Dietary Intakes of Animal and Plant Proteins and Risk of Colorectal Cancer: The EPIC-Italy Cohort

SIMPLE SUMMARY: After breast and prostate cancer, colorectal (CRC) is the third most frequent cancer in men and women. It is unclear if protein-rich diets other than red meat elevate risk or even lower CRC occurrence at specific colon locations. The aim of this study is to assess the associations of animal and plant protein intakes with CRC risk in middle-aged Italian men and women. Our findings show that replacing animal proteins with plant proteins was associated with a lower risk of rectal cancer but not of colon cancer, while replacing animal proteins with plant-based proteins from high-glycemic-index (GI) foods was associated with an increased colon cancer risk. These results have important public health implications as they suggest that both refined high-GI foods and meat might have site-specific roles in the pathogenesis of CRC. ABSTRACT: We prospectively investigated the associations of protein intake with colorectal cancer (CRC) risk in middle-aged Italian men and women. Food consumption was assessed by validated Epic semiquantitative food-frequency questionnaires. Multivariable Cox models stratified by center, age, and sex, adjusted for confounders, estimated the associations of animal and plant protein consumption with CRC risk by subsite. Among 44,824 men and women, we identified 539 incident CRCs after a median follow-up of 14 years. Replacing animal proteins with plant proteins was associated with a decreased risk of rectal (HR, 0.71; 95% CI, 0.55–0.92) but not colon cancer. By contrast, replacing animal proteins with plant proteins from high-glycemic-index (GI) foods was associated with an increased risk of proximal and distal (including sigma) colon cancer (HR, 1.23; 95% CI, 1.07–1.40) but not when animal proteins were replaced with plant proteins from low-GI foods (HR, 0.93; 95% CI, 0.79–1.11). Further evaluation revealed that the increased colon cancer risk was limited to the substitution of proteins from red and processed meat, as well as dairy and eggs, with vegetable proteins from high-GI foods. Participants in the highest quintile of animal protein intake had higher plasma glucose and cholesterol levels than those in the lowest quintile. By contrast, higher intake of plant proteins from low-GI foods was inversely associated with fasting insulin and HOMA-IR levels. In conclusion, replacing animal proteins with plant proteins from high-GI foods was associated with an increased risk of colon cancer.