Women who consume high amounts of ultra processed food (UPFs) are at higher risk of developing a potential precursor to bowel cancer, a new study suggests. Experts said that the study provides insight on how diet can influence early changes in the bowel.

Writing in the journal Jama Oncology, experts said that women who regularly eat more servings of UPFs – such as processed sauces, crisps, processed meats and many ready meals – are at a significantly higher risk of developing a growth in the bowel called an adenoma. These growths are a type of polyp and are not cancerous, but they can develop into cancer over a long period of time.

Most bowel cancers develop from an adenoma. Researchers have been trying to discover the reason behind a rise in bowel cancer cases among younger adults. According to Cancer Research UK (CRUK), incidence rates of bowel cancer among people aged 25-49 have increased by 62% since the early 1990s.

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The new study examined information on thousands of nurses in the US who were tracked from 1991 through to 2015. Information on UPF intake was gathered using food surveys taken every four years. Researchers studied 29,105 women with an average age of 45.

Among these women, 1,189 cases of early-onset adenomas were identified, according to the study, which was funded by Cancer Grand Challenges – a global research initiative founded by Cancer Research UK and the National Cancer Institute in the US.

Those with the highest consumption of UPFs were 45% more likely to have these early-onset adenomas, compared to those with the lowest consumption of UPFs. Those who ate the highest proportion of UPFs ate around 9.9 portions a day.

CRUK said a typical diet of this many servings of UPFs could include: one bowl of sweetened breakfast cereal, one slice of white toast with margarine or jam, a flavoured yoghurt cup or breakfast bar for breakfast; a pre-packaged supermarket sandwich, a packet of crisps and a can of coke or flavoured drink for lunch; a frozen pizza or oven chips and chicken nuggets with ketchup and mayonnaise on the side for supper and an evening treat of ice cream or biscuits.

Those who ate the fewest UPFs consumed an average of 3.3 servings each day. “These data highlight the important role of UPFs in early-onset colorectal tumorigenesis and support improving dietary quality as a strategy to mitigate the increasing burden of early-onset colorectal cancer,” the authors wrote.

Dr Andrew Chan, lead author of the study, from Harvard Medical School and Massachusetts General Hospital in the US, said: “We’re seeing more cases of bowel cancer in younger adults, and we still don’t understand why. Our research is exploring possible factors such as diet, lack of exercise and disruption to the gut microbiome, which may all play a role.

“Our study suggests these foods could be linked to a higher risk of developing polyps. However, more research is needed to confirm this link. This means looking at larger and more diverse groups of people and investigating how the body responds to these foods to understand their role in early changes in the bowel.”

Cancer Grand Challenges scientific committee chairman and Cancer Research UK’s chief clinician, Professor Charles Swanton, said the study helps “shed light on how diet and other factors are associated with gut health and changes in the bowel linked to cancer risk”.

Fiona Osgun, head of health information at Cancer Research UK, added: “While this study doesn’t directly measure cancer risk, it offers useful insight into how diet might influence early changes in the bowel that sometimes lead to cancer. Our diets are shaped by the world around us, from food prices, marketing and local availability.

“This can make healthy choices harder. We need broader changes – from food policy to public health initiatives – to make healthier diets more accessible for everyone. Our overall diet matters more for cancer risk than any single food type.”