Q. How can I get enough fiber on a low-FODMAP diet? I’ve been on this diet for a while, and I’m not eating as many high-fiber foods as I used to.
A. Low-FODMAP diet does not equal low-fiber diet. Low-FODMAP servings of fruit, vegetables, beans, lentils, nuts, seeds and whole grains can (and should) be part of your low-FODMAP diet to help you get enough fiber. Keep the low-FODMAP phase of the diet short, so you can eat your favorite high fiber foods again as tolerated later on in the FODMAP elimination diet process.
What is fiber?
Beautiful, tasty, and low-FODMAP food sources of fiber: a wedge of squash with skin, stuffed with quinoa and garnished with pecans.
Fibers are certain types of carbohydrate found in plant foods. The building blocks of fiber are sugars, linked together like a chain. Those links cannot be broken down by digestive enzymes; that is actually part of what defines them as fibers. Fibers stay in the gut, where they are an important source of food for the normal gut microbiome. The gut microbiome is the community of bacteria and other microbes present in your large intestine (colon). Fibers that feed the good bacteria in your gut microbiome are called prebiotics.
I like to use the word fibers whenever I can, with a “s” on the end—fibers are not just one thing. There are many different types of fibers found in food, and they all have a role to play in good health. There are many ways to describe fibers, but the characteristic that determines which fibers are FODMAPs is the “chain length”, in other words the number of sugar molecules linked together.
O is for oligosaccharides.
In the FODMAP acronyms, O is for oligosaccharides, which means “short chains sugars”. Two very short chains sugars, fructans (chains of fructose) and GOS (chains of galactose), fall under the FODMAP umbrella. Biochemists might described them as sugars, but functionally they are fibers (they are carbohydrates that cannot be broken down by digestive enzymes).
F is for (Rapidly) Fermentable
Fructans and GOS, being very short chains of sugars, are small molecules. Small molecules have a very high surface area compared to their volume. Bacteria can quickly eat their way around and through them, rapidly producing gas, which results in uncomfortable symptoms for people with IBS if we eat too much of them at one time. Only the most rapidly fermentable fibers are FODMAPs. Longer-chain fibers are fermented slowly enough to cause less trouble with excess gas and bloating and they are good food sources for a healthy gut microbiome. Resistant starches are other well-tolerated prebiotic substances in food that are technically fibers. When starchy foods like rice, potatoes, oatmeal, and cornmeal are cooked and cooled, the starch molecules in them change to forms that resist digestion. These resistant starches serve as food for the gut bacteria, but due to their tremendous molecular size, they are only slowly fermented.
Too much of a good thing?
Fibers are good for you. In addition to serving as prebiotics, fibers are filling, helps maintain healthy blood sugar and cholesterol, and help us have formed, regular bowel movements. But too much of a good thing can cause miserable gastrointestinal symptoms for many people with IBS. The FODMAP elimination diet will help you learn your limits. Even on the low-FODMAP phase of the diet, do the best you can to eat food sources of fibers at every meal, using the strategies below. (For the record, 20-35 grams of fiber daily would be nice to aspire to.)
Don’t be an over-achiever
Do NOT just stop eating high fiber foods that have small low FODMAP serving sizes. I meet too many people that just stop eating beans and fruits and vegetables on their low FODMAP diets. You’ll only be hurting your nutrition and your food quality of life if you try to eat no FODMAP fibers at all.
Add some chickpeas or beans to your low-FODMAP salad to get more fiber!
Choose 2-3 low-FODMAP servings of fruit, and 3-4 low FODMAP servings of vegetables every day. Eat them unpeeled for extra fiber.
Choose 1-2 low-FODMAP servings of nuts or seeds every day. Add 2 tablespoons of walnuts or pecans to your salad, or snack on peanuts. Chia and flax seeds taste good in oatmeal and smoothies.
Choose whole grains at each meal, such as oatmeal, brown rice, quinoa, or whole-wheat sourdough bread.
Add 2-3 tablespoons of beans or lentils to your soup or salad.
Fiber as a food ingredient
Get your fiber from the whole foods suggested above. I don't recommend processed foods with most types of added, isolated food fibers for people with IBS who are following low-FODMAP diets. These are common causes of IBS symptoms. Examples of these isolated food fibers to avoid are inulin, chicory root, chicory root extract, beet fiber, soy fiber, and other industrial fiber ingredients that are added to food to boost the fiber content. Bars, gluten-free baked goods, breakfast cereals, protein powders and shake mies often have added fibers because they would be otherwise poor fiber sources. If the front of the package says, "high fiber!" or “low net carbs”, be sure to read the fine print of the ingredients section.
Fiber supplements
What about fiber supplements? I generally discourage changing, stopping or starting fiber supplements during the elimination diet process. Sometimes, if constipation doesn’t improve as much as hoped on the first few weeks of the elimination phase, it is helpful to add one. In that case, I tend to recommend those made of psyllium husk, starting with a very small serving and increasing slowly over time. Other good candidates are acacia gum or fiber and partially hydrolyzed guar gum. Avoid fiber supplements made of inulin, which is an out-and-out FODMAP.
Originally published June 4, 2014. Updated in 2020, and again more recently on March 24, 2025.
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