In a randomized trial, people with irritable bowel syndrome with diarrhea (IBS-D) had significant pain and symptom relief on a diet that starves gut bacteria of some of their favorite foods, according to a new study.

The "low FODMAP" diet restricts foods that are high in fermentable oligo-, di- and monosaccharides and polyols (FODMAPs), short-chain carbohydrates that are poorly absorbed by the body but quickly fermented by intestinal bacteria. Fermentation produces gas and excess liquid, and may underlie the symptoms of IBS, the authors write in American Journal of Gastroenterology.

"FODMAPs are a family of fermentable carbohydrates that when ingested by healthy people do not cause gastrointestinal symptoms," said lead author Dr. Shanti L. Eswaran of the University of Michigan in Ann Arbor. "We are not really sure why those with irritable bowel syndrome are sensitive to these types of fermentable carbohydrates."

Ten to 15 percent of U.S. adults may have irritable bowel syndrome (IBS), symptoms of abdominal pain and changes in bowel movement patterns usually marked by either diarrhea or constipation. The condition is most common in women and people under age 45, according to the National Institutes of Health. Though there is no cure, diet, medication, probiotics and mental healthcare can help treat the symptoms.

"The existing guidelines for dietary changes in patients with IBS are based more on a common sense approach," Eswaran told Reuters Health by email.

Current guidelines include avoiding trigger foods and keeping a regular meal schedule, Eswaran and coauthors write, but these recommendations are not evidence-based and often ineffective.

FODMAPS include high-fiber foods and simple sugars that certain intestinal bacteria thrive on fermenting. Many vegetables and fruits and all wheat products are high in FODMAPS, and restricted on the diet. Some vegetables and fruits, most protein sources, and oats, rice and quinoa are low in FODMAPS and permitted on the diet.

The researchers compared one group of patients with IBS-D on a low FODMAP diet to a group following dietary recommendations for IBS based on modified guidance from the National Institute for Health and Care Excellence (mNICE). The mNICE group was instructed to eat small frequent meals, avoid trigger foods like wheat products and starches, limit fresh fruit, avoid the artificial sweetener sorbitol and avoid excess alcohol and caffeine.

For the four-week study, patients modified their diets to one of the two options and rated whether their overall IBS symptoms had been adequately relieved for at least half of the final two weeks of the study.

Of the 92 people randomized into the trial, 84 completed the four-week diet period. Among participants on the low FODMAP diet, 52 percent experienced adequate relief in the last two weeks, compared to 41 percent of the mNICE dieters.

Compared to scores rating abdominal pain, bloating, consistency of stool, frequency and urgency at the beginning of the study, the low FODMAP diet led to greater reductions in average daily scores than the mNICE diet.

"There are many treatments for IBS available, and there isn't one approach that will work for everyone," Eswaran said. "The medications that we currently have for IBS definitely don't work for everyone."

"The low FODMAP diet is part of the treatment options that we can offer to patients, especially those who are motivated to get better through non-pharmaceutical routes and those that have pain and bloating as a main component of their IBS symptoms," she said.

Some people do very well on the low FODMAP diet and more physicians and patients are adopting it, said Sheila Crowe of the University of California, San Francisco, who was not part of the new study.

"Any time you have to have a dietary intervention, you have to have education, have to have worked with a dietitian," Crowe said.

Low FODMAP in particular is complicated and not very social at times - you can't go out and have pizza, wine, or beer with friends as you might otherwise, and it can be difficult to keep track of what foods are okay and what are not, she told Reuters Health.

"It can be a little hard for people to adhere to but many of us in the business offer our patients this option," and it appears to be safe, she said.

More information on IBS is available from the National Institutes of Diabetes and Digestive and Kidney Diseases and information on the low FODMAP diet is available on the website of Monash University in Melbourne, Australia, where the diet was developed.