How the Low-FODMAP Diet for IBS Works, and How to Get Started

Grilled chicken and mixed greens are both low-FODMAP foods to incorporate in the restriction phase of the diet.
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Belly pain and bloating due to irritable bowel syndrome (IBS) can put a crimp in your day-to-day activities and may even squash your appetite. But what you eat — and more to the point, what you avoid eating — can make a significant difference in how you feel. And that's where the low-FODMAP diet fits in.

What Are FODMAPs?

FODMAPs are carbohydrates (or sugars) that you may not be able to completely digest or absorb if you have IBS. FODMAP stands for "fermentable oligosaccharides, disaccharides, monosaccharides and polyols." Yes, that's a mouthful — but fortunately, you don't have to commit the phrase to memory. Just know that foods high in FODMAPs can trigger or exacerbate IBS symptoms.

Foods containing FODMAPs can pull water into your gut, which can lead to gas, bloating and constipation, Kate Scarlata, RDN, LDN, author of The Low-FODMAP Diet Step by Step, tells "They're fast food for gut bacteria," she explains.

Which Foods Contain FODMAPs?

You might be surprised by the wide variety of food considered high in FODMAPs — ranging from apples to yogurt. "FODMAPs are in many healthy foods," Scarlata explains. "They're not innately bad, but they are common triggers for people with IBS."

Foods you may need to avoid or eat in smaller quantities include:

  • Fruits: apples, cherries, watermelon, peaches and nectarines
  • Dairy: milk, yogurt, cottage cheese and ice cream
  • Vegetables: artichokes, asparagus, cauliflower, beans, snow peas, onion and garlic
  • Grains: wheat, barley and rye
  • Sweeteners: high-fructose corn syrup, agave syrup and honey
  • Sugar-free food: gum and candy

Most people have no problem eating FODMAP-containing foods. "But for the 15 percent of Americans that are impacted by irritable bowel syndrome, the low-FODMAP diet will manage symptoms in about 50 to 70 percent of them," Scarlata says. (A paper published in the August 2017 issue of Gut, which reviewed 10 randomized controlled trials, found that 50 to 80 percent of patients experienced symptom relief on the diet.)

Different people have different sensitivities, but certain foods seem to be more poorly tolerated than others. "Hands down, onions seem to be the most problematic," Scarlata says. "Garlic is probably next up on the list."

Read more: What Vegetables Can I Eat With IBS?

A low-FODMAP diet may be able to alleviate symptoms of your IBS with constipation.
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Where Did the Diet Come From?

Researchers at Monash University in Melbourne, Australia, were the first to propose a low-FODMAP dietary approach to alleviate abdominal symptoms in people with IBS. The team described the history of the diet in a February 2017 review article in The Journal of Gastroenterology and Hepatology.

Although certain "gas-producing foods" were recognized as potential culprits, there hadn't been a collective term to describe these bothersome "short-chain" carbohydrates until the group at Monash fleshed out the FODMAP concept in 2005. The low-FODMAP diet has come a long way since then. It's now considered "a front-line therapy for IBS," Peter Gibson, MD, head of gastroenterology at Monash and part of the team that pioneered the approach, points out in the review article.

In fact, the American College of Gastroenterology (ACG) does suggest a low-FODMAP diet for symptom improvement in people with IBS. The group's advice, described in a monograph published in a June 2018 supplement to The American Journal of Gastroenterology, is based on a number of randomized controlled trials demonstrating that the diet led to "adequate relief" of symptoms in roughly half of patients.

The available evidence supports a possible benefit of the low-FODMAP approach for overall symptom relief, ACG concludes. However, the organization points out that none of the trials evaluated the diet's long-term efficacy or people's ability to stick with it over time.

ACG also notes that there is much less evidence to support a gluten-free diet for IBS. It cites two studies involving IBS patients who reported that their symptoms were controlled by a gluten-free diet. These people were then randomized to either a diet spiked with gluten — or not. Ultimately, the studies showed no statistically significant impact on IBS symptoms between the two groups.

Alleviating IBS Symptoms

IBS is known as a functional gastrointestinal disorder because symptoms arise from the interaction of the gut and the brain, not some problem with the digestive tract itself, such as polyps or a tumor. Roughly 12 percent of people in the U.S. have IBS, and it is twice as common in women than men, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

The thinking is that people with IBS may be more sensitive to pain signals sent from the gut to the brain than other folks. And that may change how the muscles in the bowel contract.

Generally, people with IBS have a mix of normal and abnormal bowel habits. So you may feel OK some days and then experience an IBS flareup that leads to your primary symptoms — whether it's constipation, diarrhea or a mix of both — on other days.

"Someone struggling with IBS can at times feel helpless in finding the solution to their pain and discomfort," says Yvette Perrier Quantz, RDN, LDN, a Louisiana-based dietitian with Ochsner Health System's Eat Fit program. Nutrition therapy and stress management play an important role, she says, and "for some patients, eating a diet low in fermentable carbs may be helpful."

"If the low-FODMAP diet is followed incorrectly or for the wrong reasons, you could be set up for nutritional deficiencies as well as a decrease in healthy gut bacteria."

How Does a Low-FODMAP Diet Work?

