Gastric bypass

Alternative names
Bariatric surgery - gastric bypass; Roux-en-Y gastric bypass


Gastric bypass surgery is one type of procedure that can be used to cause significant weight loss if you are very obese. The surgery reduces your body’s intake of calories. Calorie reduction is accomplished in two ways:

  1. After the surgery, your stomach is smaller. You feel full faster and learn to reduce the amount that you eat at any given time.
  2. Part of your stomach and small intestines are literally bypassed (skipped over) so that fewer calories are absorbed. Unfortunately, sometimes nutrients are lost as well.

The surgery is only right for you if you meet certain strict criteria described later in this article.


Prior to any weight loss operation, your doctor will give you a complete medical examination and evaluate your overall health.

A psychological evaluation will be given to you. This will determine whether you are ready to adhere to a healthier lifestyle. If you are not ready to make lifestyle changes (and have not tried hard to do so already), you will not be considered eligible for the procedure. Without changing your lifestyle, the surgery will not be a success.

You will also receive extensive nutritional counseling before (and after) your surgery.

The surgery is performed under anesthesia. There are two basic steps:

  • STEP 1 - The first step in the surgical procedure makes your stomach smaller. The surgeon divides the stomach into a small upper section and a larger bottom section using staples that are similar to stitches. The top section of the stomach (called the pouch) will hold your food.  
  • STEP 2 - After the stomach has been divided, the surgeon connects a section of the small intestine to the pouch. When you eat, the food will now travel from the pouch through this new connection (“Roux limb”), bypassing the lower portion of the stomach. The surgeon will then reconnect the base of the Roux limb with the remaining portion of the small intestines from the bottom of the stomach, forming a y-shape.

This “y-connection” allows food to mix with pancreatic fluid and bile, aiding the absorption of important vitamins and minerals. You still may experience poor absorption of certain nutrients.

The risk of malabsorption is of greater concern in gastric surgeries that skip over a larger portion of the small intestines. These are performed much less commonly than the Roux-en-Y gastric bypass as described.


Gastric bypass can be performed using a laparoscope. This less-invasive technique allows the surgeon to make smaller incisions, which lowers the risk of large scars and hernias after the procedure.

First, small incisions are made in your abdomen. The surgeon passes slender surgical instruments through these narrow openings. The surgeon also passes a camera (laparoscope) through one of these small openings and watches through a lens and video monitor to do the surgery.


Weight loss surgery can be divided into three types:

  • Restrictive procedures reduce the size of your stomach.  
  • Malabsorptive procedures alter the flow from your stomach to your intestine, causing poor absorption of calories, vitamins, and minerals in the intestine.  
  • Combination procedures involve characteristics of both restrictive and malabsorptive procedures.

Gastric bypass surgeries are combination procedures that use both restriction and malabsorption to achieve weight loss.

Because it is a combination approach, it tends to be more successful for weight loss than purely restrictive surgeries. However, your body may not absorb vitamins and minerals properly.

Restrictive-only procedures are not as successful. It is easy to “cheat” and eat too much food, over-stretching the newly created stomach pouch.


Gastric bypass surgery may be an option if you are significantly obese and have tried unsuccessfully to lose weight on diet and exercise programs and are unlikely to lose weight successfully with non-surgical methods.

Gastric bypass surgery is not a “quick fix” for obesity. The surgery can take several hours and has risks and possible complications. For example, vomiting following the surgery is not uncommon because of eating more than the new, small stomach can accommodate.

Your commitment to diet and exercise must be very strong because even after the surgery, you must adhere to these lifestyle changes. Otherwise, complications from the surgery are likely to develop.

The procedure may be considered for obese individuals who have:

  • A Body Mass Index (BMI) of 40 or more. BMI is a calculation based on height and weight that is used to determine whether you are of normal weight or are overweight. Someone with a BMI of 40 or more is at least 100 pounds over their recommended weight. A normal BMI is between 18.5 and 25.  
  • A BMI of 35 or more along with a life-threatening illness that can be made better with weight loss, such as sleep apnea, type 2 diabetes, and heart disease.


