Introduction
Many of us are familiar with that uncomfortable, heavy sensation after a meal—the stubborn afternoon bloating, unpredictable bowel movements, or the persistent lethargy that leaves you wondering why your digestion feels so unpredictable. When your stomach feels unsettled, it is easy to assume you need an exotic supplement or an intense dietary overhaul. In reality, supporting your digestive system often begins by identifying and reducing the everyday items that actively disrupt your internal environment.
Your gut is not simply a biological processing tube for food. It is a bustling, complex ecosystem home to trillions of micro-organisms—collectively known as the gut microbiome—that influence everything from nutrient absorption and immune defence to mood regulation and metabolic health. When this delicate ecosystem is fed foods that promote inflammation, irritate the intestinal lining, or starve beneficial microbes, your digestion quickly signals its distress.
This guide explores what foods not to eat for gut health, explains the physiological mechanisms behind digestive irritation, and provides practical, wholesome alternatives. We will also examine how to recognise when your digestive complaints warrant a closer medical look. For a broader introduction to the subject, explore this guide to how to improve gut and digestive health.
At Blue Horizon, we believe that sustainable health decisions come from understanding the broader clinical picture rather than jumping to rapid conclusions. We advocate a phased, sensible approach: start by speaking with your GP to rule out underlying medical conditions, monitor your daily habits and symptoms with structured self-tracking, and consider targeted blood tests if you need deeper clinical insight into systemic inflammation, nutritional status, or metabolic function.
Understanding the Gut Microbiome and Digestion
To understand why certain foods cause digestive disruption, it helps to examine how the gastrointestinal tract functions when operating smoothly.
From the moment you swallow, food journeys through the oesophagus into the stomach, where gastric juices and acids break down proteins. It then moves into the small intestine, where digestive enzymes from the pancreas and bile from the liver break down fats, carbohydrates, and proteins into microscopic molecules for absorption into the bloodstream. Whatever cannot be digested passes into the large intestine (colon).
Oesophagus ➔ Stomach ➔ Small Intestine ➔ Large Intestine (Colon)
(Transit) (Acid Breakdown) (Enzyme Digestion) (Microbial Fermentation)
The colon is where the vast majority of your gut microbes reside. Think of your gut microbiome as a diverse botanical garden. Beneficial bacteria flourish when nourished with diverse plant fibres and polyphenol compounds. In return, these bacteria ferment these fibres into short-chain fatty acids (SCFAs), such as butyrate, acetate, and propionate. SCFAs nourish the cells lining the colon, reinforce the protective mucosal barrier, and help regulate systemic inflammation.
When you consume foods that are nutrient-poor, heavily processed, or laden with chemical additives, the ecological balance shifts. Beneficial species struggle to survive, while opportunist organisms multiply. This imbalance—known clinically as dysbiosis—can weaken the gut's mucosal barrier, slow or excessively accelerate transit time, and trigger digestive discomfort. You can learn more about this process in this guide to checking the gut microbiome.
Key Takeaway: A balanced gut relies on a resilient community of microbes and a sturdy mucosal barrier. Disruptive foods can alter microbial diversity and irritate the intestinal wall, leading to symptoms like bloating, gas, and irregular bowel habits.
Gut Health
What Foods Not to Eat for Gut Health: 7 Key Disruptors
While individual tolerances vary, research has identified several categories of food and ingredients that consistently undermine microbial balance, irritate the gut lining, and impede normal digestive motility.
1. Ultra-Processed Foods and Industrial Additives
Ultra-processed foods (UPFs)—such as ready meals, packaged snack cakes, industrial sliced breads, and processed meats—make up a large proportion of the modern Western diet. These items are systematically stripped of natural fibre, vitamins, and minerals while being fortified with artificial flavours, stabilisers, and emulsifiers.
Emulsifiers (such as polysorbate-80, carboxymethylcellulose, and mono- and diglycerides) are added to processed foods to improve texture and extend shelf life. However, physiological studies suggest that these compounds can act much like detergents in the digestive tract. They can erode the delicate layer of mucus that coats and protects the intestinal wall. When this mucosal barrier thins, bacteria come into closer contact with the epithelial cells underneath, which can provoke low-grade intestinal inflammation and digestive sensitivity.
