FGF21 and Obesity: No differences were observed between men and women, but people with overweight/obesity (mean BMI 28.6) had serum FGF21 levels of 291.8 ng/L (range 144.5-512.0), while lean controls (mean BMI 22.3) had significantly lower FGF21 levels of 208.7 ng/L (range 94.4-325.7) (28).