FAQ - Surgery - Changes after bariatric surgery

Smaller stomach

The volume of the sleeve stomach is only about 15% of the original stomach and the RYGB-pouch has the size of an egg, the pouch of the OAGB is a bit larger. It is therefore not possible to eat large amounts of food. This of course contributes greatly to weight loss, because people are not able to eat large amounts of unhealthy food. However, people are also not able to eat sufficient amounts of nutritious food, increasing the risk of deficiencies.

Little/no gastric acid

The hormone gastrin stimulates the production of gastric acid. The section of the stomach where gastrin is produced, is largely resected. In the sleeve stomach only little gastric acid is produced and in the RYGB not at all. An acidic enviroment is needed for an effective absorption of iron, only then can non-haem iron (Fe3+, in plant products) be reduced to haem iron (Fe2+, in animal products). Only haem iron can be absorbed effectively by the body. Furthermore, gastric acid is needed to detangle proteins in order for enzymes to cut them in smaller parts, so they can be absorbed. Also gastric acid is necessary to release vitamin B12 from the proteins to which it is attached in foods.  

No instrinsic factor

Intrinsic factor is no longer being produced in the sleeve stomach. Production is still taking place in the RYGB-pouch, however intrinsic factor is no longer released from the stomach, probably because food never passes this part of the stomach. Intrinsic factor is necessary for the active absorption of vitamin B12. As vitamin B12 is detached from the proteins, it passes from the stomach to the small intestine and it binds with intrinsic factor. Bound together, intrinsic factor and vitamin B12 travel to the end of the small intestine (ileum), where receptors recognize the complex. Without intrinsic factor vitamin B12 can only be absorbed passively along the lenght of the small intestine. Only 1% of the vitamin B12 intake will be absorbed passively. 

Little Ghrelin

The production of ghrelin is decreased and therefore people will experience less hunger, leading to less food intake. Ghrelin is also in a lesser degree produced in the first part of the small intestine (duodenum) and, in case of SG, aproximately a year after the surgery, the production of ghrelin at this site will increase, taking production over from the stomach. People with SG have about one year to change their lifestyle and eating behavior, before they will experience hunger again. This is one of the factors associated with weight regain after surgery. 

Faster passage of food along the digestive tract

After RYGB, there is no longer a pylorus that keeps the food inside the stomach and to release it in small portions into the small intestine. In case of SG, removal of the lower part of the stomach might result in faster gastric emptying, giving the small amount of gastric acid even less time to enact on the food. However studies on this topic are inconclusive. Studies on bowel motility after SG are scarce, however it seems that, compared to an intact gastro-intestinal tract, the food moves faster through the duodenum, the section of the small intestine where most of the (passive) absorption takes place, leaving less time for absorption. The entering of large amounts of (sugar rich) food in the small intestine, may cause dumping syndrome (also called ‘rapid gastric emptying’).  

Decreased food tolerance

Patients experience most often intolerance to red meat, dairy products, rice, pasta and bread. By having trouble eating animal products, people are at risk for an insufficient intake of B-vitamines, including vitamin B12, which is not found naturally in foods of plant origin. Meat is also a major source of protein and iron. The type of iron found in read meat (haem iron) is more easily absorbed and used by the body than the iron in plant foods. In general, food intolerance improves with time. 

Vomiting

Vomiting is one of the possible complications after surgery and affects mostly the SG patients and in a lesser degree RYGB patients. Vomiting might be a consequence of ‘dumping syndrome’. Dumping syndrome is commonly seen after RYGB. Dumping syndrome can also occur after SG, possibly due to the rapid gastric emptying. Vomiting is especially a risk factor for vitamin B1 deficiency, because vitamin B1 needed for the production of gastric acid.