LEP and Anxiety: Supporting the idea of a direct relationship between the diet, the microbiome and neuronal homeostasis and mental health, recent studies have demonstrated that the microbiome plays a pivotal role in the regulation of leptin and insulin sensitivity through production of bioactive metabolites, which affect tryptophan metabolism, neurotransmitter synthesis, particularly for serotonin and dopamine, and production of neurotrophic factors, promoting anxiety- and depressive-like behaviors that can be ameliorated by antibiotic treatment in animal models [291].