What is a low-FODMAP diet? And can it help your digestive issues?

A registered dietitian answers six common questions about the low-FODMAP diet.
As tempting as it might be to start self-experimenting with a low-FODMAP diet for your IBS, you should only do so under medical supervision after ruling out other conditions.
As tempting as it might be to start self-experimenting with a low-FODMAP diet for your IBS, you should only do so under medical supervision after ruling out other conditions.Getty Images

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By Samantha Cassetty, RD

If you’re one of the 10% to 15% of people who suffer from irritable bowel syndrome (IBS), a GI disorder that can cause constipation or diarrhea, pain, bloating, tweaking your diet to discover foods that trigger those symptoms can be game changing. Research suggests that most people with IBS experience significant improvement with a low-FODMAP diet, but it’s a complicated plan. Here’s what you need to know before you get started on a low-FODMAP diet.

1. What does FODMAP stand for?

The acronym stands for: Fermentable, Oligosaccharides, Disaccharides, Monosaccharides And Polyols.

FODMAPs are a collection of carbohydrates that are found in a range of foods. The term fermentable just means that these short-chain carbohydrates aren’t properly absorbed in your gut and they can produce gas. Each of the other terms refers to the category of carbohydrates that may be the culprit. Here’s a sampling of foods within each group, but note that some foods contain more than one type of FODMAP.

Oligosaccharides has two subgroups: fructans and galacto-oligosaccharides (GOS).

  • Fructans: Asparagus, artichokes, wheat, rye, garlic, onions, inulin additives, chicory root
  • GOS: Soybeans, black beans, kidney beans, pistachios

Disaccharides refer to lactose, which is a type of sugar found in dairy foods.

  • Lactose: Milk, yogurt, cottage cheese, ricotta cheese, frozen yogurt, ice cream

Monosaccharides pertain to fructose, which is found in fruit, some veggies and certain sweeteners.

  • Fructose: honey, agave, apple, mango, watermelon, sugar snap peas

Polyols appear in sugar alcohols, which are used in certain low-sugar processed foods, but they also naturally appear in some fruits and veggies.

  • Apples, blackberries, cauliflower, mushrooms and the additives mannitol, sorbitol and maltitol

These are just a sampling of foods in each group. But it does show that even within each category, there are a range of foods that contain the triggering carbohydrates. And often, those foods seem unrelated. For example, you probably don’t typically consider asparagus and whole wheat bread as being similar in any way, however they both contain fructans, and so they’re grouped together on a low-FODMAP plan.

2. What is a low-FODMAP diet?

A low-FODMAP diet begins by eliminating high-FODMAP foods, like those mentioned above. This just a sampling of the foods that need to be eliminated on this plan; many others are included on the complete list.

The strict elimination phase is intended to provide symptom relief. In this phase, it’s likely that you’re eliminating some foods that don’t trigger symptoms, but in order to test that theory, you first need to eliminate all the potentially triggering foods so you feel better.

Next comes the re-introduction phase. This is a critical step. Since symptoms are not only physically debilitating but can also severely impact your quality of life, you might feel tempted to carry on with a total FODMAP elimination once you feel better. But that’s not advised. The truth is, most of the high-FODMAP foods are very healthy and the indigestible carbohydrates they supply help feed the beneficial bacteria in your gut, so they’re important for keeping you and your immune system healthy. If you extend a low-FODMAP total elimination beyond what’s medically needed, it may lead to unfavorable changes in your gut bacteria.

As you reintroduce foods, the goal is to see which foods cause your symptoms and to discover your tolerance to different portion sizes. For example, you might be able to enjoy a 1/4 cup of chopped mango in a fruit salad whereas a larger portion might produce symptoms.

The reintroduction phase is very methodical because the diet involves testing specific foods in specific amounts, and then waiting a few days before reintroducing another food. As you go along, you’ll keep track of any symptoms you experience.

Once you’ve identified your trigger foods, you’ll reach the third phase of the plan, which is the personalization phase. This is the time to start adding all the foods you can tolerate back into your menu.

It’s important to follow a low-FODMAP diet under the guidance of a registered dietitian who can help you navigate the complexity of both the elimination phase and the reintroduction phase, and who can help ensure you’re optimizing your nutrition while on this plan. A dietitian can also help you personalize the plan to suit your lifestyle and make sure you’re maximizing your enjoyment while exploring this diet.

3. Is a low-FODMAP diet gluten free?

Not quite. Gluten is a protein that’s often found in carb-rich foods, like wheat, barley and rye. The elimination phase of a low-FODMAP diet focuses on reducing certain carbohydrates. Gluten is found in many of the carbohydrates that contain fructans, so you’ll be minimizing those sources of gluten in your diet, but other sources, like soy sauce, are still tolerated and permitted (unless you also have a gluten intolerance or soy allergy). If you believe you have a gluten sensitivity, fructans may be the true dietary offender. In one study among people who were on a self-imposed gluten-free diet (and who didn’t have celiac disease), a 7-day challenge with both a fructan- and gluten-containing energy bar revealed that the fructans were the cause of the troubling symptoms.

There are gluten-free foods that contain FODMAPs, as well as low-FODMAP foods that contain gluten, which is why it’s important to work with a health professional to determine the cause of your symptoms instead of limiting your diet unnecessarily.

4. Is a low-FODMAP diet dairy free?

It doesn’t have to be. Though lactose may be a trigger of your GI woes, there are lactose-free dairy products that you can enjoy — even during the elimination phase of the diet. Also, hard cheeses, like parmesan and cheddar cheese, are low in lactose and small portions are usually well-tolerated.

5. Should you follow a low-FODMAP diet for other GI concerns?

It’s not clear if it would be helpful to follow a low-FODMAP diet for other GI conditions, like Crohn’s disease or colitis. The evidence isn’t convincing. Still, there may be an underlying reason to try the low-FODMAP diet — for example, if you have one of these conditions and suffer from a lot of gas and bloating. It won’t help reduce inflammation, but it may help resolve some of the unpleasant symptoms.

6. What's the best way to get started on a low-FODMAP diet?

As tempting as it might be to start self-experimenting with a low-FODMAP diet, you should only do so under medical supervision after ruling out other conditions. There are a number of disorders, such as Crohn’s disease and colitis, that can cause similar symptoms as IBS, but are managed quite differently so it’s important not to self-diagnose your condition or to start a low-FODMAP diet without speaking to your physician and registered dietitian first.

If a low-FODMAP diet is recommended, you’ll want to begin by setting aside the high-FODMAP foods you have at home and stocking up on low-FODMAP foods. Your dietitian can help steer you toward whole and packaged foods that get the green light. A shopping list, recipes and meal plans will make it even easier to follow a low-FODMAP diet, so it’s a good idea to work with a registered dietitian who can provide these valuable resources.