Some people who are obese but still respond well to insulin have higher levels of a hormone called FGF21 in their blood compared to obese people whose bodies don’t respond as well to insulin—even though they weigh about the same.

What we've found so far suggests that obese individuals who maintain better insulin sensitivity may have higher levels of FGF21 compared to those who are insulin resistant, despite similar body weight [1]. Our analysis of the available research shows that FGF21, a hormone involved in metabolic regulation, appears to be elevated in certain obese individuals who still respond well to insulin [1]. This pattern was observed across 43 supporting assertions, with no studies in this set reporting the opposite effect. While we do not yet know why this association exists, it points to a possible link between FGF21 and metabolic health in the context of obesity. We want to be clear: this does not mean FGF21 improves insulin sensitivity or causes better metabolic outcomes. We’re only reporting what the data shows—an association between higher FGF21 levels and better insulin response in some people with obesity. There is no evidence from this analysis explaining whether FGF21 drives these differences or is simply a marker of underlying metabolic function. Based on what we’ve reviewed so far, the evidence leans toward higher FGF21 levels being present in obese individuals with better insulin sensitivity compared to those who are insulin resistant [1]. However, we don’t yet have enough information to determine cause, effect, or clinical implications. Practical takeaway: If you're obese and metabolically healthy, your body might show different hormone patterns—like higher FGF21—but we don’t know yet if that matters for long-term health or can be changed through diet, exercise, or other habits.