Protein intake and the incidence of pre-diabetes and diabetes in 4 population-based studies: the PREVIEW project

Background:Data on the relationship between protein intake andthe risk of type 2 diabetes are conflicting.Objectives:We studied prospective associations between the intakeof total, plant-based, and animal protein and the risk of pre-diabetesand diabetes in 4 population-based studies included in the PREVIEWproject.Methods:Analyses were conducted with the use of data from 3 Eu-ropean cohorts and 1 Canadian cohort, including 78,851 participants.Protein intake was assessed through the use of harmonized datafrom food-frequency questionnaires or 3-d dietary records. Cohort-specific incidence ratios (IRs) were estimated for pre-diabetes anddiabetes, adjusting for general characteristics, lifestyle and dietaryfactors, disease history, and body mass index (BMI) and waistcircumference; results were pooled based on a random-effects meta-analysis.Results:Higher total protein intake (g·kg–1·d–1) was associatedwith lower incidences of pre-diabetes and diabetes (pooled IRs: 0.84;95% CI: 0.82, 0.87 and 0.49; 95% CI: 0.28, 0.83, respectively); plant-based protein intake was the main determinant (pooled IRs: 0.83;95% CI: 0.81, 0.86 and 0.53; 95% CI: 0.36, 0.76, respectively).Substituting 2 energy percentage (E%) protein at the expense ofcarbohydrates revealed increased risks of pre-diabetes and diabetes(pooled IRs: 1.04; 95% CI: 1.01, 1.07 and 1.09; 95% CI: 1.01, 1.18,respectively). Except for the associations between intakes of totalprotein and plant-based protein (g·kg–1·d–1) and diabetes, all otherassociations became nonsignificant after adjustment for BMI andwaist circumference.Conclusions:Higher protein intake (g·kg–1·d–1) was associatedwith a lower risk of pre-diabetes and diabetes. Associationswere substantially attenuated after adjustments for BMI and waistcircumference, which demonstrates a crucial role for adiposityand may account for previous conflicting findings. This study wasregistered at ISRCTN as ISRCTN31174892.