Irritable bowel syndrome nutritional approach

Nutritional support for Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a gastrointestinal disorder that can cause persistent discomfort. It is a group of symptoms—including abdominal pain and changes in the pattern of bowel movements without any evidence of underlying damage. These symptoms occur over a long time, often years.

The prevalence of irritable bowel syndrome (IBS) in the UK is estimated at 17% overall; it is twice as common in women as in men, with 23% of women and 11% of men experiencing the condition.1,2

This blog discusses factors which may contribute to the development of IBS and nutritional approaches that are frequently adopted in an attempt to relieve the symptoms.

Skip to Key Takeaways

What is IBS?

Irritable bowel syndrome (IBS) is a chronic functional disorder of the lower gastrointestinal tract, an often debilitating condition with a complex aetiology.3 It is the most common diagnosis made by gastroenterologists around the world and can have a significant impact on life quality and health care utilisation.4,5


The pathogenesis of IBS appears to be multifactorial, with the following factors playing a role:4

  • Diet
  • Intestinal microbiota
  • Heritability and genetics
  • Low-grade inflammation and disturbances in the neuroendocrine system of the gut

Many patients and practitioners also consider that the onset of symptoms can be linked to life events or periods of stress and anxiety and this is also a factor which is likely to play a direct role in the pathogenesis.2

Women appear to have more frequent and severe IBS symptoms during menses compared to other phases of the menstrual cycle and studies suggest that female sex hormones influence the severity of IBS symptoms.6

Small Intestinal Bacterial Overgrowth (SIBO), which refers to an overgrowth of bacteria in the small intestine, may be a cause of IBS. The causes of SIBO seem to be multi-faceted but have been mainly attributed to low stomach acid, poor gut motility, low pancreatic (digestive) enzymes, poor immune function or previous bacterial infections.

Diagnostic tests for SIBO (culture, and glucose and lactulose-hydrogen breath tests) have been criticised for their lack of specificity and sensitivity.7  (In medical diagnosis test sensitivity is the ability of a test to correctly identify those with a condition or disease, in other words the true positive rate; whereas test specificity is the ability of the test to correctly identify those without it, i.e. the true negative rate. Specificity and sensitivity are expressed as percentages.)

Antibiotics – Data suggests that subjects with IBS are more likely to report a recent course of antibiotics. A prospective study in which consecutive patients prescribed antibiotics for non-gastrointestinal complaints were more than three times as likely to report chronic bowel symptoms as controls.8

Poor Motility – Three types of motility occur in the gut – known as peristalsis, segmentation contraction and the migrating motor complex (MMC).

  • Peristalsis is a series of wave-like muscle contractions that moves food to different processing stations in the digestive tract. The process of peristalsis begins in the oesophagus when a bolus of food is swallowed.
  • Segmentation, which occurs mainly in the small intestine, consists of localised contractions of the circular muscles in the digestive tract.  The segmentation motor activity of the gut facilitates mixing of contents and absorption of nutrients.
  • The migrating motor complex is a motility pattern that occurs during fasting. One of its purposes is housekeeping – to ‘sweep’ bacteria from the small intestine back into the large intestine and impairment to the MMC may be a contributory factor to SIBO. In a normal MMC there are 4 phases.

If there is dysfunction within any of the above three movement patterns, gut motility may be decreased, leading to constipation, changes in the gut microbiome, pain, and other digestive symptoms. Particularly, a decrease in phase III activity of the MMC, the most active phase of its four phases, has been shown to be absent in cases of IBS as well as SIBO.10

Please note that IBS should not be confused with IBD, which refers to inflammatory bowel disease – which includes the conditions of ulcerative colitis and Crohn’s disease.

Ulcerative colitis – small ulcers and inflammation develop on the inside of the colon and sometimes the rectum, with symptoms of urgent and bloody diarrhoea, pain and continual tiredness.

Crohn’s disease – inflammation, deep ulcers and scarring to the wall of the intestine often occurs in patches, affecting anywhere along the gastrointestinal tract from the mouth to the anus. The areas most commonly affected are the small intestine and colon. The main symptoms are abdominal pain, urgent diarrhoea, tiredness and weight loss.

