Gastric bypass surgery promotes weight loss by dramatically decreasing the size of the stomach and allowing only small amounts of food to be eaten at one time. This procedure comprises two steps: partitioning of the stomach and reconstruction of the gastrointestinal tract.

First a small, thumb-sized pouch is created from the upper stomach using surgical staples. This process leaves the larger part of the stomach non-functional.

Second, the small intestine is divided into two parts. One end is then attached to the stomach pouch. The other end, which is still connected to the part of the stomach that is no longer functional, is reattached to the intestinal tract to enable drainage of the gastric juices.

With this procedure, food bypasses most of the stomach and part of the small intestine, thus reducing food intake and disrupting calorie absorption.

The procedure involves removing two-thirds of the stomach along its length so instead of looking like a pouch, it looks like a long tube or shirt-sleeve. The smaller stomach tube remains attached to the intestines, thus ensuring a normal digestion process and proper nutrient absorption.

Gastric sleeve surgery can be performed as a stand-alone procedure or as the first stage in a gastric bypass procedure and generally has fewer potential complications than gastric bypass surgery.

The procedure consists of two steps: reduction of the stomach and looping of the small intestine to connect to the smaller stomach.

First, the left part of the stomach is detached along the entire length of the stomach, leaving a long narrow tube. Then a loop of the small intestine is brought up and attached to the stomach tube. This process bypasses the upper part of the intestine while still enabling drainage of gastric juices from the detached part of the stomach.

Gastric banding surgery uses an inflatable band to reduce the size of the stomach. The aim is to slow and limit the amount of food that can be consumed at one time and thus promote gradual weight loss.

The procedure entails placing an inflatable band around the upper part of the stomach to make the stomach pouch smaller. This procedure does not affect gastric emptying time, but it does limit food intake, reduce appetite and slow digestion.

The band works by reducing the size of the top of the stomach, so it can only hold just over 100 milliliter of food at a time. It fills up quickly, slowing the passage of food through the digestive tract. Fullness is registered by the upper part of the stomach. Consequently, reducing that part of the stomach, means the person will feel hungry less often and full more quickly and for longer.

As the patient loses weight, the band will need adjustment to continue to be effective. This is done by adding a saline solution through a small access port placed just under the skin.

This is the least invasive weight loss surgery and is completely reversible. However, it may not be appropriate for patients who are extremely obese, have complicating medical issues or have previously had abdominal surgery.

Duodenal switch surgery combines food intake restriction with reduced calorie absorption, resulting in higher weight loss. It also has a 98% “cure” rate for type 2 diabetes.

The procedure is quite complex and involves reducing the size of the stomach, removing the gallbladder and rerouting the intestines – 4 steps in all:

1. Around 70% of the left side of the stomach is removed creating a cylindrical-shaped pouch that connects the esophagus to the small intestine.

2. The top of the small intestine is then cut, leaving part of the duodenum (where most of the body’s chemical digestion takes place) attached to the stomach and removing the gallbladder.

3. Next, the lower part of the small intestine is cut approximately 1 meter from where it connects to the large intestine. The duodenum is then attached to the part that is still connected to the large intestine.

4. Finally, the end of the loose part of the small intestine is attached to the part of the small intestine that connects the duodenum to the large intestine. This lets the gastric juices mix with the food from the stomach in the last section of the small intestine.

This procedure may be performed as open surgery or laparoscopically. After surgery, patients will, need to take vitamin supplements for the rest of their lives.