Lead
A study published Thursday in JAMA Oncology found that higher consumption of ultra‑processed foods is associated with an increased risk of precancerous colorectal adenomas in women under 50. Researchers analyzed data from more than 29,000 participants in the Nurses’ Health Study II and followed them from 1991 through 2015. Women who derived about one‑third of daily calories from ultra‑processed foods were roughly 1.5 times more likely to develop adenomas before age 50 than those who ate the fewest. The pattern was specific to adenomas; the study did not find a similar link for serrated lesions.
Key Takeaways
- Study cohort: Data from 29,168 women in the Nurses’ Health Study II, enrolled 1989 (ages 24–42), followed 1991–2015 with diet questionnaires every four years.
- Outcome: About 1,200 women developed adenomas; those in the highest ultra‑processed food intake group (~one‑third of calories) had ~1.5× the risk compared with the lowest intake group.
- Lesion types: The association was observed for adenomas (the lesion type that underlies most colorectal cancers) but not for serrated lesions.
- Food categories: Diets higher in sugar and artificial sweeteners showed the strongest association, followed by higher intake of sauces, spreads and condiments.
- Population limits: The analysis included only women, the majority identifying as white; authors note further study is needed in men and more diverse populations.
- Public health context: Colorectal cancer rates have risen markedly in people under 50; routine screening typically begins at age 45, leaving younger adults less likely to be screened.
Background
Colorectal cancer incidence in adults younger than 50 has increased substantially over recent decades, prompting researchers to search for environmental and lifestyle drivers beyond genetics. Ultra‑processed foods — convenience items defined by multiple industrial processing steps and additives — now represent a large share of calories in many Western diets, particularly among children and younger adults. Prior research has linked these products to higher rates of obesity, type 2 diabetes, depression and premature mortality, raising concern they could also contribute to early‑onset colorectal disease.
The Nurses’ Health Study II is a long‑running prospective cohort established in 1989 to track health outcomes in female registered nurses. Detailed diet questionnaires administered every four years allowed investigators to estimate the share of calories from ultra‑processed foods and relate that exposure to pathology found at colonoscopy. Because most colorectal cancers develop from adenomas, studying precancerous polyps provides an early indicator of cancer risk pathways.
Main Event
Investigators categorized participants by the proportion of daily calories coming from ultra‑processed foods and tracked diagnoses of two types of precancerous colorectal lesions: adenomas and serrated lesions. All participants had at least one colonoscopy before the age of 50, which enabled lesion detection prior to routine screening ages. Approximately 1,200 women were diagnosed with adenomas during follow‑up; statistical models adjusted for known confounders showed a clear positive association between higher ultra‑processed food intake and adenoma risk.
The increased risk concentrated in women whose diets derived about one‑third of calories from ultra‑processed items. The study identified specific subcategories — diets high in sugars and artificial sweeteners, and higher consumption of sauces, spreads and condiments — as most strongly associated with adenoma occurrence. By contrast, researchers did not observe a meaningful relationship between ultra‑processed food intake and serrated lesions in the same cohort.
Lead author Dr. Andrew Chan and colleagues interpreted the adenoma‑specific finding as potentially important because most colorectal cancers arise from adenomatous polyps. Experts not involved in the work emphasized the clinical importance of polyp detection and removal, while noting that many younger adults are not routinely screened and might carry undetected lesions for years.
Analysis & Implications
The observational nature of the study means causality cannot be established from these results alone. Nonetheless, the magnitude and specificity of the association — focused on adenomas rather than all lesion types — strengthen the plausibility of a diet‑related effect on early colorectal carcinogenesis. Potential biological pathways include increased gut inflammation, alterations to the gut microbiome, and metabolic effects mediated by obesity or type 2 diabetes, all of which have been tied to colorectal neoplasia in prior studies.
