Hippocrates, the Greek physician regarded as the founding father of medicine, once said that all diseases begin in the gut. This, of course, would make sense for mood disorders too.
It comes as no surprise that the gut microbiome plays a very important role in our mood regulation and thus issues with the gut microbiome can be connected to anxiety and depression.
The brain and the gut communicate via a gut-microbiome-brain axis, which is what forms connections between gut bacteria and the brain. A growing body of evidence indicates that a disrupted gut microbiome may contribute to a variety of cognitive and mood disorders, including [i] [ii] [iii] [iv]:
Attention deficit hyperactivity disorder (ADHD)
Sensory processing disorder
Obsessive compulsive disorder (OCD)
The brain and the gut can interact directly through the vagus nerve, which connects the central nervous system to the digestive tract. The vagus nerve can be activated by many molecules found in the gut which are known to affect the nervous system.
Short-Chain Fatty Acids (SCFAs) are created when dietary fibre is broken down by gut bacteria into anti-inflammatory short-chain fatty acids (SCFAs). SCFAS can be hugely beneficial for our gut and brain health. Gut microbes promote serotonin production in the colon [v]. Serotonin functions as a key neurotransmitter in both the gut and brain and is key in influencing nerve signalling in the central nervous system, which includes brain activity [vi].
One particular example is butyric acid, which has been shown to slow the progression of diseases such as Parkinson’s in animal studies [vii].
A healthy gut promotes a normal stress response. Mice which were given antibiotics to clear their guts of bacteria were seen to have an exaggerated stress response indicated by high levels of stress hormones[viii].
Anxiety Disorder, Depression and Low Mood:
Anxiety disorder manifests as a feeling of fear and dread that can negatively affect productivity, our relationships and our overall quality of life. Since gut dysbiosis can lead to anxiety, re-establishing the gut microbiota can help to reduce anxiety-driven behaviour.
In mice studies, after being given certain Campylobacter bacterial strains, the mice developed anxious and abnormal behaviours, thought to be via activation of the amygdala, a region in the brain that is often implicated in cases of anxiety[ix].
Several human studies have found microbiota differences between patients with anxiety and/or depression compared to healthy control groups. In one study, lower levels of a particular bacterial genus, Faecalibacterium, correlated with more severe depression [x].
Fermented foods: such as include kimchi, yogurt, kefir, kombucha and sauerkraut, can improve gut health by populating the gut with beneficial gut bacteria. This may increase serotonin levels in the gut. Up to 90% of your body’s serotonin is produced by the mass of healthy bacteria in your gut [xi] [xii].
Nuts, seeds and avocado: Plant-based sources of many essential nutrients for mental fitness including omega 3 fatty acids, protein and fibre for reduced inflammation and improved cognition. Avocados cotain many nutrients benefical for mental health: omega3 fats, magnesium, vitamin C, vitamin E, B vitamins and antioxidants [xvii].
Turmeric: A powerful anti-inflammatory and antioxidant spice that helps the brain resist damage from oxidative stress and also has been found to help healthy cognition. Scientists are also exploring how curcumin may be related to depression and mood disorders [xviii] [xix].
Leafy Greens: Leafy greens contain high levels of folate and magnesium, which are beneficial for neurotransmitter function and for reducing the risk of depression. Good examples are: spinach, swiss chard, arugula, watercress, dandelion greens, kale and mustard greens.
Berries: Berries are rich in many beneficial plant compounds with antioxidant activity such as anthocyanins, polyphenols, fibre and vitamin C. Wild blueberries contain a very high amount of antioxidants and therefore are great to help boost and preserve brain activity. Other good examples of berries include raspberries, blackberries, blackcurrants, elderberries, acai, goji and strawberries. Different colours indicate different antioxidant compounds in the fruit, so including a variety in your daily intake is vital for the best effects [xx][xxi].
Green Tea: Green tea contains many useful compounds which can cross the protective barrier into the brain (blood-brain barrier). L-theanine increases the activity of the inhibitory neurotransmitter GABA, which has anti-anxiety effects. It also increases dopamine and the production of alpha waves in the brain [xxii] [xxiii].
Manipulating the gut microbiota supplementally with psychobiotics and prebiotics have been seen to alter brain function and applying to gut-brain axis disorders, such as depression and autism [xxiv]. Psychobiotics is a term used to refer to live bacteria that might confer mental health benefits by affecting microbiota of the host organism.
Some probiotics have been shown to improve symptoms of stress, anxiety and depression [xxv]. Prebiotics are foods which fuel the production of beneficial bacteria in the gut, they have been shown to reduce the amount of stress hormone in the body, called cortisol [xxvi]
Vitamin D is a neuro-steroid that can protect against depression and anxiety. It helps to reduce inflammation and the effects of oxidative stress on the brain to promote a healthy stress response [xxvii].
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[ii] Wang Y, Wang Z, Wang Y, Li F, Jia J, Song X, Qin S, Wang R, Jin F, Kitazato K, Wang Y. The Gut-Microglia Connection: Implications for Central Nervous System Diseases. Front Immunol. 2018 Oct 5;9:2325. doi: 10.3389/fimmu.2018.02325.
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[vii] R. St. Laurent, L.M. O’Brien, S.T. Ahmad. ‘Sodium butyrate improves locomotor impairment and early mortality in a rotenone-induced Drosophila model of Parkinson’s disease’, Neuroscience, Volume 246, 2013,
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[xiii] Scholey A, Owen L. Effects of chocolate on cognitive function and mood: a systematic review. Nutr Rev. 2013 Oct;71(10):665-81. doi: 10.1111/nure.12065.
[xiv] Parker G, Parker I, Brotchie H. Mood state effects of chocolate. J Affect Disord. 2006 Jun;92(2-3):149-59. doi: 10.1016/j.jad.2006.02.007. Epub 2006 Mar 20.
[xv] Bozzatello P, Brignolo E, De Grandi E, Bellino S. Supplementation with Omega-3 Fatty Acids in Psychiatric Disorders: A Review of Literature Data. J Clin Med. 2016 Jul 27;5(8):67. doi: 10.3390/jcm5080067.
[xvi] Giles GE, Mahoney CR, Kanarek RB. Omega-3 fatty acids influence mood in healthy and depressed individuals. Nutr Rev. 2013 Nov;71(11):727-41. doi: 10.1111/nure.12066. Epub 2013 Oct 22.
[xviii] Ramaholimihaso T, Bouazzaoui F, Kaladjian A. Curcumin in Depression: Potential Mechanisms of Action and Current Evidence-A Narrative Review. Front Psychiatry. 2020 Nov 27;11:572533. doi: 10.3389/fpsyt.2020.572533.
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[xxii] Nathan PJ, Lu K, Gray M, Oliver C. The neuropharmacology of L-theanine(N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent. J Herb Pharmacother. 2006;6(2):21-30.
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