The Mediterranean diet (MedDiet) has emerged as a promising dietary strategy for the prevention and management of type 2 diabetes mellitus (T2DM). This narrative review provides a comprehensive synthesis linking the biological pathways of the MedDiet with established clinical evidence. Adherence to this traditional dietary pattern—characterized by a high intake of fiber, complex carbohydrates, antioxidants, and healthy fats—has demonstrated significant benefits in terms of glycemic control, enhanced insulin sensitivity, and overall metabolic health. Mechanistically, the review explains how the MedDiet improves health by modulating key physiological processes, including anti-inflammatory and antioxidant pathways, the regulation of branched-chain amino acid metabolism, the enhancement of short-chain fatty acid production via gut microbiota modulation, and upregulated incretin effects. Importantly, this review explains how the MedDiet complements modern medications, including glucagon-like peptide-1 (GLP-1) receptor agonists and sodium–glucose cotransporter-2 (SGLT-2) inhibitors. By integrating molecular mechanisms with human clinical outcomes, this narrative review addresses multiple aspects of the MedDiet in both the prevention and management of T2DM including glycemic control, weight management, and cardiovascular risk reduction, rendering it a valuable dietary strategy for both the prevention and treatment of this chronic condition.

B-group vitamins (B1, B2, B3, B5, B6, B7, B9, B12) are water-soluble micronutrients essential for energy metabolism, one-carbon metabolism, neurotransmitter synthesis, and redox homeostasis. This chapter provides a comprehensive clinical review of B-vitamin status across internal medicinegynaecology, and neurology. In obesity and diabetes, B-vitamin insufficiency frequently coexists with metabolic dysfunction, contributing to insulin resistance, endothelial dysfunction, and cardiovascular risk, with metformin, GLP-based therapies, and bariatric surgery further depleting B12 and folate. In female reproductive medicine, folate-mediated one-carbon metabolism modulates ovulation, implantation, and pregnancy outcomes, with additional specificities in polycystic ovary syndrome and sickle cell disease. Neurologically, B-vitamin deficiency remains an important reversible cause of encephalopathy, myelopathy, peripheral neuropathy, and cognitive decline, while vitamin B6 excess causes dose-dependent sensory neuropathy. In elderly patients, age-related physiological and socioeconomic changes increase deficiency risk, particularly for B12. The chapter emphasizes shared mechanisms of B-vitamin metabolism and deficiencies, including homocysteine regulation, outlines practical monitoring strategies using functional biomarkers, addresses drug-nutrient interactions, and provides evidence-based supplementation guidelines. A unified, precision-medicine approach integrating early recognition, appropriate laboratory evaluation, and targeted supplementation/therapy optimizes outcomes across disciplines.