Gut health problems: why your digestion is off and how to find out

Dysbiosis: an imbalance in the gut microbiome

Dysbiosis describes a disruption of the normal microbial balance in the gut, characterised by reduced diversity, overgrowth of potentially harmful species, and loss of beneficial bacteria that produce key metabolites including short-chain fatty acids (SCFAs) such as butyrate. Butyrate is the primary fuel source for colonocytes (the cells lining the colon) and plays a direct role in maintaining gut barrier integrity, suppressing inflammation, and regulating immune responses. When butyrate-producing bacteria such as Faecalibacterium prausnitzii and Roseburia decline, the downstream effects ripple across multiple systems far beyond digestion.

Ultra-processed diet and low fibre intake

The single most impactful driver of gut dysbiosis at a population level is dietary fibre insufficiency combined with high ultra-processed food consumption. Gut bacteria feed primarily on dietary fibre (particularly fermentable polysaccharides), producing SCFAs as a byproduct. Most UK adults consume well below the recommended 30g of fibre per day. Ultra-processed foods contain emulsifiers, artificial sweeteners, and preservatives that directly alter gut bacterial composition, reduce diversity, and disrupt the mucus layer protecting the gut lining. Research consistently shows that people consuming 30 or more different plant foods per week have significantly higher gut microbiome diversity than those eating a narrower range.

Antibiotic use

Antibiotics are the most potent known disruptor of the gut microbiome. A single course can reduce bacterial diversity by 30 to 90 per cent, with some species taking months to years to recover. Repeated antibiotic courses, common in childhood and recurring infections, cumulatively deplete bacterial diversity in ways that can persist into adulthood. The disruption created by antibiotics is also a common trigger for post-antibiotic IBS, food sensitivities, and recurrent digestive problems in people who previously had no gut symptoms.

Chronic stress and the gut-brain axis

The gut and brain are in constant bidirectional communication through the enteric nervous system, vagus nerve, and systemic signalling via gut-derived neurotransmitters. Approximately 90 per cent of the body's serotonin is produced in the gut, and gut bacteria directly influence its production. Chronic psychological stress alters gut motility, increases gut permeability (allowing bacterial compounds to enter circulation), and shifts the microbiome composition toward bacteria associated with inflammation. This explains the common clinical observation that gut symptoms worsen dramatically during periods of sustained stress or psychological difficulty.

Impaired gut barrier integrity (leaky gut)

The gut barrier is a single-cell-thick lining that separates the gut lumen from the bloodstream. When bacterial diversity declines and butyrate production falls, the integrity of tight junction proteins that seal this barrier weakens, allowing bacterial fragments and undigested food particles to enter circulation. This triggers systemic low-grade inflammation and immune activation, which has been linked to conditions including autoimmune disease, skin conditions, joint pain, and brain fog. Zonulin, a protein that regulates tight junction permeability, is elevated in people with increased gut permeability and can be measured in stool or blood.

Sleep disruption

The gut microbiome follows a circadian rhythm, with different bacterial communities becoming more or less active across the day-night cycle. Chronic sleep restriction and irregular sleep timing disrupt this rhythm, shifting the microbiome toward compositions associated with metabolic dysfunction, higher inflammation, and impaired glucose metabolism. People with consistently poor sleep show measurably lower microbiome diversity than those with regular, adequate sleep, independent of diet and other lifestyle factors.

Medications beyond antibiotics

Proton pump inhibitors (PPIs), commonly prescribed for acid reflux, alter the gut's pH environment in ways that reduce diversity in the small intestine and promote overgrowth of species associated with dysbiosis. Non-steroidal anti-inflammatory drugs (NSAIDs) increase gut permeability and disrupt the protective mucus layer. Many other common medications, including some antidepressants, metformin, and certain blood pressure medications, have measurable effects on microbiome composition that are increasingly recognised in the research literature.

