The low FODMAP diet isn't new — it goes back to 2005, when Australian researchers coined the term — but mainstream interest in it is a relatively recent phenomenon.

Originally conceived as a treatment for irritable bowel syndrome (IBS), FODMAP also has uses as a diagnostic tool, helping patients identify and eliminate the specific foods that trigger IBS symptoms such as stomach pain, diarrhea, gas and bloating.

Although the diet is increasingly being prescribed as an IBS treatment, long-term, large-scale randomized clinical trials are still lacking, and peer-reviewed studies that have been conducted have demonstrated mixed results.

Current IBS Treatment Guidelines from the American College of Gastroenterologists recommend a limited trial of a low FODMAP diet to improve global symptoms, citing very low quality of evidence as rationale for their conditional recommendation.

Contradicting earlier, more promising results, a recent study published in the American Journal of Clinical Nutrition found no significant difference between IBS patients' remission of symptoms when comparing the low FODMAP diet with traditional dietary advice.

In an editorial accompanying the study, Dr. Eamonn Quigley, chief of Gastroenterology at Houston Methodist and director of its Underwood Center for Digestive Disorders, suggests the modest results may be due to the clinical trial's short three-week timeframe or the relatively lower intake of FODMAPs in general among the Chinese population studied.

To help put matters in context for clinicians uncertain whether to recommend the diet to their IBS patients, we asked Dr. Quigley to share insights gleaned from clinical practice and current available literature.

Q: How does the low FODMAP diet work?

FODMAP is an acronym for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. These small carbohydrates — fructose, lactose, sugar alcohols, fructans and galactans – are not very well absorbed in the gut.

High FODMAP foods, such as apples, onions, beans, garlic, dairy, wheat and honey, can cause extra water to be pulled into the stool as part of the digestive process, resulting in cramping and diarrhea. Additionally, when there's undigested food in the large intestine, it attracts bacteria, leading to rapid fermentation, increased gas production, bloating and discomfort.

When part of a typical mixed diet, most people can eat these foods without experiencing digestive problems. But some people are much more sensitive to even small amounts, particularly people with IBS.

The idea behind the diet is to first eliminate all high FODMAP foods for a period of four to eight weeks. Assuming there is a noticeable reduction in symptoms, the next step is to reintroduce foods slowly and systematically. The goal is to identify the specific foods or food types that cause digestive issues, as well as those that do not. The final stage is to go back to a healthy, varied diet while avoiding the foods that trigger the worst symptoms.

Many high FODMAP foods are fruits, vegetables and legumes and are inherently very healthy. If they're not causing issues, we want patients to eat them. In general, we don't want to restrict people any more than is absolutely necessary to cause a major reduction in symptoms and improvement in quality of life.

Q: Do you have any concerns about the diet?

I think it's worse to have an incomplete understanding of the diet than to not know about it at all. I'm not sure if everyone realizes it should only be done under the supervision of a dietitian or physician.

It's quite complex and restrictive. It's kind of like going dairy-free, gluten-free, nut-free, sugar-free, alcohol-free, low-fat and keto all at once. That's difficult for most of us to do for a single day, much less for weeks or months at a time. It's important to make sure nutritional needs are met, because we don't necessarily want patients to lose weight, or to lose it in an unhealthy or stressful manner. And when it comes to reintroduction, you have to be very precise and clinical or else you'll muddy the results and not wind up with the answers you're seeking about specific foods to avoid — which was the whole point.

My concern is that people will see results in the highly restrictive first phase and feel like they should keep that up long-term. Even if they do have the discipline for that, we don't know that it is healthy. There are questions about long-term effects on the gut microbiome. And there are implications for the patient's mental health. IBS is already challenging to live with, and I think we need to be careful about adding new levels of anxiety around food and eating, which is not only necessary and pleasurable, but an important part of people's social life as well.

Q: What response have you seen from patients?

Well, broadly speaking, I think patients are excited and relieved to have a clinically endorsed diet they can try to help relieve their IBS symptoms.

For many years, the only dietary advice most IBS patients received from their physicians was to use a fiber supplement. Meanwhile, these same patients were busy telling us that meals exacerbate their symptoms and pleading with us to search for a dietary explanation for their troubles. Finally, there are a number of diet-based investigations and tools in our IBS toolkit, of which the low FODMAP diet is a prominent one.

It's clear that dietary change has a role to play in IBS treatment. With regard to the low FODMAP diet, what the research shows is similar to what we've observed clinically, which is that it works with widely varying degrees of success to reduce IBS symptoms for the majority of patients — at least in the short term.

Unfortunately, we are less clear on predictors of response, how long it works, how long patients can reasonably sustain it (especially if their list of prohibited foods is extensive) and what negative effects there might be on the microbiome after an extended period of time.

In my opinion, it is worth trying if the patient is committed to doing it correctly and has the necessary support. That's something we have a responsibility to provide if we are going to recommend it.