The Second Brain: Why Gut Health Is Central to Whole-Body Wellness

Thursday 8 May 2025

Have you ever had to rush to the bathroom before a big event or felt butterflies in your stomach when you're falling in love? It's no coincidence—your gut and brain are deeply connected. In fact, they originate from the same group of cells during early embryonic development. As the body forms, the brain moves to one end and the gut to the other, but they stay linked via the vagus nerve, creating what’s known as the gut-brain axis.

Figure 1: Schematic of healthy gut-brain axis (Source: Bajic et al., 2018).

This powerful communication system explains why stress can trigger stomach-aches, why excitement flutters in your belly, and why gut health so profoundly influences your mood.

But digestion is just one part of the gut's story. Often called the second brain, your gut has its own nervous system, produces vital neurotransmitters like serotonin (90% of which is made in the gut!), and houses 70–80% of your immune system. Constantly, it’s sending and receiving messages from the brain, shaping your emotions, stress response, and overall health.

Here’s another astonishing fact: humans have around 23,000 genes, fewer than a tomato, which has 33,000. What makes us uniquely complex is our intimate relationship with the gut microbiome, which is home to millions of microbial genes. These tiny organisms are crucial for digestion, immunity, and mental well-being.

The Common Thread in Chronic Illness: Dysbiosis

Working with chronically ill clients and reviewing their test results, I’ve seen a recurring pattern: many health issues trace back to gut imbalances.
When harmful bacteria, fungi, and parasites outnumber beneficial microbes, a condition called dysbiosis develops. This leads to the overproduction of toxins like lipopolysaccharides (LPS) and triggers inflammation not only in the gut but throughout the body.

Dysbiosis is linked to a wide range of health issues, including:
•   Digestive disorders like IBS and constipation
•   Skin conditions like eczma
•   Mental health struggles
•   Chronic fatigue
•   Autoimmune diseases
•   Allergies
•   Heart disease
•   Metabolic disorders like obesity, diabetes, and fatty liver
•   Neurodegenerative diseases such as Parkinson’s and Alzheimer’s

In short, your gut health influences nearly every system in your body.

Have You Heard the phrase ‘a Leaky Gut’?

To understand why gut health matters, let’s look at the digestive system.
Food travels from the mouth to the stomach, then into the small intestine where nutrients are absorbed, before continuing through the large intestine and exiting the body.
Your digestive tract is essentially an external environment within your body. In the small intestine, just a single layer of epithelial cells—intestinal epithelial cells (IECs)—separates this "outside world" from your internal systems.

Yes, just one thin layer stands between you and potentially harmful substances.

These cells are connected by tight junctions that act as gatekeepers: letting nutrients in while keeping out toxins, pathogens, and undigested food. However, chronic stress, inflammation, toxins, food sensitivities, and dysbiosis can cause these junctions to loosen. The result is hyperpermeability, or what’s commonly called leaky gut.

When this happens, unwanted substances enter the bloodstream, triggering widespread inflammation and burdening the immune system.

And since the gut and brain are so interconnected, a leaky gut can often lead to a leaky brain, compromising the blood-brain barrier, which is essential for protecting your brain from harmful invaders.

Figure 2: Healthy Gut versus Leaky Gut (Credit: Mibrobiome lab)

The Vital Role of Good Bacteria

The good bacteria in your gut aren’t just along for the ride—they actively support your health by:

•   Breaking down complex carbs, fibre, and proteins into usable nutrients
•   Crowding out harmful microbes
•   Maintaining a strong gut lining
•   Reducing inflammation
•   Producing mood-regulating neurotransmitters like serotonin, GABA and dopamine
•   Regulating metabolism and blood sugar
•   Lowering risk for autoimmune and heart conditions
•   Supporting healthy weight management
•   Maintaining the integrity of the blood-brain barrier

The good news

Your gut microbiome isn’t fixed—you can actively improve it through diet, lifestyle, and stress management!
Think of your gut like a car park with limited spaces. You want to fill those spots with beneficial bacteria so harmful ones have nowhere to settle.

Unfortunately, modern habits work against this goal. Diets high in processed foods, sugar, and inflammatory oils disrupt your microbiome. Low fibre intake starves beneficial bacteria of the fuel they need to thrive.

How to Build a Healthier Gut

One of the best steps you can take is to diversify your diet.

Aim to eat 30 to 50 different types of fibre-rich foods each week, focusing on leafy greens, a wide range of vegetables, herbs and spices, nuts and seeds, grains, as well as beans and legumes.

Every trip to the market is a chance to add variety. Try new produce, whole grains, and spices. The more diverse your diet, the more resilient your microbiome.

Add more fermented food to your diet like sauerkraut, kefir, natto, kombucha, Pickles (fermented, not vinegar-brined), miso and yoghurt.

And don’t forget to eat the rainbow— berries, pomegranate, carrots, beetroot, purple cabbage. Different colours feed different gut microbes.

Lifestyle Also Matters

It’s not just what you eat—how you live affects your gut, too:
•   Move daily – Exercise supports gut motility and microbial balance
•   Sleep well – Poor sleep harms the microbiome
•   Manage stress – Chronic stress can weaken the gut lining and alter your microbiome

Your gut isn’t just about digestion. It shapes your immunity, mental health, energy levels, and even how you age.

With consistent, intentional changes—more fibre, fermented foods, regular movement, quality sleep, and stress care—you can build a healthier gut and, in turn, a healthier you.