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Women under 50 who have a diet high in ultra-processed foods (UPFs) stand a greater risk of having abnormal growths in their bowel that can lead to cancer, research suggests.
Ultra-processed foods are typically defined as industrially produced products that are often ready-to-eat, contain little in the way of whole foods, fibre and vitamins, and are typically high in saturated fat, sugar, salt and food additives.
While the concept is not without controversy, not least around whether all UPFs are unhealthy, studies have suggested such foods are associated with a host of health problems, from higher risk of heart disease to early death.
Now researchers say women who have a greater intake of UPFs have a greater risk of the early onset of a common type of bowel polyp known as conventional adenomas.
Dr Andrew Chan, the lead author of the study based at Massachusetts General hospital in the US, said the study was prompted by an effort to understand what was driving rising rates of bowel cancer in younger people.
“The vast majority of these polyps do not become bowel cancer. But at the same time, we know the vast majority of bowel cancers we see in young people arise from these precursor lesions,” he said.
Writing in the journal Jama Oncology, Chan and colleagues report how they studied data collected as part of the US-based Nurses’ Health Study II (NHS II), which began in 1989 and involved female nurses born between 1947 and 1964.
From 1991, participants were asked to complete a food questionnaire every four years in which they reported how often they had eaten various items over the previous 12 months.
The team studied data from 29,105 participants who had completed the questionnaires, undergone a colonoscopy at some point after 1991, and did not have a prior history of polyps, inflammatory bowel disease or any type of cancer other than non-melanoma skin cancer.
These participants were followed until June 2015, by which time all had reached the age of 50. By then, 1,189 cases of early-onset conventional adenomas and 1,598 cases of another type of polyp, known as a serrated lesion, had been recorded.
The team divided participants into five equal sized groups based on their UPF consumption, finding that compared with the group that ate the least UPF – on average 3.3 servings a day – the group that ate the most – on average 9.9 servings a day – had a 45% greater risk of having early onset conventional adenomas once factors such as BMI, smoking and physical activity were taken into account.
However, there was no associated risk of developing serrated lesions.
The study has limitations including that it is based on participants’ recall of food, may be complicated by difficulties in classifying foods as UPFs, did not look at the development of bowel cancer itself, and cannot prove UPFs cause the development of polyps.
However, Chen said there were several plausible mechanisms that could explain the results, noting UPFs had been associated with metabolic disorders linked to obesity and type 2 diabetes that were associated with an increased risk of bowel cancer. He also said UPFs could promote a general state of chronic inflammation, or might impact gut microbes and the gut lining.
Chan said while it was likely the results would also hold for men, more research was needed.
“It doesn’t suggest that if you eat UPFs, that you are inevitably going to develop cancer. That’s certainly not our message,” he said. “But it’s a piece of the puzzle in terms of what might be driving underlying cancer rates.”
Fiona Osgun, the head of health information at Cancer Research UK, said that while the study did not directly measure cancer risk, it offered a useful insight into how diet might influence early changes in the bowel that sometimes led to cancer.
Osgun added that policy-level changes were needed to make healthier diets more accessible for everyone. “Our overall diet matters more for cancer risk than any single food type,” she said.