Standard NHS testing for gut symptoms typically involves stool tests to rule out infection or blood, blood tests to exclude coeliac disease, thyroid dysfunction, and anaemia, and in persistent cases a referral for colonoscopy or endoscopy. These investigations are important for excluding serious pathology, but they do not assess the composition or function of the microbiome, which is the primary driver of functional gut symptoms in the majority of people without structural disease.

A comprehensive gut microbiome test uses DNA sequencing of a stool sample to identify and quantify the thousands of bacterial species living in your large intestine. Unlike traditional stool cultures (which only grow a limited number of species in the lab), DNA sequencing captures the full microbial picture. The assessment includes:

Bacterial diversity is a primary indicator of gut health. Higher diversity is associated with better metabolic function, more robust immune regulation, and greater resilience to dietary or environmental perturbation. Low diversity is a consistent finding in people with IBS, inflammatory bowel conditions, obesity, type 2 diabetes, and metabolic syndrome.

Beneficial and potentially harmful species are assessed relative to population norms. Key beneficial species include Akkermansia muciniphila (which supports gut barrier integrity and metabolic health), Faecalibacterium prausnitzii (a major butyrate producer and anti-inflammatory species), and Bifidobacterium species (important for SCFA production and immune regulation). Key potentially harmful overgrowths include Clostridium difficile, pathogenic E. coli strains, and Candida yeast species.

Functional markers including short-chain fatty acid production capacity, gut permeability indicators, and inflammatory markers (such as calprotectin) add clinical context to the composition data by showing not just which bacteria are present but what they are producing and what the gut environment looks like.

For people with persistent gut symptoms, combining a microbiome test with a blood panel (checking for coeliac antibodies, thyroid function, anaemia, and inflammatory markers) gives the most complete investigation. Blood markers can identify conditions that cause gut symptoms secondary to another process, while microbiome testing investigates the primary gut ecosystem. Your expert consultation can help determine which combination is most relevant to your symptom profile.

Dietary diversity and the 30-plant rule

Consuming 30 or more different plant foods per week is the single most consistently evidence-supported dietary approach to improving gut microbiome diversity. Plant foods include vegetables, fruits, legumes, whole grains, nuts, seeds, and herbs: variety is more important than quantity, since different bacteria specialise in fermenting different types of fibre and polyphenols. A narrow diet, even a healthy one, can selectively favour certain bacterial communities at the expense of overall diversity.

Fermented foods and live cultures

Regular consumption of fermented foods (natural yogurt with live cultures, kefir, sauerkraut, kimchi, miso, kombucha) has been shown in randomised controlled trials to increase microbiome diversity and reduce inflammatory markers more effectively than a high-fibre diet alone over a six-week period. The mechanism involves both direct introduction of live bacterial cultures and the metabolites produced during fermentation, which create a gut environment that supports existing beneficial species.

Stress management and the vagus nerve

Given the direct bidirectional connection between the gut and the nervous system, stress management interventions with evidence for gut benefit include regular aerobic exercise (which increases vagal tone and directly modulates gut bacterial composition), mindfulness and breathwork (which activate the parasympathetic nervous system and reduce gut motility dysregulation), and adequate sleep. These are not peripheral suggestions but mechanistically direct interventions for the gut-brain axis.

Targeted probiotic and prebiotic supplementation

Not all probiotic supplements have the same evidence base or species composition. Specific strains with meaningful clinical evidence for gut health include Lactobacillus rhamnosus GG (for post-antibiotic recovery and IBS), Bifidobacterium longum (for gut barrier function and anxiety), and Saccharomyces boulardii (a yeast probiotic effective in reducing C. difficile recurrence and traveller's diarrhoea). Prebiotic fibres (inulin, FOS, GOS, resistant starch) feed existing beneficial bacteria and are often more impactful than adding new strains. Knowing your microbiome composition helps identify which targeted interventions are most likely to benefit your specific bacterial profile.