Author: Rob Corso
There is a living, dynamic universe within you. A biological ecosystem so sophisticated that it influences everything from your mood and metabolism to your immune system and mental health. It is a pillar of wellness that scientists are only beginning to understand. That understanding will potentially revolutionise how we think about human health.
Every second of every day, trillions of microscopic bacteria, fungi, and other microorganisms are dancing around in this internal universe. These vast communities of microbes (primarily residing in your large intestine) form what scientists call . . .
What was once considered solely digestion is now recognised as a complex and highly synchronised internal world essential to physical health and mental wellness.
The gut’s microbial community is so vast, complex, and influential that it essentially behaves as its own autonomous organ—a second brain, if you will.
This topic can be dense and is often discussed using technical biological terms. While much of the research is generally consistent, some discrepancies exist across various studies. Our aim is to distil and present the information as clearly and accurately as possible.
By now, you’ve likely heard the phrase “gut microbiome” quite a bit. Perhaps you know about probiotics and maybe even prebiotics. Even without knowing exactly what it is or how it works, you know the gut microbiome is important.
Here are some wild facts you should know about the gut:
There are more bacterial cells in your body than human cells (40 trillion vs. 30 trillion).
There are at least 1,000 distinct species of bacteria (likely many more) living in the gut. Each performs different tasks in the body. Not all bacteria are bad.
The gut microbiome weighs approximately 2-5 lbs (about the weight of a pineapple).
Around 90% of the body’s serotonin, our body’s “happy” chemical, is produced in the gut.
Your gut contains significantly more neurons than your spinal cord.
About 70-80% of the body’s immune cells are located in your gut’s lymphoid tissue and interact with your microbiome.
Understanding how the gut microbiome affects your health requires exploring three fundamental areas of influence: metabolism, immunity, and the gut-brain connection.
Your gut microbes transform the food you eat into energy and compounds your body can use. They break down fibre into short-chain fatty acids, which nourish your intestinal cells, regulate inflammation, improve insulin sensitivity, and regulate blood sugar levels. Our gut bacteria produce several essential vitamins that our bodies cannot synthesise on their own. The primary vitamins produced include vitamin K and various B vitamins.
Your gut microbiome is a sophisticated training ground for your immune system. From birth, microbes help immune cells distinguish between what’s friendly and what’s dangerous. Our earliest exposure to microbes—through vaginal delivery, breast milk, and skin-to-skin contact—helps set up our immune system’s baseline.
About 70–80% of the body’s immune cells reside in the gut wall, where they maintain the gut barrier, prevent “leaky gut,” and determine what to attack. Leaky gut occurs when the gut barrier becomes permeable, allowing harmful substances into the bloodstream. This triggers something called endotoxemia, a series of inflammatory responses throughout the body.
The relationship between microbes and immunity is so fundamental that scientists now believe many modern immune disorders, allergies, and chronic inflammation may stem from disrupted microbial communities.
“How is it that the bugs in your gut are connected to your wellbeing? I could go on and on. Everything is connected to the microbiome. How does that make sense given our paradigm? If you are going to your psychiatrist with low mood are they saying, let me look at your poop? Well, they should, okay, literally they should.”
—Dr. Mark Hyman, Eudēmonia Summit 2024
So why do they call it your second brain? For three main reasons:
The gut and brain are connected through neural, hormonal, and immune pathways, with a superhighway called the vagus nerve as a key component in the bidirectional relationship between these organs.
Second, your gut has its own nervous system, called the enteric nervous system (ENS). It’s often referred to as the “second brain” because it can operate independently of our first brain. It’s an autonomous and self-sustained system, and the ENS has many of the same neurons and neurotransmitters that our first brain has.
Third, and maybe most important, is the neurochemical influence, by which the gut microbiome can profoundly influence our mental and emotional health. Because of the gut–brain axis, emotional and cognitive centres of the brain are directly linked to intestinal functions. This helps explain why digestive health often correlates with mental health.
Research has shown that microbiome disruptions may contribute to anxiety, depression, and even neurodegenerative conditions. Conversely, psychological stress can alter your gut microbiome, creating a feedback loop between mind and microbes. The connection is so strong that scientists have found that transplanting gut bacteria from people with depression into healthy rats can actually make the rats exhibit depressive behaviours. And studies have shown that people with depression or anxiety often have a less diverse microbiome.
In short, a healthy gut could trigger better moods and better brain function.
Your gut microbiome is shaped by a complex interplay of factors—from the food you eat to the environment you live in—working together to influence your overall health and well-being.
Insufficient fibre and excessive consumption of highly refined carbohydrates, processed foods, and refined sugars are among the most common gut disruptors. What you eat has such a profound impact on your gut that your microbes can respond rapidly to dietary changes, often within 24-48 hours. However, establishing a stable and healthy microbiome composition requires consistent, healthy dietary habits.
Chronic stress and poor sleep have a negative impact on your gut microbiome, as does a sedentary lifestyle that doesn’t prioritise regular exercise.
Heavy reliance on certain prescription drugs all contributes to gut dysregulation. Antibiotics can be particularly detrimental, as they significantly alter the gut microbiome by killing both harmful and beneficial bacteria indiscriminately.
Everything from where you live, the cleaning products you use, and the air you breathe has an impact. The chemicals, pollutants, and pesticides you’re exposed to all influence the stability of your microbiome.