2. Artificial Sweeteners and Sugar Alcohols
Non-nutritive artificial sweeteners (such as sucralose, aspartame, and saccharin) are widely marketed as healthy alternatives to sugar. While they reduce calorie counts, their impact on the microbiome can be problematic.
Research indicates that certain artificial sweeteners can alter the composition and metabolic activity of gut bacteria. Furthermore, polyols or sugar alcohols (such as sorbitol, xylitol, and maltitol), frequently found in "sugar-free" confectionery, chewing gums, and protein bars, are poorly absorbed in the small intestine. When they travel down to the colon, they exert an osmotic effect—drawing large volumes of water into the bowel—while being rapidly fermented by bacteria. This commonly results in watery stools, abdominal cramping, and severe flatulence.
3. Greasy, Deep-Fried Foods and Industrial Trans Fats
Fried takeaway foods, battered items, and pastries cooked in repeatedly heated vegetable oils present a double challenge for the digestive tract:
- Delayed Gastric Emptying: High concentrations of heavy fats trigger the release of hormones that slow down stomach emptying. This prolonged digestion often leads to feelings of intense fullness, nausea, and upper abdominal pressure.
- Lower Oesophageal Sphincter Relaxation: High-fat meals can cause the muscular valve at the top of the stomach to relax, allowing acidic gastric contents to escape upward into the oesophagus, causing heartburn and acid reflux.
- Bile Acid Alterations: Digesting large amounts of low-quality fats requires the liver and gallbladder to secrete significant amounts of bile acids. In the colon, excess unabsorbed bile acids can irritate the bowel wall, promoting loose stools and altering bacterial strains.
4. Excessive Added Refined Sugars
A diet high in refined table sugar, high-fructose corn syrup, and sweetened beverages can disrupt the delicate balance of your intestinal flora. Simple sugars are rapidly absorbed in the upper digestive tract, but when consumed in excess, they spill into the lower bowel.
Refined sugars can feed fast-growing, less beneficial micro-organisms, allowing them to outcompete beneficial bacterial strains that depend on complex dietary fibres. Over time, high-sugar diets have been associated with a reduction in microbial diversity and an increase in gut wall permeability, impairing the natural barrier function of the intestine.
5. Excessive Alcohol and High-Caffeine Carbonated Drinks
What you drink has just as profound an effect on your digestive tract as what you eat:
- Alcohol: Ethanol is a direct mucosal irritant. It disrupts the tight junctions between intestinal epithelial cells, allowing unwanted particles to pass into the circulation. Chronic or heavy drinking alters the gut microbiome, suppresses digestive enzyme secretion, and frequently causes sudden bowel urgency.
- Excess Caffeine and Carbonation: While moderate plain coffee or tea can provide beneficial polyphenols for some, high caffeine intake stimulates gastric acid production and speeds up gut motility excessively. When combined with carbonation (such as in energy drinks or fizzy colas), the gas introduces physical distension in the stomach, worsening bloating, belching, and acid reflux.
Dietary Disruptor Primary Digestive Impact
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Ultra-Processed Emulsifiers ➔ Thins the protective intestinal mucus layer
Sugar Alcohols / Polyols ➔ Draws water into colon; causes cramps/gas
Deep-Fried Foods ➔ Delays stomach emptying; triggers acid reflux
Excess Refined Sugar ➔ Promotes dysbiosis; reduces microbial diversity
High Alcohol Intake ➔ Irritates mucosal lining; increases permeability
6. Processed and High-Fat Charred Meats
Processed meats—such as sausages, bacon, ham, and hot dogs—frequently contain chemical preservatives like nitrates and nitrites, alongside high levels of sodium and saturated fat.
When gut bacteria break down compounds found abundantly in red and processed meats (such as L-carnitine and choline), they produce a metabolite called trimethylamine (TMA), which the liver converts into trimethylamine N-oxide (TMAO). High circulating levels of TMAO are associated with vascular inflammation and altered metabolic health. Additionally, cooking fatty meats at very high temperatures creates heterocyclic amines and polycyclic aromatic hydrocarbons, which can irritate the digestive lining and reduce the overall diversity of beneficial bacteria in the colon.
