Restrictive Vs. Bypass weight loss surgery – the way Mother Nature put our guts together makes a lot of sense. The way we bariatric surgeons re-arrange guts also makes sense. There are two broad categories of weight loss surgery: “restrictive” (or “portion control”) and “malabsorptive,” (or “bypassed”).

All weight loss surgeries have some restrictive components to them. The purely restrictive bariatric procedures are Lap-band surgery (recently determined to not be restrictive) and the vertical banded gastroplasty. All weight loss surgeries allow you to feel full, or “satiated” with smaller quantities of food.

VBGLap-bandRNYDuodenal
Switch
BPD
Restrictive
only
Nerve StimulationRestrictive and malabsorptiveRestrictive and malabsorptiveRestrictive and malabsorptive

There is no pure “malabsorptive” weight loss surgery. The last one was the jejunal-ileal bypass, and that did not work well. Weight loss surgeries that have a malabsorptive component include the Roux en Y bypass, the duodenal switch, and the bilio-pancreatic diversion. These weight loss surgeries do not cause “malabsorption.” Instead, some of the small bowel is bypassed so that you become less efficient at absorbing food. The increased success of these weight loss surgeries is directly related to the malabsorptive component. In fact, the higher the BMI of the patient, the better they do with a longer bypassed limb.

How we restrict super-sized fast food meals

The stomach is one organ that regulates a lot of what we do in weight loss surgery. Weight loss surgeons make the stomach smaller so that it cannot hold as much food. Every operation does this differently. The most radical operations are the “micro pouches,” which are a version of the Roux en Y gastric bypass that make the upper pouch hold about one-half an ounce. The larger pouches are found with the bilio-pancreatic diversion that only holds 8 to 9 ounces. Again, this is rarely done in the United States, as most weight loss surgeons prefer the duodenal switch, which is the “upgraded” model.

VBGLap-bandRNYDuodenal
Switch
BPD
1 ounceIt’s been recently determined that the Lap-band does not restrict the amount of food you can eat. It eliminates your desire for food.1/2 to 1 ounce4-8 ounces8-9 ounces

The job of the stomach is to reduce the size of the food particles so they can be expelled into the small bowel and more easily digested. It does this by producing acid, which helps break things down, and an enzyme called pepsin. Once the food particles are 1-2 millimeters in size, they are expelled into the duodenum through the pylorus. If they cannot be broken down, they may remain in the stomach for a long time or be vomited. This is how bezoars are formed, from material that is too large to be expelled and cannot be broken down into smaller pieces.

When the stomach is distended, a signal is sent to your brain that you are full, and it needs to empty. This signal is a complex mechanism involving several hormones. Ghrelin is a hormone that is manufactured by cells in the stomach, and is released when it is empty. When Ghrelin levels are high, you feel hungry. After a meal, the levels become quite low. Obese patients have low levels of Ghrelin that are attributed to chronic eating. In patients who have undergone gastric bypass weight loss surgery, Ghrelin levels are also low—which means these patients feel satisfied and full.

The simple goal of weight loss surgery is to make you feel satisfied with less. The longer food is kept in the stomach, the longer you are satisfied. Certain foods do not remain for a long period of time, such as liquids, high carbohydrate breads and potatoes, and other soft mushy foods. Foods that remain longer produce a feeling of “satiety” (or not needing more food) include proteins, such as meat, fish, and poultry, as well as low glycemic carbohydrates, such as lentils, beans, most vegetables (except potatoes) and fats. The more fiber there is in a carbohydrate, the longer it appears to keep you satisfied (of course there are always exceptions).

How we keep food in the smaller stomach

VBGLap-bandRNYDuodenal
Switch
BPD
Small stoma, which cannot be enlarged as it is reinforcedSmall stoma, which can be adjustedSmall stoma, with a diameter of 1/2 inchThe pylorus, the normal mechanismSmall stoma, constructed to be about 1/2 inch
Vertical Banded Gastroplasty (VBG) weight loss surgeryLap-band weight loss surgeryRoux en Y Gastric Bypass (RNY) weight loss surgeryDuodenal Switch weight loss surgeryBilio-pancreatic diversion (BPD) weight loss surgery

The operations help to keep food in the stomach as long as possible. Normally this job is done by the pylorus, which regulates when food or liquid may leave the stomach. The duodenal switch operation is the only operation that allows this normal mechanism to take place. This is one of the advantages cited for those who perform this weight loss surgery. As with most procedures, the more you can maintain a normal anatomy, the better—hence, the duodenal switch allows for a more normal food intake, a more normal mechanism for satiety, and allows patients to have fibrous foods, all of which cannot be done with the other weight loss surgeries.

For the RNY and BPD the anastomosis, or opening between the stomach and small bowel is made small during the procedure. The inner diameter of this opening (or stoma) is about 1/2 inch. If it becomes larger than this, food passively enters the small bowel and no feeling of satiety is generated.

The analogy is an hourglass—if you make the opening between the top of the hourglass and bottom of the hourglass larger, then the hourglass empties quicker. The same thing happens with the anastomosis—the larger the opening, the faster the food empties, and the quicker you feel hungry again.

The advantage of lap-band surgery is that the weight loss surgeon can adjust the size of the stoma, allowing for maximum feeling of satiety. In people who need more nutrition, like women who become pregnant, we open the stoma to allow in more nutrition.

For all weight loss surgeries, the types of food that can overcome the sensation of fullness are the same: mushy foods, milkshakes, potatoes, breads, pastas. Essentially, no matter what the operation, no operation that will overcome high glycemic index carbohydrates.

“It’s the carbs, Barb”—said a ten-year post op weight loss surgery patient

Barbara Metcalf has been working with obese patients for many years. She was talking to a weight loss surgery patient who had a duodenal switch ten years ago, lost over 120 pounds, and maintained herself between 160 and 170 pounds. The only time she regained weight was when she was laid up after a leg fracture, but she lost that forty pounds quickly. She finds she can maintain her desired weight easily, as long as she monitors her carbohydrate intake. Even for the duodenal switch procedure, which maintains the most normal of the digestive process, carbohydrates can cause weight gain, and limiting them promotes weight loss.

In summary, the success of weight loss surgery depends upon making you feel full for a long period of time. Weight loss surgeons help ensure that success by reconstructing the pouch to be small, and by making the opening into the digestive system small. The weight loss surgery patient is responsible for the rest of the success by eating a diet that will remain in the pouch for a long period of time (these include proteins and low glycemic index carbohydrates).