Common Symptoms of IBS

Characteristic symptoms are abdominal pain or discomfort in association with an alteration in stool form or frequency.

Pain and Cramping – Abdominal pain is the most common symptom and a key factor in diagnosis. This pain usually occurs in the lower abdomen or the entire abdomen but is less likely to be in the upper abdomen alone. Pain typically decreases following a bowel movement or passage of wind.11 Bloating and general discomfort in the abdomen are common, which can unfortunately be aggravated by some medications used during treatment. Nausea and loss of appetite may also be present.

Diarrhoea – One of the most common symptoms of IBS is diarrhoea. It affects roughly one-third of patients with IBS.12 Accelerated bowel transit in IBS can also result in a sudden, immediate urge to have a bowel movement. High body mass index (BMI) has been associated with fast regional bowel transit and may therefore influence some stool-related symptoms in IBS.13

Constipation – IBS can also cause constipation as well as diarrhoea. Constipation-predominant IBS is the most common type, affecting nearly 50% of people with IBS.14 Constipation in IBS includes abdominal pain that eases with bowel movements.

Alternating Constipation and DiarrhoeaMixed or alternating constipation and diarrhoea affects about 20% of patients with IBS.14

Medical interventions

The medical approach to the condition focusses on symptom relief with prescription drugs to reduce pain and intestinal muscle spasms, anti-diarrhoea preparations, laxatives for constipation and anti-depressants.

Nutritional interventions

An ideal start is for clients to record a diary of their food intake plus a detailed diary of symptoms and any lifestyle events that may occur during periods of symptom aggravation. This information may provide evidence for food or stress inciters and assist in establishing the most suitable support.


Unfortunately, there is no single intervention for IBS as symptoms can vary greatly between individuals.

Sugar, sweeteners, refined and processed foods, a lack of natural fibre and inadequate hydration may be responsible for symptoms of bloating, pain, flatulence, diarrhoea and constipation.

For those who do experience constipation, adequate fibre, fluids and regular exercise can often result in improved transit time, thereby reducing bloating, flatulence and pain.

Over the years the medical recommendation in relation to fibre consumption has changed from ‘promoting and increasing fibre intake’ to ‘avoiding and reducing fibre intake’ to ‘may be suitable for some’.

Insoluble fibre

Insoluble fibre found for example in grains, nuts, potatoes and cauliflower provides bulk and helps speed up the rate of intestinal transit, thereby helping to ensure regular bowel movements and the avoidance of constipation. However, introducing large quantities of insoluble fibre to the diets of clients with IBS is likely to cause problems, particularly if the diet previously contained highly refined foods.

A gradual change to the diet is essential, introducing those foods which are easier to digest in the initial changes and in small portions. Clients frequently perceive wheat bran as an important source of fibre and a healthy option, however, bran can be an undesirable irritant on the bowel and contains traces of gluten, and hence is not ideal.

Soluble fibre

Most foods contain a combination of insoluble fibre and soluble fibre but may be predominant in one type. Soluble fibre is often the best fibre to introduce and good sources include fruit, vegetables, pulses and oats. Introducing these foods, cooked initially, may increase patient tolerance by providing them in an easier-to-digest form.

A gradual increase in both variety and quantity is likely to achieve more successful results. For those that seem unable to tolerate these foods then consideration of FODMAPs may be relevant.


FODMAPs are dietary sugars and carbohydrates which are easily fermented by gut bacteria and which can exacerbate symptoms of gas, bloating and pain. Therefore, it is often very useful to remove them from the diet for a limited period.

FODMAPs stand for:


Oligosaccharides (e.g. fructans found in wheat, garlic, onion and chicory etc. and galactans found in legumes including beans, peas and lentils)

Disaccharides (e.g. lactose found in milk products)

Monosaccharides (e.g. fructose found in fruits, honey, high fructose corn syrup etc.)


Polyols (found in sweeteners containing isomalt, mannitol, sorbitol, xylitol plus stone fruits such as avocado, apricots, cherries, nectarines, peaches and plums)

After excluding high FODMAP foods for a month, foods from each FODMAP group should be reintroduced, one at a time (e.g. foods containing fructose, then foods containing lactose etc.).

