NPPA and Obesity: KP also plays an important role in tryptophan metabolism, and excessive expression of KP was associated with insulin resistance (IR), which can lead to obesity and T2DM [25, 35]; 4-(2-aminophenyl)-2,4-dioxobutanoic acid and kynurenic acid were the metabolites of KP, which were increased in the state of T2DM and decreased after SFE treatment.