Bowel cancer was once a disease found largely in older adults but cases are rising among adults under the age of 50, figures suggest.
Experts said early-onset bowel cancer, which affects people in this age bracket, has “substantially” risen around the world since 1990, and the UK has one of the fastest-rising rates.
It is not clear what is behind the increase, though obesity is thought to be a possible factor.
Experts at King’s College London and health science company Zoe are searching for 250,000 adults across the UK to take part in the study.
The trial, known as Prospect-UK, will track people over a period, analysing diet and lifestyle factors.
Participants will complete questionnaires on their diet, lifestyle, environment, health and other factors.
Researchers will ask for their information to be linked to their electronic health records so cancer cases can be tracked.
A small group will be asked to write more detailed diet diaries and hand in blood and stool samples.
“Over just a few generations our lifestyles, diets and environments have changed dramatically,” said Professor Sarah Berry, chief investigator of the trial and professor of nutritional sciences at King’s College London.
“But we don’t know which of these changes are increasing people’s risk of bowel cancer or which ones could help reduce it.
“We urgently need large-scale, long-term data to uncover the true causes of early-onset bowel cancer.”
Figures from Cancer Research UK show there are about 48,200 new bowel cancer cases in the UK every year, including around 2,900 in those aged 25 to 49.
The charity said that between the early 1990s and 2019, overall cancer incidence rates in 25 to 49-year-olds in the UK rose by 24%.
Dr Rosiered-Brownson Smith, study research associate at King’s College London, said: “Although rates of early-onset bowel cancer are rising, it remains relatively uncommon, which means we need large groups of people to take part in research to help us understand why we are seeing this worrying trend.
“At the same time, our food environment has become increasingly complex, and this means we need to look at diet in much greater detail.
“In the UK, around 60% of our calorie intake comes from highly processed foods, but these foods are not all the same.
“They can differ substantially in their ingredients, processing methods and nutritional composition, even within the same food category.”
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Dr Smith said they are collecting detailed, brand-level information about foods consumed for the first time to better understand which foods and dietary patterns may be linked to the development of early-onset bowel cancer.
“Combining detailed dietary information with long-term health data, we hope Prospect-UK will help us better understand the complex relationship between what we eat and our risk of disease,” she added.
