Functional Nutrition for Irritable Bowel Syndrome

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What is IBS?

Irritable bowel syndrome (IBS) is a group of symptoms that includes abdominal pain and changes in bowel habits (diarrhea and/or constipation) (1).

It is considered a syndrome rather than a disease because a direct cause has not yet been determined (2).

There are three subtypes:

  • IBS with diarrhea (IBS-D)
  • IBS with constipation (IBS-C)
  • IBS with mixed bowel habits (IBS-M)

How common is IBS?

IBS is the most commonly diagnosed gastrointestinal disorder (1).

In the United States, it affects between 3% and 20% of the population, and women are nearly twice as likely to be diagnosed as men (3).


What are the symptoms?

The most common symptoms include the following (4):

  • Abdominal pain
  • Bloating
  • Cramping
  • Constipation
  • Diarrhea
  • Fatigue
  • Gas

What causes IBS?

The underlying causes of IBS are not entirely clear and tend to vary depending on the patient.

Potential causes include the following:

1. Altered gut motility

There is some evidence that patients with IBS-D have rapid gastrointestinal transit, while those with IBS-C have normal or slow transit (56).

Changes in transit time may explain alterations in bowel habits (diarrhea or constipation) in these patients (7).

However, other symptoms (abdominal pain, bloating) do not seem to be related to these changes (7).

2. Visceral hypersensitivity

Research shows that IBS patients exhibit visceral hypersensitivity, which means that they have an increased perception of pain in response to distention or other movement in the intestines (8).

Around 60% of patients experience visceral hypersensitivity, mainly those with the IBS-D subtype (9).

It’s unclear exactly why this occurs, but inflammation and dysbiosis may be involved (10).

3. Gut-brain interactions

Some researchers have proposed a biopsychosocial model of IBS, in which genetics, psychological factors, disturbances in the gut-brain axis, and environmental stressors all contribute to symptoms (11).

There is evidence that IBS patients have altered brain activity that increases pain-related fear (121314).

It has also been well-established that anxiety and depression are common in individuals with IBS (15).

Still, more research is needed to fully understand these gut-brain interactions in IBS.

4. Gut infections

Infectious gastroenteritis (also known as infectious diarrhea) is linked with a sevenfold increase in IBS risk (16).

Patients who have bacterial infections, especially Clostridium difficile, are more likely to develop IBS than those with viral infections (17).

Post-infectious IBS is a term used to describe patients who can trace the development of their symptoms back to a case of infectious gastroenteritis (18).

It’s unclear exactly why this occurs, but it may be related to increases in inflammation, intestinal permeability, and dysbiosis that often occur as a result of infection (19).

5. Dysbiosis

In IBS, levels of proinflammatory bacteria (such as enterobacteriaceae) tend to be higher, while levels of lactobacillus and bifidobacterium are lower (20). 

Also, the IBS-C subtype is associated with higher levels of methanogens (methane-producing bacteria) (20). 

It is thought that dysbiosis results in abnormal levels of fermentation in the intestines, which could be responsible for IBS symptoms (21).

6. Low-grade inflammation

The presence of low-grade (mild) inflammation in IBS has been well-established (2122).

These patients tend to have increased concentrations of systemic pro-inflammatory cytokines and higher numbers of mast cells in the intestinal mucosa, as well as a higher rate of mast cell activation (which results in the release of inflammatory mediators) (232425).

Inflammation can affect the enteric (intestinal) nervous system, which may lead to the changes in digestion and motility that are typically seen in IBS (26).

7. Altered intestinal permeability

Increased intestinal permeability (colloquially known as leaky gut) is common in individuals with IBS, particularly those with the IBS-D subtype (272829).

Inflammation triggered by increased gut permeability may play a role in the development of IBS (30).

8. Genetics

A mutation in the SCN5A gene has been linked with abdominal pain and is present in up to 2% of individuals with IBS (313233).

This gene encodes sodium channels, which are involved in the conduction of electrical impulses and are found in cardiac, nerve and intestinal cells (343536).

It is thought mutations in this gene result in altered sodium channels, which may disrupt gastrointestinal motility (31).

Still, the majority of research suggests that genetic factors play only a small role in the development of IBS (2137)

9. Adverse reactions to food

Most IBS patients believe their symptoms are related to the foods that they eat, suggesting that adverse food reactions may play a role (383940).

Hypersensitivity reactions can promote inflammation, which may contribute to dysmotility and increased pain perception (41).

However, more research is needed to determine exactly how adverse food reactions may be involved in the development of IBS (42).

