A recent randomized, double-blind study found that supplementing with the probiotic, Bacillus coagulans spore, provided significant symptom relief for those suffering from major depressive disorder (MDD).(1) In this study, researchers recruited 40 MDD patients and randomly divided them into either a control group or an experiment group. The experiment group received one tablet of B. coagulans probiotic per day for 90 days. Results indicated that the treatment group experienced a significant decrease in clinical symptoms of depression, and improved quality of life and quality of sleep. Researchers speculate that these positive results may be due to the short-chain fatty acid (SCFA) production of B. coagulans and other similar spore forming bacillus strains. SCFAs have potent anti-inflammatory and anti-microbial effect in the GUT, which contribute many beneficial effects to the host.

Bacillus subtilis is another probiotic species that has been studied in pigs for its ability to produce the serotonin precursor known as tryptophan.(2) Gut microbe derived tryptophan is directly correlated to serotonin production in the brain, since it can pass the blood-brain barrier. Serotonin is known as a happy molecule (in correct balance), which may help reduce aggression.(3) Results of a recent animal study involving chicken confirmed that the use of B. subtilis spore supplementation reduces aggressive behavior in hens and increases serotonin levels as well. Researchers highlight that although this is not a human clinical trial, the outcome is promising considering that “neural circuitry for aggression and social behavior appear to be evolutionarily conserved across the vertebrates”.

Disruptions to the gut barrier are also thought to have negative consequences on mental health; like I’ve always stated, “inflammation in the GUT equals inflammation in the brain”. The gut barrier of the large intestine protects the body against the invasion of pathogens and dangerous molecules, such as lipopolysaccharide (LPS). When this protective lining is damaged, due to stress, poor diet, antibiotics, overuse of pharmaceuticals and other factors, LPS can leak into the blood stream leading to systemic inflammation and autoimmune diseases. This condition is known as leaky gut syndrome. If LPS crosses the blood-brain barrier, it can injure areas of the brain that effect mood, and cause neuroinflammation. Leaky gut sydrome has recently been proposed as a significant contributor to the onset of depression.5 In fact, recent evidence shows that administration of LPS to mice induces depressive-like symptoms.(4)

1. Majeed M, Nagabhushanam K, Arumugam S, Majeed S, Ali F. Bacillus coagulans MTCC 5856 for the management of major depression with irritable bowel syndrome: a randomised, double-blind, placebo controlled, multi-centre, pilot clinical study. Food Nutr Res. 2018;62:10.29219/fnr.v62.1218. Published 2018 Jul 4. doi:10.29219/fnr.v62.1218

2. Bjerre K, Cantor MD, Nørgaard JV, Poulsen HD, Blaabjerg K, Canibe N, et al. Development of Bacillus subtilis mutants to produce tryptophan in pigs. Biotechnology Letters. 2017;39:289-295.

3. Cheng HW, Jiang S, Jiaying H. Gut-Brain Axis: Probiotic, Bacillus subtilis, Prevents Aggression via the Modification of the Central Serotonergic System. InTechOpen. 2019 DOI: 10.5772/intechopen.86775

4. Dang R, et al. Predictable chronic mild stress promotes recovery from LPS-induced depression. Molecular Brain. 2019; 12(42): 1-12.