There are three major procedures involved in obesity-related surgery. They are:

In Roux-en-Y' gastric Bypass procedure, a smaller, upper portion of the stomach will be formed by Laparoscopic surgical 'stapling' method.  The upper stomach pouch thus formed restricts the amount of food, which the person can consume.  Also, a portion of the small intestine is bypassed, which delays the mixing of food with digestive juices.  As a consequence, complete calorie absorption is prevented in the person.

In 'sleeve gastrectomy' surgical stapling is done along the longitudinal axis (lengthwise-vertically) due to which the stomach is converted in to a long thin tube and the excluded part of the 'no-longer-in use' stomach is removed through a small incision.

In 'Laparoscopic adjustable gastric banding', a band is placed around the upper most part of the stomach, which thus separates the stomach in to a functional smaller portion and a non-functional larger portion.  This band, which is placed through the laparoscopic incision, can be adjusted further either to increase or decrease the 'stomach capacity'.  "All these procedures are categorised under the "restrictive methods" of Bariatric surgery. 

There are other methods such as BPD (Bilio Pancreatic Diversion), Duodenal Switch (DS) which are categorised as the malabscorptive procedures. 

Some patients may need a combination of restrictive and malabsorptive procedures.

However, a candidate's fitness for 'malabsorptive procedure' will be assessed based on several blood tests, mainly to know whether the person has already got any protein deficiency or not, so that he/she should not suffer further deficiency of proteins, after the surgery, since the surgery aims at decreasing the absorption.

Depending on the type of the surgery, nearly 36% to 90% of a person's EBW (Excess Body Weight) can be lost. 
However, a patient will not wake up from the surgery with any weight loss!

Patients will lose weight gradually to the extent of 30 to 50% of their EBW in the first six months after the Bariatric surgery and by the end of twelve months a person would have lost nearly 77% of his EBW. 
Bariatric Surgery is safe in expert hands and in a survey of over ten thousand patients, the mortality rate for weight loss surgery was 0.3%. 

Along with the other pre-operative screening procedures, it is very much essential that a female candidate who wishes to undergo the weight loss surgery should avoid pregnancy for at least two years after undergoing the surgery.  Experts are of the opinion that a woman in her reproductive years should avoid the stress of pregnancy during the period of rapid weight loss, and postpone conceiving till her 'weight loss' reaches the stabilization phase.

A person wanting to undergo the weight loss surgery should discuss with his doctor the available surgical options. 

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