Gastric bypass and other types of weight-loss surgery — also called bariatric or metabolic surgery — involve making changes to your digestive system to help you lose weight.

Bariatric surgery is done when diet and exercise haven't worked or when you have serious health problems because of your weight. Some weight-loss procedures limit how much you can eat. Others work by reducing the body's ability to absorb fat and calories. Some procedures do both.

While bariatric surgery can offer many benefits, all forms of weight-loss surgery are major procedures that can pose risks and side effects. Also, you must make permanent healthy changes to your diet and get regular exercise to help ensure the long-term success of bariatric surgery.

Bariatric surgery is done to help you lose extra weight and reduce your risk of possibly life-threatening weight-related health problems, including:

• Certain cancers, including breast, endometrial and prostate cancer.
• Heart disease and stroke.
• High blood pressure.
• High cholesterol levels.
• Nonalcoholic fatty liver disease (NAFLD) or nonalcoholic steatohepatitis (NASH).
• Sleep apnea.
• Type 2 diabetes.

Bariatric surgery is often done only after you've tried to lose weight by improving your diet and exercise habits.

Who it's for

In general, bariatric surgery could be an option for you if:

• Your body mass index (BMI) is 40 or higher, called extreme obesity.
• Your BMI is 35 to 39.9, called obesity, and you have a serious weight-related health problem, such as type 2 diabetes, high blood pressure or severe sleep apnea. In some cases, you may qualify for certain types of weight-loss surgery if your BMI is 30 to 34 and you have serious weight-related health problems.

Bariatric surgery isn't for everyone who is severely overweight. You may need to meet certain medical guidelines to qualify for weight-loss surgery. You likely will have an extensive screening process to see if you qualify. You also must be willing to make permanent changes to lead a healthier lifestyle.

You may be required to participate in long-term follow-up plans that include keeping track of your nutrition, your lifestyle and behavior, and your medical conditions.

And keep in mind that bariatric surgery is expensive. Check with your health insurance plan or your regional Medicare or Medicaid office to find out if your policy covers such surgery.

As with any major procedure, bariatric surgery poses potential health risks, both in the short term and the long term.

Bariatric surgery risks can include:

• Excessive bleeding.
• Infection.
• Reactions to anesthesia.
• Blood clots.
• Lung or breathing problems.
• Leaks in your gastrointestinal system.
• Rarely, death.

Longer term risks and complications of weight-loss surgery vary depending on the type of surgery. They can include:

• Bowel obstruction.
• Dumping syndrome, a condition that leads to diarrhea, flushing, lightheadedness, nausea or vomiting.
• Gallstones.
• Hernias.
• Low blood sugar, called hypoglycemia.
• Malnutrition.
• Ulcers.
• Vomiting.
• Acid reflux.
• The need for a second surgery or procedure, called a revision.
• Rarely, death.

If you qualify for bariatric surgery, your health care team gives you instructions on how to prepare for your specific type of surgery. You may need to have lab tests and exams before surgery. You may have limits on eating and drinking and which medicines you can take. You may be required to start a physical activity program and to stop any tobacco use.

You also may need to prepare by planning for your recovery after surgery. For instance, arrange for help at home if you think you'll need it.

Bariatric surgery is done in the hospital using general anesthesia. This means you're unconscious during the procedure.

The specifics of your surgery depend on your individual situation, the type of weight-loss surgery you have, and the hospital's or doctor's practices. Some weight-loss surgeries are done with traditional large incisions in your abdomen. This is known as open surgery.

Today, most types of bariatric surgery are performed laparoscopically. A laparoscope is a small, tube-shaped instrument with a camera attached. The laparoscope is inserted through small cuts in the belly. The tiny camera on the tip of the laparoscope allows the surgeon to see and operate inside the abdomen without making the traditional large cuts. Laparoscopic surgery can make recovery faster and shorter, but it's not the best option for everyone.

Surgery usually takes several hours. After surgery, you awaken in a recovery room, where medical staff watches you for any complications. Depending on your procedure, you may need to stay a few days in the hospital.

Types of bariatric surgery

Each type of bariatric surgery has pros and cons. Be sure to talk to your doctor about them. Here's a look at common types of bariatric surgery:

• Roux-en-Y (roo-en-wy) gastric bypass. This procedure is the most common method of gastric bypass. This surgery is typically not reversible. It works by decreasing the amount of food you can eat at one sitting and reducing absorption of fat and calories.