7. Overly Pungent or Harsh Spices (For Sensitive Individuals)
Culinary herbs and spices such as turmeric, ginger, and cumin offer natural antioxidant and anti-inflammatory properties. However, hot spices containing high concentrations of capsaicin (found in chillies, cayenne pepper, and hot sauces) can overstimulate pain and thermal receptors in the gastrointestinal tract.
For individuals with a sensitive stomach or an irritated bowel, capsaicin can accelerate transit time through the intestines too quickly, leading to abdominal pain, burning sensations, and loose stools. If you notice clear discomfort following spicy meals, it is wise to reduce the heat level in favour of gentler flavourings like fresh herbs, rosemary, thyme, and mild ginger.
Foods Marketed as "Healthy" That May Disrupt Digestion
It is relatively straightforward to recognise that greasy fast food is detrimental to gut health. However, many people unknowingly disrupt their digestion by relying on items marketed as wellness foods.
Sweetened Fruit Yoghurts
While natural, live yoghurt is an exceptional source of beneficial probiotic cultures, many commercially flavoured varieties are packed with added refined sugars, artificial syrups, and thickeners. A single pot of flavoured yoghurt can contain as much sugar as a small dessert, which can counteract the benefits of its live bacteria. Always opt for plain, unflavoured natural yoghurt or Greek yoghurt, adding your own fresh berries for natural sweetness.
Mass-Market "Brown" and "Wheat" Breads
Shoppers often choose sliced brown bread believing it to be a high-fibre wholefood. However, many supermarket loaves are simply refined white flour coloured with caramelised sugars and packed with shelf-extending emulsifiers and preservatives. These commercial additives can irritate the gut lining. Choosing traditionally fermented wholemeal sourdough or 100% whole-grain loaves with minimal, recognisable ingredients provides true prebiotic fibre without the unwanted additives.
Heavily Processed Plant-Based Meat Substitutes
Plant-based eating offers substantial benefits for gut health when centered on whole vegetables, beans, lentils, and nuts. However, highly processed meat alternatives are often constructed from isolated soy or pea proteins, bound together with industrial gums, refined vegetable oils, and heavy flavour enhancers. These refined mixtures lack the natural cellular structure of whole plants and can be difficult for a sensitive gut to process smoothly.
"Light" and "Diet" Snack Bars
Protein bars, keto snacks, and low-calorie diet treats frequently use a combination of refined protein isolates, synthetic fibres (like soluble corn fibre), and artificial sweeteners or polyols to keep calorie counts low. This artificial mixture is a common culprit behind unexplained bloating, stomach gurgling, and wind.
Herbal Laxative Teas
Many over-the-counter "detox" or "slimming" teas contain senna or cascara. These are stimulant herbal laxatives that work by directly irritating the nerves in the bowel wall to force muscular contractions. While they may produce a quick bowel evacuation, regular use can damage intestinal nerve function, lead to electrolyte imbalances, and worsen chronic sluggishness once stopped.
Clinical Caution: If you experience sudden, severe abdominal pain, persistent vomiting, unexplained weight loss, or notice blood in your stool, do not attempt dietary adjustments on your own. These are red-flag symptoms that require prompt evaluation by your GP or urgent medical attention via NHS 111, A&E, or 999.
How Dietary Disruption Affects the Body Beyond the Tummy
The effects of consuming gut-disrupting foods extend far beyond occasional bloating or indigestion. Because the digestive tract is intricately connected to the rest of the body, poor gut health can contribute to a range of systemic symptoms. This broader perspective is also discussed in this guide to improving gut health and digestive wellbeing.
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│ Poor Dietary Choices │
│ (UPFs, Refined Sugars, Additives, Fat) │
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│ Gut Dysbiosis & Mucosal Irritation │
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│
┌──────────────────────────┼──────────────────────────┐
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┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐
│ Systemic Energy │ │ Skin Health & │ │ Nutrient │
│ & Brain Fog │ │ Flare-ups │ │ Malabsorption │
│ (Gut-Brain Axis)│ │ (Inflammation) │ │ (Iron, B12, D3) │
└─────────────────┘ └─────────────────┘ └─────────────────┘
Energy Levels and Post-Meal Lethargy
An inflamed or imbalanced gut can impair energy production. When the microbiome is out of balance, the body expends significant immunological energy managing low-grade inflammation along the intestinal tract. Furthermore, meals high in refined carbohydrates and unhealthy fats cause rapid spikes and steep drops in blood glucose, leaving you feeling drained, foggy-headed, and sluggish shortly after eating.