During the reintroduction, symptoms should be monitored and if a FODMAP group of foods causes problems then continue to eliminate this group. It should be noted that avoiding FODMAPs will not remove SIBO but help modulate the symptoms.

Please note that a low FODMAP diet involves initially restricting a considerable number of foods which some may find very difficult; however it is not intended to be a long-term diet and because of the restrictive nature and complexity it is best followed with the guidance of a practitioner.

Remove dysbiotic bacteria from the small intestine

Primarily, the main intervention for SIBO needs to be the removal of the bacterial overgrowth, as avoiding foods which are exacerbating symptoms will not be enough.

Natural antimicrobials can be useful for removing bacteria from the small intestine. These include:

Caprylic acid – a natural dietary fatty acid which assists in the maintenance of normal intestinal micro-flora and can help inhibit the growth of opportunistic fungi such as Candida albicans. Coconut oil is a good source.

Garlic – long standing use as an anti-microbial.

Oregano – broad spectrum anti-microbial activity.

Grapefruit seed extract – research shows evidence for anti-bacterial activity against gram-positive and gram-negative bacteria.

Green tea – anti-bacterial and anti-fungal activity.

It is sometimes advisable to take a live bacteria supplement along with the anti-microbial (although take at least two hours apart from each other) to help ensure a healthy balance of gut flora in the large intestine. If SIBO has been confirmed (or is strongly suspected) then an initial period (e.g. four to six weeks) of anti-microbials without live bacteria may be recommended.

Gluten sensitivity and IBS

Wheat is a staple carbohydrate in Western diets, often being consumed in some form at every meal and snack. It contains a protein called gluten. Gluten is also found in rye and barley. Oats contain no gluten as such, but since oats are often grown and processed along with wheat, most conventional oat products contain traces of gluten. Since the publication of a number of studies on the effects of gluten on human digestion by researchers such as Dr Alessio Fasano and his colleagues, public interest in gluten-related issues has increased.15

The protein gluten increases gut permeability (i.e. leaky gut) for a while after it is eaten. This happens to some degree in everyone every time foods containing gluten are eaten. This can lead to an immune response and be a contributory factor in inflammation. A healthy body will ‘mop up’ the inflammation and repair the leakiness of the gut until gluten is eaten again and the process starts again. However, because gluten containing foods are often eaten at every meal and snacks in between – the body’s capacity to ‘repair’ the gut after eating these foods may be exceeded, and this can increase the likelihood of developing a sensitivity to gluten – a condition referred to as ‘non-coeliac gluten sensitivity’ (NCGS) which is linked to many conditions and symptoms can include anxiety, depression, skin eruptions, bloating, constipation and / or diarrhoea and more.

Gluten can also trigger an autoimmune condition in the small intestine called coeliac disease (CD) whereby the cells (enterocytes) lining the digestive tract are severely damaged and inflamed and digestion is significantly impaired, the only treatment for this is to completely avoid gluten.

Some patients who have been diagnosed with irritable bowel syndrome (IBS) report a lessening of symptoms when they follow a gluten-free diet. Although various diets have been suggested to benefit IBS patients, the largest body of evidence relates to two specific diets; a diet low in fermentable oligo-saccharides, di-saccharides, and mono-saccharides, and polyols (FODMAPs) and a gluten-free diet.16

The 5-Step Plan for IBS/leaky gut

Nutritional therapy practitioners use a 5-step programme for IBS, developed by Dr Jeffrey Bland. This is discussed in depth in a previous blog on leaky gut.

Supplementary Support

Probiotics are live microorganisms with therapeutic potential for gastrointestinal disease. Probiotics have a beneficial effect on intestinal mucosa via several proposed mechanisms that include suppression of the growth and binding of pathogenic bacteria, improvement of the barrier function of the epithelium, and alteration of the immune activity of the host.17 In addition, probiotics may improve bowel dysmotility.18

In one trial, IBS patients were found to have an abnormal pro-inflammatory IL-10/IL-12 ratio, which was normalised in conjunction with symptom alleviation by consumption of the probiotic Bifidobacterium infantis.19

Saccharomyces boulardii

For those who have an imbalance of bacteria or Candida (a fungus that causes thrush), the use of Saccharomyces boulardii may be suitable. This beneficial yeast has been subject to much research with positive outcomes with regard to Candida infections, bacterial infections and antibiotic-associated diarrhoea.

