Given that TNF-α stimulates fstl3 in vitro and given the elevated levels of TNF-α in patients with obesity and insulin resistance [16], we measured fstl3 in response to E. coli lipopolysaccharide (LPS), TNF-α, and IL-6 infusions in humans. Here, FSTL3 is linked to obesity due to melanocortin 4 receptor deficiency.