Pertubuhan Sains & Kesejahteraan
Science & Wellness Organisation
(PPM-013-05-16022012)
Gut-Brain Axis
How Your Gut Influences Your Brain, Mood, and Mental Health
Gut Brain Axis
The gut brain axis is a two-way communication system between your digestive tract and brain. This connection operates through neural pathways (like the vagus nerve), hormones, immune response and microbial metabolites, allowing your gut to impact your emotions, vice versa.
Gut Microbes produce neurotransmitters like Serotonin, Dopamine and Gamma-Aminobutyric Acid (GABA) which affect mood and brain function.
Stress and anxiety can alter gut movement, secretion and microbial balance.
How Does the Gut Talk to The Brain?
Microbial Neurotransmitter
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Certain bacteria like Lactobacillus and Bifidobacterium produce GABA.
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Streptococcus and Enterococcus can produce serotonin.
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These chemicals signal the brain via the vagus nerve.
Metabolites & Immune Signals
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Gut bacteria break down fiber into SCFAs (short-chain fatty acids) like butyrate, which reduce inflammation and support brain health.
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An imbalanced gut can cause “leaky gut” and lead to brain inflammation via immune signaling.
Vagus Nerve & Stress Response
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The vagus nerve is a direct highway from the gut to the brain.
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Gut microbes regulate the HPA stress axis, which controls your response to stress.
You can shape your gut microbiome through diet, probiotics, and lifestyle.
Gut Microbiome and Mental Health
Depression and Anxiety
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Studies show lower gut bacterial diversity and fewer butyrate-producing bacteria (like Coprococcus) in people with depression.
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Gut microbes affect serotonin, dopamine, and GABA production which is critical to mood balance.
Probiotics Work
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Clinical trials reveal 4–8 weeks of probiotic supplements can reduce depression and anxiety symptoms.
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Prebiotics (fiber that feeds good bacteria) also reduce stress and promote calm.
Cognitive Function
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In older adults, low levels of Bifidobacterium and gut imbalances correlate with poorer memory and mental sharpness.
Gut–Brain Axis in Disease
Irritable Bowel Syndrome (IBS)
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1 in 3 IBS patients also has anxiety or depression.
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Stress worsens symptoms and IBS discomfort increases stress.
The Role of Diet in Gut-Brain Health
Fiber & Prebiotics
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Promote SCFA production, reduce inflammation, and improve mood.
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Found in: fruits, vegetables, whole grains, legumes.
Probiotics
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Add beneficial bacteria to the gut (e.g., Lactobacillus, Bifidobacterium).
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Found in: supplements, yogurt, kefir.
Fermented Foods
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Natural probiotics + polyphenols + enzymes.
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Include: kimchi, sauerkraut, miso, kombucha.
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One study showed a 32% drop in stress levels with a fermented food diet.
A healthy gut equals a healthier mind.
What Happens When “Bad” Gut Bacteria Take Over?
When your gut contains too much "bad" bacteria which is a condition called "Gut Dysbiosis", it can negatively affect your brain and mental health in several important ways.
Clostridium Deficile
Proteus
Escherichia Coli
Bacteroides
Klebsiella
How "Bad" Gut Bacteria Happens?
Poor Diet
(High Sugar, Low Fibre)
Antibiotics
Chronic Stress
Infection
How Bad Gut Bacteria Affect the Brain?
Increased Gut Permeability (“Leaky Gut”)
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Bad bacteria can damage the gut lining.
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This allows toxins, pathogens, and undigested food particles to leak into the bloodstream.
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The immune system reacts, causing systemic inflammation, which also affects the brain.
Health Impact: Chronic inflammation is linked to depression, anxiety, and cognitive decline.
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Supporting gut health may prevent or alleviate conditions like anxiety, depression, IBS, and even neurodegenerative diseases.