Scientific Study

Dietary proteins are important modulators of glucose metabolism. However, few longitudinal studies have evaluated the associations between intake of protein and protein type and risk of type 2 diabetes (T2D). We investigated the associations between total, animal, and vegetable protein and incident T2D in 72,992 women from the Nurses' Health Study (1984-2008), 92,088 women from Nurses' Health Study II (1991-2009) and 40,722 men from the Health Professionals Follow-up Study (1986-2008). During 4,146,216 person-years of follow-up, we documented 15,580 cases of T2D. In pooled multivariate models including body mass index, participants in the highest quintiles of percentage of energy derived from total protein and animal protein had 7% (95% confidence interval (CI): 1, 17) and 13% (95% CI: 6, 21) increased risks of T2D compared with those in the lowest quintiles, respectively. Percentage of energy intake from vegetable protein was associated with a moderately decreased risk of T2D (comparing extreme quintiles, hazard ratio =0.91, 95% CI: 0.84, 0.98). Substituting 5% of energy intake from vegetable protein for animal protein was associated with a 23% (95% CI: 16, 30) reduced risk of T2D. In conclusion, higher intake of animal protein was associated with an increased risk of T2D, while higher intake of vegetable protein was associated with a modestly reduced risk.