A new study published in JAMA Oncology points to a possible link between ultra-processed foods and early-onset colorectal cancer in women under 50. The research tracked nearly 30,000 women for more than two decades and found that those who ate the most ultra-processed foods had a 45 percent higher risk of developing precancerous polyps.
Cancer cases in young adults have risen sharply worldwide over the past three decades. Gastrointestinal cancers, including colorectal cancer, are growing faster than other types among younger people. According to the American Cancer Society, one in five people diagnosed with colorectal cancer is now under 55. Because routine screening does not begin until age 45, many cases are caught late.
Researchers used data from the Nurses’ Health Study II, which has followed tens of thousands of women since 1989. For this analysis, they focused on 29,105 female participants under 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. Every four years, the women reported how often they ate various foods. The researchers then categorized those foods by level of industrial processing.
Ultra-processed foods include items such as packaged breads, sweetened beverages, flavored yogurts, breakfast cereals, snack foods, and ready-to-eat meals. These foods are often calorie-dense and low in nutrients, and they contain additives to improve taste, texture, or shelf life.
Women who consumed about 5.7 servings of ultra-processed foods per day, roughly one-third of their daily calories, had a 45 percent higher risk of developing conventional adenomas. These are the type of polyps most likely to become colorectal cancer over time. The link was not seen with serrated lesions, another type of polyp. This suggests that ultra-processed foods may trigger specific biological changes that set the stage for cancer.
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, and also breakfast cereals, packaged breads, and bottled condiments.
Possible mechanisms
Scientists have strong hypotheses about how ultra-processed foods might drive precancerous changes. These foods can trigger chronic low-grade inflammation throughout the body, including the gastrointestinal tract. Inflammation creates an environment where cells are more likely to accumulate DNA damage and mutations. Ultra-processed 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 harmful bacteria. Additionally, many ultra-processed foods contain advanced glycation end products, compounds formed when proteins or fats combine with sugars during high-heat processing. These compounds can build up in body tissues and are linked to oxidative stress and inflammation.
What this means
With early-onset colorectal cancer on the rise and screening still recommended to start at 45, prevention becomes important. The study suggests reducing ultra-processed staples such as packaged breads, sweetened yogurts, cereals, flavored coffee creamers, and bottled sauces. Prioritizing fiber-rich whole foods, aiming for 25 to 35 grams of fiber daily from vegetables, beans, whole grains, berries, nuts, or seeds, can support gut health. Keeping sugary drinks to a minimum is also advised. Choosing products with shorter ingredient lists may help avoid ultra-processed items.
Warning signs of colorectal cancer include persistent changes in bowel habits, blood in the stool, unexplained weight loss, ongoing abdominal cramping, and unusual fatigue. When caught early, colorectal cancer has a survival rate above 90 percent.
Limitations
The study focused exclusively on white female nurses, so 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 a role in the relationship between diet and disease. The core message is that diet may change cancer risk decades before symptoms appear, and unlike genetic factors, diet is something that can be altered.
