Women under 50 who have a diet high in ultra-processed foods (UPFs) are more likely to develop abnormal bowel growths that can sometimes lead to cancer, according to a new study published in the journal JAMA Oncology. The research found that those with the highest consumption of these foods had a 45% greater risk of early-onset conventional adenomas compared with those who ate the least.
The study analysed data from the US-based Nurses' Health Study II, which began in 1989 and involved female nurses born between 1947 and 1964. From 1991, participants completed food questionnaires every four years, reporting how often they had eaten various items in the previous year. The team examined information from 29,105 women who had undergone a colonoscopy after 1991 and had no prior history of polyps, inflammatory bowel disease, or cancer apart from non-melanoma skin cancer.
Participants were followed until June 2015, by which point all had reached the age of 50. During that time, 1,189 cases of early-onset conventional adenomas and 1,598 cases of another type of polyp called serrated lesions were recorded. When divided into five groups based on UPF consumption, the highest-consuming group, averaging 9.9 servings a day, had a 45% greater risk of early-onset conventional adenomas than the lowest group, which averaged 3.3 servings a day, even after accounting for factors such as body mass index, smoking, and physical activity. No such risk was observed for serrated lesions.
The study's limitations include its reliance on participants' recall of what they ate and the difficulty of classifying foods as ultra-processed. It did not directly measure bowel cancer cases and cannot prove that UPFs cause polyps. However, the lead author, Dr Andrew Chan of Massachusetts General Hospital, said there were plausible mechanisms, including links to metabolic disorders, chronic inflammation, and changes in gut microbes and the gut lining.
Chan noted that while the findings likely apply to men as well, further research is needed. He stressed that eating UPFs does not mean someone will inevitably develop cancer, but it adds to the puzzle of rising bowel cancer rates in younger people. Fiona Osgun, head of health information at Cancer Research UK, said the study offered useful insight into how diet might influence early bowel changes, though overall diet matters more for cancer risk than any single food type. She added that policy changes are needed to make healthier diets more accessible.