Vaginal birth, breast milk, and avoiding early exposure to antibiotics positively shape your initial microbiome.
Gut imbalance can manifest in surprising ways, affecting not just digestion but your immune system, mood, skin, energy levels, and more. Here are some key warning signs to watch for.
Digestive Issues: irregular bowel movements, bloating, gas or abdominal discomfort, acid reflux, or heartburn
Immune System Issues: recurring infections, slow wound healing, frequent colds, severe seasonal or food allergies, chronic inflammation
Cognitive Signs: mood changes, brain fog, , irritability
Skin Problems: acne, eczema, rosacea, dry or itchy skin, rashes
Unusual Fatigue: low energy that doesn’t improve with rest, difficulty sleeping
Food Sensitivities: new sensitivities to previously tolerated foods, gluten or dairy intolerance emerging
Hormonal Indicators: irregular menstrual cycles, worsening PMS symptoms, weight fluctuation
It cannot be overstated how important a healthy gut microbiome is to your overall wellness. Disruptions in gut microbiota and gut permeability have been connected to both the causes and effects of a wide range of conditions and diseases, some of which may surprise you.
So what can we do to nurture our gut health and support a balanced microbiome?
Food is mood. This might sound ambitious, but research from the American Gut Project suggests aiming to eat 30 different plant foods weekly. Each colour represents different compounds that feed diverse bacterial communities. Focus on fruits, vegetables, tubers, whole grains, nuts, seeds, and legumes.
This will also get you lots of fibre, which is very important for colon health. A recent study found that higher total dietary fibre intake was associated with a significantly reduced risk of colon cancer. As a rule, aim for 30g of fibre per day.
Fermented foods promote and add healthy bacteria to your gut. These foods include yogurt with live cultures, kombucha, kimchi, sauerkraut, tempeh, pickles in brine, sourdough bread, and miso.
Probiotics are “good” bacteria that live in and promote a healthy gut, and are found in the fermented foods listed above. Prebiotics are fibres from plants that serve as food for the probiotics in your gut. We want a diet that includes both, but there are also ways to supplement these.
This is ubiquitous health advice, but it is important to mention that excess sugar and processed foods can promote the growth of harmful bacteria and cause inflammation. In particular, foods high in artificial sweeteners and emulsifiers can alter microbial populations and intestinal barriers.
Staying hydrated helps maintain the gut’s protective barrier, which aids in preventing conditions like leaky gut.
Stress does all kinds of wacky things to your gut. It impacts digestion, harms the gut’s protective lining (leading to leaky gut), and disrupts the communication of the gut-brain axis, which can lead to mental health issues. Regularly practising meditation, yoga, or anything else that relieves stress in a healthy way is important.
Aerobic work, strength training, and restorative movement all promote microbial diversity and enhance gut barrier function. Incorporating a balance of brisk walking or jogging or cycling, yoga or pilates, and strength training is a good regimen for a healthy gut—and a generally healthy life.
Incorporating a 10-minute walk after meals has been shown to reduce blood sugar levels up to 35%. Stable blood sugar is important for maintaining a healthy gut microbiome, and it lowers stress and reduces gas and bloating.
Gardening exposes you to a diverse range of microorganisms through your skin, which can support immune function and improve mood. Plus, time outdoors increases vitamin D levels through exposure to sunlight, which also supports gut barrier integrity.
A diet that prioritises a wide range of plants and incorporates fermented foods should be your primary focus.
You should always consult with a doctor and consider getting tested to understand the health of your gut.
When choosing supplemental probiotics, select products with multiple strains and rotate brands periodically to introduce different beneficial species. Also, certain strains may aid in digestive health, while others might support immune function. Consult a healthcare professional to identify the strain best suited to your health needs, as effects vary from person to person.
You can also consider introducing supplemental prebiotics, but start slowly to avoid digestive discomfort. Some use natural antimicrobial compounds berberine occasionally to help maintain microbial balance. Finally, Vitamin D may increase microbial diversity, help regulate intestinal barrier integrity, and support immune function in the gut.
Exciting new treatments and technologies are emerging that could revolutionise how we approach gut health and overall wellness.
This concept is being actively researched, although it’s still in early stages. It uses genetically engineered probiotics for tailored interventions based on individual characteristics and needs.
Advanced sequencing technologies are used to map individual gut microbiomes. The development of AI-powered platforms for personalised recommendations is an active area of research and commercial development.
Wearable technologies are offering unprecedented insights into digestive system functioning with non-invasive gut health tracking.
Simply put, our mental health and physical well-being are dependent on a well-functioning, balanced, and diverse microbiome. It’s our second brain, and nurturing this internal ecosystem is one of the most powerful investments we can make into our long-term health.
That health is a direct reflection of our lifestyle, environment, and choices. By supporting this invisible ecosystem, we’re investing in our overall health and well-being in ways that science is only beginning to understand.
As you embark on your journey to optimise your gut health, remember that your microbiome responds best to consistent, nurturing care. Small, daily choices accumulate to create sustainable habits and significant changes. Listen to your body, stay curious about new research, and approach this complex internal world with curiosity and patience.
Disclaimer: This newsletter is provided for educational and informational purposes only and does not constitute providing medical advice or professional services. The information provided should not be used for diagnosing or treating a health problem or disease, and those seeking personal medical advice should consult with a licensed physician.
