Researchers followed nearly 30,000 female nurses for 24 years to understand how ultra-processed foods affect colon health. They found that women who ate the most ultra-processed foods—like packaged snacks, sugary drinks, and fast food—had a 45% higher risk of developing precancerous growths in their colon before age 50. These growths, called adenomas, can turn into cancer if not removed. The study suggests that eating fewer processed foods and more whole foods might help protect younger women from early colon cancer.

The Quick Take

  • What they studied: Whether eating lots of ultra-processed foods increases the chance of developing precancerous growths in the colon before age 50
  • Who participated: 29,105 female registered nurses in the United States, average age 45, followed for 24 years from 1991 to 2015. All participants had at least one colon screening during the study.
  • Key finding: Women who ate the most ultra-processed foods had a 45% higher risk of developing conventional adenomas (precancerous growths) compared to women who ate the least. This finding remained strong even after accounting for weight, diabetes, and overall diet quality.
  • What it means for you: Reducing ultra-processed food intake may help lower your risk of developing precancerous colon growths before age 50. This is especially important for younger women. However, this study shows association, not definite cause-and-effect, and individual risk varies based on many factors.

The Research Details

This was a prospective cohort study, which means researchers followed the same group of people over time and tracked what they ate and what health problems developed. The researchers used the Nurses’ Health Study II, which began in 1989 and included female registered nurses across the United States. Every 4 years, participants filled out detailed questionnaires about their food intake. Researchers classified foods using the NOVA system, which divides foods into four categories based on how processed they are. Ultra-processed foods are those with added ingredients like sugar, salt, oils, and artificial substances. The study tracked participants from 1991 to 2015, and only included women who had at least one colonoscopy or sigmoidoscopy (colon screening) before age 50 and had no previous cancer or colon polyps.

This research approach is important because it follows real people over many years in their everyday lives, rather than testing in a lab. This makes the findings more relevant to how people actually eat and live. The researchers also carefully collected information about many other factors that could affect colon cancer risk, like weight, exercise, smoking, and overall diet quality. This helps them determine whether ultra-processed foods specifically are the problem, not just poor diet in general.

This study has several strengths: it followed a large number of people (nearly 30,000) for a long time (24 years), used detailed food records collected regularly, and confirmed all colon findings through medical records and pathology reports. However, the study only included female nurses, so results may not apply equally to men or other groups. Also, participants self-reported their food intake, which can have errors. The study shows association between ultra-processed foods and colon growths, but cannot prove that ultra-processed foods directly cause these growths.

What the Results Show

Among the 29,105 women studied, researchers found 1,189 cases of conventional adenomas (the most common type of precancerous growth) and 1,598 cases of serrated lesions (another type of precancerous growth). Women ate an average of 5.7 servings of ultra-processed foods per day, which made up about 35% of their total daily calories. Women in the highest group of ultra-processed food consumption had a 45% increased risk of developing conventional adenomas compared to women in the lowest group. This increased risk remained significant even after researchers adjusted for body weight, type 2 diabetes, fiber intake, folate, calcium, vitamin D, and overall diet quality scores. The association was strong and consistent across different analyses.

Interestingly, higher ultra-processed food intake was not associated with increased risk of serrated lesions, another type of precancerous growth. This suggests that ultra-processed foods may specifically affect the development of conventional adenomas rather than all types of colon growths. The findings were consistent across different age groups within the study population and remained significant when researchers looked at different types of ultra-processed foods.

Previous research has shown that ultra-processed foods are linked to various health problems including obesity, type 2 diabetes, and overall cancer risk. However, this is one of the first large studies to specifically examine the connection between ultra-processed foods and early-onset colorectal cancer precursors in women. The findings align with growing evidence that diet quality significantly impacts colon health, particularly in younger adults where early-onset colorectal cancer rates have been increasing.

This study only included female registered nurses in the United States, so results may not apply to men, other racial or ethnic groups, or people in other countries with different food systems. Participants self-reported their food intake, which can be inaccurate from memory or social desirability bias. The study shows association, not causation—we cannot definitively say that ultra-processed foods cause these growths. Other unmeasured factors could contribute to the findings. Additionally, women who participated in the study may have been more health-conscious than the general population, which could affect how the results apply to everyone.

The Bottom Line

Based on this research, consider reducing ultra-processed food consumption and increasing whole foods like fruits, vegetables, whole grains, and legumes. This recommendation has moderate confidence because the study shows a strong association but cannot prove causation. Aim to get less than 30% of daily calories from ultra-processed foods if possible. Combine this with regular colon cancer screenings as recommended by your doctor, especially if you have other risk factors.

This finding is particularly important for women under 50 years old, as early-onset colorectal cancer rates are increasing in this group. Anyone with a family history of colorectal cancer, inflammatory bowel disease, or other colon cancer risk factors should pay special attention. People of all ages can benefit from reducing ultra-processed foods. However, this study specifically examined women, so men should look for additional research about how these findings apply to them.

Changes in colon health from dietary improvements typically take months to years to develop. Precancerous growths develop over time, so reducing ultra-processed foods now may help prevent their formation in the future. If you make dietary changes, you may notice other health benefits like improved energy, better digestion, or weight changes within weeks to months. Colon cancer screening recommendations vary by age and risk factors, so discuss appropriate screening timing with your doctor.

Want to Apply This Research?

  • Track daily ultra-processed food servings and aim for a target of 4 or fewer servings per day. Log specific items like packaged snacks, sugary drinks, fast food, and processed meats. Monitor the percentage of daily calories from ultra-processed foods, aiming to keep it below 30%.
  • Replace one ultra-processed food item daily with a whole food alternative. For example: swap a packaged snack for fresh fruit, replace a sugary drink with water or unsweetened tea, or choose grilled chicken instead of processed deli meat. Start with one substitution and gradually add more as it becomes routine.
  • Weekly review of ultra-processed food intake patterns to identify your biggest sources (drinks, snacks, meals, etc.). Monthly assessment of progress toward reducing servings and percentage of calories. Track any digestive changes or energy improvements. Set quarterly goals to progressively reduce ultra-processed foods while increasing whole foods. Consider pairing this with regular colon cancer screening as recommended by your healthcare provider.

This research shows an association between ultra-processed food consumption and increased risk of precancerous colon growths in women under 50, but does not prove that ultra-processed foods directly cause these growths. Individual risk varies based on genetics, lifestyle, and other factors. This information is for educational purposes and should not replace professional medical advice. If you have concerns about colorectal cancer risk or colon health, consult with your healthcare provider about appropriate screening and dietary recommendations for your specific situation. Women should follow their doctor’s recommendations for colorectal cancer screening based on age, family history, and personal risk factors.