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Well supported

How much prior knowledge a chapter assumes. New here? Start with “Beginner”. You can pick several.

Chapters that readers rate at 4 out of 5 stars or more on average for this question. An average only exists from 3 ratings. You can choose several.

Opportunistic pathogens

Germs that only become a problem when the balance is off. 3 chapters – expand
  • Level:Intermediate After antibiotics: C. difficile and faecal transplants A germ that can take over after antibiotics, and a treatment that works better than any drug. AntibioticsFaecal transplantProbioticsDiarrhoeaGut infectionsBile acidsToxins and mould Established How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
  • Level:Intermediate When the gut does not settle after an infection Stomach bug, food poisoning, traveller's diarrhoea: why symptoms sometimes stay. Gut infectionsIBSDiarrhoeaBile acids Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
  • Level:Intermediate Saccharomyces boulardii: the probiotic yeast Why a yeast survives antibiotics, what it is proven to help with, and when it can become dangerous. ProbioticsAntibioticsDiarrhoeaGut infections Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. Community

Microbial diversity

Why many different species keep the gut stable. 1 chapter – expand
  • Level:Intermediate Gut tests: what they show and what they do not Microbiome analysis, zonulin, IgG, breath test, calprotectin: which tests are worth it. Tests and diagnosticsCoeliac disease and glutenInflammation Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. Community

Gut-brain axis

How stress, sleep and nerves steer digestion. 1 chapter – expand
  • Level:Intermediate Gut-directed hypnotherapy and psychological therapy: treatment via the gut-brain axis Why gut-directed hypnotherapy and CBT are among the best-proven treatments for IBS, how they work, what apps can do, and why "limbic retraining" is something else. PsychotherapyIBSStress Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.

Digestive function

Stomach acid, bile and enzymes as groundwork for the gut. 6 chapters – expand
  • Level:Intermediate Stomach acid, bile and enzymes The groundwork in the stomach and small intestine determines what reaches the large intestine. Acid blockersMedicationBile acidsAlcoholBloatingTests and diagnostics Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
  • Level:Intermediate Pelvic floor: when stool won’t come out properly Why straining sometimes does not help, how a defecation disorder shows itself and why biofeedback works better than laxatives. ConstipationExerciseTests and diagnostics Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
  • Level:Intermediate Acid blockers (PPIs): what they change in the gut and how to stop them properly Proton pump inhibitors are among the most widely used medicines in the world. They are very effective for reflux and ulcers, but change the gut flora and nutrient absorption. What is established, what is not, and how to stop them. Acid blockersMedicationGut infectionsAllergies Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
  • Level:Intermediate The digestive chain: how stomach acid, bile and pancreas set each other off Digestion is a relay race: the head starts, the acid passes the signal to the duodenum, hormones call up bile and enzymes. Who sends which signal, and what happens when one link is weak. Bile acidsAcid blockers Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
  • Level:Intermediate Digestive enzymes from mouth to colon: who breaks down what Saliva, stomach, pancreas, gut wall and bacteria each contribute their own enzymes. A map of where each enzyme works, and what happens when one is missing. FODMAPBloatingCoeliac disease and glutenTests and diagnostics Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
  • Level:Intermediate Nutrient deficiency in gut problems: when food no longer arrives Why gut symptoms can leave you short of iron, vitamin B12, vitamin D, the fat-soluble vitamins and zinc, how to read blood results correctly and when supplements really help. NutrientsVitamins and fatty acidsDiarrhoeaTests and diagnosticsBody weight Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.

Small intestine colonisation

When bacteria grow where few belong. 1 chapter – expand
  • Level:Intermediate Doing low-FODMAP right The best-studied diet for bloating, and why it is only meant to be temporary. FODMAPBloatingIBS Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.

Immune system and inflammation

The gut as the body's largest immune organ. 1 chapter – expand
  • Level:Intermediate Crohn’s disease and ulcerative colitis: understanding inflammatory bowel disease In Crohn’s disease and ulcerative colitis, the immune system permanently attacks the gut wall. What distinguishes the two, what role genes, smoking, antibiotics and gut microbiota play, why early treatment matters, and what diet, probiotics and faecal transplants really achieve. InflammationDiarrhoeaTests and diagnosticsMedicationAntibioticsNutrientsProbioticsFaecal transplantMediterranean diet Established How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.