**2. Bariatric surgery methods**

### **2.1 Roux-en-Y gastric bypass (RYGB)**

The surgical treatment that is still considered a standard technique and widely used for the treatment of morbid obesity is RYGB [6, 7]. In RYGB, a small gastric pouch attaches to the small intestine and bypasses the stomach, duodenum, and proximal jejunum [8]. Recently, RYGB is the second most common operation worldwide, sleeve gastrectomy (SG) preceded that [9]. Although RYGB frequency is surpassed worldwide by sleeve gastrectomy (SG), long-term results in weight reduction, remission of comorbidities also changing quality of life, are well documented and make the RYGB a common bariatric procedure [6, 7, 10]. For these good results, identifiable factors are mostly a combination of mechanisms of action, which include mild malabsorption by bypassing a reasonable part of the jejunum, mechanical restriction of calorie intake due to the small gastric pouch, and hormonal changes like a decrease in the production of ghrelin, early secretion of PYY and changes in various incretin levels, such as GLP1 [11]. For patients with gastroesophageal reflux disease, many are seen as the gold standard treatment and it is recommended as the first method of choice for patients with type 2 diabetes mellitus [12]. Hepatic hypersensitivity to insulin has been shown to improve within a week after RYGB, and after months, after major weight loss, insulin sensitivity in adipose tissue and skeletal muscle also improves [13]. However, due to changes in intestinal anatomy after LRYGB, the internal hernia can occur through the Petersen space mesenteric defect or the mesenteric jejunojonostomy defect during follow-up [10]. After LRYGB, a frequent complication is small bowel obstruction [14]. Fasting bile acid levels increase after RYGB but do not increase after SG [15]. Long-term complications may occur. Re-interventions are sometimes needed. In very rare cases, a return to normal anatomy may be due to severe dumping syndrome, gastric bypass malnutrition, excessive

weight loss, postprandial hypoglycemia, or recurrent marginal ulcers [9]. Long-term complications, such as anemia, may not be diagnosed by non-bariatric specialists. Anemia causes include folate, iron, and B12 deficiency. Bleeding marginal ulcers, and selenium, copper, and vitamin A deficiency are the less common causes [16].
