Factors leading to increased deficiency risk after a Sleeve Gastrectomy
The Sleeve Gastrectomy (SG) has become the most performed metabolic procedure worldwide1. The risk of developing deficiencies and therefore the need of long-term supplementation, was initially considered low. However, an increasing number of studies have reported that in SG patients, deficiencies are as common as in RYGB patients2-5. In the first year after surgery, 42% of SG patients develop one or more nutritional deficiencies6.
Although the gastro-intestinal tract remains relatively largely intact with an SG, there are still several reasons why patients are at risk of developing nutritional deficiencies:
Decreased food intake
Several factors lower the food intake post-SG. The procedure significantly reduces the volume of the stomach, making it impossible to eat large amounts of food. Additionally, the part of the stomach that produces ghrelin, the hormone that stimulates appetite, is removed. This decrease in food intake leads to weight loss, but also contributes to the risk of developing nutritional deficiencies. Since the sensation of appetite comes back after the first postoperative year, behavioral change within that first year is crucial.
Decreased food tolerance
This is mostly the case for red meat, dairy products, rice, pasta and bread7-9. Lowered intake of animal food sources leads to an insufficient intake of B-vitamins, including vitamin B12, which is not naturally found in foods of plant origin. Moreover, meat is a major source of protein and iron. The type of iron found in red meat (haem iron) is more easily absorbed and used by the body than the iron in plant food sources. In general, after SG, food tolerance improves with time7-9.
Faster passage of food along the digestive tract
Removal of the lower part of the stomach might result in faster gastric emptying, however studies on this topic are inconclusive10. 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 section of the small intestine where most of the (passive) absorption takes place, leaving less time for absorption.
Decreased production of gastric acid
The production of gastric acid is stimulated by gastrin. Since this hormone is produced in the section of the stomach that is removed, the SG leads to a decrease of the production of gastrin and gastric acid in the stomach. Gastric acid is required for the conversion of the ingested non-haem iron (Fe3+, in plant based products) to haem iron (Fe2+, in animal products). Only haem iron can be absorbed by the body. When gastric acid production is impaired, iron absorption is reduced substantially11.
Decreased production of Intrinsic Factor
The section of the stomach that produces gastric acid and intrinsic factor, both required for vitamin B12 absorption, is resected in SG12. Gastric acid is needed to release vitamin B12 from protein. As vitamin B12 passes from the stomach to the small intestine, it binds with intrinsic factor. Bound together, the intrinsic factor-vitamin B12 complex travels to the end of the small intestine (ileum), where receptors recognize the complex. Vitamin B12 is gradually and actively absorbed into the bloodstream. Without intrinsic factor, vitamin B12 can only be diffused passively througout the entire small intestine, accounting for only 1% of absorption13.
Vomiting
Vomiting is one of the possible complications after SG and affects approximately 8% of the patients, according to a study by Major et al14. Vomiting might be a consequence of ‘dumping syndrome’. Dumping syndrome is commonly seen after RYGB, when a large amount of foods suddenly enters the intestines. Dumping syndrome can also occur after SG, possibly due to the rapid gastric emptying15. Vomiting is especially a risk factor for vitamin B1 deficiency, because vitamin B1 needed for the production of gastric acid16.
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References
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