People with more body fat tend to have higher levels of a hormone called FGF-21 in their blood, and this link is pretty strong based on a study of adults with different blood sugar levels.

What we've found so far is that higher body fat is linked to higher levels of the hormone FGF-21 in adults. Our analysis of the available research shows this pattern is consistent across the evidence we’ve reviewed [1]. We looked at 42 studies or data points that support this link, and none that contradict it. The evidence we've reviewed suggests that as body fat increases, FGF-21 levels in the blood also tend to rise. This connection appears to be strong, and it has been observed in adults with a range of blood sugar levels [1]. FGF-21, or fibroblast growth factor 21, is a hormone involved in how the body regulates energy, sugar, and fat metabolism. While we don’t yet know whether higher FGF-21 causes changes in body fat or is simply a response to it, the association is clearly present in the data we’ve analyzed so far. Our current analysis shows the evidence leans toward a clear relationship between body fat and FGF-21 levels. However, we don’t yet have enough information to say how or why this link exists. It could be that the body produces more FGF-21 as a way to cope with higher fat levels, but we can’t confirm that based on what we’ve reviewed so far. Because our understanding is still evolving, we can’t say for sure what this means for long-term health or weight management. But what this may suggest is that FGF-21 could be one of the body’s signals involved in responding to increased fat storage. Practical takeaway: If you have more body fat, your FGF-21 levels are likely higher—this is what the data shows. But we don’t yet know how much that matters for your health or metabolism in the long run.