Diaeta, dietary advice for Irritabe Bowel Syndrme (IBS)

Irritable Bowel Syndrome (IBS)

 Pierre ABOU-ZEID Registered Dietitian and Nutritionist
Pierre Abou-Zeid

Registered Dietitian and Nutritionist

Abdominal pain, bloating, intestinal transit disorders, excessive flatulence, incomplete evacuation and nausea.

Irritable Bowel Syndrome (IBS) is a chronic and relapsing disease. Symptoms often wax and wane, and the severity of symptoms varies within and between individuals. Because IBS symptoms vary widely, diagnostic criteria have been developed to classify patients according to the predominant symptom type.

Irritable Bowel Syndrome (IBS) is a very heterogeneous condition, in terms of :

  • pathophysiological factors contributing to the disease,
  • predominant symptoms,
  • the natural progression of the disease, and
  • response to treatment.

This heterogeneity is also observed with the severity of symptoms which may differ between individuals and also within the same individual over time. The severity of IBS symptoms can be classified as mild, moderate, or severe.

Irritable Bowel Syndrome (IBS) is considered a chronic disease, characterized by exacerbations that worsen and change over time.

The types of symptoms experienced by people with Irritable Bowel Syndrome (IBS) can also change over time. People most often transition from IBS-Constipation or IBS-Diarrhea to a mixed subtype (IBS-M), but less often transition from IBS-C to IBS-D (or vice versa).

Irritable Bowel Syndrome (IBS) should be diagnosed by a physician, who should take a careful history and use the Rome IV criteria as a guideline.

The Rome Foundation was founded in the 1980s and uses experts to provide guidelines on the diagnosis and treatment of functional bowel disease. The Rome criteria allow patients to be subclassified based on their predominant bowel habit (using the Bristol stool chart) into IBS-C, IBS-D, IBS-M, or IBS-I (unknown) (see definitions below).


Recurring abdominal pain on average at least 1 day per week over the past 3 months, associated with two or more of the following :

  • Related to defecation
  • Associated with a change in stool frequency
  • Associated with a change in the shape (consistency) of the stool.

A diagnosis of Irritable Bowel Syndrome (IBS) is often made to patients in uncertainty and after considerable delay; long after the first symptoms appear. For example, one study showed that 1/4 of patients with IBS visited a healthcare professional at least 5 times before a formal diagnosis was made, while another showed that the average time to first diagnosis of IBS was 7 years old. These problems are compounded by the use of uncertain language around the diagnosis of IBS (for example, you may have some IBS). This scenario contributes to anxiety about the cause of persistent symptoms and diminishes patients' ability to accept their diagnosis and engage in effective treatments.

There are currently no pathophysiological tests available to adequately diagnose IBS, so symptoms play an important role in establishing a positive diagnosis. However, as the symptoms of IBS overlap with many other organic diseases, there is a risk of misdiagnosis.

Common symptoms that overlap between IBS and other more serious organic diseases include abdominal pain, bloating, altered bowel habits, excessive gas, incomplete evacuation, and nausea.

Celiac disease

Celiac disease is a chronic autoimmune disease characterized by enteropathy of the small intestine in response to gluten ingestion in genetically predisposed individuals. The only reliable treatment for celiac disease involves a lifelong, strict gluten-free diet.

Celiac disease must be ruled out before a diagnosis of IBS is made. This is important for several reasons, for example :

  • There is considerable overlap between the symptoms of IBS and celiac disease, with symptoms such as bloating, abdominal pain, and chronic diarrhea common to both diseases.
  • Celiac disease is up to 4 times more common in people with IBS than in healthy people.
  • Although celiac disease is relatively uncommon (affecting about 1% of the world's population), it goes undiagnosed in the majority of cases.

These factors create a risk of misdiagnosis, whereby people with undiagnosed celiac disease may be misinformed that they have IBS. Misdiagnosis of IBS is problematic because the two conditions require very different treatments. Additionally, gluten exposure in people with undiagnosed celiac disease is associated with a range of complications, including nutrient deficiencies, osteoporosis, infertility and lymphoma.

The patient's dietary gluten intake is the key factor that determines the type of celiac screening tests to be performed.

