CD40LG and obesity due to melanocortin 4 receptor deficiency: Some studies indicate that fatty acid-induced metabolic dysfunction or impaired insulin secretion is associated with obesity [15, 16]; for example, one animal study demonstrated that saturated fatty acids in VAT increased IgM levels via stimulation of the B cell Toll-like receptor 4 (TLR-4) in a manner similar to lipopolysaccharide [17].