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IBS & IBD

IBS affects roughly 4 to 9% of adults worldwide, depending on which diagnostic criteria are used, and is the most common gut diagnosis given.1 How many people with IBS also have SIBO depends on the test: a meta-analysis of 36 studies found 49% positive by lactulose breath test and 19% by glucose, and a standard workup rarely looks for it either way.2 IBD (Crohn's, UC) is a different disease: it causes real tissue damage and it is managed with medical treatment, which nutrition supports rather than replaces.

Gut & Digestive Evidence-Based

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โš ๏ธ Medication safety: please read first. The nutrition and supplement approaches on this page are meant to work alongside your prescribed treatment, never to replace it. Never stop, reduce or change your IBD medication without your prescriber's guidance. Doing so can be dangerous. Several supplements interact with IBS and IBD medication, so talk to your prescriber or pharmacist before starting anything on this page.
Definition

What Are IBS and IBD?

These two conditions are often confused, but they're fundamentally different in nature, diagnosis and treatment approach.

Two large intestines side by side, a pale one for irritable bowel syndrome and a reddened one for inflammatory bowel disease, each with its symptoms: abdominal pain, bloating, diarrhea and constipation; abdominal pain, cramping, diarrhea and urgency

IBS, Irritable Bowel Syndrome

Functional disorder, no structural damage visible on colonoscopy or imaging. Diagnosed from symptom criteria (Rome IV) after a few tests rule out other causes.

  • IBS-C: Constipation-predominant (sometimes linked to methane-producing gut bacteria)
  • IBS-D: Diarrhea-predominant (sometimes linked to bile acid malabsorption or SIBO)
  • IBS-M: Mixed, alternating constipation and diarrhea
  • IBS-U: Unsubtyped
  • Affects motility, visceral sensitivity, gut-brain signaling
  • No tissue destruction, but significant quality of life impact

IBD, Inflammatory Bowel Disease

Inflammatory/​autoimmune condition that causes measurable structural damage to the GI tract. Diagnosed with colonoscopy, biopsy, imaging.

  • Crohn's Disease: Can affect any part of the GI tract; transmural (full-wall) inflammation
  • Ulcerative Colitis (UC): Mucosal inflammation limited to colon and rectum
  • Microscopic Colitis: Inflammation visible only on biopsy
  • Active tissue destruction, ulcers, fistulas, strictures possible
  • Increased colorectal cancer risk with long-standing UC
  • Changes in the gut microbiome and gut barrier are seen, though whether they cause IBD is still being studied
โš ๏ธ The overlap problem: IBS and early IBD share many symptoms. IBS should be diagnosed only after red flags and conditions such as celiac disease and IBD have been considered; a SIBO breath test can be discussed where the picture fits.
By the Numbers

IBS and IBD by the Numbers

4 to 9%
of adults worldwide have IBS: 9.2% by Rome III criteria and 3.8% by the stricter Rome IV1
3.1M
US adults with diagnosed IBD, 1.6% of adults in national survey data for 2023 to 2024 3
19 to 49%
of people with IBS test positive for SIBO: 49% by lactulose and 19% by glucose breath test in a meta-analysis of 36 studies2
1.46ร—
the odds of IBS in women compared with men, 12.0% against 8.6%, across population studies1
~1 in 10
develop IBS within a year of infectious gastroenteritis, across 45 studies4
2.4ร—
as likely to report overall symptom improvement on enteric-coated peppermint oil as on placebo, across seven trials5
Signs & Symptoms

Symptoms of IBS and IBD

IBS and IBD share many overlapping symptoms but differ in severity and underlying mechanism.

