| Food & hand hygiene | Do this | ●●●Strong | Established clinical | Refrigerate perishables within 2h (1h above 90F); the 40-140F danger zone and handwashing prevent foodborne GI illness. | Food safety & hand hygiene (CDC) (opens in a new tab) |
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| Total Fiber | Eat enough of | ●●●Strong | RCT / meta-analysis | Soluble fibre (psyllium) is first-line for constipation, raising stool frequency and easing straining. | Fibre for chronic constipation (opens in a new tab) |
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| Ultra-processed food — cut back | Do this | ●●●Strong | RCT / trial | Emulsifiers (CMC, P80) in ultra-processed food disrupt the gut barrier and microbiome, promoting GI symptoms and inflammation. | Dietary emulsifiers & gut (opens in a new tab) |
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| Ultra-processed food — cut back | Do this | ●●●Strong | RCT / trial | Emulsifiers (CMC, P80) in ultra-processed food disrupt the gut barrier and microbiome, promoting GI symptoms and inflammation. | Randomized Controlled-Feeding Study of Dietary Emulsifier Carboxymethylcellulose, Gastroenterology 2022 (opens in a new tab) |
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| Added Sugars | Don't overdo | ●●Moderate | RCT / meta-analysis | Excess free sugars/fructose drive osmotic diarrhoea, gas and bloating. | Free sugars & osmotic/fermentation GI (opens in a new tab) |
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| Alcohol — cut back | Do this | ●●Moderate | RCT / meta-analysis | Alcohol lowers LES pressure and raises reflux esophagitis and ulcer risk. | Alcohol & upper-GI disease (opens in a new tab) |
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| Anchor foods | Watch this | ●●Moderate | RCT / meta-analysis | Whole-food, fibre-rich meals improve IBS and functional GI symptoms. | Diet & gut-brain axis (IBS) (opens in a new tab) |
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| Breath/mind (slow breathing) | Do this | ●●Moderate | RCT / meta-analysis | Slow diaphragmatic breathing reduces reflux and functional GI symptoms. | Diaphragmatic breathing & reflux/IBS (opens in a new tab) |
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| Cardio (moderate + intervals) | Do this | ●●Moderate | RCT / trial | Moderate aerobic exercise reduces IBS symptom severity and improves motility. | Exercise & IBS (opens in a new tab) |
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| Choline | Don't overdo | ●●Moderate | Established clinical | Excess choline causes GI distress - vomiting, diarrhoea, stomach cramps - plus sweating and fishy body odour. | Choline excess & GI (opens in a new tab) |
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| Colours a day | Watch this | ●●Moderate | RCT / meta-analysis | Diverse plant intake supports microbiome diversity and bowel regularity. | Plant diversity & microbiome (opens in a new tab) |
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| Cook real food | Do this | ●●Moderate | RCT / trial | Cooking from whole ingredients cuts exposure to emulsifiers/additives linked to GI symptoms. | Home cooking avoids additives (opens in a new tab) |
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| Copper | Don't overdo | ●●Moderate | Established clinical | Acute copper excess causes gastroenteritis - abdominal pain, nausea, vomiting, diarrhoea - with erosive gastropathy. | Copper toxicity & GI (opens in a new tab) |
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| Daily movement baseline | Do this | ●●Moderate | Review / narrative | Regular activity speeds colonic transit and reduces constipation. | Physical activity & bowel function (opens in a new tab) |
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| Iron | Don't overdo | ●●Moderate | RCT / trial | Oral iron commonly causes nausea (~22%), constipation (~24%) and heartburn. | Oral iron GI side effects (opens in a new tab) |
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| Loneliness — reduce | Watch this | ●●Moderate | RCT / meta-analysis | Chronic stress/loneliness worsens IBS and functional GI symptoms via the gut-brain axis. | Gut-brain axis & stress (opens in a new tab) |
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| Magnesium | Eat enough of | ●●Moderate | Review / narrative | Low magnesium associates with constipation; magnesium eases it osmotically. | Magnesium & constipation (opens in a new tab) |
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| Magnesium | Don't overdo | ●●Moderate | Established clinical | Excess magnesium pulls water into the bowel, causing diarrhoea (it is used as a laxative). | NIH Office of Dietary Supplements — Magnesium (opens in a new tab) |
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| Saturated fat | Don't overdo | ●●Moderate | Review / narrative | High saturated-fat intake slows emptying and aggravates reflux/dyspepsia. | High saturated-fat & GI (opens in a new tab) |
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| Selenium | Eat enough of | ●●Moderate | Review / narrative | Selenium deficiency alters gut microbiota, is common in IBD (~31%), and can cause chronic diarrhoea and intestinal inflammation. | Selenium & gut microbiota/IBD (opens in a new tab) |
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| Selenium | Don't overdo | ●●Moderate | Established clinical | Excess selenium (selenosis) causes GI upset - nausea, diarrhoea, vomiting - plus metallic taste and garlic breath. | Selenosis & GI (opens in a new tab) |
