The Low-FODMAP Diet: 9 Things Nutritionists Need You to Know

A low-FODMAP diet may help ease certain digestive disorders, like IBS, but there are some downsides. Registered dietitian Samantha Cassetty explains it all.

What’s a low-FODMAP diet?

You may have run across the idea of a low-FODMAP eating approach—especially if you’re among the 10 to 15 percent of people who suffer from irritable bowel syndrome (IBS), which can cause symptoms such as constipation, diarrhea, belly pain, gas, and bloating.

The basic concept is that you eliminate categories of foods that may be contributing to your symptoms, and then carefully add them back until you find the culprit (or culprits).

The low-FODMAP diet may also help people with other digestive issues: Small intestinal bacterial overgrowth (SIBO), which can overlap with IBS, is one.

There’s also research suggesting that a low-FODMAP diet may offer some relief to people with Crohn’s disease and colitis.

(Here’s the difference between ulcerative colitis vs. Crohn’s disease.)

That all sounds great, but a low-FODMAP diet can be complicated to follow, and it’s not meant to be a long-term solution.

If you’re curious about this diet, first talk to your doctor or a registered dietitian to see whether it’s right for you and get appropriate guidance with the plan.

Here’s what to know about a low-FODMAP diet, plus some helpful tips to keep in mind when considering this type of diet for your gut health.

What exactly does FODMAP stand for?

Before you determine whether this diet is right for you, understand what exactly it’s limiting. FODMAP is an acronym that stands for (and it’s a mouthful):

  • Fermentable
  • Oligosaccharides
  • Disaccharides
  • Monosaccharides
  • And
  • Polyols

That’s a somewhat mystifying list of terms, but basically FODMAPs are a collection of specific carbohydrates that are found in a variety of foods. They draw water into the colon while also feeding colonic bacteria—and that can increase gas production.

This promotes distention and contributes to gastrointestinal problems, including abdominal pain, gas, bloating, burping, constipation, and diarrhea.

Types of FODMAPs

FODMAP-containing carbs generally fall into one of a few main categories. If you want to know where your favorite foods fit in, you can check the list below. Keep in mind, these are just a few of the foods in each grouping.

If your health care provider suggests a low-FODMAP diet, he or she will give you a more detailed list of foods to limit or avoid.

Another thing to remember: A single food may have more than one type of FODMAP in it.

Oligosaccharides

This type of FODMAP includes two subgroups: fructans and galacto-oligosaccharides (GOS).

  • Fructan-containing foods: asparagus, artichokes, barley, wheat, rye, garlic, onions, and inulin additives
  • GOS-containing food: Beans, like kidney beans and black beans

Disaccharides

This refers to lactose, a natural sugar found in dairy foods, including milk, yogurt, and ice cream.

Monosaccharides

This FODMAP type refers to fructose, a natural sugar found in honey, fruit, and some veggies.

Polyols

This type of FODMAP is found in sugar alcohols—they’re used to sweeten sugar-free/low-sugar foods—but they’re also found naturally in some fruits and veggies, such as apples, blackberries, cauliflowers, and mushrooms.

Can a low-FODMAP diet really help GI issues?

A 2020 review in the journal Nutrients suggests that a low-FODMAP diet can provide relief for IBS when compared with other diets, such as a gluten-free diet.

As researchers noted in the Nutrients review, studies suggest that among people with inflammatory bowel diseases, such as Crohn’s disease, the low-FODMAP diet relieved symptoms in 78 percent of people.

This included a reduction in pain and bloating, which can have a dramatic impact on someone’s quality of life.

However, a low-FODMAP diet doesn’t seem to improve the underlying intestinal inflammation associated with inflammatory bowel diseases.

One small study of 52 patients with Crohn’s disease or ulcerative colitis and gut issues, published in Gastroenterology, found that 52 percent of people who followed a low-FODMAP diet for four weeks reported gut health relief, compared with 16 percent of those following a control diet.

For people with SIBO, limiting FODMAP intake deprives bad bacteria of their food source, which may help alleviate symptoms. Still, antibiotics are often considered the primary treatment for SIBO.

(These are the FODMAP foods people with IBS should avoid.)

Close-up of young woman with tablet cooking in kitchen at homeWestend61/Getty Images

How to follow a low-FODMAP diet

Unlike other diets, following a low-FODMAP way of eating is a two-part process.

Right now, your GI system is a mess, and you’re not feeling so great. Before you know which foods are upsetting your stomach, you need a clean slate. That’s why you’ll start with elimination, then move on to reintroduction.

Phase 1: Elimination

Initially, a low-FODMAP diet involves a strict elimination phase that lasts up to six weeks.

Since you’re eliminating all FODMAP sources in your diet, you may be cutting some foods that don’t trigger your symptoms.

That’s totally fine. At this point, the goal is to eliminate any potential triggers so you can wipe out your symptoms before pinpointing specific food triggers.