Not everyone is a candidate for the laparoscopic (minimally invasive) approach. If you weigh more than 350 pounds or if you have had abdominal surgery in the past, you are probably NOT a good candidate for laparoscopy. Your surgeon will determine the best and safest approach for you.


The risks of gastric bypass surgery include:

  • Bleeding  
  • Infections  
  • Follow-up surgeries to correct complications, or to remove excess skin  
  • Gallstones due to significant weight loss in a short amount of time  
  • Gastritis (inflammation of the lining of the stomach)  
  • Vomiting from eating more than the stomach pouch can hold  
  • Iron or vitamin B12 deficiencies (if they occur) can lead to anemia  
  • Calcium deficiency (if it occurs) can contribute to the development of early osteoporosis or other bone disorders

Follow up surgeries may be less likely if gastric bypass is performed with a laparoscope.

Another common complication from gastric bypass is “dumping syndrome.” The symptoms often include:

  • Nausea and vomiting  
  • Diarrhea  
  • Bloated feeling  
  • Dizziness  
  • Sweating

You can lessen these symptoms by following your dietitian’s guidelines very carefully, especially during the first two months after surgery.

Expectations after surgery

The weight loss results of gastric bypass surgery are generally good. Most patients lose an average of 10 pounds per month and reach a stable weight between 18 and 24 months after surgery. Often, the greatest rate of weight loss occurs in the very beginning (that is, just following the surgery when you are still on a liquid diet).

After the surgery, you will need to follow up with your doctor fairly often during the first year. During those visits, your physician will be evaluating your physical and mental health status, including any change in weight and your nutritional needs. You will likely see a dietitian during those visits as well.

The surgery is not a solution in and of itself. While it can train you to eat smaller quantities and feel full more quickly, you still have to do much of the work. To achieve weight loss and avoid complications from the procedure, you must exercise and eat properly - according to important, healthy guidelines that your doctor and nutritionist will teach you.


You will usually need to stay in the hospital for 4 to 5 days after gastric bypass surgery. Your doctor will approve your discharge to home once you can do the following:

  • Move without too much discomfort  
  • Eat liquid and/or pureed food without vomiting  
  • No longer require pain medication given by injection

You will remain on liquid or pureed food for several weeks after the surgery. Even after that time, you will feel full very quickly, sometimes only being able to take a few bites of solid food. This is because the new stomach pouch initially only holds a tablespoonful of food. The pouch eventually expands. However, it will hold no more than about one cup of thoroughly chewed food (a normal stomach can hold up to one quart).

Upon follow up, your doctor will determine if you need replacement of iron, calcium, vitamin B12, or other nutrients. Supplements, such as a multivitamin with minerals, will be prescribed to provide any nutrients that you may not be getting from your diet. This lack of nutrients can occur because you are eating less and because the food moves through your digestive system more quickly.

Once your diet begins to consist of more solid food, remember to chew each bite very slowly and thoroughly.

You will be instructed on eating small meals frequently throughout the day, rather than large meals that your stomach cannot accommodate.

Your new stomach probably won’t be able to handle both solid food and fluids at the same time. So, you should separate fluid and food intake by at least 30 minutes and only sip what you are drinking.

You won’t be able to tolerate large amounts of fat, alcohol, or sugar. You should reduce your fat intake, especially fast food meals, deep-fried foods, and high-fat foods, as well as high-sugar foods like cakes, cookies, and candy.

Exercise and the support of others (for example, joining a support group with people who have undergone weight loss surgery) are extremely important to help you lose weight and maintain that loss following gastric bypass. You can generally resume exercise 6 weeks after the operation. Even sooner than that, you will be able to take short walks at a comfortable pace, with the approval and guidance of your doctor. Exercise improves your metabolism, while both exercise and attending a group support can boost your self-esteem and help you stay motivated.

Johns Hopkins patient information

Last revised: December 4, 2012
by Janet G. Derge, M.D.

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