What Is a Low FODMAP Diet?

If you or anyone you know has irritable bowel syndrome (IBS), a condition with symptoms ranging from abdominal pain to diarrhea or constipation, you may have heard of the low FODMAP diet.

FODMAP is an acronym for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols. These are types of carbohydrates in food that move slowly through the small intestine and attract water. When they reach the large intestine (colon), FODMAPs are fermented by microbes, producing gas.

The combination of more fluid and gas can distend the bowel and lead to uncomfortable gastrointestinal (GI) issues, including bloating, abdominal pain, diarrhea, and constipation. Most people can eat foods high in FODMAPs and either do not encounter these symptoms or have them at levels that are only slightly bothersome after a meal. But people with IBS tend to have a highly sensitive GI system and are therefore more likely to experience pain and discomfort.

Doctors aren’t sure exactly what causes IBS, and there is no cure for the condition; instead, providers work with patients to help them learn how to manage their symptoms. Strategies include dietary and lifestyle changes and, in some cases, medication to treat certain symptoms.

Numerous studies have shown that a diet low in FODMAPs can help alleviate symptoms in people with IBS. “Patients can often expect about a 30% improvement in all IBS symptoms if they respond to the FODMAP diet,” says Eric Jordan, MD, a Yale Medicine gastroenterologist. “In other words, it might not completely remove symptoms, but it can help a lot.”

It is also thought to sometimes be helpful for people with other GI conditions, such as SIBO (small intestinal bacterial overgrowth). “There isn’t great evidence that a low FODMAP diet helps SIBO, but it’s reasonable to try for people who want to avoid medications,” says Dr. Jordan.

But it’s important to note that this elimination diet, which is complicated and restrictive, is a tool and not something people should experiment with on their own. “It’s best to work with a registered dietitian, and it is reserved for people with IBS diagnosed by a medical provider,” says Jill Deutsch, MD, a Yale Medicine gastroenterologist, specializing in functional GI disorders.

Below, we provide more information on FODMAPs and how a diet low in them may alleviate GI symptoms.

FODMAPs are carbohydrates (sugars, starches, and fiber) in food or food additives. They are broken down into five categories:

1. Fructans, which are found in garlic, onions, and wheat
2. Fructose, which is found in fruits, honey, and high-fructose corn syrup
3. Galactans, which are found in beans and legumes
4. Lactose, which is found in dairy products
5. Polyols, which are found in fruit with pits (apples, avocados, cherries) and in sugar alcohols

People with IBS often have issues with motility (the movement of food through the digestion system) and/or a sensitive GI wall. Therefore, if foods high in FODMAPs distend the bowel and increase gas, those with IBS are more likely to feel bloated or experience abdominal pain, cramping, diarrhea, and constipation. However, it’s highly variable how much, if at all, any particular high FODMAP food affects someone with IBS.

The low FODMAP diet was developed by researchers at Monash University in Melbourne, Australia. It is an elimination diet, which means you stop eating all foods that are high in FODMAPs. The list of foods high in FODMAPs is extensive, but examples, by category, include:

• Vegetables: garlic, onions, asparagus, broccoli, cabbage, leeks, mushrooms
• Fruits: apples, avocados, bananas, cherries, dried fruit, fruit juice, grapes, peaches
• Dairy and alternatives: cow’s milk, custard, evaporated milk, ice cream, yogurt
• Proteins: black-eyed peas, chickpeas, lentils, kidney beans, pinto beans, soybeans, some marinated meats/poultry/seafood, some processed meats
• Breads and cereals: wheat/rye/barley-based breads, breakfast cereals, biscuits, and snack products
• Sugars and sweeteners: high-fructose corn syrup, honey, sugar-free candy
• Nuts and seeds: cashews, pistachios

After about two to six weeks of avoiding all foods high in FODMAPs, you add the eliminated foods back in, one food at a time, from each category to see if symptoms return. You should allow about three days between reintroducing each food before trying another. Once you discover which foods cause symptoms, you can avoid or limit consumption of those in the future.

People should work with a medical provider and/or a dietitian for this diet because it can be difficult to both identify high FODMAP foods and ensure you are continuing to get the proper nutrients into your diet.

Dr. Jordan also notes that Monash University has an app that helps determine high and low FODMAP foods.

FODMAPs are found in a wide range of foods, but some naturally have more or less than others. Examples of foods that are low in FODMAPs are:

• Vegetables: eggplant, green beans, carrots, cucumbers, lettuce, potatoes, zucchini
• Fruits: cantaloupe, kiwi, mandarin, orange, pineapple
• Dairy and alternatives: almond milk, brie cheese, feta cheese, hard cheeses
• Proteins: eggs, firm tofu, plain cooked meats/poultry/seafood, tempeh
• Cereals, grains, and breads: corn flakes, oats, quinoa/rice/corn pasta, sourdough spelt bread
• Sugars and sweeteners: dark chocolate, maple syrup, rice malt syrup, table sugar
• Nuts and seeds: macadamias, peanuts, pumpkin seeds, walnuts

IBS patients who follow the low FODMAP diet, especially during the elimination phase, may eat less fiber, which is needed to support beneficial microbes in the gut. In the short term, a diet like this may lessen symptoms for some IBS patients, but these diets are difficult to maintain for a long time, especially for people who cannot tolerate a large number and variety of FODMAPs.

While a low FODMAP diet can significantly reduce symptoms for many people, the hope is that they can add enough items back into their diet to get the nutrients they need without experiencing discomfort. Given the complexities of this diet and of IBS in general, working with a medical provider and a dietitian is key.