  • If a patient is on a gluten-containing diet, a diagnosis of celiac disease can be safely made using serologic testing and duodenal biopsy. However, if a patient is on a gluten-free diet, these tests may provide false negative results.
  • Patients on a gluten-free diet can either undergo genetic testing, followed by gluten challenge and duodenal biopsies, or undergo gluten challenge and then undergo serological testing +/- duodenal biopsies.

Inflammatory Bowel Disease (IBD)

Inflammatory bowel disease is characterized by chronic inflammation involving the gastrointestinal tract in genetically susceptible individuals. The most common types of inflammatory bowel disease are Crohn's disease (transmural inflammation involving any part of the gastrointestinal tract), ulcerative colitis (mucosal inflammation limited to the colon), and indeterminate colitis. Microscopic colitis, a common cause of chronic non-bloody diarrhea due to immune infiltration of the colonic epithelium, is another lesser-known form of inflammatory bowel disease.

Diverticular disease

When diverticula become infected, it can lead to acute diverticulitis and symptoms of abdominal pain, altered bowel habits, and/or rectal bleeding.

Cancers (for example, ovarian or bowel cancer)

Large bowel cancer is one of the most common cancers in many developed countries. Early detection of precancerous polyps is important and can be done by colonoscopy.

Pelvic floor disorders

A subset of patients with gastrointestinal symptoms may have pelvic floor dysfunction. Common defecation disorders include dyssynergic defecation (in patients with constipation-like symptoms), while patients with chronic urgent diarrhea may have anal sphincter weakness. These conditions are more commonly reported in women, including those with eating disorders.


Endometriosis is a chronic inflammatory gynecological condition that can cause significant pain and infertility. The condition is thought to be caused by a retrograde flow of blood and menstrual tissue through the fallopian tubes into the pelvis. Here, endometrial tissue cells implant on the organs and tissues of the pelvic and abdominal cavities. Once implanted, lesions that respond to hormones associated with the menstrual cycle develop, leading to an inflammatory response and leading to adhesions, chronic pain, and in some cases, subfertility.

Endocrine disorders

The most common endocrine disorder that may go unnoticed in patients with IBS symptoms is thyroid dysfunction.

Pancreatic exocrine insufficiency

About 6% of patients with IBS symptoms have exocrine pancreatic insufficiency. Symptoms that may signal the presence of pancreatic exocrine insufficiency include abdominal symptoms that occur after ingestion of a high-fat meal; fatty and bulky stools that are difficult to pass; and fat-soluble vitamin deficiency.

Bile acid malabsorption

Bile acids are synthesized from cholesterol in the liver and are involved in the absorption of lipids in the small intestine. After their role in the formation of micelles in the small intestine, they are generally reabsorbed in the terminal ileum and taken up by the liver. The circulation of bile acids is very efficient, with 95% typically being recycled. The remaining portion of bile acid (~5%) that is not reabsorbed reaches the colon, stimulating electrolyte and water secretion. Bile acids that reach the colon have marked effects on motility, reducing transit time and causing symptoms of diarrhea, bloating, urgency and faecal incontinence.


People with diagnosed or undiagnosed IBS have often already sought advice from alternative medicine practitioners, such as naturopaths, massage therapists, and herbalists. These practitioners offer patients a range of investigations, diagnoses and alternative treatments, some of which are based on uncertain scientific principles. Diagnoses based on uncertain scientific principles are called pseudo-diagnoses. These diagnoses pose a risk to patients as they can delay correct diagnosis and treatment. Commonly encountered pseudo-diagnoses in this population include non-celiac gluten sensitivity and candidiasis.


A large proportion of people with IBS associate food intake with the development of gastrointestinal symptoms. Therefore, dietary restriction (based on scientific evidence or not) to control gastrointestinal symptoms is common in this population.

Foods commonly implicated in causing IBS symptoms include dairy products, wheat products, caffeine, cabbage, onion, peas, beans, and spicy/oily/smoky foods.

  • Fat

    Observational data suggests that dietary fat may trigger IBS symptoms in some people.

    Symptoms associated with eating fatty meals include abdominal pain, abdominal distention and bloating, increased gas, and loose stools.

    Adverse reactions to the ingestion of fatty meals could be explained by the well-documented presence of hypersensitivity and abnormal bowel reflexes in people with IBS. These translate into normally unperceived stimuli inducing symptoms in people with IBS. Fat ingestion may also increase visceral hypersensitivity, increase small bowel motility, and slow intestinal gas transport. The effects of fat ingestion on gas transport have been demonstrated in studies comparing the effects of duodenal lipid infusion in IBS patients and healthy subjects. In one study, infusion of duodenal lipids was shown to slow intestinal gas transport to a greater extent in participants with IBS than in healthy subjects. A similar study showed that infusion of duodenal lipids increased pain and discomfort more in people with IBS than in healthy subjects.

