We predicted that 1) SCFA concentrations would be lower in patients with MDD compared to controls, 2) that C-Reactive Protein (CRP) would be higher in patients with MDD compared to controls and positively associated with symptom severity in MDD, 3) SCFA concentrations would be associated with inflammation (as measured by CRP) and that 4) higher SCFAs at baseline would predict remission from depression during treatment-as-usual. Here, CRP is linked to depressive disorder.