LEP and obesity due to melanocortin 4 receptor deficiency: By infusing recombinant murine leptin in lean mice consuming a low-fat diet – to achieve circulating concentrations that mimicked those of age-matched diet-induced obese (DIO) mice – we sought to create a mouse model of elevated circulating leptin concentrations without the metabolic “confounds” of diet-induced obesity (e.g. elevated FFA and glucose, insulin insensitivity, fatty liver, etc.).