Gut health sources
27 topics and 44 sources behind Alma’s gut answers. Alma spots patterns, not diagnoses. These organizations do not endorse Alma.
Constipation
Dietary fiber and constipation
Solid Good trials or a conditional guideline recommendation
Fiber is the most common first step for constipation and is suggested by the AGA and ACG guideline, with low certainty. Among fiber supplements, psyllium has the best support. Add fiber slowly and drink fluids with it, because a sudden increase can cause gas and bloating.
- American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation.American Gastroenterological Association and American College of Gastroenterology, 2023
- British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults.British Dietetic Association, 2025
- Eating, Diet, & Nutrition for ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- An assessment of nutrition and physical activity guidelines for adult patients with chronic constipation: A systematic review.Clinical Nutrition ESPEN, 2025
Psyllium (ispaghula) for constipation and IBS
Solid Good trials or a conditional guideline recommendation
Psyllium is a soluble fiber and the best-supported fiber supplement for constipation. In IBS, a meta-analysis found soluble fiber helped while bran did not. Effects are modest, and it works best taken with enough fluid.
- American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation.American Gastroenterological Association and American College of Gastroenterology, 2023
- British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults.British Dietetic Association, 2025
- The effect of fiber supplementation on irritable bowel syndrome: a systematic review and meta-analysis.American Journal of Gastroenterology, 2014
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- Exploratory Comparative Effectiveness Trial of Green Kiwifruit, Psyllium, or Prunes in US Patients With Chronic Constipation.American Journal of Gastroenterology, 2021
- Eating, Diet, & Nutrition for Irritable Bowel SyndromeNational Institute of Diabetes and Digestive and Kidney Diseases, 2017
Prunes and constipation
Early Small trials or observational studies
Prunes have been tested in a few small trials, mostly against psyllium rather than placebo. One review found prunes did better than psyllium and a US trial found prunes helped, but a 2025 pooled analysis found no difference from psyllium on stool consistency. Treat prunes as a reasonable food to try, not a proven cure. These sources did not test prune juice.
- Systematic review: the effect of prunes on gastrointestinal function.Alimentary Pharmacology and Therapeutics, 2014
- Exploratory Comparative Effectiveness Trial of Green Kiwifruit, Psyllium, or Prunes in US Patients With Chronic Constipation.American Journal of Gastroenterology, 2021
- British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults.British Dietetic Association, 2025
Kiwifruit and constipation
Early Small trials or observational studies
Two green kiwifruit a day raised bowel movements in constipated adults in an international trial, and did about as well as psyllium in other trials. The evidence is small and the biggest trial had kiwifruit-industry authors. Kiwifruit powder supplements did not change stool frequency or softness in the BDA analysis.
- Consumption of 2 Green Kiwifruits Daily Improves Constipation and Abdominal Comfort-Results of an International Multicenter Randomized Controlled Trial.American Journal of Gastroenterology, 2023
- Exploratory Comparative Effectiveness Trial of Green Kiwifruit, Psyllium, or Prunes in US Patients With Chronic Constipation.American Journal of Gastroenterology, 2021
- British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults.British Dietetic Association, 2025
Rye bread and constipation
Early Small trials or observational studies
Eating rye bread raised stool frequency a little more than white bread in two small trials, but the amount used was 6 to 8 slices a day, which many people will not manage. The BDA analysis also found rye bread made overall constipation symptoms worse than white bread.
- British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults.British Dietetic Association, 2025
High-mineral water and constipation
Early Small trials or observational studies
Drinking 0.5 to 1.5 L a day of water rich in magnesium and sulphate for 2 to 6 weeks made people more likely to report improvement than low-mineral water. It did not change stool frequency, overall symptoms or abdominal pain. Ordinary tap water in the UK has far less magnesium than the waters tested.
- British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults.British Dietetic Association, 2025
Fluids, water and constipation
Early Small trials or observational studies
Not drinking enough can contribute to constipation, and agencies advise drinking enough, especially when adding fiber. But the sources we reviewed did not test extra water in people who are already well hydrated, and the 2025 BDA constipation guideline made drink recommendations only for high-mineral water. Think of fluids as fixing low intake, not as a treatment on their own.
- Symptoms & Causes of ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- Treatment for ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- Eating, Diet, & Nutrition for ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation.American Gastroenterological Association and American College of Gastroenterology, 2023
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults.British Dietetic Association, 2025
Magnesium oxide for constipation
Solid Good trials or a conditional guideline recommendation
Magnesium oxide is an over-the-counter laxative that two guidelines support, though they disagree on how certain the evidence is. It should not be used by people with kidney problems because magnesium can build up. It can also cause loose stools.
