Could your gut be contributing to brain fog?

A growing body of research suggests that digestive health may play an important role in how clearly the brain functions day to day. While we often think of the gut and brain as separate systems, they are in constant communication, and disruption on one side can be felt on the other.

If you walk into a room and forget why you went in there, lose your train of thought mid-conversation, can't quite find the words you need or need to reread the same paragraph three times before it sinks in (not necessarily once in a while, but often), these are all common experiences of what's often called "brain fog". It isn't a medical diagnosis in itself, but a collection of cognitive symptoms affecting memory, concentration, mental clarity and processing speed.

There are many possible causes, including poor sleep, chronic stress, hormonal changes, medication and blood sugar fluctuations. But increasingly, scientists are also looking at the gut microbiome as part of the picture.

 The gut-brain axis

Your digestive system and brain communicate through a complex, two-way network known as the gut-brain axis. This involves the vagus nerve, the enteric nervous system (often called the "second brain"), immune signalling, hormones and the substances produced by trillions of gut bacteria.

The gut microbiome, the community of bacteria, fungi and other microorganisms living in your digestive tract, helps digest food, supports immunity and produces compounds that may influence brain function. Emerging evidence suggests that gut microbiota composition can influence brain function, behaviour and cognition, though the relationship is complex and likely works in both directions rather than as a simple cause and effect.

 How digestive health may influence mental clarity

Several overlapping mechanisms may help explain why digestive symptoms and brain fog can occur together.

Inflammation

When the digestive tract is irritated, immune chemicals may enter the circulation and contribute to wider, low-grade inflammation. Persistent inflammation may interfere with communication between brain cells, and gut bacteria are understood to produce metabolites that affect mucosal immunity and immune responses in ways that go on to influence cognitive function.

Some people notice their mental clarity dips alongside digestive symptoms such as bloating or altered bowel habits, though this doesn't necessarily mean inflammation is the sole cause.

Microbial metabolites

Gut bacteria ferment dietary fibre into short-chain fatty acids (SCFAs) such as butyrate. These help nourish the cells lining the colon, support the intestinal barrier and regulate immune activity, and are also thought to play a role in gut-brain signalling. The enteric nervous system, with close to 100 million neurons of its own, communicates with the brain via neural, endocrine and immune pathways, with gut-derived SCFAs and neurotransmitters acting as local chemical messengers along the way.

Nutrient absorption

The brain relies on a steady supply of nutrients, and digestive conditions that interfere with digestion or absorption can increase the risk of deficiency. Vitamin B12, folate, iron, vitamin D, magnesium and omega-3 fatty acids are all particularly relevant to cognitive and neurological health.

Many bowel conditions and diseases, along with certain medications, can all affect nutrient status, which is one reason persistent brain fog shouldn't automatically be put down to stress or ageing.

Blood sugar fluctuations

A meal dominated by refined carbohydrates can cause blood glucose to spike and then fall, and for many people this is accompanied by tiredness, irritability or a mid-afternoon slump in concentration. Combining carbohydrates with protein, fibre and healthy fats can help provide a steadier release of energy throughout the day.

Constipation and slow motility

Constipation is associated with altered gut microbiota, reduced microbial fermentation and changes in gut-brain signalling, and may also disrupt sleep, both of which can affect concentration. It's worth considering the whole picture, including hydration, fibre intake, thyroid function and activity levels, rather than viewing bowel and brain as unconnected.

Stress and sleep

The gut-brain relationship works both ways: stress can alter gut motility and microbial composition, while ongoing digestive discomfort can raise anxiety and disturb sleep. If bloating, reflux or bowel urgency regularly wakes you at night, your brain fog may be driven as much by sleep disruption as by anything happening in the gut itself.

Is brain fog related to a specific food?

It's tempting to pin brain fog on one culprit, such as gluten, dairy or sugar. But removing multiple foods without good reason can reduce dietary variety, fibre and nutrient intake, and may make matters worse rather than better.

A genuine allergy or bowel disease or diagnosed intolerance needs proper management, but for most people it's more useful to look at overall eating patterns, meal timing and digestive function than to label individual foods as universally "good" or "bad". Keeping a short food, symptom, sleep and bowel diary can help identify genuine patterns worth investigating further.

 Supporting your gut and brain together

There's no single "brain fog diet", but a few foundations tend to support both digestive and cognitive health:

• Eat regular, balanced meals containing protein, fibre and healthy fats.
• Include a wide variety of vegetables, fruits, pulses, nuts, seeds and whole grains, increasing fibre gradually if your intake is currently low.
• Choose omega-3-rich foods such as oily fish where appropriate.
• Stay well hydrated to support bowel regularity.
• Include fermented foods such as live yoghurt or kefir if they agree with you.
• Reduce reliance on ultra-processed foods that crowd out more nutrient-dense choices.
• Prioritise consistent sleep and waking times.
• Move regularly, as activity supports motility, metabolic health and brain function.
• Avoid taking multiple supplements or random probiotics without first considering what's actually driving your symptom.

When to seek further help

Because brain fog has so many potential causes, ongoing or worsening symptoms are worth discussing with your GP, who may want to check iron, vitamin B12, folate, thyroid function or blood glucose. Seek urgent medical advice if cognitive changes appear suddenly, or occur alongside facial weakness, difficulty speaking, severe headache, loss of balance or significant confusion.

A nutritional therapist can look at your diet, digestive symptoms, bowel habits, medications and lifestyle together to help identify what may be contributing, working alongside your medical team where appropriate. The gut is rarely the only piece of the brain fog puzzle, but for many people, it's one worth paying closer attention to.

 References

• Alavian F, Safaeian M. How the gut microbiome shapes learning and memory: A comprehensive review. IBRO Neurosci Rep. 2025 Aug 11;19:491-506. doi: 10.1016/j.ibneur.2025.08.005. PMID: 41601564; PMCID: PMC12834025.
• Liu, X., et al. (2026). Gut microbiota impact on cognitive function in humans. Nutrients, 18(3), 369. 
• Dipalma, G., Marinelli, G., Ferrante, L., et al. (2025). Modulating the gut microbiota to target neuroinflammation, cognition and mood: A systematic review of human studies with relevance to fibromyalgia. Nutrients, 17(14), 2261.