Woman jogging through lush park in a bright yellow jacket
Woman jogging through lush park in a bright yellow jacket
Woman jogging through lush park in a bright yellow jacket

One Anastomosis Gastric Bypass (OAGB)

One-anastomosis gastric bypass, or OAGB, is a surgical procedure to help people lose weight. It is also known as a mini gastric bypass or omega loop bypass.

What You Need to Know

  • OAGB is a weight loss surgery that reduces the amount of food the stomach can hold and changes the intestine to absorb fewer calories.
  • Like other bariatric procedures, OAGB encourages weight loss by making you feel full faster.
  • OAGB is easier and faster to perform than traditional gastric bypass

What is OAGB?

One-anastomosis gastric bypass is a bariatric (weight loss) procedure that helps people with obesity eat less and absorb fewer calories so they can lose weight.

OAGB reduces both hunger and calorie absorption. A normal stomach can hold a liter or more of food. Bariatric surgery such as OAGB removes part of the stomach along its large, outer curve to create a small pouch. Removing this part of the stomach lessens the amount it can hold so you feel full faster.

Research suggests that decreasing the stomach volume may also reduce hormones that signal the brain that you’re hungry.

In OAGB, the surgeon creates the pouch with surrounding stomach tissue and connects it with a portion of the small intestine through a surgical opening called an anastomosis. The anastomosis allows food to enter the small intestine at a point further along, bypassing a portion of the small intestine. Digestive enzymes from the liver and pancreas function normally, breaking food down in the remaining small intestine.

Shortening the length of the digestive tract through bypassing some of the small intestine lessens the amount of food (and calories) absorbed by the body.

OAGB vs. Traditional Gastric Bypass

Both one-anastomosis gastric bypass and a traditional Roux-en-Y gastric bypass, address obesity by creating a smaller pouch out of the stomach and bypassing some of the small intestine. Both procedures help the patient feel full after eating less food than before.

Research comparing the two procedures shows that their results are comparable in terms of addressing obesity and its related health conditions such as diabetes.

There are some differences between OAGB and traditional bypass:

  • Traditional gastric bypass operations create two anastomoses (openings connecting stomach pouch to intestine, and intestine-to-intestine) whereas OAGB creates only one anastomosis (stomach pouch to intestine).
  • OAGB can be simpler and faster to perform than a traditional gastric bypass. It is a laparoscopic procedure, meaning surgeons use tubes inserted through multiple small incisions (cuts) in the skin.
  • The pouch created by the one-anastomosis approach is slightly larger than the one created by traditional bypass. The Roux-en-Y procedure creates a pouch about the size of an egg; the one created by OAGB is about the size of a banana. This does not affect the results; studies show the weight loss outcomes for both procedures are similar.

Preparing for OAGB

If you and your surgeon have decided that one-anastomosis gastric bypass is an appropriate procedure for you, you will receive instructions on how to get ready.

  • Learning and support. Your doctor may recommend an education program that informs you about the surgery and what to expect or help you connect with support groups of other patients undergoing bariatric procedures.
  • Preparation diet. For a couple weeks before the OAGB, you may be on a high-protein, low-calorie diet.
  • Avoiding some medications. As your procedure date nears, your doctor may advise you to stop taking NSAIDs such as aspirin or ibuprofen.
  • Washing the night before. You may be given special soap or towelettes to wash with the night before your surgery. Be sure to concentrate cleansing on your belly.

You may be in the hospital for at least 1 night, so pack your personal essentials (toothbrush, glasses, phone or tablet chargers, CPAP, etc.) along with comfort items such as headphones, sleep mask, small pillow and books.

On the morning or day of your procedure:

  • Bring your insurance information and your driver’s license or other identification
  • Dress comfortably
  • Do not use makeup, fingernail polish, perfume, lotions or deodorant.
  • Leave your credit cards, jewelry and other valuables at home.
  • Ensure you have someone to pick you up at the hospital when you are ready to return home.

How is OAGB performed?

OAGB takes place in a hospital and is performed laparoscopically while you are asleep under general anesthesia.

