Bloating: what causes it, which tests can help and how to reduce it

Gut microbiome imbalance and bacterial overgrowth

The gut is home to trillions of microorganisms that play a central role in digestion. When the balance of bacteria becomes disrupted, a condition known as dysbiosis, fermentation of undigested food increases, producing excess gas. Small intestinal bacterial overgrowth (SIBO) is a related pattern in which bacteria that normally reside in the large intestine colonise the small intestine. Carbohydrates reaching these misplaced bacteria are rapidly fermented, producing hydrogen and methane gases that cause distension, bloating after eating, and in some cases alternating constipation and diarrhoea. Bloating test UK searches often reflect people who have experienced bloating for months without a clear dietary explanation, and SIBO or dysbiosis is frequently the underlying mechanism.

Food intolerances and malabsorption

Lactose intolerance, fructose malabsorption, and sensitivity to fermentable carbohydrates (FODMAPs) are among the most common dietary drivers of bloating. When the gut lacks sufficient digestive enzymes, unabsorbed sugars reach colonic bacteria and are fermented, generating gas. The resulting bloating tends to be dose-dependent and timing-specific, appearing predictably after certain foods rather than constantly. A gut microbiome test can reveal the bacterial composition contributing to fermentation, while a blood panel can identify whether coeliac disease or nutrient deficiencies associated with malabsorption are present.

Coeliac disease and gluten sensitivity

Coeliac disease, which affects around 1 in 100 people in the UK, causes an immune reaction to gluten that damages the small intestinal lining. Bloating is a cardinal symptom, alongside diarrhoea, fatigue, and in some cases iron deficiency. Non-coeliac gluten sensitivity can produce similar bloating without the autoimmune mechanism. Both require investigation: coeliac disease can be identified through blood antibody testing (tTG-IgA) and genetic markers, while routine blood testing can rule out associated anaemia and nutrient deficiency.

Hormonal fluctuations and the gut-hormone axis

Bloating and hormones are closely connected, particularly in women. Oestrogen and progesterone both influence gut motility and fluid retention. Many women notice pronounced bloating in the week before menstruation, during perimenopause, and at other hormonal transition points. This hormonal bloating tends to shift across the cycle and is often accompanied by other symptoms such as mood changes, fatigue, or breast tenderness. A blood panel that assesses hormonal markers alongside inflammation and thyroid function provides a more complete picture.

Thyroid dysfunction and slowed gut motility

The thyroid regulates metabolic rate throughout the body, including the speed at which food moves through the digestive tract. An underactive thyroid reduces gut motility, allowing food to sit and ferment for longer before passing through. This creates a pattern of bloating and constipation that responds poorly to dietary changes alone, because the underlying driver is hormonal rather than nutritional. TSH, Free T4, and Free T3 are all relevant markers when bloating accompanies persistent fatigue and cold sensitivity.

Stress and the gut-brain axis

Chronic psychological stress alters gut function through the gut-brain axis, changing motility, increasing intestinal permeability, and shifting the composition of the microbiome. People under sustained stress often notice that gut symptoms worsen regardless of what they eat. Elevated cortisol suppresses digestive enzyme production and alters the balance of bacteria in the colon, which can amplify gas production and bloating. Inflammation markers such as CRP can reflect the systemic inflammation that often accompanies both stress and gut dysfunction.

Coexisting conditions that can present as bloating

Bloating can also be a symptom of conditions including inflammatory bowel disease, ovarian health changes, and in rare cases more serious underlying pathology. A persistent, progressive change in bloating, particularly when accompanied by unexplained weight loss, blood in stool, or bloating that does not shift across the day, warrants prompt GP assessment. The testing outlined on this page is most useful for people with established bloating patterns that have not responded to straightforward dietary changes.

Testing for bloating depends on whether the driver appears to be primarily gut-based, systemic, or a combination of both. A gut microbiome test provides a detailed analysis of bacterial composition, revealing dysbiosis patterns and populations associated with excessive gas production. A blood panel addresses the systemic layer: coeliac antibodies, thyroid markers, inflammation indicators, and nutrient status.

Stride Optimal Biome analyses the gut microbiome using stool sample sequencing, identifying the balance of bacterial species, markers of gut inflammation, and patterns associated with fermentation, IBS, and dysbiosis. It provides direct insight into whether the gut bacterial environment is contributing to persistent bloating.

Stride Optimal Bloods includes CRP (inflammation marker), TSH, Free T4, Ferritin, Vitamin D, Vitamin B12, tTG-IgA (coeliac screen), homocysteine, full lipid panel, HbA1c, and more.

Why both matter for bloating: persistent bloating rarely has a single cause. Testing the microbiome alongside systemic blood markers gives a complete picture of what is happening at the gut level and what systemic factors may be contributing. It also rules out conditions such as coeliac disease and thyroid dysfunction that are frequently missed because their bloating symptoms are attributed to diet. Both include a 1:1 expert consultation to walk through your results in the context of your specific symptoms.

If bloating has been present for a long time without investigation, the most useful starting point is identifying whether it is primarily gut-driven, systemic, or both. A GP can test for coeliac disease and thyroid function as a first step. A gut microbiome test adds the layer of bacterial composition that standard NHS tests do not cover.

Dietary approaches that support gut balance

The low-FODMAP approach, developed at Monash University, is the most extensively researched dietary intervention for bloating linked to fermentable carbohydrates. It involves temporarily restricting short-chain carbohydrates that are poorly absorbed and rapidly fermented, before reintroducing foods systematically to identify individual triggers. This is best undertaken with dietitian support, as long-term restriction can reduce microbiome diversity. Tracking symptoms alongside food choices, and ideally alongside biomarker data, gives a far more reliable picture than elimination alone.

Supporting microbiome diversity through food

A varied plant-based diet rich in different fibre types feeds a wider range of beneficial bacterial species. Research consistently shows that people eating 30 or more different plant foods per week have significantly greater microbiome diversity than those eating fewer. Fermented foods such as kefir, live yoghurt, and sauerkraut introduce beneficial bacteria and have been shown in controlled trials to increase microbiome diversity and reduce inflammatory markers. These are additive strategies that work alongside, rather than instead of, identifying the specific bacterial imbalances contributing to your pattern.

Managing the gut-brain-stress connection

Stress management is not a soft recommendation: it is mechanistically relevant to bloating. The vagus nerve, which runs between the brain and the gut, responds to psychological state and directly regulates gut motility, digestive enzyme production, and the inflammatory environment of the gut. Practices that measurably activate the parasympathetic nervous system, including diaphragmatic breathing, regular moderate exercise, and consistent sleep, have been shown to improve gut motility and reduce bloating frequency. Tracking biomarker shifts alongside lifestyle changes is the most reliable way to confirm whether a particular approach is working for your individual biology.

Addressing thyroid and hormonal contributors

If thyroid function is identified as a contributing factor, optimising thyroid hormone levels through appropriate medical management typically improves gut motility and reduces bloating within weeks to months. Hormonal bloating linked to the menstrual cycle often responds to targeted nutritional support for oestrogen metabolism, including adequate dietary fibre and cruciferous vegetables that support hepatic oestrogen clearance. Retesting relevant markers after a sustained period of dietary or lifestyle change provides objective evidence of whether the approach is making a difference.