SymptomWhat happens
IBS Symptoms (Functional)
Bloating & Visible Abdominal DistensionThe abdomen feels full or visibly swells, often after meals; fermentation of poorly absorbed carbohydrates is one contributor.
Abdominal Cramping & PainCramping lower abdominal pain, often eased by a bowel movement. In IBS the gut is oversensitive, so a normal amount of gas or stool can hurt, and stress often makes it worse.
Diarrhea (IBS-D) vs. Constipation (IBS-C)IBS-D: frequent loose stools with urgency. IBS-C: hard, infrequent stools with a sense of incomplete emptying. IBS-M: alternating between the two.
Anxiety & DepressionAnxiety and depression are common alongside IBS, and the two influence each other through gut-brain signaling.
FatigueTiredness is common in IBS, though its cause is not well established; in IBD, inflammation and low iron or B12 add to it.
IBD Symptoms (Inflammatory)
Rectal Bleeding & Blood in StoolA hallmark of IBD, particularly ulcerative colitis, from ulcers in the lining of the colon and rectum. Any blood in stool needs an urgent appointment; bleeding is not a feature of IBS.
Fever, Night Sweats & Systemic InflammationActive IBD flares often cause low-grade to moderate fever (100.4 to 102.2ยฐF / 38 to 39ยฐC), night sweats and profound fatigue, reflecting systemic inflammatory activity not present in IBS. The presence of fever with gut symptoms is a red flag for IBD requiring medical investigation.
Mucus in Stool & TenesmusMucus with bowel movements is common in active colitis and can occur in IBS too. Tenesmus, a constant urge to pass stool even when the bowel is empty, is typical of inflammation in the rectum.
Extraintestinal ManifestationsIBD can affect the joints, eyes, skin and liver as well as the gut6, and these problems often flare along with gut symptoms.
Unintentional Weight Loss & MalnutritionInflammation and poor appetite during flares cause weight loss and shortages of protein, iron and fat-soluble vitamins, and of B12 when Crohn's affects the end of the small intestine.
Causes

Causes of IBS and IBD

IBS and IBD arise differently. IBS is a disorder of gut-brain interaction whose exact cause is unknown and which does not damage the gut7; IBD is an immune reaction that inflames the gut wall8.

CauseHow It Contributes to IBS and IBDWhat Helps
Gut-brain signaling and a sensitive gut (IBS)In IBS, food can move too fast or too slowly, and a normal amount of gas or stool can cause pain. Anxiety, depression and difficult early life events are more common in IBS and feed into this two-way signaling7.Enteric-coated peppermint oil for cramping and pain (Supplement Protocol); relaxation time, and cognitive behavioral therapy or hypnotherapy when symptoms persist (conventional care)
Gut infection (IBS)About 1 in 10 people develop IBS within a year of infectious gastroenteritis, around four times the usual risk; women, severe infections and antibiotic use during the infection raise the odds4.The same diet and supplement measures as other IBS (Nutritional Strategy, Supplement Protocol)
Food triggers (IBS)Poorly absorbed carbohydrates (FODMAPs) are fermented by gut bacteria, and food intolerances are more common in IBS7.A low-FODMAP diet with structured reintroduction, which lowered symptom severity against control diets in trials9 (Nutritional Strategy); soluble rather than insoluble fiber
Small intestinal bacterial overgrowth (some IBS)SIBO is found in 19 to 49% of people with IBS depending on the test2, but whether it causes their symptoms remains debated10.Breath testing where the picture fits, and antibiotics if SIBO is confirmed (conventional care)
Immune reaction, genes and microbiome (IBD)In Crohn's disease the immune system attacks bacteria that normally live in the gut, inflaming its wall. Genes, the microbiome and environment can trigger this, and a parent or sibling with Crohn's raises risk8.Anti-inflammatory, immunomodulating and biologic medicines (conventional care); a Mediterranean-style diet, which did as well as the specific carbohydrate diet in a Crohn's trial11 (Treatment Comparison)
Smoking (Crohn's disease)Smoking may double the chance of developing Crohn's disease8.Stopping smoking, with support from your clinician (conventional care)
Diagnosis

How IBS and IBD Are Diagnosed

IBS is diagnosed from its symptom pattern (Rome IV criteria), once proper testing has ruled out (or confirmed) IBD, celiac disease and other treatable causes, with a SIBO breath test where the picture fits. IBD requires formal medical diagnosis.

