Low FODMAP Diet 101

By Anne Danahy MS RDN


The low FODMAP diet has gained much attention as a way to help manage symptoms of irritable bowel syndrome (IBS). It can be difficult to navigate at first, but for patients who work with a dietitian to implement it, the results can be life changing. Here’s what you should know about this diet, and how to help your patients get started.

What Are FODMAPs?

FODMAP is an acronym for fermentable oligo-, di-, mono-saccharides and polyols. They’re different types of small chain carbohydrates that in some people, may be poorly absorbed in the small intestine. They draw water into the gut, and they’re rapidly fermented by bacteria in the large intestine. This increases symptoms like gassiness, bloating, diarrhea or constipation in people with irritable bowel syndrome (IBS).

The low FODMAP diet, initially introduced by Monash University in Australia, restricts all or some of these foods to a certain degree, and may help alleviate symptoms.

The diet was controversial in the past because there was a lack of scientific evidence to support its use. In addition, there were concerns that it may be too restrictive and nutritionally inadequate and promote an unfavorable gut microbiota. Some of the long-term effects of the diet are still in question. (1) However, current research supports its effectiveness.

About the Research

Over the past decade, data from randomized controlled trials, case-controlled studies, and observational studies has shown that following a low FODMAP diet reduces both overall and individual symptoms of IBS, such as abdominal pain, bloating, constipation, diarrhea, abdominal distention, and flatulence, in up to 86% of patients. (2)

A 2016 meta-analysis published in the European Journal of Nutrition reviewed 22 different studies on use of the diet in patients with IBS symptoms. Researchers concluded that there is strong evidence to support the use of the low FODMAP diet in these patients, as there is significant improvement in all symptoms, generally within the first seven days. (3) With regard to specific symptoms, it seems to be especially helpful for reducing gas and bloating, but least helpful for constipation.

While nutritional adequacy of the diet doesn’t seem to be an issue, there are still questions about potential changes in the gut bacteria in those who follow a restrictive version of the diet for a long term. Studies have shown that reducing FODMAP-rich foods reduces the number of total bacteria in the gut within a few weeks, but not the diversity of microbes. (1, 4, 5) However, gradually increasing FODMAP foods can increase the number of good bacteria.

Most of the research does point out that patient adherence is key, and patients are more likely to be successful implementing and following through with the diet if they work with a dietitian who is trained in it. The low FODMAP diet isn’t a one-size-fits-all plan. Instead, it can, and should be individualized, based on preferences and nutritional needs.

While patients should usually start out with a full restriction for four to six weeks, it’s important to gradually and systematically add foods back, based on tolerance. The key is working with patients to help find their FODMAP tolerance threshold, rather than having a complete and permanent restriction of FODMAP foods. (5)

Starting the Diet: High FODMAP Foods to Avoid

The following is a brief list of foods that are high in the various types of FODMAP carbohydrates:

Oligosaccharides: These include fructans and galactans found mainly in wheat, rye, barley, onions, garlic, shallot, scallions, leeks, artichokes, inulin, soybeans and other legumes, cashews and pistachios.

Disaccharides: The most common disaccharide is lactose, found in milk, cream, ice cream, yogurt, and soft cheeses.

Monosaccharides: These come from fruits and high fructose foods. The highest sources include agave, honey, high fructose corn syrup, apples, pears, cherries, mango, watermelon, dried fruit, sugar snap peas, and sun-dried tomatoes.

Polyols: These are found in sugar alcohols like sorbitol, xylitol, mannitol, as well as mushrooms and cauliflower which are high in mannitol.

The list of high FODMAP foods to limit is extensive, and it’s easy for patients to get overwhelmed. RDs should educate about what to avoid in the initial stages, but also focus on ways to incorporate low FODMAP foods. Some of these include lactose-free dairy and dairy alternatives; small amounts of raspberries, strawberries, blueberries, pineapple; leafy green vegetables, carrots, parsnips, zucchini; rice, quinoa and other gluten-free grains.

Excellent resources are available online, through Monash University. They also offer a convenient app to quickly identify high and low FODMAP foods when grocery shopping or planning meals

The Bottom Line

Dietitians play an essential role in making the FODMAP diet work for patients, not only by educating and helping them navigate the diet, but also, by helping them achieve enough variety in their diet, prevent any unnecessary over-restriction, and maintain gut health. Because medical nutrition therapy for IBS can be complex, if you don’t work with these patients often, it’s also worthwhile to find RDNs in your area who are trained in the FODMAP diet, so you can refer patients.


  1. Hill P, Muir JG, Gibson PR. Controversies and recent developments of the low-FODMAP diet. Gastroenterology & hepatology. 2017 Jan;13(1):36. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5390324/

  1. Nanayakkara WS, Skidmore PM, O'Brien L, Wilkinson TJ, Gearry RB. Efficacy of the low FODMAP diet for treating irritable bowel syndrome: the evidence to date. Clin Exp Gastroenterol. 2016;9:131–142. Published 2016 Jun 17. doi:10.2147/CEG.S86798 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4918736/

  1. Marsh A, Eslick EM, Eslick GD. Does a diet low in FODMAPs reduce symptoms associated with functional gastrointestinal disorders? A comprehensive systematic review and meta-analysis. European journal of nutrition. 2016 Apr 1;55(3):897-906. https://pubmed.ncbi.nlm.nih.gov/25982757-does-a-diet-low-in-fodmaps-reduce-symptoms-associated-with-functional-gastrointestinal-disorders-a-comprehensive-systematic-review-and-meta-analysis/

  1. O'keeffe M, Jansen C, Martin L, Williams M, Seamark L, Staudacher HM, Irving PM, Whelan K, Lomer MC. Long‐term impact of the low‐FODMAP diet on gastrointestinal symptoms, dietary intake, patient acceptability, and healthcare utilization in irritable bowel syndrome. Neurogastroenterology & Motility. 2018 Jan;30(1):e13154. https://pubmed.ncbi.nlm.nih.gov/28707437-long-term-impact-of-the-low-fodmap-diet-on-gastrointestinal-symptoms-dietary-intake-patient-acceptability-and-healthcare-utilization-in-irritable-bowel-syndrome/

  1. Halmos EP, Gibson PR. Controversies and reality of the FODMAP diet for patients with irritable bowel syndrome. Journal of gastroenterology and hepatology. 2019 Jul;34(7):1134-42. https://pubmed.ncbi.nlm.nih.gov/30945376-controversies-and-reality-of-the-fodmap-diet-for-patients-with-irritable-bowel-syndrome/