FGF21

Where it comes from

Made in

Liver above all; some from fat, muscle and pancreas

Sent out by

Prolonged fasting, a protein-poor diet, fructose and alcohol, and cold; it rises in obesity and fatty liver disease

Acts on

• Fat tissue (adiponectin, fat burning)
• Hypothalamus (sweet and alcohol preference)
• Liver
• Brown fat

What it does

• Shifts the body to burning fat during fasting
• Curbs the appetite for sugar and alcohol in mice and in human genetic studies; in people a sugar load raises it within hours ¹
• Protects the liver against fat and injury; levels rise as the disease worsens

In medicine

• No approved medicine. Pegozafermin, a long-acting analogue, improved fibrosis in 26 to 27 percent of patients against 7 percent on placebo over 24 weeks in a 219-patient phase 2b trial ²
• Efruxifermin did the same in its own phase 2b trial, and both have moved into phase 3 for metabolic liver disease ³

Beyond the body’s own use

• FGF21 variants shape how much sugar and alcohol people like, one of the clearest diet-related signals in human genetics ¹
• Fibroblast growth factors are named as a class on the World Anti-Doping Agency’s Prohibited List and banned at all times, in and out of competition ⁴
• Nothing containing FGF21 is approved; the analogues exist only inside trials, and what they have shown is less liver scarring rather than weight loss ²