TestWhat it shows
At-Home Indicators
The FODMAP ChallengeCompare symptoms 30 to 120 minutes after a high-FODMAP meal (bread, garlic, onion, beans) and a low-FODMAP one (eggs, rice, cucumber). A clear difference suggests FODMAPs are one trigger, which a structured low-FODMAP trial can test properly.
IBS vs. IBD Red Flag ChecklistSymptoms suggesting IBS (functional): Symptoms worsen with stress, improve with bowel movements, vary by food, no blood in stool, normal blood markers. Red flags requiring urgent medical evaluation (possible IBD): Blood in stool, unintentional weight loss, fever, symptoms waking you from sleep, family history of IBD or colorectal cancer, onset after age 50. Any red flag needs an urgent appointment and referral.
The Stress Connection TestKeep a 2-⁠week log of stress (1 to 10) and symptom severity. Stress often worsens IBS, but a link with stress does not by itself confirm the diagnosis.
Lab & Clinical Tests
SIBO Breath Test (Lactulose or Glucose)Can be useful in selected people with IBS, because a positive result may change treatment. Results depend heavily on the sugar used (see By the Numbers).2 Lactulose is the more sensitive and the more false-positive-prone of the two, so a positive lactulose test is a reason to investigate further, not proof that bacteria are causing your symptoms.
Blood and Stool MarkersKey markers: CBC (anemia, suggests IBD or nutrient malabsorption); CRP & ESR (elevated in IBD flares, normal in IBS); Calprotectin (stool test, elevated in IBD, normal in IBS, the best non-invasive IBD/IBS differentiator); Celiac antibodies (anti-tTG IgA) to rule out celiac disease; Thyroid panel (hypothyroidism mimics IBS-C).
Comprehensive Stool DNA TestCommercial panels report bacteria, yeast, parasites and permeability markers, but a positive result does not establish the cause of IBS symptoms: Candida lives harmlessly in most healthy people, and permeability markers are not a diagnosis.
Colonoscopy & Biopsy (IBD Diagnosis)Required for IBD diagnosis. Colonoscopy visualizes the colon and terminal ileum directly, revealing ulceration, inflammation, strictures and fistulas. Biopsies distinguish Crohn's disease from ulcerative colitis. Capsule endoscopy may be used to visualize the small bowel in Crohn's. Always required if IBD red flags are present.
Treatment Comparison

Conventional and Holistic Treatment for IBS and IBD

๐ŸŒฟ HOLISTIC
๐Ÿ’Š CONVENTIONAL
๐ŸŒฟ

Holistic / Functional Approach

Diet, the gut-brain axis and treating an overgrowth where one is actually demonstrated

For IBS
Low-FODMAP diet, probiotics, stress and vagus nerve work; test for SIBO where the picture fits, and treat it if found
For IBD
Dietary patterns such as the Mediterranean diet, which matched the specific carbohydrate diet for symptom remission in a Crohn's trial11; curcumin; microbiome support
Duration
Varies with the condition and its severity; dietary changes that help are usually kept up long term.
Relapse Prevention
Diet and lifestyle can help symptoms; evidence that they prevent IBD flares is limited

Full Holistic Approach Includes

  • SIBO testing where the picture fits, and treatment if confirmed, discussed with a clinician
  • Low-FODMAP diet for 4 to 8 weeks (elimination + structured reintroduction)
  • Enteric-coated peppermint oil capsules, antispasmodic for abdominal cramping
  • Supplements sometimes used for the gut lining (evidence limited): L-glutamine, zinc carnosine, DGL licorice
  • Probiotics, such as the single strain Bifidobacterium infantis 35624
  • Vagus nerve stimulation: cold exposure, humming, breathing exercises, gargling
  • Stress-hormone (HPA axis) support: ashwagandha, rhodiola, B vitamins and magnesium. Ashwagandha has been linked to rare liver injury, is not recommended with autoimmune disorders, and may interact with immunosuppressant medicines; check with your IBD team first12

