Indications for the Gastric Bypass

The National Institutes of Health (NIH) have recommended the following criteria for Bariatric surgery, which includes gastric bypass procedures:

  • People who have a Body Mass Index (BMI) of 40 or higher. Or,
  • People with a BMI of 35 or higher with one or more related co-morbid conditions (there are 30 co-morbidities that are connected with morbid obesity and a full list can be found at the American Society of Bariatric Surgeons' website).

Generally, it is for people who are at least 100 pounds (45 kg) over their "ideal weight."

Techniques for the Gastric Bypass

The gastric bypass is the most commonly performed operation for weight loss in the United States. In the U.S, approximately 140,000 gastric bypass procedures were performed in 2005, an amount dwarfing the number of Lap-Band®, duodenal switch and vertical banded gastroplasty procedures done. Furthermore, since the gastric bypass has been performed for almost 50 years, surgeons have become very comfortable with the understanding of the risks and benefits of the procedure. By sheer volume of cases combined with the volume of scientific research, the gastric bypass has become the "gold standard" operation for weight loss in the U.S.

One of biggest advancements in the gastric bypass operation has been the technique used to enter into the abdomen, the laparoscopic approach. Although the laparoscopic approach has a number of potential advantages over the traditional open operation, the training and expertise necessary to perform the laparoscopic approach safely is considerable.

Advantages of the Laparoscopic Approach

  1. Generally 5 tiny incisions are necessary. Four are about a half inch long and one is 1 inch long. These incisions are too small for any significant infection to occur and the risk of developing a hernia is less than one percent. The risks of infection, wound problems and hernias are close to 30 percent with the traditional open procedure.
  2. The operation, in expert hands, can be performed quicker than an open operation. In fact, average operating room times are close to one hour. Less time in the operating room means less anesthesia and anesthesia-related complications.
  3. Less pain. Patients, although sore in the first few hours, need only Tylenol with Codeine the day after surgery. Many patients do not require any medications for pain by the time they go home.
  4. Quicker return to work. Patient can often return to work in one week. However, it is generally recommended to take two weeks off work to be on the safe side.
  5. Better operation. The operation is performed under magnification. Doctors are able to see details that are difficult in the open approach.
  6. As patients are walking the day of surgery and discomfort is easily controlled, patients are at lower risk to develop blood clots, pneumonia, bed sores or other complications resulting from prolonged immobility.

The gastric bypass (GBP) has been proven in numerous studies to have good long-term weight loss. The average weight loss often peaks at 18-24 months after surgery, but half of all the weight loss often occurs in the first six months. The gastric bypass, through multiple studies, has been shown to improve or cure diabetes, hypertension, arthritis, venous stasis disease, certain types of headaches, heartburn, sleep apnea and many other disorders. Most importantly, the gastric bypass has demonstrated significant improvements in quality of life.

Regardless of the entry technique (laparoscopic or open), most surgeons perform the operation in a very similar manner. The stomach is cut to form a small pouch (usually one ounce in size) and the remaining stomach and first 1-2 feet of small intestine are bypassed. In the standard gastric bypass, the amount of intestine bypassed is not enough to create malabsorption of proteins and other macronutrients. However, the bypassed portion of intestine is especially adept at absorbing calcium and iron thus, anemia and osteoporosis are the most common long-term complications of the gastric bypass and must be prevented with lifelong mineral supplementation. Other clinically significant deficiencies have been identified such as thiamine and Vitamin B12. Lifelong follow-up with a bariatric program is mandatory to monitor and prevent nutritional complications. Most surgeons recommend specific supplements to prevent these long-term complications.

Unlike the duodenal switch, the gastric bypass does not require removal of any part of the stomach. The unused stomach survives well with no demonstrable long-term problems. In fact, the unused stomach produces important enzymes. Intrinsic Factor, for instance, is crucial in the absorption of Vitamin B12 and is only made in the stomach.

Although the most commonly performed GBP (sometimes called the proximal bypass) involves little or no malabsorption, some surgeons modify the gastric bypass to incorporate a significant amount of malabsorption for the purpose of augmenting weight loss. This modification, called a distal gastric bypass, has significantly more nutritional complications than the proximal gastric bypass. Whether long-term weight loss is superior to the proximal GBP or whether the malabsorptive complications are worth the possible improvements in weight loss have not been well studied. Many surgeons reserve the distal GBP for very select circumstances.

How the Gastric Bypass Works

The mechanism in which the gastric bypass works is complex. After surgery, patients often experience significant changes in their behavior. Most state that they do not get hungry frequently and that their hunger is fleeting. Patients often state that they enjoy healthy foods and lose many of their food cravings. Rarely do people feel deprived of foods. These complex behavioral changes are partially due to poorly understood alterations in the hormones and neural signals produced in the GI track that communicates with the hunger centers in the brain. One interesting hormone that has recently been studied is ghrelin. Certainly the small size of the stomach pouch restricts the volume of food people eat as well. Thus, the decrease in hunger and the rapid feeling of fullness accounts for most of the weight loss after a gastric bypass.

