For example, the enzymatic activity of poly (ADP-ribose) polymerase (PARP)1, a representative NAD+ degrading enzyme, increases in various organs such as the liver, kidney, skeletal muscle, lung, and heart owing to the accumulation of DNA damage associated with aging and HFD-induced obesity and correlates with age- and obesity-related changes in NAD+ levels [46,56,57,58]. This evidence concerns the gene PARP1 and obesity due to melanocortin 4 receptor deficiency.