Inflammatory bowel disease (IBD), encompassing Crohn’s disease and ulcerative colitis, is characterized by auto-inflammatory conditions of the gastrointestinal tract. While medications primarily manage IBD by targeting inflammation to heal the gut, many individuals continue to experience symptoms like abdominal pain, diarrhea, bloating, and constipation, even when inflammation is under control. In such cases, these persistent gastrointestinal (GI) symptoms may relate to irritable bowel syndrome (IBS) within IBD, or other Disorders of Gut-Brain Interaction (DGBI), which may be addressed with the Low-FODMAP Diet.
Understanding FODMAPs
FODMAP is an acronym that stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols. These are specific types of carbohydrates that are often poorly absorbed in the small intestine.
- Fermentable: FODMAPs are readily fermented by bacteria in the colon, producing gases.
- Oligosaccharides: This group includes fructans and galacto-oligosaccharides (GOS) found in foods like wheat, rye, onions, garlic, and legumes. These are soluble plant fibers known as prebiotics, which feed the beneficial bacteria in your gut. Sensitivity to oligosaccharides may help explain some cases of non-celiac gluten sensitivity. Since gluten-free grains are lower in fermentable sugars than grains that have gluten, some people who think they are sensitive to gluten may actually be sensitive to the oligosaccharides residing in wheat products.
- Disaccharides: Lactose, the sugar found in dairy products, is the primary disaccharide of concern. Lactose intolerance is one of the most common food intolerances worldwide.
- Monosaccharides: Fructose, the sugar found in fruits and honey, is a monosaccharide. High-fructose foods can be problematic for some individuals. But only in certain quantities and proportions, so not all fruits are affected.
- Polyols: These include sugar alcohols like sorbitol, mannitol, xylitol, and isomalt, often used as artificial sweeteners. They are also found naturally in some fruits.
How FODMAPs Affect the Gut
FODMAPs, being fermentable short-chain carbohydrates, draw more water into the intestines, which can perpetuate diarrhea. The fermentation of high-FODMAP foods by bacteria in the colon can cause bloating, gas, and cramping pain. This increased fluid and gas in the bowel leads to bloating and changes in the speed with which food is digested. This results in gas, pain and diarrhea.
The Low-FODMAP Diet: An Overview
The Low-FODMAP Diet is a temporary dietary plan that limits the intake of these fermentable carbohydrates. It is used to treat symptoms of Irritable Bowel Syndrome (IBS). Studies show that a low FODMAP diet will help to treat up to three-quarters of people with IBS and there is evidence to show that a low FODMAP diet also helps control symptoms in the majority of people with both quiescent (inactive) IBD and IBS. As some patients with IBD also have the coexistence of IBS, it may be helpful to treat persistent gastrointestinal (GI) symptoms in patients with IBD who have low levels of inflammation, where symptoms may be attributed to IBS rather than IBD.
In following the Low-FODMAP Diet, specific carbohydrates (high-FODMAP foods) are excluded for a period of time and then slowly reintroduced in order to determine which ones in particular may activate symptoms. Small daily amounts of each carbohydrate type are generally well tolerated. The cumulative effect of consuming large daily amounts of higher FODMAP carbohydrate foods may be the cause of GI distress. Higher FODMAP fruits and vegetables that are excluded include onions, garlic, apples, etc; it is recommended to specifically include fruits and vegetables that are low in FODMAPs, such as berries, nuts, carrots, green leafy vegetables, etc.
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Three Phases of the Low-FODMAP Diet
The diet consists of three distinct phases:
- Elimination Phase: During this phase, all high-FODMAP foods are eliminated from the diet for 2-4 weeks. This allows the gut to rest and symptoms to subside. At first glance, the elimination phase of the diet may seem very limited. But there’s still a good list of foods in each category that you can eat. It takes some mental discipline to follow, but you won’t go hungry on the diet.
- Reintroduction Phase: After the elimination phase, FODMAP foods are systematically reintroduced one at a time to identify specific triggers. The third phase keeps what works for you and leaves out what doesn’t.
- Maintenance Phase: This involves a long-term, personalized diet that restricts only the FODMAPs identified as triggers during the reintroduction phase.
Key Considerations for IBD Patients
People with IBD are three times more likely than the general population to have irritable bowel syndrome (IBS), which refers to a condition affecting the ‘function’ of the bowel and involves an increase in bowel sensitivity rather than inflammation of the bowel. If you have IBD, it is important to ensure that the presence and degree of inflammation is not based only on symptoms. Your doctor will interpret various tests and guide you as to whether your symptoms are inflammatory (active IBD) or functional (IBS) or both.
Important Note: The low-FODMAP diet has not been shown to reduce inflammation and is recommended for symptom relief only, rather than disease management. It is further recommended for use short term (4 weeks) rather than longer term because it may adversely affect the microbiome.