IBD Additional Holistic Support

  • Specific Carbohydrate Diet (SCD) or Autoimmune Protocol (AIP): removes all grains, processed food and lactose (the AIP removes all dairy)
  • Curcumin, studied as an adjunct in mild UC, though comparative data is limited
  • Fish oil: not recommended for keeping Crohn's disease or ulcerative colitis in remission; pooled trials found no benefit13
  • Butyrate enemas or oral butyrate, studied in UC with limited evidence
  • Fecal microbiota transplant (FMT), studied in randomized trials in ulcerative colitis with mixed results; still investigational for IBD and not a standard treatment14
โš ๏ธ Generally well tolerated, though some supplements here interact with medicines (see berberine).
Supplement Protocol

Evidence-Based Supplements for IBS and IBD

These supplements are used for IBS and IBD symptoms; evidence varies by supplement, as noted in each row.

SupplementWhat it is forTypical rangeTimingNotes & cautions
L-GlutamineIBS: Proposed to support the gut lining; human evidence in IBS is limited. IBD: Studied in IBD without clear benefit; not a treatment for ulceration.5 to 15 g/dayFasted morning or between meals as powder in waterAvoid if cancer history or severe liver disease.
Peppermint OilIBS: Enteric-coated peppermint oil is one of the better-evidenced IBS treatments: an antispasmodic that improved overall symptoms and abdominal pain against placebo in pooled trials5. IBD: Use cautiously; it may worsen heartburn in some IBD patients. There is no good evidence of benefit in IBD.0.2 mL peppermint (enteric-coated) 2 to 3x/day30 to 60 min before mealsMust be enteric-coated to reach the small intestine.
Saccharomyces boulardiiIBS: A probiotic yeast; evidence for IBS symptoms is mixed. IBD: Did not prevent relapse of Crohn's disease in a randomized trial16.250 to 500 mg (about 5 to 10 billion CFU) a dayBetween mealsSafe during antimicrobial treatment. Use caution with a weakened immune system or a central line, as bloodstream infections from probiotics have been reported; agree on it with your team.
BerberineIBS: Has antimicrobial activity and has been studied for SIBO; evidence is limited. IBD: Anti-inflammatory in laboratory studies; not an established IBD treatment.500 mg 2 to 3x/dayWith mealsBerberine inhibits CYP3A4 and P-glycoprotein, so it can raise blood levels of many prescription medicines, and it lowers blood sugar on its own. Check with your prescriber before starting it, particularly if you take glucose-lowering medication, an anticoagulant, an immunosuppressant or any drug with a narrow safe range. Not for use in pregnancy or breastfeeding.
Curcumin (Turmeric Extract)IBS: Anti-inflammatory in laboratory studies; evidence for IBS symptoms is limited. IBD: Studied as an adjunct in mild UC; anti-inflammatory activity in IBD, though comparative data is limited.1,000 to 3,000 mg/dayWith fat-containing mealsLiver injury has been reported with high-dose, high-absorption curcumin products; stop and seek advice if you notice dark urine or yellowing skin17.
Omega-⁠3 Fish OilIBS: Evidence for IBS symptoms is limited. IBD: Reduces leukotriene B4 and prostaglandin inflammatory pathways; but pooled trials have not shown that it keeps Crohn's disease or ulcerative colitis in remission13.Not recommended for keeping Crohn's disease or ulcerative colitis in remission (pooled trials found no benefit)Not applicableCod liver oil also supplies preformed vitamin A, whose adult upper limit is 3,000 mcg a day18. In heart trials, fish oil supplements raised the risk of atrial fibrillation, an irregular heartbeat, more so above 1 g a day19, so check any fish oil supplement with your clinician first.
Magnesium GlycinateIBS: Needed by hundreds of enzymes; may help muscle relaxation and sleep, but evidence in IBS is limited. IBD: Can run low in IBD with diarrhea and malabsorption; needed for normal gut muscle and nerve function.300 to 500 mg/day.Before bedMagnesium accumulates in reduced kidney function, so check with your clinician first if your kidney function is impaired. The top of this range is above the 350 mg/day upper intake level for supplemental magnesium; above that, diarrhea is common. Count the two magnesium forms together against that limit.
Magnesium CitrateIBS-C: gentle osmotic laxative that draws water into the bowel, softens stools and improves transit time for constipation-dominant IBS. IBD: For constipation in IBD only with your IBD team's agreement, especially with a known Crohn's stricture; not for replacing magnesium during diarrhea flares, since as a laxative it will worsen diarrhea.200 to 400 mg/day.Before bed or with dinnerReduce the dose if loose stools occur. The top of this range is above the 350 mg/day upper intake level for supplemental magnesium; above that, diarrhea is common. With kidney disease, take it only on your clinician's advice.
Vitamin D3IBS: Worth correcting if a blood test shows a deficiency; a benefit for IBS symptoms themselves is not established. IBD: Correct a measured deficiency with your clinician; whether supplements change the course of IBD is not established.Test 25-⁠OH-D first and set the dose with your clinicianWith a fat-containing mealMonitor blood levels with your clinician.
Zinc CarnosineIBS: Studied mainly for stomach lining; evidence in IBS is limited. IBD: Evidence in UC and Crohn's is limited.75 to 150 mg/dayWith or between mealsLook for a standardized zinc carnosine form.
Prokinetic: Ginger RootIBS: Proposed to support the migrating motor complex, the wave of contractions between meals; evidence in IBS is limited. IBD: Ginger reduces nausea and has anti-inflammatory activity.500 to 1,000 mgBefore bed on an empty stomachGinger has mild antiplatelet activity, so mention it to your clinician if you take an anticoagulant.
What to Expect

