What Is Gastric Bypass and How Does It Work?

Obesity is a serious health problem affecting the whole body. Many people do not reach their target weight with diet and exercise alone. Weight-loss surgery is another option for overcoming obesity. Gastric bypass is a type of weight-loss surgery.1,2

What is bariatric surgery?

Bariatric surgery is another term for weight-loss surgery. It involves changing the structure of the stomach and intestine.1

The 2 most common types of bariatric surgeries are:1,2

  • Gastric bypass (Roux-en-Y gastric bypass): The size of the stomach is reduced to a small pouch. It is then reattached to the small intestine.
  • Gastric sleeve (sleeve gastrectomy): This is the most common type of weight-loss surgery in the United States. In this method, about 80 percent of the stomach is removed.

What is gastric bypass?

Gastric bypass involves surgically changing the stomach and small intestine. This surgery is often done laparoscopically. This means it is done through several small cuts in your belly. In laparoscopic surgery, the doctor uses a tiny camera to see inside your belly and complete the surgery.2

During the procedure, the doctor makes a small pouch from the stomach. The pouch is about the size of a walnut. This pouch is then reattached to a new area of the small intestine.2

After the surgery, food will bypass the stomach and the first part of the small intestine. Gastric bypass restricts the amount of food you can eat. It also shortens the length of your intestines where food is absorbed.3-5

How does gastric bypass work?

Gastric bypass will permanently change the way you eat. Reducing the size of the stomach and altering the small intestine will limit the amount of food you can eat. Doing this will also limit the number of calories you absorb. This surgery also changes gut hormones to decrease appetite.4

Does gastric bypass work for weight loss?

Bariatric surgery is more effective than diet, exercise, and lifestyle changes at helping people lose weight. It is also better at keeping the weight off long term. Gastric bypass and gastric sleeve result in losing about 50 percent of excess body weight. Most weight loss occurs in the first 2 years after surgery.6,7

Who qualifies for gastric bypass?

Gastric bypass is considered for people with severe obesity who have not reached their target weight with other treatments.6

Not everyone with obesity may be a good candidate for gastric bypass. You must have in-depth physical and mental screening before surgery. Experts advise trying non-surgical treatments for obesity before considering bariatric surgery.6

Surgery may be an option if:2-6

  • Your body mass index (BMI) is 35 or higher (some centers require a BMI of 40)
  • Your BMI is 30 to 35, and you have serious weight-related health conditions (like heart disease or diabetes)
  • You are a man 100 pounds or more over your ideal body weight
  • You are a woman 80 pounds or more over your ideal body weight

If you are of Asian descent, you may qualify for surgery at a lower BMI than noted above. Check with your doctor to see if you are a candidate.6

Does insurance cover gastric bypass?

Insurance coverage for weight-loss surgery varies. Check with your health insurance provider to see if your plan covers it.3

Risks of gastric bypass

Gastric bypass is a major surgery with risks and possible complications.2,3,6

Surgical risks may include:2,3,6

  • Reaction to anesthesia
  • Bleeding
  • Infection
  • Blood clots
  • Heart and lung problems

Long-term risks of gastric bypass may include:2,3,6

  • Nausea and throwing up
  • Leaks, holes, or blockages in the stomach or intestines
  • Need for another surgery
  • Dumping syndrome – belly pain, diarrhea, and bloating after eating
  • Low blood sugar
  • Poor nutrition
  • Hair loss
  • Gallstones
  • Kidney stones
  • Hernias
  • Ulcers
  • Decreased bone strength
  • Alcohol intolerance

Benefits of gastric bypass

Gastric bypass has many benefits beyond weight loss.1,2,6,7

The below conditions may improve after weight-loss surgery:1,2,6

  • Type 2 diabetes
  • High blood pressure
  • High cholesterol
  • Fatty liver
  • Sleep apnea
  • Kidney disease
  • Heartburn
  • Asthma
  • Arthritis
  • Polycystic ovary syndrome (PCOS) and infertility
  • Sexual dysfunction

The risk of heart disease lessens after weight-loss surgery, especially if you have type 2 diabetes. Weight-loss surgery may also:6,7

  • Improve the quality of life
  • Reduce cancer risk
  • Lower the overall risk of dying
  • After gastric bypass

    Bariatric programs offer support to help you lose weight safely. Changes in diabetes, blood pressure, and cholesterol management are often needed after surgery.3

    After surgery, you will be limited to very small amounts of liquid and soft food. You will slowly be able to add solid foods back into your diet. Long-term vitamin supplements are needed to prevent low levels of:2,5

    • Vitamin B12
    • Vitamin D
    • Iron
    • Calcium
    • Folate

    The American College of Surgeons has a list of accredited bariatric programs.8

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