By: Allison Duke Bridges, M.D.
As a gastroenterologist, a significant portion of my daily practise involves treating patients with irritable bowel syndrome. Treating these patients can prove rather challenging as there are subsets that respond to differently to various treatments, likely reflecting the different proposed mechanisms of IBS such as visceral hypersensitivity, gut flora derangement and so forth. Dietary modification can be beneficial for IBS patients and the FODMAP diet can be an excellent alternative/addition to medications. FODMAP was originally discovered by a group in Australia. It is an acronym deriving from “Fermentable, Oligo-, Di-, Mono-saccharides And Polyols.” The principal behind this is that the consumption of some common dietary sugars plays a role in fermentation and in osmotic effects in the bowel as well as visceral hypersensitivity.
Fructose is a monosaccharide like glucose and galactose, and when combined with glucose forms sucrose or table sugar. Fructose is the sugar most commonly found in fruits and honey. Many processed foods contain high fructose corn syrup. Fructose may cause GI symptoms when the fructose/sucrose balance is offset. If fructose exceeds the sucrose component, malabsorption of fructose occurs.
Fructans are oligosaccharides typically found in vegetables such as asparagus, artichokes and onions, fruit such as apples and wheat. Wheat accounts for much of the fructan intake in the typical American diet. Fructan sensitivity may be why patients that test negative for celiac disease can still have improvement in their symptoms with avoidance of wheat.
Lactose is a disaccharide commonly found in milk products. Irregardless of IBS diagnosis, up to 90% of people have some degree of lactose intolerance. The rate varies significantly according to ethnicity and age. Dairy foods low in lactose include hard cheeses, sour cream and butter. These foods are considered “safe” even following the FODMAP diet. Yogurt that contains lactobacillus may be tolerated as well. Using the enzyme lactase (Lactaid), may aid in one's tolerance to this food group.
Galactan is a polymer of galactose. Galactans are found in certain vegetables such as legumes. Humans lack an enzyme to digest galactans. Consuming these foods create an osmotic effect along with fermatation, resulting in gas, bloating and diarrhea.
The final part of the FODMAP diet are the polyols or sugar alcohols (sorbitol, mannitol, and xylitol) which are found naturally in fruits such as watermelon and are commonly in diabetic sweeteners. While these may be the best choice for glucose control, they very commonly cause adverse GI side effects related to the osmotic effects.
The key to management of IBS is not necessarily more medication, or instruction to “eat more fiber.” Many foods high in fiber may also be high in fructose, fructans, or galactans actually exacerbating IBS symptoms. A food diary can be beneficial for IBS patients. Suggesting a FODMAP elimination diet, with slow re-introduction of each compoent of the diet back into their diets can help identify specific food intolerances and aid in avoiding future IBS symptoms/flares. For more information on this, I recommend a comprehensive book called IBS—Free at Last! written by a dietician named Patsy Catsos that details the FODMAP diet.
Allison Duke Bridges, M.D.
Gastroenterology Associates, N.A. P.C.