In Fish, GIP Controls Appetite Rather Than Lowering Blood Sugar — Opposite of Mammals | Research

The takeaway

Unlike its blood sugar-lowering role in mammals, GIP acts primarily as an appetite regulator in grass carp, actually raising blood glucose while modulating feeding behavior.

Opposite function in fish vs mammals
GIP raises blood glucose and regulates appetite in grass carp instead of lowering blood sugar

What the researchers found

GIP functions as an appetite regulator rather than a hypoglycemic incretin in grass carp, raising blood glucose and modulating feeding behavior — opposite to its mammalian role.

Why it matters

Understanding how incretin hormones evolved different functions across species provides insights into metabolic regulation and could improve aquaculture feeding strategies.

How the study worked

Intraperitoneal injection of synthetic grass carp GIP; 24-hour monitoring of blood glucose, hepatic gene expression (g6pase, pepck), and feeding behavior.

What this study cannot tell us

Single fish species studied; acute injection may not reflect chronic physiological role; grass carp are herbivorous, which may influence incretin function.

How to read the evidence

Controlled fish study with gene expression analysis — strong evidence in aquaculture model.

When this study was published

Published in 2026, contributing to comparative incretin biology.

The bigger picture

This challenges the assumption that incretin biology is universal — GIP's role in fish versus mammals shows how evolution repurposes the same peptide hormone for different metabolic needs across species.

Questions still open

When in evolution did GIP switch from appetite regulation to blood sugar lowering?
Could GIP-based strategies optimize feed timing in aquaculture?

Common questions

What is GIP?

GIP (glucose-dependent insulinotropic polypeptide) is a gut hormone. In humans, it helps lower blood sugar after meals. In fish, this study found it does the opposite — raising blood sugar while controlling appetite.

Why does GIP work differently in fish?

Fish and mammals evolved under very different metabolic pressures. Fish may need GIP to maintain blood sugar during fasting and regulate feeding patterns, while mammals evolved to use it for insulin release after meals.

Read the original research

Glucose-dependent insulinotropic polypeptide (GIP) acts as an appetite regulator rather than as a hypoglycemic incretin in grass carp.

Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology, 283, 111192

View on PubMed ↗Publisher’s paper ↗

Citation

Cheng, Danhong; Sun, Manjie; Huang, Jinqian; Luo, Shan; Chen, Haotian; Jin, Shengzhen; Zhang, Yanpeng; Yuan, Xiaochen. (2026). Glucose-dependent insulinotropic polypeptide (GIP) acts as an appetite regulator rather than as a hypoglycemic incretin in grass carp.. Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology, 283, 111192. https://doi.org/10.1016/j.cbpb.2025.111192