The small intestine is a long tube that is approximately 18 feet long (6 meters). The small intestine is called small because the diameter or the width of the tube is much less than the large intestine. The parts of the small intestine include the duodenum, jejunum and the ileum. The duodenum is a segment of intestine between the stomach and the jejunum that is very active in digestion where many different enzymes mix from the stomach, liver, gallbladder and pancreas.

Classified as a restrictive procedure, laparoscopic sleeve gastrectomy involves modification of the gastric fundus, which expresses various hormones associated with hunger and satiety, insulin secretion and energy balance, and is known to induce rates of type 2 diabetes remission comparable to those observed following malabsorbtive procedures such as the Roux-en-Y gastric bypass (RYGB).

Laparoscopic sleeve gastrectomy is a restrictive procedure that reduces the size of the stomach but does not alter the gastrointestinal tract or the pylorus. Because the route of ingested food through the gastrointestinal tract is not altered, nutrients are better absorbed. The patient is less dependent on vitamin supplements as the food is absorbed in a more natural manner.

Roux-en-Y gastric bypass (RYGB) surgery is one of the most commonly performed bariatric procedures, offering significant long-term benefits in terms of weight reduction and remission of obesity-related conditions including type 2 diabetes. These changes are thought to be induced via a combination of mechanisms including reduction in stomach capacity and reduced absorption of fat, in addition to the restrictions placed on consumption of highly osmolar foods such as those high in simple sugars, which can trigger symptoms including nausea, vomiting and dizziness if ingested in excessive quantities. However, these factors alone do not fully account for the success of the procedure. Various hormonal changes have been observed following RYGB surgery, prior to significant weight loss, and it is thought that such endocrine effects could also contribute towards the mechanism of action in RYGB.