Obesity is a complicated, multifactorial, and highly avoidable disease. There is a complicated relationship between type 2 diabetes mellitus (T2DM) and obesity. Surgical intervention is regarded as one of the greatest efficacious treatments for morbid obesity, where T2DM exhibits remarkable amelioration and remission. The objective of this work is to evaluate endogenous insulin by measuring postprandial C-peptide before and 6 months after LSG. We will also assess metabolic improvement, including remission of T2DM and prediabetes, 6 months after LSG. A total of 60 Egyptian patients, aged 18–60 years, with a body mass index (BMI) > 35, prediabetes, or type 2 diabetes, were recruited from bariatric outpatient clinics at Cairo University Hospitals. The study assessed the postprandial C-peptide, fasting blood sugar, HbA1C, and lipid profile before and 6 months following LSG. A significant improvement was observed in the metabolic profile in the form of reduction of BMI, HbA1c, lipid profile, and control of hypertension 6 months postoperatively. There was a significant reduction of postprandial C-peptide 6 months postoperatively. Fifty-five patients (91.7%) achieved complete remission of prediabetes and diabetes 6 months postoperatively, while 4 patients showed only improvement of diabetes and 1 patient in the prediabetic group did not achieve remission. In conclusion, LSG demonstrates encouraging outcomes in terms of metabolic profile enhancement, insulin resistance improvement as indicated by significant reduction in C-peptide level, remission of prediabetes and T2DM, and effective weight loss.