Ultraprocessed foods linked to precancerous polyps in younger adults

Colorectal cancer used to be a disease of older age. Not anymore. In the past two decades, diagnoses in adults under 50 have climbed steadily, especially in wealthy countries like the U.S. Now researchers at Harvard and Mass General Brigham have identified a significant culprit: ultraprocessed foods.

The study, published in JAMA Oncology, tracked nearly 30,000 women over 24 years and found something clear: those eating the most ultraprocessed foods had a 45% higher risk of developing adenomas — the precancerous polyps that can become colorectal cancer — compared to those eating the least. The risk wasn't sudden or threshold-based. It was linear. The more ultraprocessed food you ate, the more your risk climbed.

"The increased risk seems to be fairly linear," explains Andrew Chan, a gastroenterologist at Mass General Brigham and Harvard Medical School professor who led the research. "Meaning that the more ultraprocessed foods you eat, the more potential that it could lead to colon polyps."

What the data shows

The researchers drew from the Nurses' Health Study II, following female nurses born between 1947 and 1964 — a generation already at elevated risk for early-onset colorectal cancer. Over two decades, 2,787 of these women developed precursor polyps. Even after accounting for other known risk factors like obesity, Type 2 diabetes, and low fiber intake, the association with ultraprocessed foods held firm. It wasn't a secondary effect. It was primary.

What makes this finding actionable is its specificity. This isn't abstract epidemiology. It's a measurable relationship in a real population, and it points to something people can actually change.

But Chan is careful not to oversell the finding. "Diet isn't a complete explanation for why we're seeing this trend," he says. "We see many individuals in our clinic with early-onset colon cancer who eat very healthy diets." The researchers are now hunting for other risk factors — environmental exposures, infections, genetic susceptibilities — that might explain the cases that diet alone doesn't account for.

They're also refining their understanding of ultraprocessed foods themselves. Not all processed foods carry equal risk. Some may be far more harmful than others, and isolating which ones could sharpen prevention strategies even further.

For now, the message is straightforward: if you're under 50, reducing ultraprocessed foods appears to be one concrete way to lower your risk of developing precancerous polyps. It won't eliminate that risk entirely, but in a disease that's rising faster in younger people than anywhere else, incremental protection matters.