The primary means by which the Gastric Sleeve operation works is by removing the storage capacity of the stomach. Because of this the patient has a subjective feeling of fullness with a much smaller amount of food. This means that he/she can more easily control his/her hunger and stop eating sooner. The new capacity of the narrower stomach is hard to measure but likely is between 4 and 8 ounces.

Several studies on the amount of time it takes the new stomach to empty are somewhat in conflict, and therefore, the stomach transit time is of doubtful importance. A slower transit time would improve the feeing of fullness (satiety), but a faster transit time could help generate several intestinal hormones that have a negative affect on hunger, specifically PYY and PIP. These are generated in the duodenum – the first part of the small intestine – and their action is not yet well understood.

One intestinal hormone shown to be favorably affected by the Gastric Sleeve operation is Ghrelin. This is produced in the part of the stomach that is removed, and therefore, drops to a low level in the bloodstream after the operation. Ghrelin is important for how the brain perceives hunger, and low levels cause the patient to be less hungry – turning down the drive to take in too many calories.

Because of a combination of the above factors the Gastric Sleeve operation has demonstrated excellent weight loss for almost all patients. Its ability to produce very good weight loss – as good as or better than the LapBand – with no implantation of a foreign body - and the ability to avoid some of the complications related to the rearrangement of the intestinal tract, as seen with the gastric bypass, makes the Gastric Sleeve a very attractive option for weight loss surgery for the future.