IAA, has been reported to be produced by the flora from tryptophan metabolism and can alleviate inflammation related to alcoholic liver disease [30] and obesity [31] by directly or indirectly regulating the balance between proinflammatory and anti-inflammatory cytokines (TGF-β, TNF-α, IL-10, and IL-22). Here, TGFB1 is linked to obesity due to melanocortin 4 receptor deficiency.