FODMAP Explained: “F” stands for Fermentable

Published on: 01/08/2019

Welcome to my FODMAP Explained series! This is a set of articles I have dedicated to explaining the acronym FODMAP and giving practical tips to avoid symptoms while including as wide a variety of foods as possible. Let’s start from the beginning: the letter “F” in FODMAP, which stands for “fermentable”.

FODMAP Explained: “F” stands for Fermentable

The first letter of the acronym FODMAP goes to the very core of why some foods trigger the uncomfortable, painful symptoms of Irritable Bowel Syndrome (IBS). That’s because they are highly and rapidly fermentable. What this means is that they are poorly absorbed in the small intestine and continue to travel down the GI tract and reach the large intestine (or colon).

Once there, our friendly gut bacteria feast on them. These foods are their fast food! As a result of this fermentation, they produce gases and other by-products (short-chain fatty acids, SCFA). Although this is a good thing, in people with IBS, the gas production may lead to bloating, pain, and changes in motility (diarrhea or constipation).

Why It’s Important to Include Fermentable Fibers

Given that fermentable foods might trigger gut symptoms, you might wonder whether you should just avoid them. Unfortunately, that’s not a good idea, at least not for the long term. That’s because we want to keep feeding our friendly gut bacteria their favorite foods, so they can continue to thrive and live happily in our gut.

Indeed, they can do a lot for us!  For example, they can benefit digestion, aid in the absorption of minerals, and even produce some vitamins for us. In addition, they keep the “bad” bacteria away and increase the function of our immune system.

Not All Fermentable Fibers are FODMAPs

What distinguishes FODMAPs from other fermentable fibers is the speed at which they are fermented. Those that are rapidly fermentable may lead to symptoms. On the other hand, those that are slowly fermentable produce gas at a more steady rate and are more gentle on the GI tract. This means that you can have some fermentable foods without experiencing the side effects of fermentation (excess gas, bloating, or other gut symptoms).

Bottom line: what can you eat?

Choose foods rich in slowly fermentable fibers (low FODMAP prebiotics) to avoid reducing the number of friendly bacteria in your gut (if we don’t feed them, they die). These include vegetables, fruits, whole grains, legumes, and nuts. Try my Chai-Spiced Overnight Oats recipe to start your day with some good-for-your-gut fiber.

Avoid or limit foods rich in rapidly fermentable fibers for a short time (a few weeks). For example, garlic/onions or artichokes; wheat, rye, and barley and their products (cereals, pasta, bread), nuts such as cashews and pistachios (the “O” in FODMAP). Other foods that our gut bacteria like to ferment are shorter sugars such as monosaccharides (the “M” in FODMAP), disaccharides (the “D” in FODMAP), and sugar alcohols or polyols (the “P” in FODMAP).

Finally, as IBS is a very individualized condition, not everyone reacts the same way to fermentable foods. Ideally, consult with a dietitian specialized in FODMAPs (like me) to find out which ones trigger your symptoms. After you figure out your triggers, you will be able to expand your diet to include some of the more rapidly fermentable foods without experiencing gut symptoms.

Want to learn more?

Check out more Low FODMAP Diet Basics

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I’m a registered dietitian with a passion for helping women with IBS find their way back to eating without fear of painful gut symptoms and without unnecessary diet restrictions.

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