- American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation.American Gastroenterological Association and American College of Gastroenterology, 2023
- British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults.British Dietetic Association, 2025
- Symptoms & Causes of DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
Coffee, caffeine and bowel movements
Early Small trials or observational studies
In a small lab study of 12 healthy adults, caffeinated coffee stimulated the colon about as much as a meal, and more than water. Decaf had an in-between effect that was not clearly different from water or caffeinated coffee. For IBS, NICE advises limiting tea and coffee to 3 cups a day, and NIDDK advises avoiding caffeinated drinks during acute diarrhea.
- Is coffee a colonic stimulant?European Journal of Gastroenterology and Hepatology, 1998
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- Eating, Diet, & Nutrition for DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
Physical activity and constipation
Early Small trials or observational studies
Health agencies advise regular activity for constipation and IBS, but the evidence behind it is thin. A 2025 review of expert guidelines found their advice on physical activity was limited, low to moderate in strength, and sometimes conflicting.
- Treatment for ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- Symptoms & Causes of ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- An assessment of nutrition and physical activity guidelines for adult patients with chronic constipation: A systematic review.Clinical Nutrition ESPEN, 2025
Toilet routine, meals and posture
Early Small trials or observational studies
NIDDK suggests trying to go at the same time each day, such as 15 to 45 minutes after breakfast when eating helps the colon move stool. Go when you feel the urge, give yourself time, and relax your muscles or rest your feet on a footstool. This is expert advice rather than trial-tested.
- Treatment for ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- Symptoms & Causes of ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- Is coffee a colonic stimulant?European Journal of Gastroenterology and Hepatology, 1998
Iron supplements and gut side effects
Solid Good trials or a conditional guideline recommendation
Oral iron often upsets the gut. A meta-analysis of 43 trials found ferrous sulfate raised the odds of gastrointestinal side effects about 2.3 times compared with placebo, with no clear link to dose. NIDDK lists iron supplements among supplements that can worsen constipation.
- Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis.PLoS ONE, 2015
- Symptoms & Causes of ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
Diarrhea
Sugar alcohols (sorbitol, mannitol, xylitol, maltitol) and loose stools
Early Small trials or observational studies
Sugar alcohols in sugar-free gum, candy and some drinks are only partly absorbed and can cause loose stools in some people. US law requires a laxative warning on foods likely to deliver 50 g of sorbitol or 20 g of mannitol a day. Tolerance varies from person to person.
- § 184.1835 Sorbitol.U.S. Food and Drug Administration (21 CFR), 1984
- § 180.25 Mannitol.U.S. Food and Drug Administration (21 CFR), 2004
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- Symptoms & Causes of DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
- Eating, Diet, & Nutrition for Gas in the Digestive TractNational Institute of Diabetes and Digestive and Kidney Diseases, 2021
Fruit, fructose and juice and loose stools
Early Small trials or observational studies
Fruit is healthy, but large amounts of fruit or fruit juice can loosen stools in some people. NICE suggests people with IBS limit fresh fruit to 3 portions of about 80 g a day. NIDDK names fructose in fruit, juice, honey and soft drinks as a possible trigger.
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- Symptoms & Causes of DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
- Eating, Diet, & Nutrition for DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
- Eating, Diet, & Nutrition for Irritable Bowel SyndromeNational Institute of Diabetes and Digestive and Kidney Diseases, 2017
Alcohol, fizzy drinks, spicy food and high-fat meals as triggers
Early Small trials or observational studies
NICE advises people with IBS to eat regular meals, avoid long gaps, and cut back on alcohol and fizzy drinks. NIDDK lists alcohol, caffeine, sugar, sugar alcohols and high-fat foods to avoid during acute diarrhea. We did not find a graded guideline position on spicy food.
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- Eating, Diet, & Nutrition for DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
- Eating, Diet, & Nutrition for Gas in the Digestive TractNational Institute of Diabetes and Digestive and Kidney Diseases, 2021
- British Dietetic Association systematic review and evidence-based practice guidelines for the dietary management of irritable bowel syndrome in adults (2016 update).British Dietetic Association, 2016
Bile acid diarrhea as a cause of chronic loose stools
Solid Good trials or a conditional guideline recommendation
Bile acid diarrhea is a recognized, treatable cause of long-lasting loose stools that can look like IBS with diarrhea. It is more likely after gallbladder or ileum surgery. It needs medical testing and treatment, not a diet fix.
- Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition.British Society of Gastroenterology, 2018
- Symptoms & Causes of DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
Acute diarrhea: oral rehydration and when to seek care
Strong Guideline recommendation or consistent pooled evidence
For most adults, acute diarrhea passes by itself and the main task is replacing lost fluid and salts. WHO says oral rehydration solution (clean water, sugar and salt) is the treatment. Get help for blood in stool, high fever, diarrhea lasting more than 2 days, or signs of dehydration.
- Diarrhoeal diseaseWorld Health Organization, 2024
- Treatment for DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
- Symptoms & Causes of DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
- ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults.American College of Gastroenterology, 2016
Bloating and gas
Celiac disease: test before going gluten-free
Strong Guideline recommendation or consistent pooled evidence
Celiac disease is diagnosed with blood tests and usually an intestinal biopsy, and a gluten-free diet started beforehand can make the tests unreliable. Guidelines suggest checking for celiac disease in people with IBS-type symptoms. If you suspect it, get tested before cutting out gluten.
- Diagnosis of Celiac DiseaseNational Institute of Diabetes and Digestive and Kidney Diseases, 2020
- American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease.American College of Gastroenterology, 2023
- ACG Clinical Guideline: Management of Irritable Bowel Syndrome.American College of Gastroenterology, 2021
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- AGA Clinical Practice Update on Evaluation and Management of Belching, Abdominal Bloating, and Distention: Expert Review.American Gastroenterological Association, 2023
Bloating and gas
Early Small trials or observational studies
Gas and bloating have many causes, and the AGA says treatment evidence is limited. NIDDK points to fizzy drinks, swallowed air, certain carbohydrates, sugar alcohols, too much fiber and high-fat foods. A diary, slower fiber increases, and a check for celiac disease are the practical starting points.
- Eating, Diet, & Nutrition for Gas in the Digestive TractNational Institute of Diabetes and Digestive and Kidney Diseases, 2021
- Eating, Diet, & Nutrition for Irritable Bowel SyndromeNational Institute of Diabetes and Digestive and Kidney Diseases, 2017
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- AGA Clinical Practice Update on Evaluation and Management of Belching, Abdominal Bloating, and Distention: Expert Review.American Gastroenterological Association, 2023
IBS
Low-FODMAP diet for IBS
Solid Good trials or a conditional guideline recommendation
A low-FODMAP diet cuts back certain hard-to-digest carbohydrates for a short time to see whether IBS symptoms ease. It has three stages: restrict, reintroduce, then personalise to a less restrictive diet. Guidelines treat it as a limited trial, best guided by a dietitian, and not as a lifelong way of eating.
- ACG Clinical Guideline: Management of Irritable Bowel Syndrome.American College of Gastroenterology, 2021
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- British Dietetic Association systematic review and evidence-based practice guidelines for the dietary management of irritable bowel syndrome in adults (2016 update).British Dietetic Association, 2016
- The low FODMAP diet in the management of irritable bowel syndrome: an evidence-based review of FODMAP restriction, reintroduction and personalisation in clinical practice.British Dietetic Association, 2018
- Eating, Diet, & Nutrition for Irritable Bowel SyndromeNational Institute of Diabetes and Digestive and Kidney Diseases, 2017
- AGA Clinical Practice Update on Evaluation and Management of Belching, Abdominal Bloating, and Distention: Expert Review.American Gastroenterological Association, 2023
Probiotics: what guidelines actually say
Early Small trials or observational studies
Probiotics show a mixed picture. A 2014 meta-analysis found them helpful in IBS, but the AGA's 2020 review rated the overall evidence low, with 44 different strains or combinations tested and most in only one trial. For constipation the 2025 BDA analysis found low-certainty benefit and no strain it could recommend. The AGA advises against them for bloating.
- AGA Technical Review on the Role of Probiotics in the Management of Gastrointestinal Disorders.American Gastroenterological Association, 2020
- Efficacy of prebiotics, probiotics, and synbiotics in irritable bowel syndrome and chronic idiopathic constipation: systematic review and meta-analysis.American Journal of Gastroenterology, 2014
- British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults.British Dietetic Association, 2025
- AGA Clinical Practice Update on Evaluation and Management of Belching, Abdominal Bloating, and Distention: Expert Review.American Gastroenterological Association, 2023
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- Treatment for DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
Stress and the gut-brain axis in IBS
Solid Good trials or a conditional guideline recommendation
IBS is now understood as a disorder of gut-brain interaction, meaning the gut and brain signal each other in ways that can amplify symptoms. Guidelines list psychological therapies such as gut-directed therapy, CBT and hypnotherapy as treatment options. This does not mean symptoms are imagined.
