Association between total, animal, and plant protein intake and type 2 diabetes risk in adults: A systematic review and dose-response meta-analysis of prospective cohort studies

Background and aims

While clinical studies indicate that dietary protein may benefit glucose homeostasis in type 2 diabetes (T2D), the impact of dietary protein, including whether the protein is of animal or plant origin, on the risk of T2D is uncertain. We conducted a systematic review and meta-analysis to evaluate the associations of total, animal, and plant protein intakes with the risk of T2D.

Methods

A systematic search was performed using multiple data sources, including PubMed/Medline, ISI Web of Science, Scopus, and Google Scholar, with the data cut-off in May 2023. Our selection criteria focused on prospective cohort studies that reported risk estimates for the association between protein intake and T2D risk. For data synthesis, we calculated summary relative risks and 95% confidence intervals for the highest versus lowest categories of protein intake using random-effects models. Furthermore, we conducted both linear and non-linear dose-response analyses to assess the dose-response associations between protein intake and T2D risk.

Results

Sixteen prospective cohort studies, involving 615,125 participants and 52,342 T2D cases, were identified, of which eleven studies reported data on intake of both animal and plant protein. Intakes of total (pooled effect size: 1.14, 95% CI: 1.04–1.24) and animal (pooled effect size: 1.18, 95% CI: 1.09–1.27) protein were associated with an increased risk of T2D. These effects were dose-related – each 20-g increase in total or animal protein intake increased the risk of T2D by ∼3% and ∼7%, respectively. In contrast, there was no association between intake of plant protein and T2D risk (pooled effect size: 0.98, 95% CI: 0.89–1.08), while replacing animal with plant protein intake (per each 20 g) was associated with a reduced risk of T2D (pooled effect size: 0.80, 95% CI: 0.76–0.84).

Conclusions

Our findings indicate that long-term consumption of animal, but not plant, protein is associated with a significant and dose-dependent increase in the risk of T2D, with the implication that replacement of animal with plant protein intake may lower the risk of T2D.