Brazil 24-year study reveals why colon cancer surges in young women

A new study published in JAMA Oncology has found a link between high consumption of ultra-processed foods and an increased risk of precancerous polyps in women under 50. The findings offer a potential explanation for the global rise in early-onset colorectal cancer among young adults.

Researchers analyzed data from the Nurses’ Health Study II, which has tracked the health and diet of 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 cancer or history of inflammatory bowel disease or polyps at the start of the study.

Every four years, the women reported how often they ate various foods. Researchers categorized items based on their level of industrial processing. Ultra-processed foods include packaged breads, sweetened beverages, flavored yogurts, breakfast cereals, snack foods, and ready-to-eat meals — products that are often calorie-dense, low in nutrients, and contain additives.

Women who consumed the highest amounts of ultra-processed foods — about 5.7 servings per day, or roughly one‑third of their daily calories — had a 45% higher risk of developing precancerous polyps compared to those who ate the least. The risk was specifically linked to conventional adenomas, the type of polyp most likely to progress to colorectal cancer. No similar association was seen for serrated lesions.

The foods most strongly associated with increased risk included sugar‑sweetened beverages, ready-to-eat meals, processed meats such as hot dogs and deli slices, as well as breakfast cereals, packaged breads, and bottled condiments.

Possible mechanisms behind the link

Scientists have several hypotheses about how ultra-processed foods may drive precancerous changes. These foods are known to 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, which can lead to cancer.

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 the growth of harmful bacteria. Additionally, many ultra-processed foods contain advanced glycation end products (AGEs), compounds formed when proteins or fats combine with sugars during high-heat processing. AGEs accumulate in body tissues and have been linked to oxidative stress and inflammation.

Implications for prevention

With colorectal cancer screening currently recommended to start at age 45, prevention becomes especially important for younger women. The study suggests that reducing intake of ultra-processed staples — not just snacks — may be key. Packaged breads, sweetened yogurts, cereals, flavored coffee creamers, and bottled sauces were major contributors to ultra-processed food intake among the participants.

Researchers emphasize choosing fiber-rich whole foods, aiming for 25 to 35 grams of fiber daily from vegetables, beans, whole grains, berries, nuts, and seeds. Keeping sugary drinks to a minimum is also recommended, as they were a consistent contributor to ultra-processed food intake and have been tied to metabolic and digestive disturbances.

The study also highlights warning signs that warrant a doctor’s visit regardless of age: persistent changes in bowel habits, blood in the stool (even small amounts), unexplained weight loss, ongoing abdominal cramping, and unusual fatigue. When caught early, colorectal cancer has a survival rate above 90%.

Limitations and broader context

This study focused exclusively on white female nurses, so more diverse research is needed to understand how the findings apply across different racial, ethnic, and socioeconomic groups. Genetics, access to healthcare, environmental factors, and cultural food traditions all play roles in disease risk.

Nevertheless, the core finding is clear: diet is changing cancer risk, potentially decades before symptoms appear. The rise in early-onset colorectal cancer is unfolding alongside dramatic shifts in how food is produced, processed, and consumed. Unlike genetic risk factors, diet is a changeable behavior, offering a practical area for intervention.