Diets for irritable bowel syndrome: what you need to know

The educational content in this post, elaborated in collaboration with Bromatech, was independently developed and approved by the GMFH publishing team and editorial board.

Food is central for patients with IBS

People living with IBS often perceive food as a trigger of their digestive symptoms and many prefer nutritional intervention as first line treatment^1,2. This has led to a growing interest in the use of diet to reduce patient symptoms. Understanding the role of diet in IBS is in its infancy, but research is beginning to illuminate the food, gut microbiome and IBS connection.

84% of patients with IBS surveyed stated eating any food triggers gastrointestinal (GI) distress. The most common foods identified to cause IBS symptoms in patients include: carbohydrates, particularly those rich in FODMAPs (dairy products, brans, lentils, apple, flour and plum) followed by histamine rich foods (wine, beer, salami and cheese), fatty foods and caffeine^3,4.

Patients with IBS reduce intake of calories in attempt to reduce their symptoms⁵. For those with more severe symptoms, the greater the food avoidance, reduced quality of life and poor nutrient density of the diet⁶. Medical conditions that require or recommend diet therapy, appear to be associated with greater disorder eating risk, as observed in diabetes⁷, celiac disease⁸ and IBS⁹.

It is also important to consider that certain conditions resemble IBS and should be ruled out in the diagnostic process: small intestinal bacterial overgrowth, bile acid diarrhea, congenital sucrose isomaltase deficiency, systemic nickel allergy and high stool burden related to pelvic floor dysfunction¹⁰. This differential diagnosis will have implications for dietary management of IBS. For instance, patients with sucrase-isomaltase deficiency may not respond to a low FODMAP diet¹¹.

One size does not fit all: Checklist before recommending diet therapy

Before recommending diet therapy to an individual with IBS, the gastrointestinal provider should:

Screen for an eating disorder or disordered eating
Ensure the patient desires nutritional intervention
Confirm that eating triggers gastrointestinal symptoms (if not, a diet change is unlikely to help)
Ensure patient has the lifestyle and financial means to follow a restrictive diet

What diet to choose in IBS?

Dietary approaches with emerging evidence for IBS include:

Healthy eating habits or traditional IBS dietary advice: it is often recommended as the first-line option for patients with IBS. Recommendations include individualized dietetic advice based on patient symptom profile and habitual diet, eating smaller and more frequent meals, adequate fluid intake, modest use of alcohol, coffee, tea and fizzy drinks, 3 fruit limit, limit whole meal grains, restrict sorbitol foods if diarrhea, add flaxseed if constipation and add oats and flaxseed if bloating and flatulence^1,12.
Low FODMAP diet: A 3 phase elimination diet that involves reducing FODMAPs, a group of commonly malabsorbed carbohydrates. FODMAPs pull water into the small intestine and are fermented by the colonic gut microbiota creating gas. The 3 phases of the low FODMAP diet include: the elimination phase: where all high FODMAP foods are eliminated, followed by the reintroduction phase where FODMAP foods are systematically added back to the diet to identify food triggers and lastly the personalization phase where tolerated FODMAP containing foods are added back to the diet to create a more liberal personal diet. This diet should be followed under the supervision of a GI expert dietitian as it is not intuitive to follow and to help ensure all 3 phases are completed and the diet is balanced and nutritious^13-16.
Flexible approach to the low FODMAP diet or FODMAP gentle: it is based on a more liberal restriction of FODMAPs based on patient symptoms and dietary intake. The highest FODMAP foods that are commonly restricted include grains, dairy, legumes, some vegetables (onion and garlic, primarily) and fruits¹⁷.
Mediterranean diet pattern: a diet with vegetables, fruits, pulses (legumes), wholegrains, nuts, seeds and extra virgin olive oil, some dairy products (cheese and yogurt), moderate fish and some meat leads to positive shifts in gut microbiota and mental health^18-20.

Each diet has its own pros and cons that are discussed in detail in the accompanying infographic at the end of the post.

Dietary approaches with insufficient evidence

There is insufficient evidence that supports the role of other restrictive diets such as the gluten-free diet and low total-carbohydrate diets that exclude disaccharides and most polysaccharides (e.g., the Specific Carbohydrate Diet) for managing IBS symptoms. These diets limit dietary variety, with a potential negative effect on the composition and functions of the gut microbiome.

A GI dietitian is crucial to personalize diet based on disease history, GI symptoms, dietary preferences, as well as the social and cultural needs of the patient.

Other components in wheat beyond gluten could also play a relevant role in abdominal pain, bloating and diarrhea such as proteins (including amylase tripsin inhibitors, wheat-germ agglutinin, wheat bran and wheat protein) and carbohydrates (fructans)^21-23.
While a low-histamine diet has not been properly studied in patients with IBS, a low-histamine diet (consuming fresh and minimally processed foods and reduce high histamine foods) could help patients with IBS that identify histamine-containing foods as a trigger to their symptoms^3,11.
Malabsorption of sucrose and starches may lead to diarrhea, gas and bloating in adult patients with a sucrase-isomaltase deficiency, which can be congenital or secondary to a mucosal injury or small intestinal inflammation. A diet low in foods high in sucrose or trial of sacrosidase, an enzyme supplement that helps digest sucrose, should be trialed in patients with IBS-diarrhea or IBS-mixed pattern who do not respond to a low FODMAP diet^11,24.
Bioactive chemicals such as salicylates and atropine and hyoscyamine found in tomatoes, peppers, eggplants and white potatoes (Solanaceae family of plants) have some data suggesting that they may be involved in IBS symptoms^25,26.

Take-home messages

Diet is central for patients with IBS and the support of a specialist GI dietitian is is best to deliver a tailored approach based on disease history, dietary and lifestyle preferences of the individual.
Ideally, nutritional interventions for IBS should allow for the most liberal and nutritious diet while offering good symptom control.
The most frequently science-based diets for IBS include traditional dietary advice, a diet low in FODMAPs and a modified Mediterranean-type diet.
Diets with a lack of evidence for IBS are a gluten-free diet and a low carbohydrate diet.