GIP is definitely an incretin that's secreted within the proximal compact intestine inside the presence of nutrients from the intestine. GIP was initially named gastric inhibitory peptide as it was thought to decrease gastric acid secretion; having said that, later scientific studies shown that its primary effect is stimulating insulin https://docs.google.com/document/d/1bSE0RrndKmZ6FYu0PotYIXkNFnWcw7rtv4s8CcblqWU/edit?usp=sharing