The aim of this study was to evaluate the relative contribution of serum adipokines and adipokines from the patient's omentum-derived adipocytes (PODAs) and visceral adipose tissue (VAT) of Japanese patients with severe obesity. Secondarily, we analyzed patients' metabolic changes after laparoscopic sleeve gastrectomy (LSG). Twenty-three LSG patients and 23 non-obese patients undergoing elective abdominal surgery were enrolled. The levels of adipokines in the serum and the PODAs were measured. The clinical and metabolic data were evaluated at 6 months after LSG. The mean serum leptin levels and the mean serum plasminogen activator inhibitor type-1 (PAI-1) levels were significantly greater (p < 0.001) and the mean adiponectin levels were significantly lower in the LSG group (p = 0.006). In the measurements of the PODAs, the mean leptin levels (p < 0.001) were significantly greater and the mean adiponectin levels (p < 0.001) were significantly lower in the LSG group. The mean BMI (-12 kg/m², p < 0.001) and mean VAT (-135.5 cm², p = 0.001) were significantly decreased after LSG. In nine patients with type 2 diabetes mellitus, the reduction in VAT correlated with the change in high-sensitivity C-reactive protein (p = 0.006) and the homeostasis model of assessment of insulin resistance (p = 0.001). After 6 months, LSG markedly improved most obesity-related comorbidities. Our results suggest that LSG may contribute to VAT reduction, improved adipocyte hormone levels, and changes in gut physiology and endocrinology.