The mechanism of action of bariatric surgery is largely based on the involvement of hormones produced in the gastrointestinal tract. Conservative measures for weight reduction often fail, which is often due to compensatory changes in these hormones, for example when the body is supplied with less energy through a diet. After bariatric interventions, however, there is a reduction in the formation of ghrelin, a hormone that triggers feelings of hunger, and an increased production of hormones that cause a feeling of satiety.
Ghrelin makes you fat and happy
Ghrelin is an appetite-stimulating hormone produced in the gastric mucosa and pancreas. It influences the regions of the brain that trigger appetite and, together with leptin and cortisol, controls the feeling of hunger and satiety. In phases of hunger, the ghrelin level in the blood rises, after eating it drops. Ghrelin also slows down the metabolism of fat. The fact that weight can climb as a result of this is clearly proven. Researchers have also observed that the ghrelin level in overweight people does not drop after they have eaten something as it does in others. However, ghrelin can also have extremely positive effects. It also reduces anxiety and depression.
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| Manuel Almagro Rivas, Ghrelin-3D-predicted, CC BY-SA 4.0 |
After bariatric surgery, the ghrelin level drops, while it rises after weight loss due to diet. Gastric bypass and gastric sleeve surgery lead to a significant reduction in the concentration of ghrelin in the blood. This reduction is explained by the fact that the food bypasses the stomach via the bypass or, in the case of the gastric sleeve procedure, the part of the stomach responsible for producing the ghrelin is removed.
Cholecystokinin
Another peptide hormone of the gastrointestinal tract is cholecystokinin. It is produced in the duodenum and small intestine in special cells, the so-called I-cells. The secretion of the hormone is stimulated by fat and amino acids in the food. It is involved in the central nervous system in triggering the feeling of satiety. After a bariatric operation, especially after the gastric sleeve procedure, the cholecystokinin level increases significantly more after meals, which intensifies the feeling of satiety and leads to a long-term reduction in body weight.
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| McortNGHH, Effects of CCK on the gastrointestinal tract, CC BY-SA 4.0 |
Glucagon-like Peptide 1
The protein glucagon-like peptide 1, GLP-1 for short, is a peptide hormone produced in the intestine (L-cells of ileum and colon) and released into the bloodstream after food intake. GLP-1 plays an important role in controlling glucose metabolism and has the following effects:
- stimulation of insulin production in the pancreas
- improving/restoring glucose control
- delaying gastric emptying
- inhibition of the feeling of hunger and thirst
Gastric bypass surgery leads to increased GLP-1 production after ingestion, which is of particular benefit to patients with diabetes mellitus type 2 because the meal-dependent GLP-1 release is reduced.
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| Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute, PDB 1d0r EBI, marked as public domain, more details on Wikimedia Commons |
If gastric bypass surgery is combined with gastric sleeve procedure, additional stimulation of GLP-1 release occurs. This effect occurs very early after bariatric surgery, usually within a few days and regardless of weight reduction.
Leptin
Leptin is a hormone that is predominantly produced by the body's own fat cells (adipocytes). It reduces the feeling of hunger and increases the feeling of satiety, so it normally has an appetite-suppressing effect. In fact, the opposite is true for many obese people: despite the high concentration of the hormone in the blood, it does not inhibit the appetite as it does for people of normal weight. This effect is known as leptin resistance, the cause of which is largely unknown.
In the case of leptin resistance, the effect of the central saturation signal is disturbed, i.e. food intake is increased. The result is an endocrine (hormonal) obesity with a reduced response of the body cells to insulin.
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| Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute, PDB 1ax8 EBI, marked as public domain, more details on Wikimedia Commons |
After bariatric surgery, the leptin level in the blood drops sharply (by 75%), which can be observed after both gastric bypass and gastric sleeve surgery. The drop in leptin can already be observed a few weeks after the surgical procedure.
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