Rates of bowel cancer in people under 50 have been increasing in several countries, prompting researchers to investigate potential contributing factors.
One area of interest is the role of ultra-processed foods (UPFs)—industrially produced items that are typically high in added sugar, salt, saturated fat and food additives, and low in fibre and whole-food content.
Although the classification of UPFs is debated, previous research has linked high consumption of these products with adverse health outcomes, including cardiovascular disease and premature mortality.
A new analysi examined whether high UPF intake is associated with early development of colorectal polyps, specifically among women younger than 50. The study was led by Dr Andrew Chan of Massachusetts General Hospital, who noted that most bowel cancers originate from precursor lesions such as adenomas, even though many polyps never progress to cancer.
Researchers drew on data from the Nurses’ Health Study II (NHS II), a long-running U.S. cohort that began in 1989 and includes female nurses born between 1947 and 1964. Starting in 1991, participants completed detailed dietary questionnaires every four years, reporting how frequently they consumed a range of foods over the prior 12 months.
For the current analysis, the team examined 29,105 women who had completed these questionnaires, had undergone at least one colonoscopy, and had no previous history of colorectal polyps, inflammatory bowel disease, or cancers other than non-melanoma skin cancer. Participants were followed until June 2015, by which time all had reached age 50.
During the study period, researchers documented 1,189 cases of early-onset conventional adenomas and 1,598 cases of serrated lesions—two common types of colorectal polyps. Participants were divided into five groups based on their UPF consumption.
Women in the highest UPF-intake group, averaging 9.9 servings per day, had a 45% greater risk of developing early-onset conventional adenomas compared with those consuming the least, who averaged 3.3 servings daily. This increased risk persisted after accounting for body mass index, smoking, and physical activity. No increased risk was observed for serrated lesions.
While the study did not measure bowel cancer directly and cannot establish causation, researchers identified potential biological mechanisms. UPFs have been associated with metabolic disturbances linked to obesity and type 2 diabetes—both known risk factors for bowel cancer. They may also contribute to chronic inflammation or alter the gut microbiome in ways that could affect the bowel lining.
Dr Chan noted that similar associations might be found in men, though further research is needed. He emphasised that the findings do not imply that consuming UPFs will inevitably lead to cancer, but rather that diet may be one factor contributing to broader trends in early-onset disease.
Fiona Osgun, head of health information at Cancer Research UK, said the study provides useful insight into how diet may influence early changes in the bowel. She highlighted that broader dietary patterns matter more for cancer prevention than any single food category. Osgun also stressed the need for policy approaches that make healthier food options more accessible.
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