One study aimed to evaluate the effects of Saccharomyces boulardii on quality of life and symptoms in patients with IBS-D or mixed-type IBS. It was concluded that Saccharomyces boulardii improved quality of life but was not superior for individual symptoms in patients.20

Another study evaluated the effects of mesalazine alone, Saccharomyces boulardii alone or combined therapy of mesalazine with Saccharomyces boulardii on symptoms of IBS-D patients. Mesalazine is an aminosalicylate medicine commonly used to treat inflammatory bowel diseases.  The trial concluded that all three interventions, i.e. the use of mesalazine alone, Saccharomyces boulardii alone or combined treatment with mesalazine and Saccharomyces boulardii, improved IBS-D symptoms.21

Digestive Enzymes

If levels of digestive enzymes are low, larger undigested food molecules will be more available for fermentation by bacteria in the small intestine. Supporting with pancreatic enzymes as well as bile production, in the short term, may help with symptom relief.

Pancreatic and digestive function can be supported by:

  • Taking a digestive enzyme supplement with meals
  • Consuming bitter foods (lemon, rocket, chicory, watercress) which stimulate bile secretion
  • Taking lecithin which supports fat emulsification

Key Takeaways

  • A number of factors play a role in the pathogenesis of IBS including diet, intestinal microbiota, heritability and genetics, low-grade inflammation and disturbances in the neuroendocrine system of the gut. Stress and anxiety and antibiotic use are other important contributory factors as they will impact the composition of the microbiota.
  • Small Intestinal Bacterial Overgrowth (SIBO), where there is an overgrowth of bacteria in the small intestine, may be a cause of IBS.
  • Common symptoms of IBS are abdominal pain, cramping, bloating, diarrhoea, constipation and general discomfort in the abdomen. Nausea and loss of appetite may also be present.
  • Sugar, sweeteners, refined and processed foods, a lack of natural fibre and inadequate hydration may be responsible for symptoms of bloating, pain, flatulence, diarrhoea and constipation.
  • Soluble fibre is often the best fibre to introduce initially and good sources include fruit, vegetables (cooked), pulses and oats.
  • FODMAPs are dietary sugars and carbohydrates which are easily fermented by gut bacteria and which can exacerbate symptoms of gas, bloating and pain. It is often very useful to remove them from the diet for a limited period.
  • Natural antimicrobials can be useful for removing bacteria from the small intestine such as caprylic acid, coconut oil, garlic, oregano, grapefruit seed extract, green tea.
  • Some patients who have been diagnosed with irritable bowel syndrome (IBS) report a lessening of symptoms when they follow a gluten-free diet.
  • Probiotics are live microorganisms which have a beneficial effect on intestinal mucosa and may improve bowel dysmotility.


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If you have questions regarding the topics that have been raised, or any other health matters, please do contact me (Jackie) by phone or email at any time., 01684 310099

Jackie Tarling and the Cytoplan Editorial Team

Last updated on 18th June 2021 by cytoffice


8 thoughts on “Nutritional support for Irritable Bowel Syndrome

  1. “Thank you “an excellent detailed write up
    Lots of interesting information to digest, and very helpful

    1. Hi Natalie, if you have blood in your stools we would recommend you visit your GP who will be able to arrange suitable tests for you.

  2. Fascinating useful article. I’m wondering how diabetes and diabetes drugs affects the IBS and best ways of managing this. It seems to be well known that some drugs notably metformin can have effects on the intestine that are similar to SIBO or irritable bowel. This happened to me . The impact is worse than the diabetes. I’ve been managing these symptoms for over 10 years. It would be interesting to read more about blood sugar support and intestine and bowel symptoms

    1. Hi Su, thank you for your feedback. You are quite right that the evidence does suggest that drugs like metformin can affect gastrointestinal health through several mechanisms, including increasing the bile acid pool and altering the microbiome. It might be that you could benefit from a period of gut healing – please do get in touch with our team of nutritional therapists who will be able to help you put a protocol together –

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