Tryptophan is shunted towards serotonin production via probiotics resulting in increased serotonin reducing depressive symptoms parallel to the mechanism of SSRIs [14]. Also, Han et al. makes it evident that the inhibition of nuclear factor kappa B (NF-κB) activation and tumor necrosis factor alpha (TNFα), which play a role in the pathogenesis of depression in anxiety/depression-induced mice, can be achieved through introducing Lactobacillus mucosae NK41 and Bifidobacterium longum NK46. Here, TNF is linked to major depressive disorder.