Pregnancy is a physiological condition that increases insulin resistance (IR) due to hormonal changes, including elevated levels of estrogen, progesterone, and human placental lactogen (HPL). Such IR, especially in the later stages of pregnancy, can cause gestational diabetes mellitus (GDM), characterized by glucose intolerance first detected during pregnancy. GDM poses significant health risks for both the mother and the fetus, including the potential for pre-eclampsia, emergency C-sections, and type 2 diabetes (T2D) for the mother, as well as preterm birth, hypoglycemia, and being large for gestational age (LGA) for the baby. Proper dietary modifications can help regulate blood sugar levels, improve insulin sensitivity, and ensure healthy gestational weight gain (GWG), thereby reducing the possibility of undesirable outcomes. This paper discusses the role of energy, carbohydrate, fat, and protein, and compares the effects of the Mediterranean diet (MD) and Western diet (WD) on the risk of GDM. The main objective of this paper is to identify the most effective dietary strategies for preventing and managing GDM. The finding indicates that a MD rich in nutrient-dense foods, complex carbohydrates/lower GI, unsaturated fatty acids (FAs), and balanced protein has beneficial effects on GDM. In contrast, the WD with empty calories, simple carbohydrates/higher glycemic index (GI), saturated FAs (SFA), and animal-based protein increases the risk of GDM. Future studies should continue to explore the long-term effects of dietary interventions, integrate other lifestyle factors, and consider genetic differences to provide comprehensive management strategies for GDM.