Brain fog, anxiety, or low mood that tests can’t explain? Learn how the gut-brain connection works, what functional medicine looks for, and where to start.
You have been told your blood tests are normal. Yet you are exhausted, your thinking feels slow, your mood is flat
or your anxiety is constant, and your digestion has never quite been right.
If that sounds familiar, I want you to know two things. First, you are not imagining it. Second, these symptoms may
not be separate problems at all.
In my clinic in Edinburgh, I see this pattern again and again. Someone arrives with brain fog and fatigue, and as we
dig in, there is a gut story underneath: years of bloating, irregular bowels, antibiotics, food reactions or a period of
intense stress. It is not a coincidence. It is the gut-brain connection, and it is one of the most important ideas in
modern medicine.
Your gut and your brain are in constant two-way conversation. Researchers call this the microbiota-gut-brain
axis, and it works through several channels at once:
- The vagus nerve. This long nerve runs from your brainstem to your abdomen, and most of its fibres carry
information from the gut up to the brain, not the other way around. Your gut is constantly telling your brain
how things are going.
- The enteric nervous system. Your digestive tract has its own network of hundreds of millions of neurons,
often called the “second brain”. It can operate largely independently and communicates continuously with
the one in your head.
- Neurotransmitters. The majority of your body’s serotonin, the chemical most associated with mood, is
made in the gut, not the brain. Gut bacteria also influence GABA, dopamine and the precursors your body
needs to make them.
- The immune system. Around 70% of immune tissue sits in and around the gut. When the gut is inflamed or
irritated, immune signals travel through the blood and can influence the brain.
- The stress response. Your HPA axis, the system that governs cortisol, is wired into the gut. Stress
changes digestion, and an unhappy gut feeds back into the stress response.
Put simply: what happens in your gut does not stay in your gut.
When the gut environment is out of balance, the effects can appear far from the digestive system. Depending on
the person, I see:
- Brain fog, poor concentration and memory lapses
- Anxiety that seems out of proportion or has no clear trigger
- Low mood or a sense of flatness
- Fatigue that sleep does not fix
- Poor sleep and early waking
- Worsening menopausal symptoms, as the gut plays a role in how oestrogen is processed and cleared
It is important to say this clearly: gut health is rarely the only factor. Hormones, nutrient status, sleep, stress, thyroid
function and genetics all matter. But the gut is so often the missing piece that conventional work-ups do not look at.
Functional medicine asks why symptoms are happening, rather than simply naming them. When we look at the gut-
brain axis, these are the root causes I most often investigate.
Your gut is home to trillions of microbes. A diverse, balanced community produces short-chain fatty acids such as
butyrate, which feed the cells lining your gut, calm inflammation and support brain health. When diversity falls, or
less helpful species dominate, those protective effects weaken. Common triggers include repeated antibiotics, a
low-fibre or highly processed diet, chronic stress, infections and certain medications.
The gut lining is meant to be selective, letting nutrients through while keeping unwanted material out. When it
becomes more permeable (often called “leaky gut”), bacterial fragments and food particles can reach the immune
system and trigger low-grade, body-wide inflammation. Research links this kind of inflammation with mood changes
and cognitive symptoms. Permeability is an area of active research, and I treat it as one piece of the picture, not a
catch-all explanation.
Bacteria in the wrong place, or low-level parasitic or yeast overgrowth, can cause bloating, nutrient malabsorption
and inflammatory signals. These are frequently missed unless someone looks for them.
If the gut is not absorbing well, the brain pays the price. Iron, B12, folate, magnesium and zinc all matter for
neurotransmitter production and energy, and low levels often sit behind “normal” results that are only within range,
not optimal.
Long-term stress changes gut motility, reduces microbial diversity and increases permeability. It is a loop: stress
harms the gut, and a stressed gut amplifies the stress response.
I did not arrive at this work from a textbook alone. I recovered from inflammatory bowel disease using the
integrative approach I now use with patients. I know first-hand how unresolved gut problems affect energy, clarity
and confidence, and how it feels to be told there is nothing more to be done.
Over 20 years as a biomedical scientist, acupuncturist and Functional Medicine Practitioner, and after working with
more than 2,000 people, the gut-brain link is the thread I see running through conditions that are usually treated in
isolation.
Rather than treating your brain fog in one appointment and your bloating in another, we look at the whole system.
1. We listen to the full story. Timelines matter. When did symptoms start? What happened in the year before:
infection, antibiotics, bereavement, a baby, menopause?
2. We test, not guess. Where appropriate, advanced diagnostics can assess your microbiome, digestive function,
inflammation, nutrient levels and hormones, giving us data rather than assumptions.
3. We build a personalised plan. This usually combines nutrition, targeted supplements, lifestyle and stress
support, and sometimes acupuncture or biofeedback to calm the nervous system.
4. We work in phases. A typical approach is to remove what is driving the problem, replace what is missing,
repopulate beneficial bacteria, repair the gut lining and rebalance the nervous system.
These are not a substitute for personalised care, but they are sensible foundations for most people:
1. Eat the diversity. Aim for a wide range of plant foods across the week: vegetables, fruit, legumes, nuts,
seeds, herbs and wholegrains. Variety feeds a varied microbiome.
2. Add fermented foods gradually. Live yoghurt, kefir, sauerkraut or kimchi in small amounts. If you have
significant bloating, introduce them slowly.
3. Protect your sleep. Poor sleep disrupts both the microbiome and mood regulation. A consistent bedtime
and morning light make a real difference.
4. Build a daily nervous system reset. Even five minutes of slow breathing (a longer exhale than inhale)
activates the vagus nerve and shifts you out of stress mode.
5. Be thoughtful with unnecessary medication. Never stop prescribed medicines without medical advice,
but do ask whether long-term use of antibiotics, acid suppressants or anti-inflammatories is still needed.
Please see your GP promptly if you notice blood in your stool, unexplained weight loss, persistent vomiting,
difficulty swallowing, or a significant, sustained change in bowel habit. These need proper investigation first.
If your tests have come back normal but you still do not feel well, and you suspect your gut and brain are part of the
same story, that is where functional medicine can help.
If you are tired of being told it is “just stress”, I would love to help you find out what is really going on.
- Book a 1:1 consultation to explore your symptoms, history and testing options.
- Join one of my online workshops, including Brain Vitality and Menopause Journey, to get started with
practical, science-backed guidance.
- Download the free guide: “5 Blood Markers Your GP Doesn’t Test For” and learn what a deeper look
can reveal.
You have spent long enough being dismissed. Your symptoms are real, and they have a cause.