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| Sleep duration | Watch this | ●●Moderate | RCT / meta-analysis | Poor/short sleep worsens IBS and functional GI symptom severity. | Sleep & gut-brain axis (opens in a new tab) |
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| Sleep quality (refreshed) | Watch this | ●●Moderate | RCT / meta-analysis | Non-restorative sleep is bidirectionally linked with GI symptom flares. | Sleep quality & IBS (opens in a new tab) |
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| Sugary drinks & snacks — cut back | Do this | ●●Moderate | RCT / meta-analysis | High free-sugar/fructose loads drive osmotic diarrhoea, gas and bloating. | Fermentable sugars & GI (opens in a new tab) |
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| Tobacco / vaping — quit | Do this | ●●Moderate | Cohort / observational | Smoking weakens the lower esophageal sphincter, raising GERD and ulcer risk. | Smoking & GERD/peptic ulcer (opens in a new tab) |
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| Total Fat | Don't overdo | ●●Moderate | Review / narrative | High-fat meals slow gastric emptying and relax the LES, worsening reflux. | High-fat meals & reflux (opens in a new tab) |
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| Total Fiber | Don't overdo | ●●Moderate | RCT / meta-analysis | Excess/fermentable fibre added too fast causes bloating, gas and cramping (especially in IBS). | Too much fibre & bloating (opens in a new tab) |
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| Vitamin C | Don't overdo | ●●Moderate | Established clinical | Vitamin C above bowel tolerance (~2 g) causes osmotic diarrhoea and cramping. | NIH Office of Dietary Supplements — Vitamin C (opens in a new tab) |
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| Water / hydration | Do this | ●●Moderate | Review / narrative | Adequate fluid softens stool and eases constipation. | Hydration & constipation (opens in a new tab) |
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| Zinc | Don't overdo | ●●Moderate | Established clinical | High-dose zinc causes nausea, vomiting and GI upset. | NIH Office of Dietary Supplements — Zinc (opens in a new tab) |
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| BMI | Watch this | ●Emerging | RCT / meta-analysis | Higher BMI raises reflux/GERD risk dose-dependently (~+68% per 10 kg/m2; obesity roughly doubles risk). | Obesity & GERD meta (opens in a new tab) |
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| Caffeine — mind amount & timing | Do this | ●Emerging | RCT / meta-analysis | Caffeine can relax the LES and trigger reflux/heartburn in sensitive people. | Caffeine reflux trigger (opens in a new tab) |
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| Calcium | Don't overdo | ●Emerging | Established clinical | Calcium supplements can cause constipation, bloating and gas. | NIH Office of Dietary Supplements — Calcium (opens in a new tab) |
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| Choline | Eat enough of | ●Emerging | Mechanistic | Insufficient choline disrupts the gut barrier and promotes intestinal inflammation and altered microbiota (and fatty-liver disease). | Choline & intestinal barrier (opens in a new tab) |
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| Chromium | Don't overdo | ●Emerging | Established clinical | High-dose or inorganic chromium irritates the GI tract (gastritis, abdominal pain, vomiting, bloody diarrhoea); supplements may cause mild GI upset. | Chromium GI irritation (opens in a new tab) |
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| Iodine | Don't overdo | ●Emerging | Established clinical | Excess iodine irritates the GI tract, causing nausea, vomiting, diarrhoea and abdominal upset. | Iodine toxicity & GI (opens in a new tab) |
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| Movement (breaking up sitting) | Do this | ●Emerging | Review / narrative | Prolonged sitting associates with slower transit and more GI complaints. | Sedentary time & GI (opens in a new tab) |
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| Niacin (B3) | Don't overdo | ●Emerging | Review / narrative | High-dose niacin causes flushing with nausea and loose stools. | Niacin flushing & GI (opens in a new tab) |
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| Pantothenic acid (B5) | Don't overdo | ●Emerging | Established clinical | Large doses of pantothenic acid (~10 g/day) can cause mild diarrhoea and GI distress. | Pantothenic acid high-dose GI (opens in a new tab) |
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| Supplement discipline | Do this | ●Emerging | Established clinical | Excess supplements (magnesium, vitamin C, iron, zinc) commonly cause diarrhoea/nausea; discipline limits this. | NIH Office of Dietary Supplements — Magnesium (opens in a new tab) |
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| Total Sugars | Don't overdo | ●Emerging | RCT / meta-analysis | High total-sugar loads (incl. fructose/lactose) ferment and cause bloating/diarrhoea. | Fermentable sugars & bloating (opens in a new tab) |
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| Vitamin D | Don't overdo | ●Emerging | Established clinical | Vitamin D excess (via hypercalcemia) causes nausea, vomiting and constipation. | NIH Office of Dietary Supplements — Vitamin D (opens in a new tab) |
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