10. Disordered bile acid metabolism

Typically, bile acids (the main components of bile) are released from the gallbladder into the duodenum (the uppermost portion of the small intestine) to aid in fat absorption. They are then reabsorbed in the ileum (the final portion of the small intestine) (43).

Any bile acids that are not absorbed enter the colon, where they can cause diarrhea by increasing the secretion of water into the intestinal tract (44).

About 25% of patients with IBS-D have bile acid malabsorption, which may explain the diarrhea that they experience (45).

However, there is some debate surrounding whether this is a cause or simply a consequence of IBS (21).


What conditions commonly co-occur with IBS?

The following conditions are linked with IBS:

  • Anxiety (46)
  • Bipolar disorder (47)
  • Celiac disease (48)
  • Chronic fatigue syndrome (49)
  • Chronic pelvic pain (50)
  • Depression (46)
  • Fibromyalgia (51)
  • Gastroesophageal reflux disease (GERD) (52)
  • Non-celiac gluten sensitivity (NCGS) (53)
  • Polycystic ovary syndrome (PCOS) (54)
  • Small intestine bacterial overgrowth (SIBO) (55)
  • Temporomandibular joint disorder (56)

How is it diagnosed?

IBS is diagnosed based on the Rome IV criteria (57):

Recurrent abdominal pain on average at least 1 day/week in the last 3 months, associated with two or more of the following criteria:

  1. Related to defecation
  2. Associated with a change in frequency in stool
  3. Associated with a change in form (appearance) of stool

These criteria should be fulfilled for the last 3 months with symptom onset must be at least 6 months prior to diagnosis.

Other GI conditions must also be ruled out (like ulcerative colitis, Crohn’s disease, celiac disease, diverticulosis, etc.).

The IBS subtype is determined based on stool patterns (1):

  1. IBS with constipation (IBS-C) = at least 25% of stools are hard or lumpy and less than 25% are loose or watery
  2. IBS with diarrhea (IBS-D) = at least 25% of stools are loose or watery and less than 25% are hard or lumpy
  3. Mixed IBS (IBS-M) = at least 25% of stools are hard or lumpy and at least 25% are loose or watery

What medications may be prescribed for IBS? 

Any of the following medications may be prescribed by a doctor, depending on the patient’s symptoms (58):

  • Antibiotics (rifaximin) are sometimes used for reducing symptoms (especially bloating) in non-constipated patients.
  • Antidepressants (SSRIs) can be prescribed to reduce symptoms and alleviate abdominal pain.
  • Antidiarrheals (loperamide) are used in patients with IBS-D.
  • 5-HT3 receptor antagonists (alosetron, ondansetron) are suggested to improve motility in female patients.
  • Antispasmodics (otilonium, pinaverium, dicyclomine, etc.) are used to relax intestinal smooth muscle and normalize intestinal transit.

What are the dietary recommendations?

The following diets may be helpful for IBS:

1. Low-FODMAP diet

There is a large body of evidence showing that IBS symptoms such as abdominal pain and bloating are significantly reduced in patients following a low-FODMAP diet for up to 6 months (59606162636465).

However, several systematic reviews have found the quality of evidence to be “very low” due to a high risk of bias and lack of long-term studies (6667).

There is also evidence that beneficial gut bacteria are significantly reduced after 3-4 weeks on a low-FODMAP diet, although taking a daily probiotic may help combat these effects (6869707172).

Some practitioners argue that the low-FODMAP diet is just a “band-aid,” because it doesn’t address the underlying causes of FODMAP intolerances/IBS.

Still, one long-term study found that adherence to the diet and patient satisfaction remained relatively high (>/=80%) 2 years after initiation (73). 

2. Gluten-free diet

There is evidence that exposure to gluten triggers symptoms and increased intestinal permeability in IBS patients, which may be indicative of non-celiac gluten sensitivity (74).

Clinical trials for gluten-free diets in IBS have been conflicting, suggesting that it depends on a patient’s individual sensitivity to gluten (667576).

More research is needed to determine how non-celiac gluten sensitivity and IBS are related.

3. Lactose-free diet

Lactose intolerance is common in IBS patients (77).

Following a lactose-free diet can completely eliminate symptoms in up to 57% of IBS patients with lactose intolerance (7778).

However, not all of these patients experience significant symptom relief, and IBS patients WITHOUT lactose intolerance do not benefit from a lactose-free diet (77).

4. Ketogenic diet

The evidence to support the use of ketogenic diets in patients with IBS is VERY limited.

