The idea that the bacteria in our intestines could affect our thoughts may seem like science fiction. Research indicates that the trillions of microbes living in our gut significantly influence our cognitive abilities, emotional well-being, and decision-making processes. This fascinating connection, often called the gut-brain axis, has transformed our understanding of mental health and cognitive function.
From gut to brain: how microbes influence cognition and behaviour
The vagus nerve, stretching from the brainstem to the abdomen, is the primary communication channel between the gut and the brain. This nerve acts as an anatomical connection that allows a rapid exchange of signals from the brain to the gut and vice versa. Yet, the gut-brain connection goes beyond this - it extends via endocrine and metabolic routes, allowing brain and gut to be ‘in sync’. Through these pathways, gut microbes can exert their influence.
Memory formation and recall
In a recent study, it was found that female nurses who had taken antibiotics for prolonged periods (>2 months) ended up with inferior scores in cognitive tests such as learning, working memory, and attention tasks compared to those who had not taken such medication. Importantly, the cognition of the women who had taken antibiotics was slightly poorer when they were followed up seven years later. Although this is only a correlation, the researchers think it could be due to antibiotic-induced changes in the gut. This is one of the reasons we are advised to NOT overuse antibiotics or take them without a prescription. While they may treat an infection, they may also impact your cognitive health in the long run.
Emotional responses
An estimated 90% of serotonin, the “feel-good” hormone, is secreted by the gut enterochromaffin (EC) cells. However, this production is influenced by gut microbes. Scientists compared serotonin levels in mice with normal gut bacteria to those in germ-free mice. They discovered that EC cells in germ-free mice produced 60% less serotonin than those in mice with normal gut bacteria. Reintroducing microbes to these germ-free mice restored their serotonin levels, highlighting the indirect role of gut microbiome in serotonin production. Other microbial species, including Bacillus, Saccharomyces, and E. coli, can produce norepinephrine and dopamine. This microbial production of neurotransmitters can lead to imbalances, potentially resulting in emotional distress.
Learning capabilities
In 2012, Wall et al. demonstrated that ingestion of Bifidobacterium breve NCIMB702258, but not B. breve 6330, significantly impacted brain fatty acid composition in mice, particularly arachidonic acid (AA) and docosahexaenoic acid (DHA). These fatty acids have potential clinical implications as they play important roles in cognitive processes such as memory and learning.
Stress levels
Research suggests that gut bacteria, especially Lactobacillus species, play a crucial role in regulating daily patterns of stress hormone secretion. When gut microflora is absent, the stress response becomes hyperactive at specific times of the day. This finding suggests that manipulating gut bacteria could represent a new therapeutic target for treating anxiety and depression. Incorporating foods like curd, rich in Lactobacillus bacteria, could be a simple yet effective way to support your gut health and help regulate stress in a natural way.
Groundbreaking studies: the evidence
The sterile mouse experiment
In a landmark 2004 study at Kyushu University in Japan, researchers compared the behaviour of germ-free mice with normal mice. The germ-free mice showed significantly higher levels of stress hormones when faced with challenging situations. When these mice were later colonised with beneficial bacteria, their stress responses returned to normal. This demonstrates a direct link between gut bacteria and stress regulation.
The probiotic revolution
A fascinating study published in 2013 studied 36 healthy women in three groups. One group consumed yoghurt containing probiotics twice daily, while the others consumed no probiotics or yoghurt. After four weeks, the probiotic group showed significantly different brain activity patterns when shown emotional faces, particularly in areas associated with processing complex emotions and sensations.
The depression connection
In 2020, researchers at Katholieke Universiteit Leuven in Belgium studied the gut microbiomes of over 1,000 people diagnosed with depression. They found that depressed individuals lacked several species of gut bacteria, particularly those that produce butyrate. Butyrate is a compound that reduces inflammation and strengthens the gut barrier. Restoring these “missing” bacteria in animal models improved depressive symptoms.
Practical implications
These findings have profound implications for cognitive enhancement and mental health treatment. Consider these real-world applications:
The Western diet effect
The Western diet is defined as a modern diet rich in calories, fat, and sugar. A 2015 study conducted at Oregon State University in USA revealed that high-sugar diets can significantly disrupt cognitive function through microbiome alterations. Researchers found that diets high in sucrose cause greater alterations in bacterial composition than high-fat diets, worsening cognitive flexibility and working memory in mice. Specifically, an increase in Clostridiales bacteria and a decrease in Bacteroidales bacteria were linked to diminished intellectual performance, indicating that dietary choices can significantly influence brain function through modifications in the gut microbiome. You may have enjoyed that sugary treat at the party, but your gut microbiome might be paying the price, and so could your brain function. Maybe skip the sugar rush before your next exam!
The exercise connection
Regular physical activity offers more than just muscle gain; it also develops a healthier gut. Athletes and physically active individuals exhibit higher fecal microbial diversity compared to sedentary subjects, characterised by increased presence of health-associated microbial genera. A 2014 study by Clarke et al. found that elite athletes had much higher levels of Akkermansia, a group of gut bacteria associated with enhanced metabolism and cognitive function, compared to sedentary individuals. Another groundbreaking study published in Nature Medicine uncovered an exciting link between a specific gut bacteria and athletic performance. Researchers found that marathon runners had higher levels of Veillonella atypica after a race. When they introduced this bacterial strain to mice, the animals could run significantly longer on a treadmill. This discovery hints at the potential of gut microbes to influence physical stamina, opening new avenues for understanding the connection between our microbiome and physical performance.
What’s next?
The research on the gut-brain axis holds great potential. Scientists are currently exploring:
- Personalised psychobiotics for mental health conditions.
- Microbiome-based early diagnosis for neurodegenerative diseases
- Dietary interventions to enhance cognitive features
The gut-brain connection is an exciting reminder of how deeply our bodies and minds are linked. It is fascinating to think that what is happening in our gut can shape how we think, feel, and make decisions. Taking care of our gut health might just be as important as keeping our brain active when it comes to staying sharp and balanced. The more we learn about this hidden brain in our gut, the closer we get to unlocking new ways to improve mental health and overall well-being.
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