Skin Flare-Ups
The "gut-skin axis" describes the complex dialogue between your gastrointestinal health and your skin. Inflammatory mediators produced in an irritated bowel can circulate throughout the body, potentially contributing to skin barrier disruption, increased skin sensitivity, and flare-ups of conditions such as eczema, acne, or general dryness.
The Gut-Brain Axis and Mood
The gut produces a vast array of neurotransmitters and chemical messengers, including a significant proportion of the body's serotonin. The vagus nerve serves as a direct bi-directional communication highway between the enteric nervous system in the gut and the central nervous system in the brain. When gut microbes are disrupted by poor nutrition, signals sent to the brain can contribute to feelings of heightened stress, irritability, and low mood.
Nutrient Absorption and Deficiencies
A healthy intestinal lining is covered in millions of microscopic finger-like projections called villi, which absorb essential micronutrients from your food. Chronic irritation and dysbiosis can flatten or inflame these delicate structures. Over time, this may compromise your body's ability to efficiently absorb critical vitamins and minerals, such as iron, active vitamin B12, folate, vitamin D, and magnesium.
What to Eat Instead: Nourishing the Digestive Tract
Improving your gut health is not just about avoiding disruptive foods; it is equally about adding nourishing, biologically active wholefoods that help your microbial garden thrive.
Nourishing Food Group Key Examples Primary Benefit
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Prebiotic Fibres Oats, leeks, garlic, onions, asparagus Feeds beneficial bacteria to produce SCFAs
Polyphenol-Rich Plants Berries, leafy greens, green tea, cocoa Acts as natural antioxidants for microbes
Fermented Foods Plain live kefir, sauerkraut, kimchi Introduces live, friendly bacterial strains
Gentle Whole Grains Brown rice, quinoa, whole oats Provides bulk and promotes regular transit
Healthy Dietary Fats Extra virgin olive oil, avocados, nuts Supports cell membranes; eases inflammation
1. Diverse Prebiotic Fibres
Prebiotics are non-digestible plant fibres that pass through the upper digestive tract intact, arriving in the colon where beneficial bacteria ferment them. Excellent wholefood sources include:
- Leeks, onions, and garlic
- Slightly under-ripe bananas
- Rolled whole oats and barley
- Asparagus and Jerusalem artichokes
- Lentils, chickpeas, and beans (introduced gradually)
Aim for plant diversity. Studies suggest that individuals who consume 30 or more distinct plant-based foods each week—including vegetables, fruits, whole grains, pulses, nuts, and seeds—harbour significantly more diverse and resilient gut microbiomes than those who eat fewer.
2. Polyphenol-Rich Foods
Polyphenols are natural micronutrients found in plants that give them their vibrant colours. Most polyphenols are poorly absorbed in the small intestine, meaning they travel down to the colon where gut bacteria break them down into beneficial bioactive compounds.
Rich sources include:
- Dark berries (blueberries, blackberries, raspberries)
- Extra virgin olive oil
- Dark leafy greens (spinach, kale, Swiss chard)
- Green tea and moderate black tea
- Small amounts of high-percentage dark chocolate (85%+)
3. Naturally Fermented Foods
Fermented foods contain live, friendly micro-organisms that can temporarily colonise the digestive tract, interact with resident microbes, and support immune balance.
Consider introducing small daily servings of:
- Plain, unflavoured kefir or live natural yoghurt
- Raw, unpasteurised sauerkraut
- Traditional kimchi
- Tempeh and miso
Practical tip: When introducing fermented foods, start with just one tablespoon a day and increase gradually to give your digestive system time to adapt comfortably.
4. Hydration and Mindful Eating Practices
Digestion begins in the mouth. Chewing your food thoroughly breaks down physical structures and mixes it with salivary amylase, reducing the workload on your stomach and small intestine.
