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What Is the FODMAP Diet & Who Should Consider It?

Jan. 5, 2022 - Katie McCallum

Unless you regularly suffer from digestive discomfort, including gas, bloating, diarrhea and constipation, chances are you've never heard of the low-FODMAP diet.

It's a diet with a funny-sounding name that stands for a few technical-sounding words — Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols (the FODMAPs).

"The gastrointestinal tract has a limited capacity to digest certain sugar molecules, and these are the FODMAPs," says Dr. Eamonn Quigley, a gastroenterologist at Houston Methodist.

Most people are ultimately able to digest them, though — which is good since FODMAPs are found in so many foods, including common vegetables and fruits.

"Unfortunately, some people have a more limited capacity to digest these sugar molecules than others," explains Dr. Quigley. "And when not digested properly, FODMAPs can cause digestive distress."

This is why some people may benefit from a diet low in certain FODMAPs.

What is the FODMAP diet?

As far as diets go, the FODMAP diet is fairly unique. It starts as a highly restrictive elimination diet and, over time, transitions into one that's only slightly restrictive.

"You essentially start by eliminating all foods that contain high amounts of the various FODMAPs," says Dr. Quigley. "If your symptoms improve after a few weeks, you then slowly start introducing foods back into your diet one by one."

The goal is to identify the specific sugar molecule(s) causing your gastrointestinal distress. For instance, the diet may show that you're sensitive to just polyols and monosaccharides but handle disaccharides and oligosaccharides just fine.

"The idea is that you should arrive at a stage whereby you can probably eat most things with the exception of the few foods that are particularly problematic for you," Dr. Quigley adds. "These are the only foods you'd need to avoid going forward with the diet."

As far as the logistics of the FODMAP diet, that's where things get a bit more complex. Okay, really complex.

"In my opinion, a low-FODMAP diet should only be instituted by a physician and implemented by a dietitian who is very familiar with the diet," says Dr. Quigley. "It's incredibly complicated and many, many common vegetables that are otherwise healthy are restricted, so you need help to ensure you're implementing the diet properly."

Which foods are restricted in the low-FODMAP diet and why?

FODMAPs are found in many foods — and in varying amounts. High FODMAP foods include:

  • Such vegetables as onions, garlic, Brussels sprouts, corn and peas
  • Such fruits as apples, grapes, peaches and watermelon
  • Dairy-based products
  • Wheat-based products
  • Beans

Even within these food groups, specific food items are higher in FODMAPs than others. And not all high FODMAP foods contain high amounts of all the FODMAPs. This matters since most people are only sensitive to one or a few.

Like we said, the diet is complicated.

"This is why it's important to do this under dietary supervision," adds Dr. Quigley. "A dietitian can help you understand which foods make the most sense to reintroduce first and may even be able to identify trigger foods and where to start."

Why do these foods cause digestive distress? The answer involves what happens when these sugar molecules move into the colon without being successfully digested in the small intestine. The higher the FODMAP content, the more likely that is.

"Bacteria in the colon are delighted to see these molecules and quickly ferment them," explains Dr. Quigley. "In so doing, they produce gas, which of course leads to flatulence and bloating. This fermentation also leads to the production of other molecules that produce diarrhea."

Who exactly is a candidate for the FODMAP diet?

The initial studies determining whether the low-FODMAP diet might work started with people who suffer from irritable bowel syndrome (IBS). But after showing benefit in others, the diet has been expanded to a larger pool of people.

Still, given that most people handle FODMAPs just fine and the diet is incredibly restrictive, it isn't right for just anyone.

"The idea is that anyone who has problems with digestion or is intrinsically sensitive to distension or excess gas may benefit from trying the low-FODMAP diet," says Dr. Quigley. "It's not a panacea, it doesn't work for everybody, but it does work for some."

Your gastroenterologist may recommend the low-FODMAP diet if you have the following symptoms:

  • Abdominal bloating or distension
  • Flatulence
  • Chronic diarrhea
  • Chronic constipation

"If your doctor recommends the low-FODMAP diet, it's best to work with a dietitian to implement it so you can properly identify your trigger foods and reintroduce everything else," says Dr. Quigley. "For instance, we have a dietitian trained in the low-FODMAP diet with whom we work closely, and that makes an enormous difference in the success of trying the diet."

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