- British Society of Gastroenterology guidelines on the management of irritable bowel syndrome.British Society of Gastroenterology, 2021
- ACG Clinical Guideline: Management of Irritable Bowel Syndrome.American College of Gastroenterology, 2021
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- AGA Clinical Practice Update on Evaluation and Management of Belching, Abdominal Bloating, and Distention: Expert Review.American Gastroenterological Association, 2023
General and safety
Bristol Stool Form Scale and normal bowel frequency
Solid Good trials or a conditional guideline recommendation
The Bristol Stool Form Scale sorts stool into seven types, from hard lumps to watery. In a 1997 study, stool form tracked gut transit time better than how often people went to the toilet. There is no single normal frequency: NIDDK counts fewer than three bowel movements a week as constipation, and says only you know what is normal for you.
- Stool form scale as a useful guide to intestinal transit time.Scandinavian Journal of Gastroenterology, 1997
- Definition & Facts for ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
- Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition.British Society of Gastroenterology, 2018
Food and symptom diaries for finding personal triggers
Early Small trials or observational studies
Health agencies suggest writing down what you eat and drink, when symptoms start, and what your stools look like, so patterns can show up. The diary points to possible triggers; it does not prove them. We found no trial showing that keeping a diary improves outcomes, so treat it as a sensible method rather than a proven treatment.
- Eating, Diet, & Nutrition for Gas in the Digestive TractNational Institute of Diabetes and Digestive and Kidney Diseases, 2021
- Diagnosis of Gas in the Digestive TractNational Institute of Diabetes and Digestive and Kidney Diseases, 2021
- Eating, Diet, & Nutrition for DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
- Irritable bowel syndrome (IBS) and dietBritish Dietetic Association, 2022
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008
Lactose intolerance and how much lactose most people tolerate
Solid Good trials or a conditional guideline recommendation
Most people who react to lactose can still handle about a cup of milk's worth, 12 to 15 g, without symptoms. Cutting out all dairy is usually not needed and can leave you short of calcium and vitamin D. Smaller servings with meals, yogurt, hard cheese, lactose-free milk and lactase products are common ways to stay within your own limit.
- Systematic review: effective management strategies for lactose intolerance.Annals of Internal Medicine, 2010
- NIH consensus development conference statement: Lactose intolerance and health.National Institutes of Health, 2010
- Eating, Diet, & Nutrition for Lactose IntoleranceNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
GLP-1 medicines (semaglutide, tirzepatide) and gut side effects
Strong Guideline recommendation or consistent pooled evidence
Nausea, diarrhea, vomiting and constipation are the most common side effects of semaglutide and tirzepatide. In trials they were mostly mild to moderate and eased over time, often around dose increases. Vomiting and diarrhea can cause dehydration and kidney injury, so contact the prescriber if symptoms are severe or persistent.
- ZEPBOUND (TIRZEPATIDE) INJECTION, SOLUTION [ELI LILLY AND COMPANY]U.S. Food and Drug Administration (label hosted on DailyMed), 2026
- WEGOVY (SEMAGLUTIDE) INJECTION, SOLUTION WEGOVY (SEMAGLUTIDE) TABLET [NOVO NORDISK PHARMACEUTICAL INDUSTRIES, LP]U.S. Food and Drug Administration (label hosted on DailyMed), 2026
- Gastrointestinal tolerability of once-weekly semaglutide 2.4 mg in adults with overweight or obesity, and the relationship between gastrointestinal adverse events and weight loss.Diabetes, Obesity and Metabolism, 2022
- Gastrointestinal adverse events associated with GLP-1 RA in non-diabetic patients with overweight or obesity: a systematic review and network meta-analysis.International Journal of Obesity, 2025
Red flags: when bowel changes need a clinician
Strong Guideline recommendation or consistent pooled evidence
Most bowel changes are harmless, but some signs need prompt medical attention: blood in stool or from the rectum, black tarry stools, unintended weight loss, anemia, persistent abdominal pain, fever, vomiting, or signs of dehydration. Tell your clinician about any family history of colon cancer, IBD or celiac disease.
- Symptoms & Causes of ConstipationNational Institute of Diabetes and Digestive and Kidney Diseases, 2018
- Diagnosis of Irritable Bowel SyndromeNational Institute of Diabetes and Digestive and Kidney Diseases, 2017
- Symptoms & Causes of DiarrheaNational Institute of Diabetes and Digestive and Kidney Diseases, 2024
- Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition.British Society of Gastroenterology, 2018
- AGA Clinical Practice Update on Evaluation and Management of Belching, Abdominal Bloating, and Distention: Expert Review.American Gastroenterological Association, 2023
- Irritable bowel syndrome in adults: diagnosis and managementNational Institute for Health and Care Excellence, 2008