How Surgery Reduces Weight
Surgeons first began to recognize the potential for surgical weight loss while performing operations that required the removal of large segments of a patient's stomach and intestine. After the surgery, doctors noticed that in many cases patients were unable to maintain their pre-surgical weight. With further study, surgeons were able to recommend similar modifications that could be safely used to produce weight loss in morbidly obese patients. Over the last decade these procedures have been continually refined in order to improve results and minimize risks. Today's bariatric surgeons have access to a substantial body of clinical data to help them determine which surgeries should be used and why.

Today, the American Society for Bariatric Surgery describes two basic approaches that weight loss surgery takes to achieve change:

  1. Restrictive procedures that decrease food intake. (LapBand)
  2. Malabsorptive procedures that alter digestion, thus causing the food to be poorly digested and incompletely absorbed so that it is eliminated in the stool.(Roux en Y Gastric Bypass is actually a combination of restrictive and malabsorptive).

Restrictive Procedures
Malabsorptive Procedures that Alter Digestion

Restrictive Procedures 
The theory is simple. When you feel full, you are more likely to have reduced feelings of hunger and will no longer feel deprived. The result is that you are likely to eat less. Restrictive weight loss surgery works by reducing the amount of food consumed at one time. It does not, however, interfere with the normal absorption (digestion) of food. In a restrictive procedure, the surgeon creates a smaller upper stomach pouch. The pouch, with a capacity of approximately 1/2 to 1 oz. (15 to 30 ml), connects to the rest of the stomach through an outlet known as a "stoma." In a cooperative and compliant patient, the reduced stomach capacity, along with behavioral changes, can result in consistently lower caloric intake and consistent weight loss.

During recovery, patients must adhere to the strict specific dietary guidelines and restrictions their surgeon prescribes. While these guidelines may vary from one surgeon to the next, it is important for each patient to follow the surgeon's guidelines. When the time comes to resume eating "regular" food, the patient must learn to adapt to a new way of eating. At each meal, they are restricted to consuming approximately 1/2 to a full cup of food before feeling uncomfortably full. Patients who see the best results from a restrictive procedure are those who learn to eat slowly, eat less, and avoid drinking too many fluids, particularly carbonated beverages. If the patient fails to follow these guidelines, they can stretch the stomach pouch and/or the stoma outlet and defeat the purpose of the surgery. The effectiveness of a restrictive procedure is reduced by constant snacking or by drinking high-calorie, high-fat liquids. Failure to achieve the expected level of weight loss is usually the result of a patient failing to comply with the recommended dietary and behavior modifications, such as increased exercise and regular support group attendance.

Malabsorptive Procedures that Alter Digestion 
It can be said that some of the restrictive approaches discussed above have not always achieved the excess weight loss surgeons and patients anticipated. For this reason, procedures that alter digestion, known as malabsorptive procedures, were developed to work in conjunction with restrictive approaches. Some of these techniques involve a bypass of the small intestine, thus limiting the absorption of calories. On balance, malabsorptive or malabsorptive/restrictive procedures have resulted in an overall increase in the loss of excess weight. The risk of complications and side effects generally increases with the lengthening of the small intestine bypass. You and your surgeon must determine the risks and benefits over your lifetime with the type of weight loss surgery you choose.

Basically, weight loss operations fall into three categories: