Your brain and gut communicate in 3 different ways

The idea that the brain and gut communicate dates back to the 19th and 20th centuries, with observations by Darwin, Beaumont, and Cannon that there is a connection between your emotions, thoughts, and digestion.

While research into how the gut microbiota influences the brain – and vice versa – is still in its infancy, scientists have learned three major routes through which the gut microbiota affects the gut-brain axis:

  • Direct neural signaling (similar to mobile phone communication): the vagus nerve and the spinal nerves supplying the colon are the main communication channels between your gut and your brain.
  • Hormones, neurotransmitters, and neuroactive mediators produced by the gut microbiota (similar to post office mail communication): diet and gut microbes have a more dominant role than your genes in explaining the huge variation observed in plasma metabolites, which in turn can shape the gut and brain function.
  • Immune cells (similar to emergency-like communication, such as when a fire alarm is activated when it detects smoke): immune activation is present in a subset of patients with IBS while its impact on symptoms is not clear.

Premysl Bercik, a researcher at McMaster University focused on the gut-brain connection in the context of disorders of gut-brain interaction such as IBS, explains that accumulating evidence now shows that this microbiota-brain communication occurs in mice and humans.

 

A lot of patients with IBS suffer from anxiety and depression

Recent important studies have shown that patients with IBS –especially women– are commonly affected by anxiety (4 out 10 patients) and depression (3 out 10 patients), and anxiety symptoms. But the opposite is also true, meaning that patients with anxiety and depression have a two-fold risk of developing IBS.

The close association between anxiety and depression and IBS is important because the higher the number of psychological alterations, the higher the severity of IBS.

This explains that most patients with IBS cannot be managed alone through diet and need non-dietary means to improve their quality of life, stress, and gut symptoms, such as psychological therapies (cognitive behavioral therapy and gut-directed hypnotherapy), mindfulness, and even yoga. Good physical health is also important, and exercise and spending time in nature have shown positive psychological effects, probably indirectly impacting the gut-brain axis.

 

Are we ready to use microbiome-related interventions to improve mental health and well-being?

Several studies demonstrated that transferring microbiota from patients with either anxiety or depression can induce abnormal behavior in germ-free mice. This suggests that an altered gut microbiota could be involved in mental health disorders and psychological sequelae that patients with IBS struggle with.

Based on the link between gut microbiota and mental health, the term “psychobiotic” was first coined in 2013 by John Cryan and Ted Dinan from the University College Cork to describe live bacteria (probiotics)  that impact mental health through the gut microbiome.

 

More recently, the definition of psychobiotic has expanded to include not only probiotics, but also prebiotics and other means of influencing the gut microbiota in benefit of mental health:

  • A balanced diet that is rich in vegetables and fermented foods: people who follow a “psychobiotic diet”, i.e., rich in fruits, vegetables, grains, legumes, and fermented foods, seem to show more reduced stress. Instead of first trying popular restrictive diets that avoid the preferred fiber sources for our gut microbiota, the Mediterranean diet is better and preliminary findings showed that it helps improving gastrointestinal and psychological symptoms.
  • Some probiotics: small human studies showed the benefits of Bifidobacterium longum NCC3001 and Saccharomyces cerevisiae I-3856 for improving gut and mental health in people with IBS. In healthy adults, longum 1714 showed potential benefits in reducing stress.
  • Short-chain fatty acids: these molecules obtained from fiber fermentation by gut microbes alleviate stress symptoms and improve intestinal permeability in mice under psychological stress.

 

 

References:

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Chen L, Zhernakova DV, Kurilshikov A, et al. Influence of the microbiome, diet and genetics on inter-individual variation in the human plasma metabolome. Nat Med. 2022; 28(11) :2333-2343. doi: 10.1038/s41591-022-02014-8.

Bennet SMP, Palsson O, Whitehead WE, et al. Systemic cytokines are elevated in a subset of patients with irritable bowel syndrome but largely unrelated to symptom characteristics. Neurogastroenterol Motil. 2018 ; 30(10):e13378. doi: 10.1111/nmo.13378.

Zamani M, Alizadeh-Tabari S, Zamani V. Systematic review with meta-analysis: the prevalence of anxiety and depression in patients with irritable bowel syndrome. Aliment Pharmacol Ther. 2019; 50(2):132-43. doi: 10.1111/apt.15325.

Midenfjord I, Borg A, Törnblom H, et al. Cumulative effect of psychological alterations on gastrointestinal symptom severity in irritable bowel syndrome. 2021; 116(4):769-79. doi: 10.14309/ajg.0000000000001038.

Loughman A, Staudacher HM. How can I improve my gut health via non-dietary means? Lancet Gastroenterol Hepatol. 2024; 9(1):20. doi: 10.1016/S2468-1253(23)00412-0.

Sarkar A, Lehto SM, Harty S, et al. Psychobiotics and the manipulation of bacteria-gut-brain signals. Trends Neurosci. 2016; 39(11):763-781. doi: 10.1016/j.tins.2016.09.002.

Berding K, Bastiaanssen TFS, Moloney GM, et al. Feed your microbes to deal with stress: a psychobiotic diet impacts microbial stability and perceived stress in a healthy adult population. Mol Psychiatry. 2023; 28(2):601-610. doi: 10.1038/s41380-022-01817-y.

Staudacher HM, Mahoney S, Canale K, et al. Clinical trial: a Mediterranean diet is feasible and improves gastrointestinal and psychological symptoms in irritable bowel syndrome. Aliment Pharmacol Ther. 2024; 59(4):492-503. doi: 10.1111/apt.17791.

Pinto-Sanchez MI, Hall GB, Ghajar K, et al. Probiotic Bifidobacterium longum NCC3001 reduces depression scores and alters brain activity: a pilot study in patients with irritable bowel syndrome. Gastroenterology. 2017; 153(2):448-459.e8. doi: 10.1053/j.gastro.2017.05.003.

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