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  • Writer's pictureMarissa Mekelburg MS, RDN, CLT, HHP

What is the Low FODMAP diet?

“My doctor diagnosed me with irritable bowel syndrome (IBS) and told me to follow the FODMAP diet. I’ve done some reading on the FODMAP diet, but it seems overwhelming. Does it even work? Where do I start?”

If this sounds familiar, you are not alone. According to the International Foundation for Gastrointestinal Disorders, IBS has a worldwide prevalence of 10-15 percent, making it the most common functional gastrointestinal disorder. (1) However, compared to other conditions and disorders, relatively little is known about treating IBS.

What is the FODMAP diet?

The FODMAP diet (which is an abbreviation that stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols) was created by Monash University researchers to limit foods containing high amounts of the FODMAP short-chain carbohydrates. FODMAPS are incompletely absorbed in the gastrointestinal tract, can be easily fermented by gut bacteria and exert an osmotic effect, increasing fluid delivery into the large intestine, which can result in gas, pain and diarrhea. (2) Evidence of the FODMAP diet improving symptoms of IBS has been mounting in recent years. (3, 4, 5, 6)

The FODMAP diet was designed to be a short-term, information-gathering exercise, helping individuals with IBS identify whether FODMAP-rich foods trigger IBS symptoms. A diet limiting all foods high in FODMAPs removes important foods from the diet, and can lead to micronutrient deficiencies, negative changes in the gut microbiome and unnecessarily limited options of whole foods, especially things like fruits, vegetables and beans. In individuals with limited access to some of the pricier dietary items included in the low-FODMAP diet, deficiencies in fiber, calcium, iron, zinc, B and D vitamins and natural antioxidants may be seen. (7)

Some FODMAPs have prebiotic effects, namely fructans and galacto-oligosaccharides (also called GOS). These two types of FODMAPS are both oligosaccharides (the “O” in FODMAP). Fructans are the storage carbohydrates in vegetables including onions and garlic, and are also found in some fruits and cereal grains. GOS mainly occur naturally in legumes such as lentils and beans. A low FODMAP diet restricts the intake of these prebiotic fibers, which is the fuel for gut bacteria. Diets rich in prebiotic fiber are beneficial, and there are concerns about long-term gut health in individuals who restrict these FODMAPs.

Many point to a “load effect” or “stacking effect” of FODMAPs; that is, a single FODMAP-containing food might cause symptoms if the individual has been consuming other high-FODMAP foods throughout the day. Foods that are known to have high levels of one of more of the FODMAPs include:

Lactose: cottage cheese, ricotta cheese, cow’s milk, goat’s milk, evaporated milk, yogurt, ice cream and custard.

Fructose: asparagus, sugar snap peas, sun dried tomatoes, apples, cherries, fresh figs, mangos, pears, watermelon, agave, high-fructose corn syrup and honey.

Fructans/GOS: artichokes, garlic, leek and scallion bulbs, shallot, onion, onion and garlic powder, peas, soybeans, kidney beans, ripe bananas, currents, dates, dried figs, grapefruit, nectarine, persimmon, plums, prunes, white peaches, watermelon, rye, wheat, barley, pistachios, cashews, mature soybeans (most soy milk), baked beans, black beans, fava beans, kidney beans, navy beans and split peas.

Polyols: cauliflower, mushrooms, snow peas, apples, apricots, blackberries, cherries, nectarines, pears, yellow peaches, plums, prunes, watermelon, sorbitol, mannitol, isomalt and xylitol.

How does the diet work?

In a typical FODMAP diet trial, individuals work with a registered dietitian to design meal plans that remove all foods high in FODMAPs for a period of time, often 3-4 weeks (sometimes bit longer, depending on diet compliance and symptom resolvement). Then, a customized approach is created to reintroduce each FODMAP category, one-by-one, in a controlled way to be able to pinpoint exactly which category of FODMAPs is causing IBS symptoms. This category can be further explored to determine if all foods in the category are problematic or just a few. The reintroduction phase takes approximately 6 weeks to complete.

It's important to note, that FODMAPS do not cause IBS and merely represent an opportunity for reducing symptoms. (8) For some, FODMAP can improve their IBS symptoms but since FODMAPs are an intolerance and don’t involve the immune system, those with food sensitivities most likely will not experience a reduction in symptoms. This can be a clue that there is something else going on and is a great time to work with a functional nutrition expert to dig deeper to identify and address the underlying root cause of IBS. For example, if IBS symptoms are being caused by an underlying dysbiosis (a lack in number or diversity of beneficial bacteria), IBS symptoms may temporarily be relieved by following a low FODMAP diet plan but the low FODMAP diet also has the unintended consequence of reducing the abundance of total fecal bacteria and reducing specific bacteria that are known to be markers of health (9) ultimately, potentially exacerbating the dysbiosis if on the diet for too long.

What can I do next?

If you are struggling with symptoms of IBS and are interested in trying a low FODMAP elimination diet and reintroduction trial, I would love to help you navigate the nuances of the diet and develop an inclusive, personalized eating plan. The FODMAP diet can be a good first step to reducing IBS symptoms while we work together on identifying the underlying root cause of your IBS.

Get started today by scheduling an initial visit or if you are interested in an online course that will walk you through all three phases of the low FODMAP diet, you can purchase the Low FODMAP Fix here.


1 International Foundation for Gastrointestinal Disorders. “Statistics, Facts About IBS.” About IBS, Accessed Sept. 28, 2019.

2. Barrett JS, Gibson P. Fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) and nonallergic food intolerance: FODMAPs or food chemicals? Therapeutic Adv in Gastroenterology 2012; 5: 261-268.

3. Ong DK, Mitchell SB, Barrett JS et al. Manipulation of dietary short chain carbohydrates alters the pattern of gas production and genesis of symptoms in irritable bowel syndrome. J Gastroenterol Hepatol 2010; 25: 1366–1373.

4. Shepherd SJ, Gibson PR. Fructose malabsorption and symptoms of irritable bowel syndrome: guidelines for effective dietary management. J Am Diet Assoc 2006; 106: 1631–1639.

5. de Roest RH, Dobbs BR, Chapman BA et al. The low FODMAP diet improves gastrointestinal symptoms in patients with irritable bowel syndrome: a prospective study. Int J Clin Pract 2013; 67: 895–903.

6. Staudacher HM, Whelan K, Irving PM et al. Comparison of symptom response following advice for a diet low in fermentable carbohydrates (FODMAPs) versus standard dietary advice in patients with irritable bowel syndrome. J Hum Nutr Diet 2011; 24: 487–495.

7. Catassi G, Lionetti E, Gatti S, Catassi C. The low FODMAP diet: many question marks for a catchy acronym. Nutrients 2017; 9: 292.

8. Gibson PR, Shepherd SJ. Evidence-based dietary management of functional gastrointestinal symptoms: The FODMAP approach. J Gastroenterol Hepatol. 2010; 25(2): 252-8.

9. Halmos EP, Christophersen CT, Bird AR, Shepherd SJ, Muir JG, Gibson PR. Consistent Prebiotic Effect on Gut Microbiota With Altered FODMAP Intake in Patients with Crohn's Disease: A Randomised, Controlled Cross-Over Trial of Well-Defined Diets. Clin Transl Gastroenterol. 2016;7(4):e164.


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