Purpose: 
Bariatric surgery is performed to help you in losing excess weight and reduce the risk of potentially life-threatening weight-related health problems, like:

• Heart disease
• Stroke (a condition in which the blood supply to the brain is stopped)
• High blood pressure
• Sleep apnea (a serious sleep disorder in which the breathing repeatedly stops and starts)
• Diabetes
• Non-alcoholic fatty liver disease (accumulation of fat in the liver in people who drink little or no alcohol) or non-alcoholic steatohepatitis (an advanced form of non-alcoholic fatty liver disease)

Indications:
Bariatric surgery is usually indicated in the following cases:

• Body mass index (BMI) (weight in kilograms divided by height in square meters) is 40 or more than 40, which indicates extreme obesity.
• Body mass index is between 35 and 39.9, which indicates obesity, along with certain health problems, like high blood pressure, diabetes, or severe sleep apnea.
• Body mass index between 30 and 34 along with serious weight-related health problems.
• It is essential to perform bariatric surgery on people who are willing to make permanent changes to their lifestyle, like eating a healthy and well-balanced diet, exercising regularly, and keeping your medical diseases under check.

1. Physical examination: The doctor examines the patient physically. The height and weight of the patient are measured to calculate the BMI of the patient. The medical history and family history of the patient are also noted.
2. Blood tests: A blood test helps in evaluating the different blood parameters and the levels of the various nutrients in the blood. Certain medical disorders, like diabetes or thyroid diseases, can also be diagnosed using blood tests.
3. Chest x-ray: This test helps the doctor in checking the condition of the internal organs within the chest area, that is, the heart and lungs. 
4. Electrocardiogram (ECG): This test helps in recording the electrical activity of the heart. It helps in detecting any heart-related problems.

The procedure is generally performed under general anesthesia, which means that the patient is put to sleep during the procedure.
The type of surgery performed depends on the severity of the condition and the overall health status of the patient.
The surgery can be performed in the following ways:

1. Laparoscopically: A laparoscope is a small tube with a camera on one end. It is inserted through small incisions or cuts in the abdomen or stomach area. The camera on the tip of the laparoscope allows the surgeon to view and operate inside the abdomen without making traditional large incisions. The recovery is quicker than the traditional method.

2. Traditional method: This surgery is performed by making large, open incisions in the stomach area.

The different types of bariatric surgeries and their procedure are as follows:

1. Roux-en-Y gastric bypass:

• This is the most common method of performing gastric bypass.
• The surgery is normally not reversible.
• The procedure works by decreasing the amount of food that can be eaten by a person at one sitting and reducing nutrient absorption.
• The surgeon cuts across the top of the stomach and seals it off from the rest of the stomach.
• The resulting pouch is small in size and can approximately hold only an ounce of food. In normal circumstances, the stomach can hold about 3 pints of food.
• The surgeon then cuts the small intestine and sews a portion of it directly onto the pouch.
• The food goes into the small pouch of the stomach and directly into the small intestine that is sewn to it.
• The food bypasses most of the stomach and the first section of the small intestine, and instead directly enters into the middle portion of the small intestine.

2. Sleeve gastrectomy:

• The procedure involves the removal of approximately 80% of the stomach, leaving behind a long, tube-like pouch.
• The smaller stomach cannot hold too much food.
• The smaller stomach produces less of the appetite-regulating hormone ghrelin, which lessens a person’s desire to eat.
• This procedure causes substantial loss of weight without rerouting of the intestines.
• The procedure requires a shorter hospital stay than other procedures.

3. Biliopancreatic diversion with duodenal switch:

• This procedure is a two-part surgery. 
• The first part involves performing a procedure similar to a sleeve gastrectomy.
• The second part involves connecting the end part of the intestine to the duodenum (the first portion of the small intestine that connects to the stomach) near the stomach area, thereby bypassing the major portion of the intestine.
• This type of surgery limits how much one can eat and reduces nutrient absorption.
• The surgery involves risks like vitamin deficiency and malnutrition.

The complications associated with bariatric surgery are:

• Bleeding
• Infection
• Blood clot formation
• Allergic reaction to anesthesia
• Lung problems
• Breathing problems
• Leakage in the gastrointestinal system
• Bowel obstruction
• Dumping syndrome (a condition in which the food moves very quickly from the stomach to the duodenum) causing diarrhea, flushing, nausea, vomiting, lightheadedness
• Gall stones (a hardened deposit of digestive fluid in the gall bladder, which is a small, pear-shaped organ situated under the liver)
• Hernia (bulging of a tissue or organ through an abdominal opening)
• Hypoglycemia (low blood sugar)
• Ulcers
• Malnutrition
• Vomiting 
• Acid reflux (a digestive disease in which the stomach acid flows into the food pipe to irritate its lining)
• Requirement of a second or revision surgery 
• Death

• The patient will be kept on a liquid diet after the surgery.
• Over the next few weeks following the surgery, the patient will gradually move to pureed food and then solid food.
• The meals will be much smaller due to the small stomach.
• It is important to make significant lifestyle changes following the surgery to lose the weight and keep it off.
• The patient will have to follow dietary guidelines, exercise regularly, and probably have to take vitamins or other supplements for the rest of their lives.
• Follow-up appointments are recommended to monitor the health of the patient after the surgery.
• Loss of weight due to bariatric surgery may help in improving or resolving conditions that are related to being overweight, and also improve the quality of life.
• In some cases, the patient may lose weight initially due to the surgery, but may eventually regain some of the weight if proper lifestyle guidelines are not followed.