One small study found that 4 weeks on a very low-carbohydrate diet (20 grams/day) resulted in significantly improved gastrointestinal symptoms in participants with IBS-D (79).

Larger controlled studies are needed to determine whether the ketogenic diet provides any benefit over other diets.

5. Elimination diets 

Elimination diets involve the removal of select foods from the diet until symptoms subside, followed by a gradual reintroduction to determine which foods, if any, are triggering symptoms. 

There is some evidence that elimination diets based on food-specific IgG antibodies can reduce symptoms in IBS patients (8081828384).

However, IgG testing is not considered a reliable marker for diagnosing adverse food reactions (85868788).

It’s possible that participants in the studies actually DID have inflammatory hypersensitivity reactions to some of the eliminated foods, but it’s also possible that some foods were eliminated unnecessarily, because they weren’t actually causing symptoms, despite the presence of IgG antibodies.

Also, when relying on IgG testing, any adverse reactions not involving IgG pathways will go undetected.

The theory behind the use of elimination diets for IBS is solid. Research has shown that food can provoke a pro-inflammatory immune response in the intestines of some people with IBS (91). 

However, more research is needed to validate the use of personalized testing to guide these diets (92).

Special Notes:

It should also be noted that restrictive diets are not appropriate for all people, especially those at risk of maladaptive eating behaviors, with a history of disordered eating or certain mental health conditions, or food insecurity (93).

Care should be taken to evaluate all of these factors before embarking on a restrictive diet.


Foods to Avoid

Many people with IBS choose to avoid the following:

1. Alcoholic beverages

Binge drinking (defined as 4+ alcoholic drinks/day), but not moderate or light drinking, is associated with increased gastrointestinal symptoms (diarrhea, nausea, abdominal pain) in IBS patients (94).

2. Caffeine-containing beverages?

Caffeine is known to stimulate gut motility, which is often dysfunctional in IBS patients (95).

Coffee is among the top ten foods reported by individuals with IBS to cause diarrhea and abdominal pain (96).

However, no clinical trials have examined the effect of caffeine on IBS symptoms (97).

3. Processed foods?

Consumption of ultra-processed foods (cake, soda, hot dogs, etc.) is linked with a 25% higher risk of IBS (98).

More research is needed to see if these foods actually exacerbate IBS symptoms.


Which fiber supplements are beneficial?

1. Partially hydrolyzed guar gum (Sunfiber)

Guar gum is a soluble, fermentable fiber derived from the seeds of the guar plant (99).

When used as a supplement, it is typically partially hydrolyzed (broken down into smaller units), which makes the fiber easier to digest (100).

Limited evidence suggests that partially hydrolyzed guar gum (PHGG) supplementation (5-10 g/day) may reduce bloating and gas, as well as other symptoms, in IBS patients (101102103104).

2. Psyllium

Psyllium is a soluble, gel-forming fiber that acts as a bulk laxative (105).

It is thought to alleviate constipation by supporting the growth of beneficial gut bacteria and increasing stool water content (106).

Weak evidence suggests that psyllium supplementation (6-12 grams/day) may reduce abdominal pain but not quality of life or flatulence in patients with IBS (107108)


Do any other supplements help?

1. Peppermint oil

Menthol, the main constituent of peppermint oil, may reduce inflammation and promote smooth muscle relaxation in the GI tract (109110).

Relatively strong evidence supports the efficacy of peppermint oil supplementation (200-750 mg/day) for reducing pain and improving overall symptoms in patients with IBS (111112).

Adverse effects tend to be mild and temporary, with the most common adverse effect being heartburn (111).

IBgard is a popular brand.

2. Iberogast

Iberogast (also known as STW-5) is a liquid supplement containing 9 herbal extracts (bitter candy tuft, lemon balm leaf, chamomile flower, caraway fruit, peppermint leaf, licorice root, angelica root, milk thistle fruit, and greater celandine herb).

It is marketed for the treatment of functional gastrointestinal disorders (including IBS) and may work by relaxing smooth muscle cells and reducing inflammation in the GI tract (113).

Only one trial has examined the effects of Iberogast on IBS, and the results showed that supplementation (20 drops, 3 times/day) significantly reduced abdominal pain and overall symptoms (114).

Iberogast can be purchased here.

3. Melatonin

Melatonin is a hormone that regulates sleep patterns and is secreted by the pineal gland in response to darkness (115).

It may also play a role in GI motility, inflammation, and pain (116).

Melatonin supplementation (3 mg at bedtime) may reduce abdominal pain and overall symptoms in IBS patients (117118).

However, some studies have found no benefit (119).

