Gastric bypass is surgery that helps you lose weight by changing how your stomach and small intestine handle the food you eat. In a Gastric Bypass (also called "Roux-en-Y" gastric bypass), a surgeon creates a small pouch at the top of the stomach. This pouch becomes the new stomach. Surgeons then connect the pouch to the middle part of the small intestine, bypassing the upper part of the small intestine.

After the surgery, the stomach pouch holds a lot less food than a normal-sized stomach. A person will eat less, feel full sooner and be less hungry.  Fewer calories and nutrients are absorbed because the small intestine is shorter.

People who get gastric bypass tend to lose more weight than people who get the gastric sleeve. The gastric bypass procedure is not reversible.

There are 2 steps during gastric bypass surgery:

• The first step makes your stomach smaller. Your surgeon uses staples to divide your stomach into a small upper section and a larger bottom section. The top section of your stomach (called the pouch) is where the food you eat will go. The pouch is about the size of a walnut. It holds only about 1 ounce (oz) or 28 grams (g) of food. Because of this you will eat less and lose weight.
• The second step is the bypass. Your surgeon connects a small part of your small intestine (the jejunum) to a small hole in your pouch. The food you eat will now travel from the pouch into this new opening and into your small intestine. As a result, your body will absorb fewer calories.

Gastric bypass can be done in two ways. With open surgery, your surgeon makes a large surgical cut to open your belly. The bypass is done by working on your stomach, small intestine, and other organs.

Another way to do this surgery is to use a tiny camera, called a laparoscope. This camera is placed in your belly. The surgery is called laparoscopy. The scope allows the surgeon to see inside your belly.