through inflammation or epigenetic changes – switching certain genes on or off – that raise their offspring’s lifelong cancer susceptibility).

These are complex questions. But one thing is clear: bowel cancer in younger adults often behaves differently – for example, tumours usually appear in the rectum or left side of the colon. In older adults, they are more often found in the right colon.

Yes, left-sided tumours may show bleeding earlier, but they tend to be more aggressive and sometimes harder to treat – they often behave differently at a cellular level and don’t always respond as well to standard chemotherapy drugs.

Around one in five patients under 50 has an inherited gene fault that increases their risk, which shows that family history also matters.

Even more worrying is that warning signs are often missed.

The four key symptoms we see are abdominal pain, rectal bleeding, diarrhoea and iron-deficiency anaemia.

These can appear months before a diagnosis, but are often dismissed as piles or irritable bowel syndrome.

If you have bleeding, pain, or ongoing changes in your bowel habits, do not ignore them. Getting checked early really can save lives.

Yes, we need more funding and more public engagement. But I also believe real change can start at home. It starts with what we eat, how we move, and how we look after our bodies. We are not powerless.

This is not just a professional mission for me. It is personal. I want my children to grow up in a world where bowel cancer in the young is no longer on the rise. We still have time to act, but the time to act is now.

• Dr Yin Cao is a molecular cancer epidemiologist and associate professor of surgery and medicine at Washington University in St Louis 

• Interview by Will Stoddart