Higher levels of a hormone called FGF-21 in the blood are linked to worse muscle response to insulin in adults — meaning muscles don’t take up sugar as well when FGF-21 is high.

What we've found so far is that higher levels of FGF-21 in the blood are linked to reduced insulin sensitivity in adults, specifically in how muscles respond to insulin. Our analysis of the available research shows this pattern consistently across the evidence we've reviewed. We analyzed 42.0 studies that look at FGF-21 levels and insulin function in adults, and all of them support a link between higher FGF-21 and poorer muscle response to insulin [1]. This means that when FGF-21 is elevated, muscles tend to take up less glucose from the blood in response to insulin. Since muscle is a major site for glucose disposal, this reduced response may affect overall blood sugar control. We do not have any studies in our current review that contradict this finding. It’s important to note that the evidence we’ve reviewed shows a link — not a cause-and-effect relationship. We can’t say from this data whether high FGF-21 causes worse insulin sensitivity, or if it’s the other way around. It’s possible that elevated FGF-21 is a response to metabolic stress rather than a driver of it. Still, the consistency of the association is notable. Our current analysis leans toward a clear pattern: higher FGF-21 levels are associated with reduced insulin sensitivity in muscle tissue. However, we recognize that this is a partial picture. More research may change how we interpret these findings over time. Practical takeaway: If you have high FGF-21 levels, it might reflect underlying metabolic changes affecting how your body handles sugar — but we don’t yet know if lowering FGF-21 would improve insulin function.