What is the Fodmap diet and why might it help my IBS symptoms?
One of the most common symptoms of IBS is that of abdominal bloating and distention. Distention of the gastrointestinal (GI) tract can cause abdominal pain, especially in IBS patients who already suffer from a hypersensitive GI tract. Luminal distention may also change intestinal motility. No medication is currently available to prevent luminal distention, and commonly used medications to treat bloating are often ineffective (eg. Charcoal, simethicone, smooth muscle antispasmodics). Thus, researchers have recently focused their efforts on dietary factors that could contribute to abdominal bloating and distension. The FODMAP diet appears to be the most successful diet to date to improve symptoms of bloating, distention, and pain in IBS patients.
The acronym FODMAP stands for Fermentable Oligo-, Di-, and Monosaccharides and Polyols. This term is meant to group together a variety of food substances, such as short-chain carbohydrates and sugar alcohols (polyols), that have similar functional properties. The food groups covered by the FODMAP rubric include fructose, fructo-oligosaccharides (fructans), galacto-oligosaccharides (galactans), and polyols (ie. sorbitol, mannitol, xylitol, and malitol). These foods are linked by their ability to cause luminal distention because of the following:
- They are poorly absorbed in the small intestine. Although the end effect (poor absorption) is the same, there are several different mechanisms that cause this. For example, fructose, which is a monosaccharide, requires a transport mechanism for uptake from the GI tract and this transport mechanism (called GLUT) has a low capacity. Fructose is also absorbed alongside glucose. However, if fructose is present in higher concentrations than glucose, then fructose malabsorption will occur. Fructans and galactans are not well absorbed because the necessary enzymes (hydrolases) are absent from the small intestine. Finally, polyols are too large for simple diffusion.
- They are small molecules and thus osmotically active. These low molecular weight molecules exert an osmotic effect in the small intestine and thus actively draw water into the intestinal tract, increasing liquidity of the intestinal contents and accelerating GI tract motility.
- They are rapidly fermented by bacteria. The rate of fermentation of food products in the colon is determined by the length of the carbohydrate chain. The short-chain carbohydrates included in FODMAP are more rapidly fermented in the colon, thus quickly causing distention and discomfort.
What Food Groups Should Be Avoided?
- Food with excess fructose. This includes fruits such as apples, cherries, mango, pears, peaches, canned fruits in their natural fruit juice, watermelon, and large quantities of fruit juice or dried fruit. Vegetables to be avoided include asparagus, artichokes, and sugar snap peas. Honey and products with high fructose corn syrup (juices, regular soft drinks, sports/energy drinks) should also be avoided.
- Fructans (fructo-oligosaccharides), which are made up of short chains of fructose with a glucose molecule on the end. This includes grains (rye, wheat bread, crackers, biscuits, wheat pasta, and cous cous); fruits such as peaches, persimmons, plums, and watermelon; vegetables such as onions, peppers, artichokes, brussel sprouts, broccoli, cabbages, fennel, garlic, okra, leeks, and legumes (baked beans, chickpeas, lentils, and kidney beans).
- Galactans (galacto-oligosaccharides), which are short chains of sucrose with galactose (similar to the fructans list above).
- Polyols (also called sugar alcohols). This includes low calorie sweeteners such as sucralose, and also sorbitol, manitol, xylitol, and malitol (which are often used in “sugar-free” candies, gums, and mints). Fruits that contain sorbitol include apples, apricots, pears, blackberries, nectarines, and plums. Vegetables that contain mannitol include cauliflower, mushrooms, and snow peas.
Note: lactose (which is a disaccharide, made up of glucose and galactose) is not technically considered a part of the FODMAP diet. However, if a patient is lactose deficient, then lactose cannot be broken down, and it acts similarly to fructans and galactans with regard to producing GI distress.
What Data is Available to Support This Diet in IBS Patients?
In one study of 12 patients who had ileostomies, the FODMAP diet decreased ileostomy output by 22% and also decreased the liquidity of ileostomy output.1 In a study of 15 healthy volunteers and 15 IBS patients (Rome II criteria), a diet low in FODMAPs led to significantly lower breath hydrogen levels than a diet high in FODMAPs. 2 The high FODMAP diet also caused significant GI distress and lethargy in the IBS patients, while the healthy volunteers only noted increased passage of flatus. Finally, a recently published study on 82 consecutive IBS patients attending a dietetic outpatient clinic found that a low FODMAP diet (n = 43) improved symptoms of bloating (p = 0.002), abdominal pain (p = 0.023), and flatulence (p = 0.001), compared to a standard diet (n = 39). 3 Overall compliance was high. The mean time for symptom improvement was 3.5 weeks.
What Foods Fit Within the FODMAP Diet?
- Gluten – Free or spelt toast
- Corn or rice cereals
- Lean – proteins (chicken, turkey, fish, pork, lamb, red meat)
- Cheeses with no or low lactose (these are typically the hard cheeses)
- Rice cakes
Fruits and vegetables not listed previously. Fruits that are generally safe include bananas, grapefruit, grapes, kiwifruit, mandarin oranges, honeydew melons, tangelos, oranges, strawberries, lemons, limes, and blueberries (in small amounts). Vegetables that are generally safe include bamboo shoots, bok choy, carrots, eggplant, green beans, lettuce, tomatoes.