Some studies had investigated the biological activity of GIP on adipocytes and indicated that GIP is implicated in adipose tissue mass and metabolism by regulating glucose uptake [41], lipolysis [42], and the activity of lipoprotein lipases [43, 44], some of which suggest the adipogenic effect of GIP with studies indicating GIPR knockout mice and chronic elevation of serum GIP levels in a transgenic mouse would inhabit diet-induced obesity [44, 45]. This evidence concerns the gene GIPR and obesity due to melanocortin 4 receptor deficiency.