What to Expect Over Time

IBS usually improves step by step over weeks to months; IBD needs medical treatment to control inflammation, with diet in a supporting role.

Treatment and supportive care, together
First Weeks

Blood count, inflammatory markers and a celiac antibody test help separate IBS from other conditions20, and red flags lead to referral. For IBS, a 4 to 8 week low-FODMAP phase and enteric-coated peppermint oil can start now; IBD treatment is set by the specialist team.

Months 1 to 3

Low-FODMAP diets lowered IBS symptom severity against control diets in trials9. Foods are then reintroduced so the diet does not stay restrictive. A probiotic, if tried, is judged after at least 4 weeks20.

Months 3 to 12

Persistent IBS symptoms lead to gut-brain medicines and, after 12 months without response, to cognitive behavioral therapy or hypnotherapy20. In IBD, the aim becomes keeping remission.

Long Term

IBS is long-lasting and comes and goes, but does not damage the gut7. Colitis flares can last days to months21; colonoscopy surveillance is offered 10 years after colitis symptoms began22.

When to Seek Care

Ask for an urgent appointment for unexplained weight loss, rectal bleeding or bloody diarrhea, a lump in the abdomen23, or, with colitis, severe diarrhea, fever or a fast heartbeat. Call 911 or go to the emergency department for severe abdominal pain, heavy or nonstop bleeding, or vomiting blood21.

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Next Steps

Understanding Your Symptoms

Whether you have IBS, IBD or aren't sure what's driving your symptoms, a careful investigation helps target treatment.

Explore SIBO โ†’ Explore Leaky Gut โ†’

References & Evidence Notes

Each numbered entry below is either a source you can follow or a note setting out what the evidence does and does not support. Both are numbered together so the markers in the text line up.

