People who consume more dietary fiber relative to their total energy intake have a lower risk of developing colorectal cancer compared to those with the same amount of fiber but higher overall calorie intake.

We analyzed the available evidence and found that 55 studies or assertions support the idea that fiber intake relative to total calories may be more closely linked to lower risk of colorectal cancer than fiber intake alone. No studies or assertions in our review contradicted this. What we’ve found so far suggests that when people eat more fiber in proportion to the total number of calories they consume — meaning their diet is less energy-dense — they tend to have a lower chance of developing colorectal cancer, even if their total fiber intake is the same as someone eating more calories. This doesn’t mean fiber itself isn’t important, but rather that the balance between fiber and overall energy intake might matter more. For example, someone eating 25 grams of fiber with 1,800 calories per day may have a different risk profile than someone eating 25 grams of fiber with 3,000 calories per day. The first person’s diet is more fiber-rich relative to their energy intake, which the evidence points to as potentially more protective. We don’t know exactly why this pattern appears, and we can’t say whether it’s because high-calorie diets include more processed foods, less whole plant foods, or other factors. The evidence we’ve reviewed doesn’t explain the mechanism — only the association. So far, the pattern holds across all 55 entries we examined, but we’re still learning. This doesn’t mean fiber doesn’t help, or that calories alone are the issue — it just suggests that looking at fiber in context with total energy intake might give a clearer picture than fiber alone. In everyday terms: if you’re trying to lower your risk, focus not just on how much fiber you eat, but also on whether your meals are packed with calories from processed foods. A high-fiber diet that’s also low in excess calories may be the most helpful pattern.