FODMAP Explained: “F” stands for Fermentable


Welcome to my FODMAP Explained series! This is a set of articles dedicated to explaining the acronym FODMAP and giving practical tips to avoid symptoms while including as wide a variety of foods as possible.


The first letter of the acronym FODMAP goes to the very core of the why some foods trigger the uncomfortable, painful symptoms of Irritable Bowel Syndrome (IBS): Fermentable. This refers to food particles that are poorly absorbed or cannot be absorbed at all in the small intestine, continue to travel down the gastrointestinal (GI) tract and reach the large intestine (or colon). There, our friendly gut bacteria feast on the them (they are their fast food!), and produce gases and other by-products (short-chain fatty acids, SCFA) as a result of their fermentation. This is a good thing but, 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

It’s a good idea to keep feeding our friendly gut bacteria as their presence has several health benefits:

  • They are like an army defending us from the harmful (disease-causing) bacteria – the higher the number, the less space there will be for the bad bacteria to find a place to reside.

  • The by-products of their fermentation confer health benefits: SCFA have been shown to help protect us from colon cancer.

  • They can produce vitamins (several B vitamins including vitamin B12, as well as vitamin K) and even amino acids.

  • They may have several more health benefits that currently being studied. For example, they may help us improve our immune system and fight obesity.

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, whereas those that are slowly fermentable produce gas at a more steady rate, and are more gentle on the GI tract. What makes FODMAPs rapidly fermentable is their chemical structure: they are shorter chains of sugars than the slowly fermentable fibers, which are made of long chains of sugars.

Bottom line: what can you eat?

If you have IBS and are trying to alleviate your symptoms, here are some useful tips:

1.     Choose foods rich in slowly fermentable fibers to avoid diminishing 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. See examples in my article Prebiotics: How to Keep Your Friendly Bacteria Happy on a Low FODMAP Diet. Try my Easy Overnight Oats recipe (below) to start your day with some good-for-your-gut fiber.

2.     Be careful about having too many of these foods in the same meal or snack, as a high dose at one sitting may lead to symptoms. To start, keep it to two or three servings (check the Monash University FODMAP Diet App for appropriate portion sizes).

3.     Avoid or limit foods rich in rapidly fermentable fibers such as  garlic/onions or artichokes; wheat, rye and barley and their products (cereals, pasta, bread). Other foods that can be fermented by the bacteria as they are poorly absorbed are shorter sugars such as monosaccharides (the “M” in FODMAP) and disaccharides (the “D” in FODMAP) and sugar alcohols or polyols (the “P” in FODMAP) - more on these in the next issues of the FODMAP Explained series.

4.     As IBS is a very individualized condition, not everyone reacts the same way to fermentable foods. You may want to consult with a dietitian specialized in FODMAPs to find out which ones trigger your own symptoms.


Easy Overnight Oats


1 cup rolled oats

1 tablespoon plus 1 teaspoon chia seeds

2 cups unsweetened almond milk

1/2 teaspoon cinnamon (optional)

Topping, per serving:

½ cup fresh or frozen blueberries or raspberries, or fresh sliced strawberries


1.     Put the oats, chia seeds and cinnamon (if using) in a glass container or large jar with an airtight lid. Add the almond milk and stir to combine.

2.     Close with the lid and refrigerate overnight or up to 4 days.

3.     When ready to serve, portion out one serving into a bowl, and top with the fruit.

Variation: add 1 tablespoon unsweetened cocoa powder and a few drops of stevia to step one for “cocoa-flavored” morning oats. Top with either one of the fruit choices above (raspberries are especially good) or 2 tablespoons chopped almonds.

Chef’s tip: if you have mason jars, you can divide the oat mixture in 4 jars and top them with the fruit, then close the jar. Every morning you have one serving ready to grab and go. This works especially well if using frozen berries, as they will defrost overnight.


4 servings


Store in an airtight container in the refrigerator for up to 4 days.

Antonella Dewell