4. Glutamine

Glutamine, the most abundant amino acid in the body, plays a role in maintaining intestinal permeability by modulating tight junction protein expression (120).

Evidence from one trial suggests that glutamine supplementation (5 grams, three times/day) significantly reduces IBS severity in up to 80% of patients (121).

More research is needed to elaborate on these promising results.

5. Vitamin D

Vitamin D deficiency is very common in IBS patients and is associated with decreased quality of life (122). 

Limited research suggests that vitamin D supplementation significantly improves vitamin D levels and improves symptoms scores in individuals with IBS (123124).

However, other studies are conflicting, and it’s still unclear exactly how vitamin D status plays a role in IBS (122125).

6. Probiotics

The evidence regarding probiotic supplementation for IBS is mixed. 

Although overall results indicate that probiotics have beneficial effects on overall symptoms and abdominal pain, it is difficult to draw firm conclusions because of the wide variety of species and strains used in the studies (126127).

One meta-analysis suggests that VSL#3 (a patented probiotic) may be effective, but more research is needed (128).

It is also worth noting that VSL#3 changed formulations a few years ago, so many of these are probably based on the old formulation. The original formulation is now sold under Visbiome

7. Aloe vera?

Although it is most often used to treat sunburns, aloe vera may also reduce gastrointestinal inflammation when ingested (129130).

There is limited, conflicting evidence that aloe vera supplementation might improve IBS symptoms (131132).

There is also concern that, when ingested, aloe vera whole leaf extract may have cancer-promoting effects, based on evidence from one animal study (133). 

8. Artichoke leaf extract?

Artichoke leaf extract (ALE) is an herbal supplement that has been used for a variety of conditions (134).

A 2001 observational study revealed that 96% of IBS patients who used ALE rated it as better than or at least equal to previous therapies they had tried (135).

Results from one clinical trial show a 26% decrease in IBS symptoms following ALE supplementation (320-640 mg/day) for 2 months (136).

However, there was no control group, so these results might be due to the placebo effect.

9. Curcumin?

Curcumin, the active component of turmeric, is known for its strong anti-inflammatory effects (137).

A 2018 meta-analysis found that curcumin supplementation (200-8000 mg/day) had a small beneficial effect on IBS symptoms, but this was not statistically significant (138).

More research is needed.


Are there any other interventions to try?

1. Exercise

Low-to-moderate intensity exercise (walking or jogging for 30-45 minutes/day, 3-6 days/week) has been shown to lower inflammation and improve IBS symptoms (139).

Yoga is also a popular choice for IBS patients because it might help reduce anxiety and quality of life (140).

One study found that yoga (twice/week) was just as effective as the low-FODMAP diet for reducing GI symptoms (141).

2. Mindfulness-based stress reduction

Mindfulness-based stress reduction (MBSR) is technique that combines mindfulness meditation with gentle yoga in order to reduce stress and disease symptoms (142)

The goal of MBSR in IBS is to reduce gut-focused anxiety and guide the patient away from emotional responses to gastrointestinal symptoms (143)

Clinical trials have shown that MBSR significantly improves symptom severity and quality of life in IBS patients (142143144).

3. Gut-directed hypnotherapy

Gut-directed hypnotherapy is a technique used to promote general relaxation and control of intestinal motility (145).

It usually involves listening to a recording that helps the patient change the way they perceive their symptoms and overall health (146).

Research suggests that this type of hypnotherapy can dramatically reduce IBS symptoms and may be just as effective as the low-FODMAP diet (145147).

However, another study found that hypnotherapy was no more effective than general relaxation techniques (148).

4. Cognitive behavioral therapy

In IBS, cognitive behavioral therapy (CBT) is used to help patients identify associations between their thoughts, emotions and behaviors with their symptoms (149).

Trained therapists can teach patients to use self-monitoring, muscle relaxation, worry control, and flexible problem solving to control their symptoms (150).

A 2014 meta-analysis found that CBT was more effective than medical treatment, although the evidence was limited by small sample sizes (149).

5. Acupuncture

Research suggests that acupuncture might reduce pain in IBS by altering serotonin and mood (151).

A recent meta-analysis found that acupuncture improved IBS-D better than drugs and had fewer side effects (152).

Patients who don’t respond well to conventional therapies or antidepressants may consider acupuncture as an alternative (153).


A Multidisciplinary Approach

Given that IBS likely has psychological, genetic, environmental, and food-related components, a multidisciplinary therapeutic approach involving physicians, psychologists, dietitians, and other wellness practitioners is optimal (154).

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