What Is the Low-FODMAP Diet for Digestive Health?

Irritable bowel syndrome (IBS) has a funny-sounding name, but it’s no laughing matter for the millions of people who have this condition — up to 15 percent of adults in the U.S., according to the American College of Gastroenterology. Studies suggest that only 1 in 4 people with IBS sees a doctor, despite the chronic constipation, diarrhea, bloating and abdominal pain.

If you have been diagnosed with IBS, you’ve likely heard of the low-FODMAP diet for digestive health. But do you really understand what this diet entails?

“The low-FODMAP elimination diet is restrictive and can be challenging to follow,” said Margie Ullmann-Weil, an outpatient registered dietitian at Lahey Hospital & Medical Center in Burlington, Massachusetts. “It’s overwhelming when you read about it online, and it’s not easy to get started on your own. The elimination phase is a short-term diet. It is not intended for people to follow this diet indefinitely. We see some degree of improvement in probably 70 percent of patients who try it. Many, many people say, ‘I wish I’d done this sooner.'”


FODMAPs are a group of carbohydrates, specifically sugars and fibers, found in foods. The letters stand for:

  • F: fermentable

  • O: oligosaccharides (wheat, garlic, onion)

  • D: disaccharides (lactose, milk sugar)

  • M: monosaccharides (certain fruits, high-fructose corn syrup)

  • A: and

  • P: polyols (sugar alcohols, such as mannitol and sorbitol)

Certain people just absorb certain FODMAPS poorly, Ullmann-Weil says.

“When these small chain carbohydrates are poorly absorbed in the small intestine, they continue undigested to the large intestine, where they are a food source for the bacteria that live there,” she said. “The bacteria can ferment these undigested FODMAP foods, and they end up causing IBS symptoms, such as bloating, distention of the abdomen, excess gas, abdominal pain, diarrhea, constipation or alternating diarrhea and constipation.”

A Low-FODMAP Diet for Digestive Health

If you have symptoms of IBS, you might be sensitive to some — but not necessarily all — FODMAP groups. The diet is a two-step process that helps you determine which ones you can eat and in what amount.

“The idea is to completely eliminate all high-FODMAP foods during the elimination phase,” Ullmann-Weil said. “Then, after about three weeks, or when symptoms subside, we systematically add back those foods one at a time, in varying doses. The goal is to find out if someone can tolerate the food and in what amounts. So we might start with wheat and have them eat one slice of bread on the first day, two slices of bread the next day and then a big plate of pasta the following day. With garlic and onion, sometimes people can tolerate it if it’s cooked, but not raw, so we encourage them to try different preparation methods during this challenge period.”

This is not intended to be a long-term diet, but rather an opportunity to learn which high-FODMAP foods you can eat.

“FODMAPs are actually really good for your digestive health,” Ullmann-Weil said. “They help to improve the biodiversity of bacteria in the gut. So you don’t want to restrict these foods unless you have a problem with them.”

Getting Expert Help

Ullmann-Weil says there are many useful FODMAP-related resources to help you begin this diet — she recommends katescarlata.com — but she strongly suggests that people with IBS work with both a registered dietitian and a gastroenterologist. It’s important to speak with your doctor because IBS symptoms can also mirror other gastrointestinal disorders.

“Sometimes IBS symptoms can be related to other things,” she said. “For example, people might experience similar gastrointestinal discomfort if they have SIBO, a small intestinal bacterial overgrowth that needs to be treated with antibiotics. Once that’s cleared up, many people feel fine and don’t need to try the FODMAP elimination diet. Sometimes constipation is related to pelvic floor dysfunction, where the muscles and nerves in the rectum don’t work properly. A gastroenterologist can refer you to a specialist for this.”

“If you try this diet, you want to do it completely and correctly and that may be difficult to do on your own,” Ullmann-Weil said.

“The list of low- and high-FODMAP foods is long, and portion control of some foods is very important. For example, a 1/2 cup cooked oatmeal is considered low FODMAP, but larger portions are high FODMAP. It is much easier if you work with someone who can help you understand not only what foods to avoid, but which foods you can eat and in what amount,” she said. “When I work with people, we start with a grocery shopping list of foods that are OK. We work on reading food labels to look out for words that indicate hidden FODMAPs, like high-fructose corn syrup or honey or inulin. I provide recommendations on the kinds of breads they can eat. We also talk about eating out, but I usually recommend people pick a period of time when they’ll do most of their eating at home, because it’s really difficult to follow any elimination diet when eating in a restaurant.”

To learn more about how a low-FODMAP diet can help your digestive health, make an appointment with a registered dietitian at Lahey Hospital & Medical Center.


*The content on this website is for informational purposes only and is not medical advice. Please consult a physician regarding your specific medical condition, diagnosis and/or treatment.

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