Studies in betaine-supplemented mice have demonstrated that betaine may improve glucose homeostasis via upregulation of fibroblast growth factor 21 (Fgf21) [55], an important metabolic regulator, reduce intramyocellular lipid accumulation and insulin resistance [56], and alter the composition of the gut microbiota to favor species associated with obesity prevention [54]. The gene discussed is FGF21; the disease is Obesity.