What Is a Low-FODMAP Diet, Exactly?

I'm just going to go right ahead and say it: Irritable bowel syndrome can be, well, a bitch. Affecting 25 to 45 million people in the U.S., the chronic condition is essentially a group of symptoms that wreak havoc on your digestive system. Think: pain, bloating, diarrhea, and/or constipation, just to name a few. And while there are a number of medications that can help ease IBS, lifestyle changes — such as reevaluating your diet (wink, wink, nudge, nudge) — are typically the first line of treatment, according to the International Foundation for Functional Gastrointestinal Disorders. And, as you've probably guessed by now, this could involve following a low-FODMAP diet.

But what is a low-FODMAP diet, exactly? And how does it work? Ahead, experts break down everything you need to know about this gut-focused eating plan, including how it works and who should follow it.

First, What Are FODMAPs?

FODMAPs refer to a group of fermentable carbohydrates (i.e. starches, sugars, fiber) that, for some people, can be difficult to digest (if not, indigestible) or poorly absorbed, thereby causing IBS-like symptoms such as gas, bloating, diarrhea, constipation, and pain, explains Katie Thomson, M.S., R.D., co-founder and CEO of Square Baby, a nutritious baby food company. More specifically, FODMAPS include fermentable oligosaccharides, disaccharides, monosaccharides, and polyols — all of which draw excess water into your small intestine and then move into your large intestine, where they're fermented by bacteria that can cause IBS-like symptoms (i.e. bloating, gas), says Thomson, who has IBS. "The combination of this water and gas in the gut contributes to altered GI motility, resulting in constipation, diarrhea, or a combination of both," adds Tamar Samuels, M.S., R.D., C.D.N., co-founder of Culina Health. That's only in people who are sensitive to FODMAPs (which, BTW, is not everyone with IBS). People without FODMAP sensitivity can "more efficiently metabolize FODMAPs," and, thus, don't get this fluid retention after eating them, explains Samuels.

While these carbs are found in a wide range of foods (ugh), certain eats are known to be higher in FODMAPS than others, including gluten-containing grains (i.e. wheat, barley, rye), some dairy products (especially milk and yogurt), as well as certain fruits and veggies (i.e. apples, asparagus). Also considered high-FODMAP culprits? Garlic and low-calorie sweeteners or sugar alcohols (i.e. xylitol, sorbitol).

Here are some common examples of foods that fall into each category, according to Thomson:

• Oligosaccharides: Gluten-containing grains such as wheat, rye, and barley; legumes such as beans and soy; nuts such as almonds and cashews; fruits such as dates and ripe bananas; vegetables such as Brussels sprouts, onions, and garlic.

• Disaccharides: Primarily dairy with lactose such as milk, yogurt, ice cream, and soft cheese.

• Monosaccharides: Fruits such as apples, cherries, pear, figs, and mango; vegetables such as asparagus and sugar snap peas; sweeteners such as honey and agave.

• Polyols: Fruits with pits and seeds such as apples, avocados, cherries, blackberries, figs, peaches, and plums; low-calorie sweeteners or sugar alcohols such as xylitol or sorbitol, found in sugar-free desserts and gum.

So, What Is a Low-FODMAP Diet? 

Despite its name (see: "diet"), a low-FODMAP diet is not just another trendy, ephemeral eating plan that requires calorie counting, macro counting, or, well, any math. Instead, it's all about restricting (and then reintroducing) certain foods known to trigger IBS-like symptoms. And it's been shown to work: In fact, up to 86 percent of IBS patients find an improvement in overall GI distress and symptoms following the eating plan, according to a 2016 scientific review.

"The goal of the diet is to help identify personal triggers for GI symptoms," says Samuels. How exactly? "Via FODMAP elimination and then a systematic reintroduction phase," she explains. Translation: eliminating quite a few foods from your diet — remember: FODMAPs are in many foods — and then slowly (and I mean slowly) adding each item back into your repertoire to determine which, if any, your gut can handle. (Related: The Best Low-FODMAP Snacks, According to Dietitians)

Another pro of the low-FODMAP diet is that it allows your GI tract time to heal, says Samuels. Giving your gut a break from FODMAPs can help to decrease any inflammation caused by impaired motility (i.e. constipation and diarrhea) brought on by these fermentable carbs, she explains.

This process can be broken down into three different "steps" — all of which should be done under the care of a registered dietitian and/or physician, according to Thomson and Samuels:

Restriction or elimination: Removing high-FODMAP foods from your diet for a period of two to six weeks or until you achieve relief from previous symptoms.

Reintroduction: Once your symptoms have improved, you can start "systematically adding back in one FODMAP food/category at a time while tracking and monitoring your symptoms to see if you have a reaction," says Samuels. Apples, for example, are high in both polyols and fructose, so they're not the best test food. Cauliflower, on the other hand, is only high in polyols, making it "ideal for testing that category," explains Samuels.

Now, this isn't an excuse to go crazy with the cauliflower and start pounding bag after bag of TJ's cauliflower gnocchi (although, yum). When testing a food, Samuels recommends eating a normal-sized portion (this guide to healthy portion sizes can help) of the food, during one meal per day for a total of one to three times during the test week. "If no symptoms occur after the first test, we increase the portion of the challenge food for the next trial," she says. "If symptoms do occur, you go back to eating low-FODMAP until symptoms resolve and you're symptom-free for three days." It's important to note that throughout this phase, you should continue following the low-FODMAP diet minus the one category you're reintroducing. (Pro tip: a food journal can make keeping track of your symptoms easier.)

And it's only when the reintroduction period is over that you can add any FODMAP category that you were able to tolerate back into your diet, notes Samuels. So, if you passed the cauliflower trial, you can add polyols back into your repertoire.

Personalization: Because people react to various FODMAPs in different ways, some people might need to eliminate or minimize certain IBS-triggering foods while others can incorporate them back into their diet sans symptoms. Just remember that the goal is to build a nutrient-dense, balanced diet that works for you, says Thomson. And on that note...

Who Should Follow the Low-FODMAP Diet?

Yes, a low-FODMAP diet has been shown to help reduce symptoms of IBS, but there's a caveat. "It's important to know that a low-FODMAP diet is not for everyone," says Thomson. "Unless you're an adult diagnosed with IBS, it's possible that the diet could do more harm than good since most FODMAPs are prebiotics — the fiber that feeds good gut bacteria and helps to maintain a healthy microbiome." You'll notice that many of the foods considered FODMAPs are full of nutrients and healthy fiber (fruits, veggies, legumes), so you don't want to cut out these items unless you're specifically trying to control IBS symptoms. (Also see: The Connection Between PCOS and IBS)

Similarly, someone with a history of disordered eating might want to steer clear of a low-FODMAP diet. "Eating disorders are often triggered by years of restricting food intake - either restricting food groups like carbohydrates, restricting when you eat, and/or restricting calories," explains Samuels. "Because the low-FODMAP diet involves restricting certain foods this can often trigger eating disorder behaviors in individuals with a history of eating disorders or disordered eating."

That being said, you should always consult a nutritionist and/or doctor to determine if this diet might be worth a try for you.