    Despite the association between fat ingestion and irritable bowel symptoms (IBS) and few plausible explanations, no high-quality research has measured the effect of a low-fat diet in the management of irritable bowel syndrome. Therefore, it is unclear whether there are causal relationships between fat consumption and IBS symptoms, or whether fat restriction improves IBS symptom control.

  • Proteins

    A number of dietary proteins have been implicated in the genesis of gut symptoms in people with IBS, including β-casein (from milk); rubisco (from spinach); wheat germ lectin; α-amylase/trypsin (ATI) inhibitors and gluten. However, the quality of evidence supporting the role of these proteins remains low.

    Gluten is the protein that has attracted the most attention due to its role in inducing abdominal symptoms in people with IBS. This interest has been fueled in part by the worldwide trend towards gluten-free eating among people without a diagnosis of celiac disease. In the United States, for example, an estimated 20% of consumers actively avoid foods containing gluten, compared to less than 1% with a diagnosis of celiac disease.

    These improvements can be mistakenly attributed to gluten, with a number of other food components reduced and/or eliminated on a gluten-free/wheat-free diet, including ATIs and fructans (from wheat). Dietary restriction of wheat affects intake of a range of nutrients, not just gluten.

  • Carbohydrates

    Carbohydrates implicated in causing IBS symptoms include fiber; prebiotics; and short-chain carbohydrates, such as lactose, sugar polyols (sorbitol and mannitol), fructose, and oligosaccharides (fructans and GOS).


    The fibers are fermented by the bacterial flora which results in the production of gas which results in distention of the intestines with pain, bloating, and excessive flatulence as a consequence.


    Lactose is a disaccharide made up of two sugar units, glucose and galactose. Sources high in lactose include cow's milk, soft cheeses, custard, sweetened condensed milk, and ice cream. To be absorbed in the small intestine, lactose must be hydrolyzed into individual sugar units (glucose and galactose) by the enzyme lactase. Lactase is mainly found at the end of the intestinal villi in the jejunum. Therefore, production of the enzyme lactase is susceptible to conditions that cause cell damage to intestinal villi, such as gastroenteritis and untreated celiac disease.

    In people who do not have enough lactase to complete the breakdown of lactose, poorly absorbed lactose draws water into the small intestine and passes undigested into the large intestine, where it is fermented by intestinal bacteria. The fermentation of poorly absorbed lactose can lead to unpleasant symptoms, including bloating, flatulence, stomach cramps and diarrhea. Lactose malabsorption that leads to unpleasant symptoms is known as lactose intolerance.

    When lactose malabsorption occurs as a result of damage to the intestinal epithelium (due to untreated celiac disease or intestinal inflammation), the condition is usually transient, with absorption improving when the epithelium heals. An important point here is that it may be helpful to retest lactose tolerance, as lactose tolerance can change over time.

    Sugar polyols

    Polyols are sugar alcohols that include sorbitol, mannitol, xylitol, and maltitol. Polyols are naturally present in certain fruits and vegetables, where they act as energy stores and osmolarity agents. Natural food sources of sorbitol include sweet corn, pears, apples, blackberries, and stone fruits. Mannitol is found naturally in vegetables, such as cauliflower, mushrooms, and snow peas. Polyols are also added to processed foods (like sugar-free chewing gum and lollipops) as sugar substitutes and humectants. Sugar polyols that have been added to manufactured foods can be identified from the following numbers on the product ingredient list: sorbitol (420), mannitol (421), maltitol (965), xylitol (967) and isomalt (953 ). Added polyols can also be identified by the statement on the product packaging, "excessive consumption may have a laxative effect".

    Because polyols are absorbed slowly and by passive diffusion, excess polyol molecules remain in the small intestine, attracting water. This increase in luminal water content leads to distension. Polyols that escape absorption in the small intestine enter the large intestine where they are fermented by bacteria in the colon, resulting in gas production (mainly hydrogen and methane) and bloating.

The informations on the Irritable Bowel Syndrome (IBS), are provided by the University of MONASH