Gut, Fatigue and Brain Fog
"All disease begins in the gut."
That saying is often attributed to Hippocrates, and after years in clinic, I truly believe there's deep wisdom in it.
When someone comes to me feeling tired and foggy, their gut is very often part of the story. And when we start caring for the gut, energy and mental clarity frequently begin to improve as a natural consequence. Whatever remains is usually much easier to work with.
How Your Gut and Brain Talk to Each Other
Your gut has its own nervous system, called the enteric nervous system. It's often described as your "second brain", containing around 500 million nerve cells and able to run much of your digestion on its own.
It's in constant conversation with your brain, mainly through the vagus nerve. Interestingly, most of that traffic flows upwards. Around 80 to 90 per cent of the vagus nerve's fibres carry messages from the gut to the brain.
So your brain is always listening to how your gut is doing. When the gut is inflamed, irritated or under strain, the brain can register that as fatigue, fog, low mood or anxiety.
The gut lining and the blood-brain barrier also work in remarkably similar ways. Both act as protective gatekeepers, and inflammation that weakens one appears to affect the other.
What I See in Clinic
Tired and foggy rarely come on their own.
The people I see often also have:
bloating, wind or fermentation
loose bowels, constipation, or both
food intolerances
a "nervous gut"
poor sleep
slow recovery from stress
little time or energy to prepare nourishing food
Each of these adds to the body's overall burden.
Sometimes this combination can be read as depression. Depression is real and deserves proper care, and I'd never want anyone to dismiss it. I simply believe it's worth looking at the gut and other physical contributors too, rather than rushing to a single conclusion.
The Stress–Gut Loop
Our gut is more of an emotional centre than we realise. It doesn't just digest our food. It also digests how we handle life.
Around 90 per cent of the body's serotonin is made in the gut. Serotonin helps us feel calm, safe and settled. While gut serotonin doesn't travel directly into the brain, it influences mood through the vagus nerve and the gut's wider signalling.
When we're stressed, we produce more stress hormones. These can change the balance of our gut microbes. As the gut becomes unsettled, it sends signals back to the brain that something is wrong, which creates more stress. And the cycle continues.
Stress also affects us mechanically. The nerves in the gut tighten, our breathing becomes shallow, and the diaphragm moves less. That reduces blood flow, oxygen and the natural movement of the gut.
This is why I find working from both directions, gut health alongside mental and emotional health, tends to bring greater, faster and longer-lasting results.
What Testing Can Reveal
Many different causes can create the same symptoms. Testing helps us narrow things down and treat the individual rather than guess.
Microbiome mapping is one of my most useful tools here. It can show markers of inflammation and gut permeability, how well you're digesting, whether opportunistic bacteria or yeasts are overgrowing, and whether you have enough of the beneficial "good guys".
Mineral testing is also valuable for brain fog. Every cell runs on energy, called ATP, produced by the mitochondria. That process depends on vitamins and minerals as its building blocks. A mineral test can reveal specific deficiencies or excesses that symptoms alone can't show.
Where I See Things a Little Differently
Probiotics. Probiotics can be very helpful, but they're not all the same. Different strains suit different situations, such as loose bowels, constipation, bloating, or even iron absorption. My preference is to choose the right one for the right condition at the right time, then take it in cycles and rotate.
What we're really aiming for is diversity. Your gut is a competitive environment. With enough beneficial microbes, there's less room for inflammatory species and yeasts such as candida to take hold. Rather than relying on one product forever, I'd rather support a rich and varied community.
Elimination diets. The low FODMAP diet, developed here in Australia at Monash University, can be very helpful for people with significant IBS symptoms. When the gut is inflamed, reducing extra stress on it makes sense.
But it's designed to be temporary. I prefer people only remove the foods they actually react to, rather than everything on the list. Many of these foods are genuinely healthy and help build a diverse microbiome.
The wonderful part is that once we repair the gut and address what's been keeping symptoms going, many people can return to the foods they once had to avoid.
Caffeine. Caffeine can be helpful, but it can also irritate the gut, affect women's hormones, and reduce iron absorption. I think of it as a foot on the accelerator, drawing out whatever is left in the tank.
It may be wiser to refill the tank properly first, and then caffeine becomes a pleasure rather than a crutch.
Three First Steps
If you're tired, foggy and your gut isn't happy, here's where I'd start:
See a functional medicine practitioner who can look at the whole picture.
Run a microbiome mapping test to see what's actually happening in your gut.
Keep a food and symptom diary to start noticing which foods you react to.
When to See Your GP
Please see your doctor if you notice blood in your stools, unexplained weight loss, a persistent change in bowel habits, symptoms that wake you at night, ongoing fever or severe abdominal pain, or if you have a family history of bowel cancer, coeliac disease or inflammatory bowel disease.
And if your mood has been low for some time, please talk to your GP as well. Caring for your gut and caring for your mental health work beautifully together.
Settling the Gut, Clearing the Mind
Brain fog and fatigue can feel frustrating and hard to explain. Very often, the gut holds important clues.
When we calm and repair the gut while also supporting the nervous system, clarity and energy often have room to return.
If you'd like to explore what's happening in your gut, I'd love to help. You're welcome to book a free discovery call, and we can look at the bigger picture together.
Rosemary Bui
Integrative Pharmacist and Holistic Health Strategist