[3D graphic art. Photo credit to Unsplash]

A new analysis released in November 2025 by Mass General Brigham and collaborating institutions reported that women who consume high amounts of ultra-processed foods face a significantly greater likelihood of developing precancerous colorectal polyps before the age of 50. 

The findings were based on long-term data from the Nurses’ Health Study II, a large U.S. cohort study that has followed tens of thousands of female nurses for decades.

The researchers found that women who ate nine to ten servings of ultra-processed foods each day had a 45 percent higher chance of developing conventional adenomas compared with women who consumed about three servings daily.

Adenomas are early-stage polyps that can potentially develop into colorectal cancer if left undetected and untreated.

The study followed more than 29,100 female nurses for a median of 13 years, using repeated dietary questionnaires to estimate long-term consumption patterns.

Researchers identified 1,189 cases of conventional adenomas detected via endoscopy before participants turned 50.

After adjusting for other risk factors such as BMI, type 2 diabetes and fiber intake, the association between high intake of ultra-processed foods and adenoma risk remained.

Ultra-processed foods most commonly included breads, breakfast foods, sauces and condiments, and sugar-sweetened or artificially sweetened drinks.

The researchers noted that no single food category was solely responsible for the increased risk.

“Our study isn’t cause and effect, so we can’t say that this is definitive,” said senior study author Dr. Andrew Chan, a gastroenterologist at the Mass General Brigham Cancer Institute in Boston.

Ultra-processed foods are typically low in fiber and high in added sugars, refined grains, sodium, and industrial additives, which can influence the gut microbiome and the intestinal lining.

Other researchers suggested that some additives and emulsifiers may contribute to inflammation or other biological changes linked to tumor initiation.

Experts also cautioned that products consumed in the 1990s are not identical to today’s versions, as formulations and additive profiles have shifted over time.

Because the dataset relied on self-reported diets, some misclassification is possible. (Dietary misclassification refers to when participants inaccurately report what or how much they eat.)

Participants were primarily White female nurses with above-average medical access, which may limit the general applicability of the findings.

Most adenomas in the cohort were detected before routine screening guidelines lowered the recommended start age from 50 to 45.

The study found no association between ultra-processed food intake and serrated lesions, another type of colon polyp. (Serrated lesions develop through a different pathway and do not always behave the same way as adenomas.)

This suggests the association may be specific to adenoma-related pathways. 

Although not all polyps become cancerous, experts note that early adenomas can gain malignant potential if left untreated.

Outside experts said the findings reinforce evidence connecting ultra-processed diets with early tumor development but stressed that further research is needed to identify mechanisms.

Clinicians advise reducing packaged or pre-prepared foods and shifting toward simple whole ingredients, which are more likely to contain fiber and fewer additives.

Doctors advise beginning screening at age 45, or earlier for those with symptoms or a family history of colorectal cancer.

The original study, published in JAMA Oncology, concludes that the association between high ultra-processed food intake and early adenoma formation warrants further investigation but should not be interpreted as direct evidence of causation.