For this reason, it is performed in people who need very much weight loss, and in case of eating habits that would lead to failure of one of the usual methods of weight loss.
The operation is performed laparoscopically with 5 small incisions. First, we separate a small part of the upper stomach with a capacity of about 40-50ml, from the rest of the stomach. Then we separate the small intestine, join its peripheral part to the small part of the stomach, and connect the central part again with the intestine at a more distant point. The result is that the food that the patient consumes enters the small part of the stomach and fills it quickly with quite small amounts causing a feeling of fullness. The food then passes through a part of the small intestine about 1 meter long (trophic helix), in which it does not mix with gastric juices, pancreatic fluids and bile, so that it is not absorbed. At the same time, the fluids that aid in digestion pass through a part of the intestine about 1 meter long, in which they do not mix with food (cholelopancreatic helix). Patients start drinking fluids in the afternoon after surgery and are discharged after 2-3 days if they can eat well. Follow a special diet for 4-6 weeks, and dietary monitoring every three months.
The operation completely changes the anatomy and metabolism of the patient, as the small size of the remaining stomach can hold less food, while the mixing of food and digestive fluids and therefore the absorption of nutrients, occurs at the junction of the two parts of the intestine, after bypassed 2 meters of small intestine. The result is that the patient feels full with less food, which is absorbed less by the intestine, and provides fewer calories to the body. If the patient consumes sweet or fatty foods, they are not absorbed, and can cause diarrhea, forcing him to comply with dietary guidelines. Changes in intestinal hormones also seem to play an important role. After surgery, the levels of ghrelin, which is the appetite hormone in the stomach, and GLP-1, which improves glucose metabolism and is involved in the treatment of type 2 diabetes, are reduced.
Gastric Bypass leads to significant weight loss, of the order of 70-80% of Extra Body Weight, while many patients manage to return to a completely normal weight. The greatest weight loss occurs in the first 6-12 months. A complete change in metabolism, through reduced appetite and less food absorption, ensures the highest success rates regardless of dietary habits, with a very low probability of recurrence of obesity, with a possible weight gain of less than 5% in five years.
The operation is technically complex and requires very advanced laparoscopic skills on the part of the surgeon, as well as a very well organized and experienced team. A complete change in the anatomy of the gastrointestinal tract, no matter how frightening it may seem, is completely reversible if desired, or in the event of excessive weight loss. The disadvantage of Gastric Bypass is the possibility of a lack of vitamins and minerals. In most cases it is treated with a preventive daily intake of a multivitamin dietary supplement. Lifelong dietary monitoring is necessary to prevent nutrient deficiencies, to identify and treat them if they occur, but also to avoid gradual weight gain after surgery.

Most patients who undergo Gastric Bypass due to rapid and significant weight loss need a plastic surgeon to repair the extra skin that remains.