Sleeve gastrectomy (sometimes referred to as gastric sleeve or vertical sleeve gastrectomy) works in many ways to achieve sustained weight loss and resolution or improvement of the obesity related health conditions.
The small volume of the stomach tube (average around 150 mL) limits the amount of food that can be consumed at any given time. Unlike a gastric band where there is one area of fixed narrowing, in sleeve gastrectomy the whole stomach tube is narrow but pliable allowing patients to eat normal meals but in small portions and feeling full afterwards. The sleeve allows patients to control food portions and improve long term eating habits. It is particularly effective in patients who tend to eat large meals.
2. Effect on Ghrelin (hunger hormone)
Ghrelin is a hunger hormone that stimulates appetite through its effect on the brain, stimulates growth hormone release which in turn increase food intake and fat storage, and directly acts on the fatty tissue to stimulate fat storage. The level of Ghrelin goes up during dieting and starvation and is partly responsible for the food craving and hunger you have experienced while on the different weight loss diets. Ghrelin is primarily produced by the part of the stomach that is removed in the sleeve gastrectomy. Therefore, after sleeve gastrectomy the Ghrelin level goes down and you don't feel as hungry despite eating a very small amount of food.
3. Rapid Stomach Emptying
Following sleeve gastrectomy the stomach empties quicker into the intestine. This resembles the effect of a gastric by pass and results in the release of different gut hormones by the small intestine (ileum) including GLP-1 and PYY. These gut hormones induce satiety (feeling full) and appetite suppression and inhibit gut motility thus increase satisfaction after meals. This is known as "The Ileal Brake".
4. The Effect of Sleeve Gastrectomy on Insulin Resistance and Type II Diabetes
The anti-diabetes effect of sleeve gastrectomy is seen even before losing weight. There is evidence that Ghrelin promotes insulin resistance and block insulin release by the pancreas. The reduced Ghrelin levels after sleeve gastrectomy increase the capacity for insulin release in response to a meal. In addition, both GLP-1 and PYY that are increased after sleeve gastrectomy increase insulin secretion in response to a meal. This is called the "Incretin Effect". As weight loss progresses insulin resistance and diabetes improved further with the loss of fat cell mass.
5. Increased Bile Acids Levels
In addition to helping fat digestion in the intestine, bile acids are also hormones that binds to FXR receptors on cells all over the body and result in increased metabolic rate and decreased in fat storage. They also stimulate the release of the gut hormones GLP-1 and PYY mentioned above. The blood level of bile acids is increased after sleeve gastrectomy and there is new evidence that this may be a major method of action for the sleeve gastrectomy. It appears that gut micro-organisms play a role in weight loss after sleeve gastrectomy.