Obesity is a public health problem that negatively affects hormonal balance and predisposes to the occurrence of serious comorbidities leading to morbidity and mortality. When the body consumes more calories than it expends, excess calories accumulate in adipose tissue, leading to the emergence of obesity. Thyroid stimulating hormone (TSH) plays an important role in the regulation of energy balance with its effect on basal metabolism and thermogenesis. During LSG, the duodenum remains functionally active in terms of absorption because the gastrointestinal tract is intact, but a low-fatty diet, restricted food intake, and alteration of the estrogen hormone level following LSG may decrease the absorption of calcium and 25-OH-vitamin D3 (vitD) in the gut of patients. VitD plays an important role in calcium-phosphorus balance, and its deficiency may lead to decreased calcium absorption, osteomalacia, osteoporosis, and secondary hyperparathyroidism (SHPT). Patients with preexisting hypothyroidism may require adjustments to levothyroxine dosages due to the substantial weight loss and metabolic changes following LSG. Early detection of levothyroxine dose modifications can improve patient health and optimal clinical response. Preoperative assessment, patient education, and individualized supplementation plans are key to optimizing outcomes, maintaining sufficient vitD levels, and preserving calcium-phosphorus homeostasis.