Another mechanism of weight loss after the gastric bypass is called dumping syndrome. Dumping syndrome causes the intolerance to sweets after surgery. Dumping may result in lightheadedness, flushing, heart palpitations, diarrhea and other symptoms immediately after eating desserts. Some people are extremely sensitive to sweets for the rest of their lives; other patients lose some or all of their sweet sensitivity over time. The exact mechanism of dumping syndrome is not entirely understood.

Complications of the Gastric Bypass

The mortality risk with the GBP in expert centers appears to be about 0.5%. Because of the increasing popularity of the procedures, some surgeons have been tempted to perform the operation without adequate training or an environment supporting long-term follow-up. Some studies have demonstrated that the mortality rate from hospitals with a low experience with the procedure is far higher than the 0.5% reported by expert centers. The American Society of Bariatric Surgeons fully supports the initiative of the Surgical Review Committee to establish rigid criteria to certify that hospitals with quality programs will be designated as a "center of excellence." The most important questions to ask your surgeon: How many surgeries have you performed? Have you had any deaths?

The two most common causes of death after a gastric bypass are an anastomotic leak and a pulmonary embolism. An anastomotic leak can be rapidly deadly if not recognized and treated early. A "leak" occurs when intestinal fluids leak out freely into the abdomen. Symptoms of a leak may include, severe chest pain, shortness of breath, anxiety, heart palpitations and abdominal pain. Prompt treatment is critical. A pulmonary embolism is caused from a blood clot that forms in the leg that breaks off and gets lodged in the lungs. Prevention is the key to this complication. Blood thinners, leg compression devices and early walking are measures used to prevent blood clots.

Other complications include bowel obstruction, strictures, ulcers, bleeding and prolonged nausea. The open operation generally has a higher frequency of wound problems such as infections and wound hernias than the laparoscopic approach. Please see the written consent form for a more detailed written listing of complications. A frank discussion with your bariatric surgeon about the risks and benefits of surgery is critical to understanding the operation.

Post-Surgery Expectations for the Gastric Bypass

The length of hospital stay after the surgery varies, but usually lasts 2 to 7 nights. Gastric bypass is overwhelmingly successful, with many patients losing over 100 pounds within the first 18 months following surgery. Gastric bypass surgery should always be accompanied by an exercise regimen.

Undergoing a gastric bypass requires patients to commit to a new lifestyle. They will no longer be able to eat large portions of food at one sitting, nor will they be able to eat foods high in or fat, which often result in gastric dumping syndrome, an unpleasant feeling of faintness caused by the sudden absorption of these foods in the shortened digestive tract. Other symptoms of "dumping" include feeling and looking flushed and some patients may feel jittery. Due to the limited amount patients can take in at any one time, they must constantly drink small amounts of water or risk dehydration.

Weight loss after bariatric surgery is described as Percent Excess Weight Loss (%EWL). Excess weight is defined as a person’s actual weight minus their ideal body weight (IBW). IBW can be estimated by the formula:

  • Men: 106+6*(height in inches-60)
  • Women: 100+5*(height in inches-60)


  • So, for a 5′5″ woman, her IBW = 100+5*(65-60) = 125 pounds
  • If that woman weighs 325 pounds, her excess weight is 200 pounds.
  • If that woman loses 100 pounds, she has lost 50% of her Excess weight (%EWL=50%)

After a gastric bypass, the reported long-term weight loss varies from person to person. We can only estimate the amount of weight loss. Also, keep in mind that many weight loss operations, including the gastric bypass have significant weight loss in the short term. Long-term weight loss is much more important. On average, the %EWL after 6 months, 1year and 2 years will be 50, 70 and 80 percent. The average patient is female with a BMI of 48. There is significant variation, such that 95% of people will have lost between 95% and 60% of excess weight at 2 years.

So, a woman who weighs 325 pounds who is 5′5″ has a gastric bypass. She would be expected to lose 160 pounds at 2 years. However, she could lose as much as 190 pounds, or as little as 120 pounds. There is one predictive factor in guessing how much weight a person will lose. Patients who are very heavy and patients that are only slightly overweight, often lose weight at a predictably different rate. For instance, a patient who weighs 600 pounds, will never achieve a weight close to ideal with any bariatric operation. That person may lose 300 pounds, losing 60% of excess weight. Furthermore, a patient who weighs only 220 pounds would be expected, on average to lose a higher percentage of excess weight that a person weighing 320 pounds. That is, the skinnier you are, the more likely you can achieve a weight closer to your ideal.

It is normal and expected to gain some weight back after 2 years. The amount of weight regain is difficult to predict. One person may not regain any weight; another may regain 30 or more pounds. On average, patients regain 10-15% of their excess weight back in the long term.

Risks of Gastric Bypass Surgery

The operation has a mortality rate of approximately 2% overall: 1% suffer immediate complications and death; another 1% will commonly have post-operative complications that lead to death within one month of surgery. This can be mitigated by compliance with the surgeon's post-operative plan and using a doctor who has performed more than 200 procedures.

A full 25% of people undergoing this operation will have some form of post-operative complication (hernia, gall stones) either requiring a further procedure or change in habits. In some instances, the normal production of intrinsic factor in the stomach wall to aid in vitamin B12 absorption is decreased. This may call for either B12 injections or sub-lingual tablets for life to aid in the breakdown of food for energy.