Dietary Intake of Animal and Plant Proteins and Risk of Gastrointestinal Cancer Mortality: Results from the Golestan Cohort Study

Background: Gastrointestinal (GI) cancers account for a significant global cancer burden, but the link between intake of proteins from different sources and GI cancer mortality is unclear. Objectives: This study examined associations between the percentage of energy received from animal protein intake (API) and plant protein intake (PPI), and mortality from esophageal (EC), gastric (GC), colorectal (CRC), and pancreatic (PC) cancers in 42,323 participants of the Golestan Cohort Study (GCS). Methods: Using data from a baseline food frequency questionnaire, hazard ratios (HRs) were estimated through Cox models, including isocaloric substitution analyses of API and PPI. Results: During 13.4 y of follow-up, 676 deaths from GI cancer occurred. We found no association between API and GI cancer mortality [HR_{Q5 vs Q1} = 1.023; 95% confidence interval (CI): 0.626, 1.673; P _{for trend} = 0.976], and a positive association between PPI and overall GI cancer mortality (HR_{Q5 vs Q1} = 2.635; 95% CI: 1.368, 5.074; P _{for trend} = 0.005). We identified no association between API and EC mortality (HR_{Q5 vs Q1} = 0.711; 95% CI: 0.377, 1.746; P _{for trend} = 0.058), and a positive association between PPI and EC mortality (HR_{Q5 vs Q1} = 5.226; 95% CI: 1.888, 14.459; P _{for trend} = 0.001). BMI and wealth score modified some of these associations. There was no association between API or PPI and GC, CRC, or PC mortality. We observed a decreasing trend in percentage of energy received from fish protein (HR_{Q5 vs Q1} = 0.766; 95% CI: 0.585, 1.004; P _{for trend} = 0.038) and legume protein (HR_{Q5 vs Q1} = 0.760; 95% CI: 0.588, 0.982; P _{for trend} = 0.042) related to GI cancer mortality. In contrast, refined grains protein showed an increasing trend (HR_{Q5 vs Q1} = 1.472; 95% CI: 1.023, 2.117; P _{for trend} = 0.027). Conclusions: In the GCS, with refined grains as the main source of PPI, we observed a positive association between PPI and GI cancer and EC mortality. Future studies should focus on food groups simultaneously.