Management of the Bariatric Surgery Patient

Publication Date: February 28, 2024

Gastrointestinal Hormones

Gastrointestinal Hormones

Gastrointestinal (GI) Hormones

  1. Gastrointestinal hormones regulate caloric balance, hunger/ satiety food digestion, and nutrient utilization via central nervous system signaling, effects on GI motility, and GI enzyme release.
  2. Common GI hormone action in response to eating includes a decrease in hunger and facilitation of digestion (delayed gastric emptying, digestive enzyme release, and post-absorptive nutrient metabolism).
  3. The jejunum, the second longest segment of the small intestine, absorbs the greatest amount of simple sugars, fatty acids, proteins, minerals and vitamins.
  4. The ileum, the longest segment of the small intestine, absorbs bile salts, vitamin B12, some vitamins and some minerals.
  5. After food intake, most GI hormones decrease hunger/increase satiety.
  6. Among the few GI hormones that increase hunger between meals are ghrelin (“hunger hormone”) and neuropeptide Y (NPY). Positive caloric balance may not always be hunger-related.
  7. Illustrative GI hormones produced by the stomach include ghrelin and gastrin.
  8. Illustrative hormones produced by the pancreas include insulin, glucagon, pancreatic polypeptide (PP), amylin, and somatostatin.
  9. Illustrative GI hormones produced by the small intestine include cholecystokinin (CCK), secretin, motilin, and glucose-dependent insulinotropic peptide (GIP — also known as gastric inhibitory peptide).
  10. Illustrative GI hormones produced by the ileum and/or large intestine include fibroblast growth factor (FGF) 19, glucagon-like peptide-1, glucagon-like peptide-2, oxyntomodulin, and peptide YY (PYY).

Nutrient Absorption

GI Hormone Regulation of Caloric Balance, Food Digestion, and Nutrient Utilization

a The biologically active PYY and PP are expressed by endocrine cells in the digestive system. Animal studies suggest NPY endocrine cells are found throughout the small and large intestine, with NPY thus being involved in both gut-brain and brain-gut axis (bidirectional signaling). NPY is mainly described as a highly abundant orexigenic peptide found throughout the brain.

Illustrative Gastrointestinal Hormones and Function

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Where Secreted Gastrointestinal Hormone Effect of Hormone on Eating Behavior Effect of Eating on Hormone Secretion Notes Effect of Gastric By-pass and Sleeve Gastrectomy
Stomach Ghrelin
(secreted by P/D1 cells)
↑ Hunger ↑ With fasting
↑ Gastric emptying/ growth hormone (GH)
Ghrelin likely to decrease with sleeve gastrectomy (not so with gastric bypass)
(secreted by G cells in antrum)
↓ Hunger ↑ Hydrochloride (HCI) acid and pepsinogen ↓ Gastric bypass
−/↑ Sleeve
Pancreas Insulin
(secreted by pancreatic beta cells)
↓ Hunger ↑ Hunger with hypoglycemia
↑ Glucose transporter 4 in adipose tissue/muscle, glycogenesis, lipoprotein lipase activity, lipogenesis
↓ Insulin resistance/ fasting insulin
↑ Insulin sensitivity/ insulin responsiveness
(secreted by pancreatic alpha cells)
↓ Hunger ↑ Glycogen to glucose
↑ Postprandial glucagon in patients with type 2 diabetes mellitus (glucagon not suppressed)
PP [secreted by PP (F) cells] ↓ Hunger ↓ Pancreatic exocrine secretion Variable
(secreted by pancreatic beta cells)
↓ Hunger ↓ Gastric emptying, glucagon −/↓
(secreted by D cells pylori antrum, duodenum, and pancreatic islets)
↓ Hunger ↓ Growth hormone, gastrin, HCI, secretin, CCK, insulin, glucagon −/↑
Small Intestine (Mainly Duodenum and Jejunum) CCK
(secreted by I-cells)
↓ Hunger ↑ Gall bladder contractility and bile, pancreatic enzymes
↓ Gastric emptying
↑ Postprandial
(secreted by S cells)
−− ↑ Pancreatic bicarbonate and bile
↓ Intestinal motility and gastric acid
GIP; Also known as Gastric Inhibitory Peptide – secreted by K cells −− ↑ Insulin
↑ Glucagon postprandial
(secreted by M or Mo cells)
↓ Hunger
(↑ with fasting)
↑ Gastric motility, interdigestive migratory contractions (borborygmi) ?
Ileum and/ or Large Intestine FGF 19 [FGF 21 is produced by the liver]
(secreted by ileal cells and regulated by farnesoid X receptors [FXR])
↓ Hunger ↓ Bile acids, glucose production
↑ Insulin sensitivity, glycogen synthesis
Glucagon like peptide-1
(secreted by ileum/colon L-cells)
↓ Hunger ↑ Insulin
↓ Glucagon, gastric emptying
Glucagon like peptide-2
(secreted by ileum/colon L-cells)
↓ Hunger ↑↑ ↑ Glucose metabolism, intestinal mucosal growth, increases absorptive surface, epithelial brush-border nutrient transporters and digestive enzymes, intestinal blood flow, postprandial chylomicron secretion
↓ Gastrointestinal motility
(secreted by ileum/colon L-cells)
↓ Hunger ↑ Glucagon-like peptide-1 (GLP-1) and glucagon receptor activity
↓ Gastric acid and gastric emptying
↑ Gastric bypass
− Sleeve gastrectomy
Peptide YY
(secreted by ileum/colon L-cells)
↓ Hunger ↓ Gall bladder and pancreatic secretions, gastric emptying

Bariatric Surgery

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...atric Surgical Procedures...

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...hysiologic Mechanisms of Weight Los...

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...Intestinal (small bowel) obstruc...

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Nutrient Considerations

...rient Consideration...

...10 TAKEAWAY MESSAGES: Bariatric Surgery N...

...AWAY MESSAGES: Microbiome The mi...

...mmon Micronutrient Deficienciesa Vitamin D defici...

...cronutrient Deficiency Replacement After Bariatr...