Blog | Tuesday, December 13, 2011

Difficult to digest carbohydrates implicated in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic condition marked by abdominal pain, bloating, and alternating constipation and diarrhea. There is no specific test for IBS and other more serious diseases like celiac disease and inflammatory bowel disease can cause similar symptoms. The good news is that when a doctor has ruled out these more serious diseases and diagnosed IBS the patient can be assured that her illness is chronic but not progressive or life-threatening. The bad news is that IBS symptoms can be quite miserable, and at their worst can interfere with work and life activities.

Myriad treatments are used for IBS, and as with any disease with myriad treatments, that means that none of them are consistently effective. I wrote five years ago about a trial that showed modest success using antibiotics for IBS but even that trial did not show an improvement in the majority of patients.

A new theory proposed by researchers in Australia holds that IBS is caused by certain sugars that are difficult to digest. These sugars pass undigested through the small intestine and are fermented by bacteria in the colon. This releases carbon dioxide which causes bloating and pain, and draws water into the colon which causes diarrhea.

These carbohydrates are called FODMAPs, which stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols, which just means small sugars that can undergo fermentation.

FODMAPs are present in lots of foods. (This Wall Street Journal article has a handy table with a list of foods high in FODMAPs and low in FODMAPs.) So eliminating them entirely requires some drastic dietary changes. Nevertheless, the Australian researches published a study in last month's issue of the Journal of Human Nutrition and Dietetics in which patients were randomized to standard care or to a FODMAP-free diet. About half of the patients in the standard group had symptom improvement, compared to about three quarters of those on a FODMAP-free diet.

Gastroenterologists who are promoting this theory recommend that patients try a FODMAP-free diet for six to eight weeks and then slowly reintroduce FODMAP-containing foods to determine what quantities they can tolerate. Unlike food allergies, complete abstinence is not necessary. It's just a matter of reducing the FODMAPs below whatever threshold causes misery.

Some caveats are necessary. The study was quite small, and it was not blinded since it's impossible not to know whether your diet is being restricted radically. So the results should be treated as suggestive but preliminary. Still, for those with severe IBS symptoms a FODMAP-free diet may be worth a try. It may be inconvenient but it's certainly safe and the worst that could happen is that it won't work.

Learn more:
When Everyday Foods Are Hard to Digest (Wall Street Journal)
Very Restricted Diet May Reduce Symptoms of IBS (WebMD)
Irritable Bowel Syndrome (National Library of Medicine information page)
An Oral Antibiotic Reduces the Symptoms of Irritable Bowel Syndrome (my post in 2006)
Comparison of symptom response following advice for a diet low in fermentable carbohydrates (FODMAPs) versus standard dietary advice in patients with irritable bowel syndrome (Journal of Human Nutrition and Dietetics)

Albert Fuchs, MD, FACP, graduated from the University of California, Los Angeles School of Medicine, where he also did his internal medicine training. Certified by the American Board of Internal Medicine, Dr. Fuchs spent three years as a full-time faculty member at UCLA School of Medicine before opening his private practice in Beverly Hills in 2000. Holding privileges at Cedars-Sinai Medical Center, he is also an assistant clinical professor at UCLA's Department of Medicine. This post originally appeared at his blog.