Association between protein diet score and colorectal adenomas risk: a prospective study

Given the significantly increased risk of colorectal adenoma in middle-aged and elderly populations, identifying modifiable risk factors remains a priority. While dietary protein is an essential nutrient in human metabolism, its relationship with colorectal adenoma remains controversial. With advances in nutritional science, contemporary dietary guidelines advocate increasing plant-based protein intake to achieve a more balanced protein consumption pattern. To provide new insights, we sought to investigate the association between colorectal adenoma risk and the Protein Diet Score, which comprehensively evaluates both protein intake and sources.

This analysis was based on data from the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. The Cox proportional hazards regression model was utilized to compute the hazard ratios (HRs) and 95% confidence intervals (CIs). Restricted cubic spline was employed to illustrate the variation in colorectal adenoma risk across the entire spectrum of the Protein Diet Score. Additionally, subgroup analyses were conducted to ascertain possible effect modifiers, and several sensitivity analyses were performed to evaluate the robustness of the findings.

During the mean follow-up period of 11.0 years, 992 newly diagnosed colorectal adenomas were identified. In the fully adjustment for potential confounders, the inverse association between Protein Diet Score and colorectal adenoma risk remained statistically significant with an HR of 0.81 (95% CI: 0.67-0.99; P_trend =0.005) comparing the highest versus lowest quartile. Restricted cubic spline analysis revealed a linear inverse relationship between Protein Diet Score and colorectal adenoma risk (P for nonlinearity =0.317). In the subgroup analyses, we observed a more pronounced inverse association between Protein Diet Score and colorectal adenoma among participants with a history of hypertension (HR _{Quartile 4 vs. Quartile 1}: 0.60; 95% CI: 0.43-0.85; P_interaction =0.017). Finally, a series of sensitivity analyses strengthened the robustness of our findings.

Our findings indicate that higher Protein Diet Score is associated with reduced colorectal adenoma incidence among middle-aged and elderly Americans, with similar findings observed for the PAR. These results provide important evidence for optimizing protein intake and source composition to promote intestinal health.