A new study published in JAMA Oncology has identified a strong link between ultra-processed foods and the risk of colorectal cancer in women under 50. Researchers analyzed data from nearly 30,000 women over more than two decades and found that those who consumed the highest amounts of ultra-processed foods had a 45% higher risk of developing precancerous polyps compared to those who ate the least.
Study details
The research drew on the Nurses’ Health Study II, which has tracked the health and lifestyle habits of tens of thousands of women since 1989. For this analysis, the team focused on 29,105 female participants under age 50 who had completed detailed food questionnaires, undergone at least one lower endoscopy, and had no prior history of cancer, inflammatory bowel disease, or colorectal polyps at the start of the study.
Every four years, the women reported how often they ate various foods. Researchers then categorized those foods based on the level of industrial processing. Ultra-processed foods include packaged breads, sweetened beverages, flavored yogurts, breakfast cereals, snack foods, and ready-to-eat meals.
Key findings
Women consuming about 5.7 servings per day of ultra-processed foods—roughly one-third of their daily calories—had a 45% higher risk of developing precancerous polyps. The link was specific to conventional adenomas, the type of polyp most likely to turn into colorectal cancer over time. The same association was not seen for serrated lesions.
The foods most strongly linked to increased risk included sugar-sweetened beverages, ready-to-eat meals, processed meats such as hot dogs and deli slices, but also breakfast cereals, packaged breads, and bottled condiments.
Possible mechanisms
While scientists cannot yet say that ultra-processed foods directly cause colorectal cancer, they have strong hypotheses. Ultra-processed foods are known to trigger chronic low-grade inflammation throughout the body, including in the gastrointestinal tract. Inflammation creates an environment where cells are more likely to accumulate DNA damage and mutations.
These foods also disrupt the gut microbiome. They tend to be low in fiber and high in additives such as emulsifiers and artificial sweeteners, which can reduce microbial diversity and promote the growth of harmful bacteria. Additionally, many ultra-processed foods contain advanced glycation end products (AGEs), compounds linked to oxidative stress and inflammation.
What this means for prevention
With early-onset colorectal cancer on the rise and routine screening not recommended until age 45, prevention becomes especially important. The study suggests that reducing ultra-processed “staples”—not just snacks—could help. Packaged breads, sweetened yogurts, cereals, flavored coffee creamers, and bottled sauces were major contributors to intake. Prioritizing fiber-rich whole foods, minimizing sugary drinks, and choosing products with shorter ingredient lists are practical steps.
Warning signs of colorectal cancer include persistent changes in bowel habits, blood in the stool, unexplained weight loss, ongoing abdominal cramping, or unusual fatigue. When caught early, colorectal cancer has a survival rate above 90%.
Limitations and context
The study focused exclusively on white female nurses, meaning more diverse research is needed to understand how these findings apply across different racial, ethnic, and socioeconomic groups. Genetics, access to healthcare, environmental factors, and cultural food traditions all play roles. However, the core message is that diet is changing cancer risk potentially decades before symptoms appear.
Cancer cases in young adults have surged nearly 80% worldwide over the past three decades. One in 24 men and one in 26 women will develop colorectal cancer during their lifetime. According to the American Cancer Society, one in five people diagnosed with colorectal cancer are now under age 55. With many cancers caught late because screening starts at 45, understanding dietary risk factors is critical.