  • You will be given a gown to wear, and a nurse will place an IV tube to give you an antibiotic and the anesthesia.
  • Once you are asleep, the surgery team will place a tube in your throat to help you breathe. Your vital signs are watched carefully.
  • The surgeon makes a series of five or six small incisions in the belly.
  • The surgeon places small cylinders called trochars into each of the small incisions to create passageways for the surgical instruments to be inserted into the abdomen.
  • Using narrow instruments, the bariatric surgeon staples off and then detaches the upper part of the stomach from the bottom. The surgeons create a long, narrow pouch out of the upper portion of the stomach.
  • Then, bypassing between 150 and 200 centimeters of small intestine, the surgeon attaches the pouch to a loop farther down.
  • An anastomosis (opening) is created between the pouch and the loop of intestine so the swallowed food in the pouch can enter the intestine at that spot.
  • When the surgery is completed, you will be moved to the recovery room and monitored carefully.

OAGB Recovery

After your surgery, you will be on a liquid to puree diet for several weeks. Your bariatric surgery team will supply details about your diet and answer any questions.

Once you advance back to a healthy solid diet, you should be eating a lot of lean protein since it will help your recovery, and some programs will suggest 60 to 100 grams of protein a day to preserve muscle mass and strengthen your body.

Your doctor will recommend you drink a lot of water. Hydration is very important to help you avoid some bariatric procedures side effects, such as upset stomach, fatigue and kidney issues.

OAGB Complications

The procedure is generally safe. A common problem after the procedure is bile reflux, which can affect about a third of patients who have had OAGB.

Bile reflux happens when bile, a digestive enzyme juice secreted by the liver, backs up from the small intestine into the stomach pouch and esophagus (the food tube leading from your mouth to the stomach pouch.) Bile can irritate the inside of the pouch, causing gastritis or inflame the esophagus, even causing erosion (Barrett’s esophagus).

To lessen the chance of bile reflux occurring:

  • Stop smoking
  • Eat smaller, less fatty meals
  • Keep your head higher than your body for a few hours after eating
  • Avoid alcohol and other foods or beverages that set off reflux discomfort

Rare complications arising soon after surgery may include:

  • Anastomosis leaks: The surgically created opening between the stomach pouch and the small intestine may leak and require additional surgery to repair.
  • Bleeding
  • Blockage in the small intestine
  • Dumping syndrome

Later complications:

  • A narrowing of the anastomosis
  • Ulcers
  • Problems due to fewer nutrients being absorbed by the small intestine, such as iron deficiency anemia
  • Failure to lose weight due to stretching of the pouch caused by overeating

OAGB Results

Typical patients lose between 50% and 80% of their excess weight* over 18 months following one-anastomosis gastric bypass. Weight loss is faster in the first six months after surgery.

A study of patients who had OAGB showed that 86% reported an improved or greatly improved quality of life after 92 months.

*Excess weight is defined as the weight over the point at which a person’s body mass index or BMI is 25

Life After OAGB

Once you have recovered from the surgery and the procedure begins to affect your intake of food and calories, weight loss can begin. To optimize your results and support your improving health, your doctor may advise you regarding eating, taking supplements, exercising and avoiding pregnancy in the first 1.5 years after the procedure.

How to Eat After OAGB

  • Small meals, eaten slowly will be easier to tolerate with a smaller stomach volume and can help you avoid the discomfort of dumping syndrome.
  • Chew thoroughly.
  • Emphasize foods higher in protein and lower in fat and sugar.
  • Avoid alcohol and limit caffeine since both can dehydrate the body.
  • Make sure you are drinking at least 8 cups (64 ounces) of water daily but avoid drinking 30 minutes before or after a meal.

Supplements. Getting adequate vitamins and minerals is very important since after OAGB you will be absorbing fewer nutrients through your food. You may need to take supplements to ensure you get enough calcium, iron, vitamin D and other nutrients.


Exercise. As you lose weight, you may find you have more energy to exercise. Making time for regular aerobic, strength and flexibility exercise will help maintain your weight loss and further improve your health.

Medications. Weight loss may improve health conditions such as inflammation, diabetes, arthritis and other conditions associated with obesity. Your doctor will monitor your progress and some people may be able to reduce or even eliminate some medications.

Pregnancy. For people seeking to become pregnant, follow your doctor’s guidelines, which may be avoiding pregnancy for 18 months following surgery. One possible result of weight loss from OAGB is improved fertility.

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