  The surgeon cuts across the top of the stomach, sealing it off from the rest of the stomach. The resulting pouch is about the size of a walnut and can hold only about an ounce of food. Typically, the stomach can hold about 3 pints of food.

  Then, the surgeon cuts the small intestine and sews part of it directly onto the pouch. Food goes into this small pouch of stomach and then directly into the small intestine sewn to it, bypassing most of the stomach and the first section of the small intestine. Instead, food goes directly into the middle part of the small intestine.

• Sleeve gastrectomy. With sleeve gastrectomy, about 80% of the stomach is removed, leaving a long, tube-like pouch. This smaller stomach can't hold as much food. It also produces less of the appetite-regulating hormone ghrelin, which may lessen the desire to eat.

  Advantages to this procedure include significant weight loss and no rerouting of the intestines. Sleeve gastrectomy also requires a shorter hospital stay than do most other procedures.

• Biliopancreatic diversion with duodenal switch (BPD/DS). This is a two-part surgery usually performed in one setting. The first step involves performing a sleeve gastrectomy.

  During the second step, the surgeon closes off the middle section of the intestine and attaches the last part directly to the first part of the small intestine, called the duodenum. This is the duodenal switch. The separated section of the intestine isn't removed from the body. Instead, it's reattached to the end of the intestine, allowing bile and pancreatic digestive juices to flow into this part of the intestine. This is the biliopancreatic diversion.

  This surgery both limits how much you can eat and reduces the absorption of nutrients. While it is extremely effective, it has greater risk, including malnutrition and vitamin deficiencies.

• Single-anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-S). Like BPD/DS, the SADI-S procedure also has two steps, with the first step being a sleeve gastrectomy.

  During the second step of the SADI-S procedure, a section of the small intestine known as the duodenum is closed off just below the new stomach sleeve. This opening below the new stomach is then connected to a part of the lower small intestine called the ileum. This is the duodeno-ileal bypass.

  The bypass routes food through only about 10 feet of the small intestine, instead of the usual 25. This means there is less time and distance for the body to absorb fat and calories.

Which type of weight-loss surgery is best for you depends on your specific situation. Your surgeon will take many factors into account, including body mass index, eating habits, other health issues, previous surgeries and the risks involved with each procedure.

After bariatric surgery

After weight-loss surgery, you generally won't be allowed to eat for 1 to 2 days so that your stomach and digestive system can heal. Then, you'll follow a specific diet for a few weeks. The diet begins with liquids only, then to pureed and very soft foods, and eventually, to regular foods. You may have many restrictions or limits on how much and what you can eat and drink.

You'll also have frequent medical checkups to monitor your health in the first several months after weight-loss surgery. You may need laboratory testing, bloodwork and various exams.

Gastric bypass and other bariatric surgeries can provide long-term weight loss. The amount of weight you lose depends on the type of surgery and your change in lifestyle habits. It may be possible to lose half, or even more, of your excess weight within two years.

In addition to weight loss, gastric bypass surgery may improve or resolve conditions often related to being overweight, including:

• Heart disease.
• High blood pressure.
• High cholesterol levels.
• Sleep apnea.
• Type 2 diabetes.
• Nonalcoholic fatty liver disease (NAFLD) or nonalcoholic steatohepatitis (NASH).
• Gastroesophageal reflux disease (GERD).
• Joint pain caused by osteoarthritis.
• Skin conditions, including psoriasis and acanthosis nigricans, a skin condition that causes a dark discoloration in body folds and creases.

Gastric bypass surgery also can improve your ability to perform routine daily activities, which could help improve your quality of life.

When weight-loss surgery doesn't work

Gastric bypass and other weight-loss surgeries don't always work as well as you might have hoped. If a weight-loss procedure doesn't work well or stops working, you may not lose weight and you may develop serious health problems.

Keep all of your scheduled follow-up appointments after weight-loss surgery. If you notice that you are not losing weight or have complications, see your doctor immediately. Your health care team can track your weight loss and investigate possible causes for your stalled weight loss.

It's also possible to not lose enough weight or to regain weight after any type of weight-loss surgery, even if the procedure itself works correctly. This weight gain can happen if you do not follow the recommended lifestyle changes, such as getting regular physical activity and eating healthy foods.