All FODMAPs aren’t created equal: working toward alternative diets to manage IBS

Two studies from Michigan Medicine may provide hope for patients with irritable bowel syndrome struggling to implement the traditional low-FODMAP diet.

The resulting papers— “FODMAPs aren’t created equal: Results of a randomized reintroduction trial in patients with irritable bowel syndrome” and “Is a Simplified, Less Restrictive Low FODMAP Diet Possible? Results from a Double-Blind, Pilot Randomized Controlled”—both appeared in Clinical Gastroenterology and Hepatology.

In the low-FODMAP diet, patients with IBS restrict their intake of certain carbohydrates (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols), before gradually reintroducing each to determine sensitivity. 

However, since this diet restricts such a wide range of foods (e.g. garlic, certain fruits, gluten-based bread), many individuals suffering from IBS find it hard to implement and even harder to stick with. 

“It’s frustrating for us as clinicians to say, ‘Here, just cut out all these things, and you'll be fine’,” said Shanti Eswaran, M.D., lead author of the first paper. 

“No one wants to live like that. So, we looked at whether or not we really need to take out everything that's in the diet. Or if, for some people, they can get away with a modified version of this restriction plan.”

In the first study, participants started on the traditional low-FODMAP restriction diet, but then had different FODMAP foods reintroduced blindly. 

The researchers found that patients reacted to an average of two FODMAPs.

The data also suggested that individual FODMAPs alone could cause symptoms—as opposed to all the FODMAPs at once.

The most significant, finding however, was that fructans and galacto-oligosaccharides (GOS) were the most likely to worsen symptoms such as abdominal pain and bloating. 

Fructans are commonly found in onions, garlic, and wheat. Foods containing GOS include legumes and cruciferous vegetables.

“That led to the second study, in which an alternative ‘FODMAP-simple’ diet was developed and implemented,” said William Chey, M.D., chief of the Division of Gastroenterology and Hepatology at Michigan, and an author on both studies. 

FODMAP-simple restricts only fructans and GOS without restricting other FODMAP groups (polyols, lactose, and fructose), while traditional low FODMAP restricts all five FODMAP groups. 

At the end of that study, FODMAP-simple led to similar reductions as low-FODMAP to key symptoms of IBS.

There are several benefits to simplifying the traditional low-FODMAP approach. 

Many patients find the diet hard to start, depending on their existing habits and available food. 

The restriction period of the process can also lead to weight loss and deficiencies in certain nutrients, such as iron and calcium.

“Cost becomes an issue, because the more exclusion you have to do, the more substitutes you'd have to purchase,” said Prashant Singh, MBBS, lead author of the second paper. 

“Let’s say you are somebody who eats green beans, beans, and chickpeas, and now you must substitute all of that. Or you're substituting in gluten-free bread or lactose-free milk, which is more expensive than lactose-containing milk. All of those costs add up very quickly.”

While the doctors involved agree more research is necessary before recommending a diet like FODMAP-simple to patients, they are encouraged that these early results could herald changes that will one day improve the lives of patients with IBS.

“Fewer people dropped out of the FODMAP-simple diet compared to the traditional low-FODMAP diet, because it was less restrictive and you're less likely to lose weight on it,” said Singh. 

“We think FODMAP simple has real potential of changing how we practice this diet in future.”

Additional authors include: Samara Rifkin M.D., Theresa Han-Markey M.S., on the first part, and Samuel W. Chey M.P.H., Gregory Dean. M.D., on the second. 

The Michigan Research Core associated with this research: Human Research

Papers cited: 

“All FODMAPs Aren't Created Equal: Results of a Randomized Reintroduction Trial in Patients With Irritable Bowel Syndrome,” Clinical Gastroenterology and Hepatology. DOI: 10.1016/j.cgh.2024.03.047

“Is a Simplified, Less Restrictive Low FODMAP Diet Possible? Results from a Double-Blind, Pilot Randomized Controlled Trial” Clinical Gastroenterology and Hepatology. DOI: 10.1016/j.cgh.2024.04.021

Sign up for Health Lab newsletters today. Get medical tips from top experts and learn about new scientific discoveries every week by subscribing to Health Lab’s two newsletters, Health & Wellness and Research & Innovation.

Sign up for the Health Lab Podcast: Add us on Spotify, Apple Podcasts or wherever you get you listen to your favorite shows.