Low FODMAP Diet Helpful For People With Certain IBS Subtype

High FODMAP foods include onions and garlic
High FODMAP foods include onions and garlic.

Lynne Daley/Getty Images

Key Takeaways

  • The low-FODMAP diet is used to help relieve gas, pain, and bloating in people with irritable bowel syndrome (IBS), but does not work for all people with IBS.
  • A new study shows that the low FODMAP diet is most effective in people with the IBS-P subtype, rather than the IBS-H subtype.
  • Having specific information about IBS subtypes and microbiome bacteria can help practitioners better predict which clients may benefit from a low FODMAP diet.

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.

Andrew Akhaphong, MS, RD, LD

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.

— Andrew Akhaphong, MS, RD, LD

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." 

Caroline Green, RDN, LD

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.

— Caroline Green, RDN, LD

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.

What This Means For You

These findings will help doctors and dietitians decide if a low FODMAP diet is the right therapeutic plan for a particular patient, once specific tests designed to identify types of IBS are developed. For now, in absence of knowing your IBS subtype, it is still worth connecting with a healthcare provider or registered dietitian to determine if a low FODMAP diet could relieve your IBS symptoms.

3 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Vervier K, Moss S, Kumar N, et al. Two microbiota subtypes identified in irritable bowel syndrome with distinct responses to the low FODMAP dietGut. Published online November 22, 2021:gutjnl-2021-325177. doi:10.1136/gutjnl-2021-325177

  2. Altobelli E, Del Negro V, Angeletti P, Latella G. Low-fodmap diet improves irritable bowel syndrome symptoms: a meta-analysisNutrients. 2017;9(9):940. doi:10.3390/nu9090940

  3. Staudacher HM, Whelan K, Irving PM, Lomer MCE. Comparison of symptom response following advice for a diet low in fermentable carbohydrates (Fodmaps) versus standard dietary advice in patients with irritable bowel syndrome: IBS symptom response to a low FODMAP dietJournal of Human Nutrition and Dietetics. 2011;24(5):487-495. doi:10.1111/j.1365-277X.2011.01162.x

By Cara Rosenbloom, RD
 Cara Rosenbloom RD is a dietitian, journalist, book author, and the founder of Words to Eat By, a nutrition communications company in Toronto, ON.