If ultra‑processed foods do contribute to adenoma formation, the public health implications could be considerable given the rapid rise in their consumption over recent decades. Messaging that reduces intake of high‑sugar, artificially sweetened and highly processed condiment‑heavy diets could form one part of a prevention strategy, alongside efforts to address obesity and metabolic disease. However, policymakers and clinicians will need stronger causal evidence — from mechanistic studies and intervention trials — before recommending specific regulatory or clinical actions.
Clinically, the study underlines a gap in current screening practices: routine population screening historically began later in life and only recently moved toward age 45, leaving younger adults less likely to have lesions detected early. In the near term, the findings may prompt clinicians to counsel higher‑risk younger patients about diet and consider earlier diagnostic evaluation when symptoms or risk factors are present.
Comparison & Data
| Measure | Value |
|---|---|
| Cohort size | 29,168 women |
| Follow‑up period | 1991–2015 (24 years) |
| Adenoma cases | ~1,200 |
| Highest UPF share (approx.) | ~1/3 of daily calories |
| Relative risk (highest vs lowest) | ~1.5× for adenomas |
| Lesion with no observed association | Serrated lesions |
The table summarizes key numerical findings reported by the authors. The relative risk figure (~1.5×) comes from comparisons between participants with the highest versus lowest reported shares of ultra‑processed foods in their diets; models accounted for multiple demographic and lifestyle covariates. Readers should note that exact effect sizes can vary across analytic models and after different adjustments, so the table presents rounded, study‑reported values for clarity.
Reactions & Quotes
Outside experts welcomed the study’s focus on a plausible, modifiable exposure but urged caution in interpretation.
“One approach we’ve been taking is trying to understand what has changed in our environment that could be driving this,”
Dr. Andrew Chan, Massachusetts General Brigham (study lead)
Chan framed the research as part of a broader effort to identify environmental trends that mirror the rise in early‑onset colorectal cancer, noting the parallel increase in ultra‑processed food consumption.
“They are looking at the first step, who is more likely to get these polyps that can turn into cancer,”
Dr. Folasade May, UCLA (gastroenterologist, not involved)
Dr. May highlighted the clinical importance of adenomas as precursors to most colorectal cancers and explained why identifying upstream risk factors is important for prevention.
“The concern is that whenever you have a polyp in a young person, that polyp is allowed to grow unnoticed,”
Dr. Christopher Lieu, University of Colorado (oncologist, not involved)
Lieu emphasized the screening gap for younger adults and why modifiable lifestyle factors deserve attention while research on causality continues.
Unconfirmed
- Whether the observed association reflects a direct causal effect of ultra‑processed foods on adenoma formation rather than residual confounding — this study is observational and cannot prove causality.
- Generalizability to men and more racially and socioeconomically diverse populations — the cohort consisted only of women, predominantly white.
- The precise biological mechanism (microbiome alteration vs inflammation vs metabolic effects) linking ultra‑processed foods to adenoma development remains unproven and requires targeted mechanistic studies.
Bottom Line
This prospective analysis adds weight to concerns that rising consumption of ultra‑processed foods may be one contributor to increasing colorectal neoplasia in younger adults, specifically through a higher risk of adenoma formation. The effect size — about a 50% higher risk for those consuming roughly one‑third of calories from ultra‑processed sources — is notable but not definitive proof of causation.
For clinicians and public‑health officials, the work supports advising patients to limit highly processed, sugar‑heavy and artificially sweetened products as part of broader strategies to reduce metabolic risk. For researchers, the study points to next steps: replicate findings in men and diverse cohorts, pursue mechanism‑focused laboratory and microbiome research, and evaluate whether reducing ultra‑processed food intake lowers adenoma or cancer risk in intervention trials.
Sources
- NBC News — reporting on the JAMA Oncology study (media)
- JAMA Oncology (peer‑reviewed medical journal; study published in this journal)
- Nurses’ Health Study II (academic cohort; long‑term epidemiologic study)
- Cleveland Clinic — colorectal polyps and adenomas (clinical reference)