INS and gestational diabetes: The meta-analysis showed a significant overall effect of supplementation on fasting insulin concentrations (SMD: − 0.53, 95% CI − 0.83, − 0.23 μIU/mL, p = 0.0006) (Fig. 4), but when the studies’ participants were grouped by presence or absence of GDM, supplementation was associated with significantly lowered insulin concentration only in pregnant women with GDM (SMD: − 0.62, 95% CI − 0.97, − 0.28 μIU/mL, p = 0.0003) (Fig. 4).