You shouldn't leap into a low-FODMAP diet just because you're having gut issues. Before starting the diet, it's important to see a clinician, such as a gastroenterologist, general practitioner or family doctor, for a diagnosis. Your doctor can rule out other causes of your bowel symptoms.

Working with a registered dietitian well-versed in FODMAPs can be a safe and effective approach for people struggling with IBS-related digestive issues, such as gas, bloating, stomach pain, diarrhea or constipation, Quantz, says.

Read more: Does Drinking Water Reduce Bloating?

The diet has three phases:

1. Restriction. During this initial phase, which can last two to six weeks, you will eliminate high-FODMAP foods from your diet and replace them with low-FODMAP alternatives. Does your typical breakfast consist of high-FODMAP foods, like wheat breakfast cereal and cow's milk? You could make a low-FODMAP swap, like sourdough spelt toast with a glass of almond milk.

2. Reintroduction. The next phase involves adding high-FODMAP foods back into your diet, one subtype at a time, over a three-day period. The goal is to identify which FODMAPs you tolerate and which ones trigger symptoms. "We're not saying, 'Eat an apple and let us know how it went,' because apples have multiple FODMAPs, and that wouldn't be very helpful," Scarlata says. So, for example, you might add back milk to a meal to test your sensitivity to lactose. Then you might revisit honey to see whether fructose is a problem for you. This phase of the diet can take eight weeks, more or less, according to Monash University.

3. Personalization. Once you've got a better sense of which groups of foods provoke symptoms and which you can tolerate, you can start to carefully expand your diet while keeping IBS symptoms under control.

A New Option: FODMAP Gentle

One of the challenges of the low-FODMAP diet is sticking with it through the elimination phase to the challenge phase, when you begin reintroducing foods to test your tolerance for each FODMAP. It takes time, Quantz says. The latter phase requires close attention to how your body responds.

If a full-blown elimination diet isn't your thing, you might appreciate a modified version. Monash researchers describe this new approach, which they've dubbed "FODMAP gentle," in a March 2019 review paper published in The Journal of Gastroenterology and Hepatology. Instead of cutting out all high-FODMAP foods, this adaptation involves reducing a few foods with high-FODMAP concentrations (think wheat, onions, apples, milk and legumes) and/or a few targeted FODMAPs.

"It's just a more flexible, less restrictive way to apply the diet," says Scarlata, who adds that this iteration of the diet may be more appropriate for a child or an elderly person with IBS. It can also be a great option for an athlete who has IBS but needs a ton of calories, she adds.

Who Shouldn't Try a Low-FODMAP Diet?

If you don't already have an IBS diagnosis, don't use the low-FODMAP diet as a diagnostic test, Quantz cautions. It should be viewed as nutritional therapy, not as a tool for diagnosing irritable bowel syndrome. Always consult a doctor about your GI symptoms to rule out more serious conditions, like celiac disease, inflammatory bowel disease or colon cancer, Quantz advises.

"If followed incorrectly or for the wrong reasons, you could be set up for nutritional deficiencies as well as a decrease in healthy gut bacteria," she notes.

Because a low-FODMAP diet limits the variety of foods you can eat, the diet can be a trigger for anyone with a history of an eating disorder or who is vulnerable to disordered eating. It's really not appropriate for people with eating disorders or anyone who has a lot of anxiety around food, Scarlata adds.

Putting It All Together

Don't assume that you'll be utterly bored on a low-FODMAP diet. There are plenty of foods from which to choose and countless delicious meals you can whip up, as well as blogs to help you navigate the restaurant scene.

So what might a low-FODMAP diet look like? Here's a sample menu:

  • Breakfast: Bowl of oatmeal topped with almond milk, strawberries and a tablespoon of sliced almonds
  • Mid-morning snack: Brown rice crackers with peanut butter or cheddar cheese
  • Lunch: Mixed greens topped with grilled chicken or salmon, sliced grape tomatoes, cucumbers, one to two tablespoons of chopped walnuts and oil-and-vinegar dressing
  • Mid-afternoon snack: Lactose-free yogurt with a handful of blueberries and a couple of teaspoons of chia seeds
  • Dinner: London broil with roasted potatoes, roasted carrots and a mixed-green salad with an oil-and-vinegar dressing

Keep in mind that a low-FODMAP diet is not a lifelong diet. Once you know your triggers, you are encouraged to use that knowledge to tweak your eating habits. Maybe you can tolerate a splash of milk in your coffee. Or you're fine with a slice of wheat toast for breakfast, but a plate loaded with high-FODMAP foods sends you over the edge. Perhaps your favorite takeout pizza has a bit of onion in the sauce. Instead of depriving yourself and stressing out about it, make a plan, Scarlata suggests. Have it on a Friday night when you're curled up on the couch and have access to your own bathroom, she says.

It's also important to know that your tolerance to FODMAPs can change over time. That may be due to changes in gut bacteria or improvements in gut motility, she explains. Which is why you might want to re-test your FODMAP tolerance at some point to see if you have more wiggle room in your diet. "Just because you react to garlic today, maybe in six months it's not going to be such a problem for you," she says.

Additional reporting by Karen Pallarito


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