Furthermore, adequate water intake is essential for gut function. Dietary fibre acts like a sponge, absorbing water to form soft, bulky stools that move effortlessly through the bowel. Without sufficient fluid, increasing your fibre intake can inadvertently lead to constipation and abdominal discomfort. Aim for 1.5 to 2 litres of plain water or herbal teas daily, spaced steadily throughout the day.
When Gut Issues Point to Something More: The Blue Horizon Method
Adjusting your diet to remove disruptive foods is a powerful first step. However, persistent digestive symptoms should never be ignored or self-treated in isolation.
At Blue Horizon, we advocate a structured, three-step journey to help you identify the root causes of your symptoms responsibly:
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│ STEP 1: Consult Your GP First │
│ Primary medical assessment to rule out underlying pathology │
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│ STEP 2: Structured Self-Check & Symptom Tracking │
│ Keep a 2-week diary of food, transit, sleep, and stress │
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┌─────────────────────────────────────────────────────────────┐
│ STEP 3: Targeted Blood Biomarker Snapshot │
│ Broad clinical panels to check inflammation, nutrition, etc.│
└─────────────────────────────────────────────────────────────┘
Step 1: Consult Your GP First
If you experience ongoing changes in bowel habit, persistent bloating, heartburn, or abdominal discomfort, your first port of call must always be your NHS GP.
Your doctor can evaluate your medical history and conduct appropriate clinical examinations to rule out conditions such as inflammatory bowel disease (Crohn's disease or ulcerative colitis), coeliac disease, Helicobacter pylori infections, gallbladder disease, or other gastrointestinal disorders. Never attempt to manage significant or worsening digestive complaints without professional medical oversight.
Step 2: Structured Self-Check and Symptom Tracking
Before making radical changes to your lifestyle, gather objective information about your body. Maintain a clear, simple diary for two to three weeks, recording:
- Food and Fluid Intake: What you ate, the timing of meals, and how quickly you ate.
- Symptom Timing: When bloating, cramps, or discomfort occur relative to your meals.
- Bowel Movements: Frequency and stool consistency using the standard Bristol Stool Chart (ranging from Type 1 hard lumps to Type 7 liquid diarrhoea).
- Lifestyle Factors: Your nightly sleep duration, daily physical activity, and subjective stress levels.
This structured diary provides your GP with clear clinical context, helping them spot patterns that might otherwise be missed during a brief appointment.
Step 3: Targeted Pathology and Blood Biomarkers
If standard baseline checks leave you feeling stuck, or if you want a comprehensive look at how your internal physiology is functioning, targeted blood testing can provide valuable context. While blood tests do not directly diagnose digestive disorders, they offer a clear snapshot of systemic markers that interact directly with digestive wellbeing.
- Inflammatory Markers (CRP): C-Reactive Protein helps assess whether systemic, low-grade inflammation is present in the body.
- Nutritional Biomarkers (Ferritin, Active B12, Folate, Vitamin D): These markers highlight whether chronic digestive issues or poor dietary intake are compromising your nutritional stores.
- Metabolic and Iron Panels (HbA1c, Iron, Transferrin Saturation): These illuminate blood sugar regulation and complete iron transport capacity.
- Thyroid Function (TSH, Free T4, Free T3): The thyroid gland acts as the body's master metabolic regulator. An underactive thyroid (hypothyroidism) frequently slows down gut motility, leading to chronic constipation and sluggish digestion, whereas an overactive thyroid can accelerate transit.
If you are considering a thyroid-related health snapshot, compare the available thyroid blood test profiles. The Thyroid Premium Bronze Blood Test provides a focused starting point covering TSH, Free T4, Free T3, magnesium, and cortisol.
For a broader assessment of nutritional and inflammatory markers, the Thyroid Premium Gold Blood Test includes ferritin, folate, active vitamin B12, vitamin D, and C-reactive protein alongside thyroid markers.
For the most extensive profile discussed in this article, the Thyroid Premium Platinum Blood Test adds Reverse T3, HbA1c, and a full iron panel. These tests should complement, not replace, professional medical care.
At Blue Horizon, our comprehensive blood profiles—including our tiered health and thyroid panels—are designed to complement standard medical care. These panels include essential cofactors such as magnesium and cortisol to provide a broader view of your overall vitality. All results are accompanied by clear clinical reference ranges, providing a practical foundation for a more productive, informed conversation with your GP or specialist.
