The study by Lee (71) showing a marked decline in hepatic CEACAM1 levels in patients with high-grade fatty liver and obesity coupled with our mechanistic studies demonstrating that redelivering CEACAM1 to the liver reverses diet-induced insulin resistance, fatty liver, and visceral obesity (27) emphasizes a critical role for CEACAM1 in metabolic control. This evidence concerns the gene CEACAM1 and obesity due to melanocortin 4 receptor deficiency.