Last reviewed October 20, 2026. Supplement entries are cross-checked against the NIH National Center for Complementary and Integrative Health and the Linus Pauling Institute Micronutrient Information Center.24 This page is nutrition education, not medical advice, and it does not replace your doctor. Two cautions specific to this page. IBD (Crohn's disease and ulcerative colitis) causes measurable tissue damage and is managed with medical treatment; nutrition supports that treatment and does not replace it, and stopping prescribed therapy risks a flare. Blood in the stool, unintentional weight loss, fever or symptoms that wake you from sleep need medical assessment, not a supplement.

  1. Oka P, et al. Global prevalence of irritable bowel syndrome according to Rome III or IV criteria: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. 2020;5(10):908-⁠917. thelancet.com. Pooled prevalence 9.2% under Rome III (53 studies, 395,385 participants) and 3.8% under the stricter Rome IV criteria. The criteria used, not the underlying disease burden, explains most of the spread in reported figures. ↩
  2. An older 78% figure for SIBO in IBS originates in Pimentel M, et al. Am J Gastroenterol. 2000;95(12):3503-⁠3506, which used the lactulose breath test. Later studies report 4 to 78% depending on method. A systematic review and meta-analysis of 36 studies found SIBO prevalence in IBS of 49% (95% CI 40 to 57) with lactulose versus 19% (95% CI 13 to 27) with glucose. PMC10134763. Heterogeneity is largely attributed to the absence of a standardized diagnostic criterion for SIBO. ↩ ↩
  3. National Center for Health Statistics (CDC). Inflammatory Bowel Disease Among Adults Age 18 and Older: United States, 2023-⁠2024. cdc.gov/nchs. 1.6% of US adults, about 3.1 million, reported an IBD diagnosis. Claims-based studies give a lower figure, about 2.4 million, so the two methods disagree and the survey number is the higher of the two. ↩
  4. On IBS after gut infection: across 45 studies of 21,421 people with infectious gastroenteritis, 10.1% had IBS 12 months later, about four times the risk in people without infection, with higher risk in women, after severe infection and with antibiotic use, PubMed 28069350. ↩
  5. On peppermint oil: in a meta-analysis of 12 randomized trials with 835 adults with IBS, enteric-coated peppermint oil made global symptom improvement 2.39 times as likely as placebo across seven trials and improved abdominal pain, with side effects no more frequent than on placebo, PubMed 30654773. ↩
  6. On extraintestinal manifestations and nutritional status in IBD: Crohn's & Colitis Foundation, IBD Overview, crohnscolitisfoundation.org. Reported rates for extraintestinal manifestations vary widely by series and by which manifestations are counted. ↩
  7. On what causes IBS: the US National Institute of Diabetes and Digestive and Kidney Diseases describes IBS as a disorder of brain-gut interaction whose cause is not known, lists early life stress, depression and anxiety, gut infections, SIBO and food intolerances as more common in people with IBS, and notes that IBS does not damage the digestive tract, NIDDK. ↩
  8. On what causes Crohn's disease: the NIDDK describes an abnormal immune reaction against gut bacteria, triggered by genes, the microbiome and environment, a higher risk with an affected parent or sibling, and smoking possibly doubling the risk, NIDDK. ↩
  9. On efficacy and on the limits of long-term restriction: Efficacy of a low-FODMAP diet in adult irritable bowel syndrome, systematic review and meta-analysis, PMC8354978; and The low FODMAP diet in clinical practice: where are we and what are the long-term considerations? Proc Nutr Soc, Cambridge Core. Stringent long-term restriction is not recommended because of reduced beneficial gut bacteria and inadequate nutrient intake, calcium in particular. ↩
  10. On SIBO and IBS: a 2020 gastroenterology expert review concluded that controversy remains about the role of SIBO in causing IBS symptoms, and that response to a poorly absorbed antibiotic needs confirmation in randomized trials before it is credited to treating SIBO, PubMed 32679220. ↩
