The association between animal protein, plant protein, and their substitution with bladder cancer risk: a pooled analysis of 10 cohort studies

Abstract

Purpose: Although total dietary protein intake has been associated with bladder cancer (BC) risk, the effect of the origin (plant or animal) and the substitutions remain to be understood. This study aimed to investigate the effect of total dietary protein, animal-based protein, plant-based protein, and their substitutions with each other on the risk of BC using a pooled analysis of 10 cohort studies. Methods: The study was conducted within the “BLadder cancer Epidemiology and Nutritional Determinants” (BLEND) study, including 10 prospective cohort studies from several European countries, the United Kingdom, and the United States. Individual data from 10 prospective cohorts containing 434,412 participants (overall male/female ratio was almost 3:1) with a total of 4,224,643.8 person-years of follow-up was analyzed. Hazard ratios (HRs) and 95% confidence intervals (CIs) for BC risk for animal and plant-based protein substitutions of 30gram (g) per day (g/day) were estimated by multivariable adjusted HRs using Cox proportional hazards models. Results: During 11.4 years of follow-up, among 434,412 participants (73.28% female), 1,440 new cases of BC were identified. After multivariable adjustment, no association was observed between the intake of total, animal-based protein, and plant-based protein and BC risk. Replacement of every 30 g/day of animal-based protein intake by the same amount of plant-based protein intake or vice versa was not associated with the risk of BC. Conclusion: In conclusion, our study found no association between protein intake—whether from animal or plant sources—and the risk of BC. Substituting animal-based protein with plant-based protein, or the reverse, did not influence BC risk. Future studies are required to provide information on the link between animal- and plant-based proteins and BC risk.