Phase 2: Reintroduction

Next comes the reintroduction phase. By now, you’re feeling better and able to experiment with different foods to determine which FODMAPs might bring on your distress.

During this phase, you’ll be instructed to test a precise amount of one FODMAP-containing food and keep track of any symptoms. Then you’ll increase the amount of that food, tracking any discomfort.

If symptoms don’t return, you’ll be ready to reintroduce another food from a different category. You’ll follow this process as you make your way through the different FODMAP categories.

For some people, being symptom-free after the initial elimination phase of the low-FODMAP diet feels so great that they’re tempted to skip the reintroduction phase, but experts recommend against that.

While reintroduction may feel like a drag, it’s crucial to follow the protocol in order to discover your individual triggers and personalize your plan with a diverse range of foods.

(These are the best foods—and recipes—for your gut health.)

The downsides of a low-FODMAP diet

While a low-FODMAP diet can help improve your symptoms and quality of life, it does have some drawbacks.

FODMAPs act as prebiotics for the beneficial bacteria in your gut. A 2018 study published in PLOS ONE found that a low-FODMAP diet led to a reduction in these healthy bugs.

Why does that matter? Well, if you extend the diet beyond what’s medically needed, it may lead to other health problems related to the diminished microbiome diversity.

Any elimination diet, including the low-FODMAP diet, also has the potential to lead to food preoccupation, which may trigger or worsen an eating disorder.

And, of course, eliminating a number of different healthful foods can make it harder to meet your fiber and other nutritional needs.

Probably the biggest downside you’ll hear from people who have tried the diet? It makes eating less fun.

How to start a low-FODMAP diet

While you may be tempted to try a low-FODMAP immediately, check with your doctor first.

There are several conditions that produce belly pain, bloating, constipation, and diarrhea, and some can be serious, so they should be ruled out. For instance, gastrointestinal distress might be a sign of a food allergy or food intolerance.

If your doctor recommends a low-FODMAP diet, work with a registered dietitian who can help make it easier to follow the elimination phase and support you through the reintroduction and personalization phases.

Here’s a sampling of foods you’ll eat on a low-FODMAP diet:

  • Veggies: Broccoli, eggplant, spinach, tomatoes, zucchini, carrots

  • Fruits: Cantaloupe; clementines; grapes; small, less-ripe bananas; pineapple; raspberries; strawberries

  • Dairy and dairy alternatives: Lactose-free milk and yogurt and unsweetened almond milk

  • Nuts and seeds: Peanuts, walnuts, peanut butter, and pumpkin seeds

  • Grains: Oats, brown rice, quinoa, and gluten-free pasta and bread made without high-FODMAP ingredients

Sample day

Here’s what a day of eating might look like on a low-FODMAP diet.

Breakfast

Oatmeal made with lactose-free milk and topped with ½ cup strawberries and 1 tablespoon each of walnuts and chia seeds.

Sip a coffee with lactose-free milk.

Lunch

Greek pasta salad made with cucumbers, tomatoes, and kalamata olives, ¼ cup drained and rinsed chickpeas, and ½ cup gluten-free brown rice pasta shells.

Season with Greek seasoning, extra-virgin olive oil, and red wine vinegar.

Dinner

Shrimp stir-fry with approved veggies (such as green beans, bamboo shoots, and sliced carrots) served over brown rice. Season with reduced-sodium soy sauce.

Snacks

Cantaloupe topped with lactose-free Greek yogurt.

Brown rice cake topped with peanut butter and sliced strawberries.

Should you try a low-FODMAP diet?

The simplest answer is if you and your health care provider feel it could help your symptoms, then yes. However, it’s complicated and can be challenging to follow.

It’s critical that you work with a registered dietitian who can help you navigate the diet while also making sure that you don’t miss out on fiber or any other important nutrients.

A dietitian can also make sure you’re getting the most enjoyment out of your plan and help you overcome individual challenges to adhering to the diet.

Next, here are the worst foods for your diet.

Sources
  • Gastroenterology & Hepatology: "Controversies and Recent Developments of the Low-FODMAP Diet"
  • Cureus: "Small Intestinal Bacterial Overgrowth: Comprehensive Review of Diagnosis, Prevention, and Treatment Methods"
  • Nutrients: "Diet Advice for Crohn's Disease: FODMAP and Beyond"
  • Gastroenterology: "Effects of Low FODMAP Diet on Symptoms, Fecal Microbiome, and Markers of Inflammation in Patients With Quiescent Inflammatory Bowel Disease in a Randomized Trial"
  • PLOS One: "A low FODMAP diet is associated with changes in the microbiota and reduction in breath hydrogen but not colonic volume in healthy subjects"

Samantha Cassetty, MS, RD
Samantha Cassetty, MS, RD, is a national nutrition and wellness expert, author, and columnist. Her latest book is "Sugar Shock." You can follow Samantha's practical balanced eating advice on Instagram @nutritionistsam.