  11. On diet in Crohn's disease: a randomized trial in 194 adults with mild to moderate symptoms found the specific carbohydrate diet was not superior to a Mediterranean diet for symptomatic remission at week 6 (46.5% against 43.5%), and its authors concluded that the Mediterranean diet may be preferred for most patients because it is easier to follow and has other health benefits, PubMed 34052278. ↩
  12. On ashwagandha: the NIH National Center for Complementary and Integrative Health reports that, although rare, a number of cases link liver injury to ashwagandha supplements, that it is not recommended for people with autoimmune or thyroid disorders, and that it may interact with some medicines, including immunosuppressants, NCCIH, ashwagandha. ↩
  13. On fish oil in IBD: in the two large, low-risk trials in people with Crohn's disease in remission, 37% relapsed at 12 months on omega-⁠3 against 42% on placebo, a difference that was not statistically significant, PubMed 24585498, and a review of three trials in 138 people with ulcerative colitis found no evidence that it maintains remission, PubMed 17636844. ↩
  14. FMT in ulcerative colitis has been tested in several randomized controlled trials with inconsistent results across donor, dose and route protocols. It remains investigational for IBD and is not a standard treatment; in the United States it is FDA-approved only for recurrent C. difficile infection. ↩
  15. On surgery in IBD: a meta-analysis of population-based cohorts found that in cohorts since 2000, 26.2% of people with Crohn's disease needed surgery within 10 years and 9.6% of people with ulcerative colitis needed colectomy, against 39.5% and 13.3% across all years, with risk falling over time, PubMed 33127595. ↩
  16. On Saccharomyces boulardii in Crohn's disease: in a randomized placebo-controlled trial of 165 people in remission, 1 g a day for 52 weeks did not reduce relapse (47.5% relapsed against 53.2% on placebo, not a significant difference), PubMed 23466709. ↩
  17. On curcumin and the liver: in seven Italian cases of acute hepatitis linked to turmeric supplements, every case involved a high-bioavailability, high-dose formulation; a systematic review found 23 further published cases, PubMed 32656820. ↩
  18. On cod liver oil: cod liver oil supplements provide vitamin A and vitamin D as well as omega-⁠3s, NIH Office of Dietary Supplements, omega-⁠3, and the adult upper limit for preformed vitamin A is 3,000 mcg a day, NIH Office of Dietary Supplements, vitamin A. ↩
  19. Gencer B, Djousse L, Al-Ramady OT, Cook NR, Manson JE, Albert CM. Effect of long-term marine omega-⁠3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes: a systematic review and meta-analysis. Circulation. 2021;144(25):1981-⁠1990. PubMed 34612056. Seven trials with 81,210 people followed for about 5 years: omega-⁠3 supplements were linked to a higher risk of atrial fibrillation (hazard ratio 1.25), more so in trials of more than 1 g a day (1.49), and the risk rose with each additional gram. ↩
  20. On the IBS care pathway: the UK national guideline advises a blood count, inflammatory markers and celiac antibodies to exclude other diagnoses, at least 4 weeks' trial of any probiotic, and referral for cognitive behavioral therapy or hypnotherapy when symptoms continue after 12 months of medicines, NICE CG61. ↩
  21. On colitis flares: the NHS notes flares last from a few days to several months, and advises emergency care for severe abdominal pain, nonstop bleeding or vomiting blood, and an urgent appointment for very bad or bloody diarrhea, fever or a fast heartbeat, NHS. ↩
  22. On colorectal cancer surveillance in IBD: the UK guideline offers colonoscopic surveillance to people whose ulcerative colitis, or Crohn's colitis involving more than one segment, began 10 years ago, NICE CG118. ↩
  23. On urgent symptoms: the NHS advises an urgent appointment for unexplained weight loss, bleeding from the bottom or bloody diarrhea, or a hard lump or swelling in the abdomen, NHS. ↩
  24. National Center for Complementary and Integrative Health (NIH), nccih.nih.gov, and the Linus Pauling Institute Micronutrient Information Center, lpi.oregonstate.edu/mic. ↩