The purpose of these interventions is to reduce the levels of ghrelin, the hormone responsible for hunger. By reducing hunger, the patient eats less. Eating less changes the daily ratio of calories consumed to calories burned, and weight loss is immediate.
The gastric balloon ( a lot are done over in Turkey) occupies space in the stomach. By occupying space, the stomach feels fuller, and the space for food is reduced. The benefit of the balloon is that it is entirely reversible, safe, and outpatient (no general anesthesia required).
The sleeve surgery ( available in Tunisia, Turkey, Poland and Czech Republic and Thailand)  involves removing a significant part (about 2/3) of the stomach to reduce its size. The stomach fills up faster with less food.

The principle is almost the same in the case of the by-pass ( also widely available in Turkey), but this intervention is only for extreme obesity, also known as morbid obesity.
The gastric band ( still offered on a customer request basis) is considered a obsolote surgery in many countries.  In that scenario, a silicone band is placed around the upper part of the stomach to prevent overconsumption of food and to eliminate the feeling of hunger. Like the balloon, the intervention is reversible but carries risks and is increasingly less recommended in favor of the Gastric Balloon, which is better suited and without serious risks.

The WHO now speaks of an obesity epidemic in the modern world. Effective and radical weight loss solutions in Bariatric medicine include the Gastric Balloon, the dissolvable balloon, sleeve gastrectomy, by-pass, and gastric band... Bariatric surgery is the preferred solution for combating overweight and obesity.

The objectives of these 3 types of surgical interventions are drastic, rapid weight loss, thus reducing excess weight. Overweight is often determined by measuring BMI, Body Mass Index. This index classifies weight gain as overweight, obesity, and morbid obesity. Overweight represents a real and concrete danger to the patient's health and almost systematically shortens life expectancy. Patients generally turn to bariatric interventions when weight loss through usual means such as diets has not yielded significant results.