Researchers studied nearly one million people across the United States and Europe to understand how different eating patterns affect colorectal cancer risk. They found that people who ate diets with less processed foods and more anti-inflammatory foods had about an 18% lower chance of developing colorectal cancer compared to those who ate less healthy diets. This large study combined information from six different research projects and tracked people for an average of 15 years, making it one of the biggest investigations into how diet influences this type of cancer.

The Quick Take

  • What they studied: Whether eating foods that don’t cause blood sugar spikes and foods that reduce body inflammation could help prevent colorectal cancer
  • Who participated: Over 900,000 adults from six major health studies in the U.S. and Europe, including men and women of different ages and backgrounds, followed for an average of 15 years
  • Key finding: People who ate the healthiest, least inflammatory diets had about 18-20% lower chances of getting colorectal cancer compared to those who ate the least healthy diets
  • What it means for you: Choosing whole foods over processed foods and eating more plants may help reduce your colorectal cancer risk, though diet is just one factor among many that affect cancer risk

The Research Details

This was a very large study that combined information from six different long-term health research projects happening in the U.S. and Europe. The researchers had to standardize how they measured food intake across all these different studies—imagine translating recipes from different countries so they all use the same measurements. They tracked over 900,000 people and recorded what they ate, then followed them for an average of 15 years to see who developed colorectal cancer. The researchers used three different scoring systems to measure diet quality: one that looked at foods that don’t spike blood sugar, one that measured inflammation-fighting foods, and one that measured overall healthy eating patterns.

The researchers carefully adjusted their analysis to account for other factors that might affect cancer risk, like age, smoking, exercise, and family history. They used a statistical method called Cox regression to calculate how much diet affected cancer risk, then combined results from all six studies together to get one overall answer.

This approach is important because previous smaller studies showed diet might affect cancer risk, but scientists weren’t sure if those findings would apply to different countries, races, and cultures with different food supplies. By combining data from nearly one million people across two continents, the researchers could see if the same dietary patterns protected people everywhere, not just in one specific group.

This is a high-quality study because it included a very large number of people (over 900,000), tracked them for a long time (15 years), and combined data from multiple well-established research projects. The researchers carefully standardized how they measured food intake across different studies. The findings were consistent across most groups, though some variation existed between countries. The study was published in a respected peer-reviewed journal. However, people self-reported their food intake, which can be less accurate than direct measurement.

What the Results Show

During the 15-year study period, about 16,500 people developed colorectal cancer. People who ate the most anti-inflammatory, low-sugar-spiking diets had an 18-20% lower risk of colorectal cancer compared to those who ate the least healthy diets. This means if 100 people eating unhealthy diets developed cancer, only about 80-82 people eating healthy diets would develop it.

All three diet quality measures showed similar protective effects: the low-insulinemic diet (foods that don’t spike blood sugar), the anti-inflammatory diet (foods that reduce body inflammation), and the overall healthy eating index all showed about 18-20% risk reduction. This consistency across different ways of measuring diet quality suggests the findings are reliable.

The protective effect was seen across different countries, age groups, and both men and women, though the strength of the effect varied somewhat between different populations. The fact that results were similar across such diverse groups suggests these dietary patterns may help prevent colorectal cancer in many different populations.

The researchers found that the low-insulinemic diet (foods that don’t cause blood sugar spikes) showed the most consistent results across different populations, with less variation between countries. The anti-inflammatory diet showed more variation between countries, possibly because different regions have different traditional foods and eating patterns. The overall healthy eating index showed the most variation, suggesting that specific food choices matter more than just general ‘healthy eating’ labels.

Previous research suggested that inflammatory foods and foods that spike blood sugar might increase cancer risk, but this was mostly shown in smaller studies or single countries. This new study confirms those earlier findings in a much larger, more diverse population. The 18-20% risk reduction is similar to what some previous studies found, but this study is stronger because it includes so many more people and different populations. The findings align with general cancer prevention guidelines that recommend eating more plants, whole grains, and less processed food.

People reported their own food intake from memory, which can be inaccurate—people might forget what they ate or estimate portion sizes wrong. The study is observational, meaning researchers watched what people ate and what happened to them, but couldn’t prove that diet directly caused the lower cancer risk (other lifestyle factors could be involved). The study included mostly people who volunteered for health research, who tend to be healthier and more health-conscious than the general population. The researchers couldn’t measure all possible factors that might affect cancer risk. Some variation existed between countries in how strong the protective effect was, suggesting diet’s impact might differ by region.

The Bottom Line

Eat more whole foods like vegetables, fruits, whole grains, and legumes while limiting processed foods, sugary drinks, and red meat. This dietary approach may reduce colorectal cancer risk by about 18-20% (moderate confidence based on this large study). These recommendations align with general cancer prevention guidelines from major health organizations. However, diet is just one factor—screening, exercise, maintaining healthy weight, and not smoking are also important for colorectal cancer prevention.

Everyone should care about these findings, especially people with family history of colorectal cancer, people over 45 (when colorectal cancer screening typically begins), and anyone interested in cancer prevention. These findings apply to diverse populations across different countries. People with specific medical conditions should discuss dietary changes with their doctor before making major changes.

You won’t see immediate results from dietary changes. Cancer develops over many years, so the protective effects of healthy eating build up over time. Most people should expect to maintain these dietary changes long-term (years, not weeks) to see meaningful cancer risk reduction. You might notice other health benefits like better energy, improved digestion, and better weight management within weeks to months.

Want to Apply This Research?

  • Track daily servings of anti-inflammatory foods (leafy greens, berries, fatty fish, nuts) and low-glycemic foods (whole grains, legumes, non-starchy vegetables) versus processed foods and added sugars. Aim for at least 5 servings of vegetables/fruits daily and limit processed foods to less than 20% of daily calories.
  • Start by replacing one processed food item daily with a whole food alternative (swap sugary cereal for oatmeal, chips for nuts, soda for water). Build a weekly meal plan featuring plant-based proteins, whole grains, and colorful vegetables. Use the app to set reminders for meal prep and track which anti-inflammatory foods you enjoy most.
  • Weekly check-ins on dietary pattern adherence using a simple scoring system. Monthly reviews of which healthy foods you’re eating most consistently. Track energy levels, digestion, and weight alongside dietary changes to see personal benefits. Set quarterly goals to gradually increase whole food intake and decrease processed food intake.

This research suggests associations between diet and colorectal cancer risk but does not prove that diet changes will prevent cancer. Individual cancer risk depends on many factors including genetics, age, screening, lifestyle, and medical history. This information is not a substitute for professional medical advice. Consult with your healthcare provider or registered dietitian before making significant dietary changes, especially if you have existing health conditions, take medications, or have a family history of cancer. Regular colorectal cancer screening as recommended by your doctor remains important regardless of diet.