Individual and Joint Associations Between Animal and Plant Protein Intakes with Impaired Fasting Glucose and Type 2 Diabetes in the Framingham Offspring Study

Given the considerable discrepancy in the literature regarding dietary protein and glucose homeostasis, we examined the prospective association between protein intake (total, animal, plant) and risk of type 2 diabetes mellitus or impaired fasting glucose (IFG). We also examined whether these associations differed by sex, body weight, or other risk factors. We included 1423 subjects, aged ≥ 30 years, in the Framingham Offspring Study cohort. Three-day dietary records at exams 3 and 5 were used to average protein intake and then adjusted for body weight residuals. Cox proportional hazard models were used to estimate hazard ratios (HR), adjusting for anthropometric, demographic, and lifestyle factors over ~16 years of follow-up. Subjects with the highest total protein intakes (≥100 g men; ≥85 g women) had a 31% lower risk of type 2 diabetes/IFG (95% CI: 0.54, 0.87). The highest (vs. lowest) category of intake of animal protein was associated with a 32% lower risk of diabetes/IFG (95% CI: 0.55, 0.83), whereas plant protein was not. Beneficial trends of total protein, especially animal, were stronger for women (HR: 0.61; 95% CI: 0.42, 0.87) than for men (HR: 0.82; 95% CI 0.58, 1.15). Subjects with lower BMI who consumed more protein had the lowest risks of diabetes/IFG. Overall, in this prospective study, higher intake of total dietary protein, including the consumption of animal protein, particularly among individuals with lower BMI and higher physical activity levels, was inversely associated with risk of incident type 2 diabetes and IFG.