Ultraprocessed foods make up a large share of many people’s diets, especially in the United States, and researchers are looking closely at how these foods may influence long-term health. A new study from Mass General Brigham offers one piece of that puzzle, focusing on adults under 50, the age group where colorectal cancer has been rising most quickly.
The research team analyzed 24 years of data from nearly 30,000 women in the Nurses’ Health Study II. Participants regularly filled out detailed diet surveys and underwent at least two lower endoscopies before age 50, giving researchers a rare long-term look at eating patterns alongside early signs of colorectal cancer.
The study, published in JAMA Oncology, found that women who ate the most ultraprocessed foods had higher rates of adenomas, specific types of colon polyps that can be precursors of early-onset colorectal cancer. Those in the highest-intake group averaged about 10 servings of ultraprocessed foods per day. Compared with women who ate the least (around three servings per day), their risk of developing conventional adenomas was 45% higher.
“Our findings support the importance of reducing the intake of ultraprocessed foods as a strategy to mitigate the rising burden of early-onset colorectal cancer,” said senior author Andrew Chan, MD, MPH. “The increased risk seems to be fairly linear, meaning that the more ultraprocessed foods you eat, the more potential that it could lead to colon polyps.”
Ultraprocessed foods include ready-to-eat or ready-to-heat items that often contain refined starches, added sugars, salt, saturated fat or additives. Examples range from packaged snacks and frozen entrées to sweetened breakfast cereals and processed meats. But the category is broad, and not all ultraprocessed foods are nutritionally equivalent. Some are clearly less healthy choices, while others can be fortified, affordable or important for food access. UPFs aren’t considered harmful simply because they’re processed; concerns arise when they displace fiber-rich, minimally processed foods that support gut and metabolic health.
Chan’s team accounted for many other factors that affect colon cancer risk, including body weight, type 2 diabetes and fiber intake.
“One of the strengths of our study was that we had detailed information about other colorectal cancer risk factors in the participants, such as such as body mass index, type 2 diabetes and low fiber intake,” Chan said. “Even after accounting for all these other risk factors, the association with ultra-processed foods still held up.”
The study did not find a link between ultraprocessed foods and serrated lesions, another type of polyp that grows more slowly and is less tied to early-onset colorectal cancer. And the authors emphasize that diet alone cannot explain why colorectal cancer is rising in younger adults.
“Diet isn't a complete explanation for why we're seeing this trend — we see many individuals in our clinic with early onset colon cancer who eat very healthy diets,” Chan said. “Identifying other risk factors for early onset colorectal cancer is one of the focuses of the work that we're leading here at the Mass General Brigham Cancer Institute.”
The findings add to growing evidence that eating patterns matter, not because any one category of food determines health, but because overall balance influences long-term outcomes. Researchers note that many people rely on ultraprocessed foods for convenience, affordability or cultural reasons, and reducing risk doesn’t require eliminating UPFs entirely. Instead, gradually creating more room for whole grains, fruits, vegetables and other fiber-rich foods may support better colon health over time.
The authors reported the following disclosures: Cao served as a consultant for Need Inc. Chan served as a consultant for Pfizer Inc. and Boehringer Ingelheim outside the submitted work.