Protein consumption during pregnancy and risk of gestational diabetes mellitus: Insights from a multi‐center case–control study

AIMS: Gestational diabetes mellitus (GDM) poses major health risks for mothers and infants. Evidence on the association between dietary protein intake and GDM risk remains inconsistent. This study investigated dietary protein quantity and quality in relation to GDM. METHODS: A hospital-based case-control study was conducted in Isfahan, Iran, involving 200 cases and 263 controls. Dietary intake was assessed using three 24-h dietary records, and protein intake was categorized into plant- and animal-based sources. Multivariate logistic regression models were applied to evaluate associations. RESULTS: Higher plant protein intake was associated with a significantly lower risk of GDM (OR = 0.34; 95% CI: 0.20-0.59). Similarly, higher seafood (OR = 0.40; 95% CI: 0.24-0.68) and egg intake (OR = 0.59; 95% CI: 0.35-0.98) were inversely associated with GDM risk. In contrast, total protein, animal protein, poultry, dairy protein, aromatic amino acids, and branched-chain amino acids showed no significant or meaningful trend with GDM risk. CONCLUSIONS: Our study did not identify significant associations between total or animal protein intake during pregnancy and GDM risk. However, higher consumption of plant protein, seafood, and eggs was associated with lower odds of GDM in multivariable-adjusted models that accounted for BMI, total energy intake, socioeconomic status, and other relevant confounders. Given the observational case-control design, these findings cannot establish causality, and the possibility of residual confounding remains. Nevertheless, the results suggest that protein-intake quality may play a role in GDM risk, warranting confirmation in prospective cohorts and randomized trials.