Low FODMAP Diet Helpful For People With Certain IBS Subtype

If you struggle with irritable bowel syndrome (IBS), you may have tried the FODMAP diet as a therapeutic measure. A new study published in the journal Gut looked at individual microbe compositions to see if the types of bacteria that are found may help predict how well someone may respond to the low FODMAP diet.

"This new research is very exciting, and shows a potential to further individualize IBS treatment with nutrition therapy," says Caroline Green, RDN, LD, a registered dietitian nutritionist specializing in intuitive eating and GI disorders in Columbia, South Carolina. "It may help us as clinicians be able to predict how well a low-FODMAP diet may work for someone, based on their type of IBS and which types of bacteria are found in their gut microbiome."

About the Study

In this study, researchers looked at specific bacteria in individual microbiomes. They wanted to see if certain types of bacteria could help them predict how well someone may respond to the low-FODMAP diet.

The researchers studied stool samples from people with IBS versus controls (people who don't have IBS) to see the response and microbiota changes after 4 weeks on a low FODMAP diet. They discovered two distinct microbiota profiles, which they called IBS-P (pathogenic-like) and IBS-H (health-like) subtypes. They also found that the low FODMAP diet was not helpful for people with the IBS-H subtype.

Interestingly, people with the IBS-P subtype did see a shift in microbiota while on the low FODMAP diet, which resulted in a better response to this dietary therapy. The researchers indicate that the low-FODMAP diet works for people with the IBS-P subtype because of the alterations in gut microbiota and the types of metabolites that are produced.

"Being able to identify specific strains of bacteria that are involved in the digestion and metabolism of specific carbohydrates may help guide the low FODMAP Diet," explains Andrew Akhaphong, MS, RD, LD, a registered dietitian for Mackenthun's Fine Foods.  "Though more research is needed, this study shows the potential that identifying specific gut bacteria may be utilized to direct how to approach the low FODMAP diet and long-term maintenance." 

What Is a Low-FODMAP Diet?

FODMAP is an acronym that stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, which are a variety of short-chain carbohydrates (sugars) that are not well absorbed in the small intestine.

"The term 'fermentable' in the acronym is attributed to the gut bacteria and their rapid ability to ferment these carbohydrates, leading to symptoms," says Akhaphong.

Foods that are high in FODMAPs include onions, garlic, bread, pasta, milk, beans, and certain fruits and vegetables. To be clear, these are very nutritious foods, but certain ones may trigger symptoms in people with IBS and may need to be avoided.

Experimenting with a low FODMAP diet can help people determine which foods cause their symptoms—but note—it is usually just a few foods, not an entire list. Studies consistently show that following a low-FODMAP diet can help reduce many IBS symptoms.

One study found that over 75% of people with IBS said their symptoms were well managed by the FODMAP diet. So, the low FODMAP diet appears to be helpful for many—but not all—people with IBS.

How a Low-FODMAP Diet Works

According to Akhaphong, there are three stages involved in the low FODMAP diet—elimination, reintroduction, and personalization or maintenance. Working with a dietitian, first, you eliminate high FODMAP foods for 2 to 6 weeks (or sometimes longer). Importantly, the elimination phase is short-lived.

"The low FODMAP diet is not meant to be followed long-term," says Akhaphong. "It requires guidance from a dietitian and/or physician to ensure nutritional adequacy." 

Next, you work with a dietitian to reintroduce a specific amount of one of the eliminated FODMAP foods to see if it triggers any symptoms. You slowly introduce one food at a time and work with a dietitian to keep track of each food and any symptoms it may cause.

"The end goal is to determine the most tolerated amount of that item before one experiences symptoms," says Akhaphong.

Importantly, it is vital that the low FODMAP diet is only used under medical supervision because it is quite restrictive and complex. What's more, a low FODMAP diet is not intended for weight loss says Green.

"A low FODMAP diet is a medical nutrition therapeutic diet, meaning it should be done under clinical supervision by a physician or gastroenterologist and dietitian for people with IBS," she says.