# Incretin effect (GIP and GLP-1)

The incretin effect is a striking observation: drinking glucose triggers a bigger insulin response than getting the same amount of glucose by IV. The difference comes from gut hormones called incretins. The two main ones are GLP-1 (glucagon-like peptide-1), released by 'L-cells' in your lower small intestine and colon, and GIP (glucose-dependent insulinotropic polypeptide), released by 'K-cells' in your upper small intestine. Together they account for 50 to 70% of the insulin you release after a meal (Baggio & Drucker, 2007). Both act on receptors on your pancreatic β-cells to boost insulin. GLP-1 also suppresses glucagon and slows your stomach emptying. In type 2 diabetes, the incretin effect is sharply reduced, mainly because GIP loses its insulin-boosting power at the β-cell, while GLP-1 secretion drops only modestly (Nauck & Meier, 2016). GLP-1 drugs, and dual GIP/GLP-1 drugs, have cut cardiovascular events and death in high-risk type 2 diabetes. Whether your natural incretin tone predicts aging in metabolically healthy people is still an open question; the evidence so far comes mainly from diabetes trials (Nauck & Müller, 2023).

## Sources

- Baggio LL, Drucker DJ. (2007). Biology of Incretins: GLP-1 and GIP. Gastroenterology. https://doi.org/10.1053/j.gastro.2007.03.054
- Nauck MA, Meier JJ. (2016). The incretin effect in healthy individuals and those with type 2 diabetes: physiology, pathophysiology, and response to therapeutic interventions. Lancet Diabetes & Endocrinology. https://doi.org/10.1016/S2213-8587(15)00482-9
- Nauck MA, Müller TD. (2023). Incretin hormones and type 2 diabetes. Diabetologia. https://doi.org/10.1007/s00125-023-05956-x

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