Adiponectin

Adiponectin is secreted by adipose tissue, and unusually its levels fall as fat mass rises — the opposite pattern to leptin. It improves insulin sensitivity in liver and muscle, promotes fat oxidation and has anti-inflammatory effects on blood vessel walls.

It matters because it helps explain why fat distribution matters more than fat quantity. Visceral fat is associated with lower adiponectin, while subcutaneous fat on the hips and thighs is associated with higher levels, which is part of why the two carry such different metabolic risk.

In practice it rises with weight loss, with exercise, and notably with the thiazolidinedione class of diabetes drugs. It is measured mostly in research rather than in routine clinical care.