Practical Steps for Long-Term Gut Balance
Restoring harmony to your digestive system is a gradual process that requires patience and consistency. Use these practical strategies to build lasting digestive health. For further ideas, read this practical guide on how to actually improve gut health.
- Make Gradual Adjustments: Avoid overhauling your entire diet overnight. Rapidly increasing dietary fibre or radically altering your meals can temporarily worsen bloating and gas. Make one or two mindful swaps each week—such as replacing a sweetened breakfast cereal with plain porridge oats topped with berries.
- Cook at Home More Often: Preparing meals from basic, whole ingredients gives you full control over what goes onto your plate, eliminating hidden emulsifiers, excessive sodium, and industrial trans fats.
- Support the Rest-and-Digest State: Digestion is controlled by the parasympathetic branch of the autonomic nervous system. Eating while rushed, stressed, or working at your desk keeps the body in a sympathetic "fight-or-flight" state, which reduces digestive enzyme output and slows stomach emptying. Take ten minutes to sit down calmly, breathe deeply, and eat without distractions.
- Keep Moving: Regular, moderate physical activity—such as a brisk 20-minute walk after lunch or dinner—stimulates natural peristalsis (the rhythmic muscular contractions of the intestines), helping to reduce gas buildup and promote regular bowel movements.
Conclusion
Understanding what foods not to eat for gut health is one of the most effective, empowering steps you can take toward improved daily vitality. By scaling back on ultra-processed items, industrial emulsifiers, artificial sweeteners, heavy fried foods, and refined sugars, you remove the primary irritants that disrupt the gut microbiome and inflame the digestive lining.
Replacing these disruptors with a diverse array of whole plant fibres, polyphenol-rich foods, and pure water provides your body with the raw materials it needs to build a resilient, balanced internal ecosystem.
Remember that health is a continuous, connected journey rather than a quick fix. If you are struggling with persistent digestive symptoms, always consult your GP first to ensure serious underlying conditions are ruled out. Track your symptoms calmly and methodically, and if you require deeper clinical visibility into your systemic inflammation, nutritional stores, or thyroid status, explore a structured blood testing panel to help guide your path forward.
FAQ
How long does it take for gut health to improve after cutting out disruptive foods?
Some improvements, such as reduced post-meal bloating, less acid reflux, and improved stool consistency, can often be felt within a few days to a week after cutting out heavy fried foods, refined sugars, and artificial sweeteners. However, rebuilding microbial diversity and supporting the regeneration of the intestinal mucosal lining is a biological process that generally takes several weeks to months of consistent, wholesome nutrition.
Is coffee bad for gut health, or should I stop drinking it?
Plain black or lightly milked coffee is not inherently harmful to gut health and is actually a rich source of prebiotic polyphenols that beneficial bacteria can feed on. However, excessive caffeine can overstimulate gastric acid production and cause bowel urgency in sensitive individuals. If you experience heartburn, acid reflux, or stomach irritation, limit your intake to one or two small cups per day, avoid drinking it on an empty stomach, and steer clear of coffee drinks loaded with sugary syrups.
Do I need to cut out all dairy and gluten to have a healthy gut?
Not necessarily. Unless you have a diagnosed medical condition such as coeliac disease, there is generally no clinical need to eliminate entire food groups. Whole grains containing gluten, such as whole wheat, barley, and rye, provide valuable prebiotic fibres for the microbiome, and plain, fermented dairy products like kefir and live yoghurt provide beneficial probiotic bacteria. If you suspect an issue, speak to your GP before making major dietary exclusions.
What should I do if I eat well but still suffer from chronic bloating and fatigue?
If you are already eating a clean, wholefood diet and continue to experience persistent digestive complaints alongside fatigue, it is essential to consult your GP. Chronic symptoms can stem from non-dietary factors such as thyroid dysfunction, which directly affects bowel motility, coeliac disease, inflammatory bowel disorders, chronic stress affecting the gut-brain axis, or underlying micronutrient deficiencies. A GP consultation combined with targeted blood testing can help illuminate the wider physiological picture. For more information about choosing between available thyroid profiles, read which thyroid blood test to choose.