Implementing the Low-FODMAP Diet
Patients with IBD seeking to implement a Low-FODMAP Diet should consult with a dietary professional. Low-FODMAP Diet may not be a good choice for everyone, particularly for those at risk of developing eating disorders. It is also difficult to implement properly, so it is best undertaken with an experienced dietitian.
Dietary Guidelines and Precautions
- Fiber Intake: Excessive fiber intake from fruits and vegetables can cause GI pain and an increased risk of a bowel obstruction, particularly in patients with strictures. Fiber-containing foods should be added in small quantities at a time to allow the body to adapt to processing more fiber and build the proper muscles and bacteria to handle fiber. Patients with strictures should take extra care to first peel fruits and vegetables and cook them well and may need to consider pureeing them initially. For patients who are not currently consuming many fiber-containing foods, slowly adding in high-FODMAP foods could cause gastrointestinal symptoms due to the fiber rather than the carbohydrates.
- Nutritional Adequacy: The risk of compromising nutritional status with a restrictive diet must be seriously considered especially as under-nutrition is already common in this patient population. People with IBD may have increased requirements of certain nutrients, so it is important that you do not restrict your diet without advice from a dietitian. As undernutrition is common in IBD, the use of restrictive diets should be supervised by a dietitian.
Low- and High-FODMAP Food Choices
Here's a general guide to low- and high-FODMAP foods:
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| Food Group | Low-FODMAP Foods | High-FODMAP Foods |
|---|---|---|
| Vegetables | Eggplant, green beans, bok choy, bell pepper, carrot, cucumber, lettuce, potato, tomato, zucchini | Artichoke, garlic, leek, onion, spring onions (high in fructans), Mushrooms, cauliflower, snow peas (high in mannitol) |
| Fruits | Cantaloupe, grapes, kiwi, orange, pineapple, strawberries | Apples, pears, mangoes, cherries, figs, nashi pears, pears, watermelon, dried fruit (high in fructose) |
| Dairy & Alternatives | Almond milk, brie and camembert cheese, feta cheese, hard cheeses, lactose-free milk, soy milk (made from soy protein) | Soft cheeses, milk, yogurt (high in lactose) |
| Proteins | Eggs, firm tofu, plain cooked meats/poultry/seafood, tempeh | Red kidney beans, split peas, falafels, baked beans (high in GOS) |
| Grains | Corn flakes, oats, quinoa flakes, quinoa/rice/corn pasta, rice cakes (plain), sourdough spelt bread, wheat-/rye-/barley-free breads | Wholemeal bread, rye bread, muesli containing wheat, wheat pasta, rye crispbread (Fructans and GOS) |
| Sweets | Dark chocolate, maple syrup, rice malt syrup, table sugar | Honey, HFCS, artificial sweeteners (high in polyols) |
| Nuts & Seeds | Macadamias, peanuts, pumpkin seeds, walnuts | Cashews and pistachios (high in GOS and fructans) |
FODMAPs and the Gut Microbiome
FODMAPs act as prebiotics in the gut, meaning they stimulate the growth of good bacteria, which is probably important if you have IBD, so always aim to minimise your FODMAP restriction. The effects of FODMAPs on the gut microbiota of patients with Crohn's disease mimic that in IBS, with a balance between prebiosis from the addition of FODMAPs and loss of prebiosis from their reduction. A dietitian can guide you on how to find the level of FODMAP restriction suitable for you.
Other Dietary Considerations for IBD
Other options for treating persistent symptoms are a Gluten-free, Dairy-Free and/or Lactose-Free Diets or avoiding Trigger Foods. While gluten-free diet is applied by patients, there are no reported interventional studies. Gluten and FODMAPs are found in the same grains, so people may feel better because FODMAPs are incidentally reduced on a gluten free diet.Low fibre and low residue diets are only recommended in special circumstances, e.g., if you are at risk of bowel obstruction (blockage). Your doctor and dietitian will tell you if this type of diet is indicated.
Scientific Evidence and Research
Studies are underway to investigate whether diet can be used to treat gut inflammation in IBD, however there is currently not enough evidence to recommend any particular diet as effective. The low-FODMAP diet, on the other hand, has efficacy similar to that seen in patients with IBS in three unblinded or observational studies of IBD cohorts who had well-controlled inflammatory disease and in one small randomized cross-over study. FODMAP intake by patients with IBD is not elevated, and, in one study, fructan intakes were lower in patients with Crohn's disease than in controls. There is no clear relationship between the level of FODMAP intake and intestinal inflammation.
A meta-analysis showed that a low FODMAP diet is beneficial for reducing gastrointestinal symptoms in patients with quiescent IBD.
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