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Jul 2 8:14am

What exactly is the FODMAP diet? Dr. Wang explains

By Rebecca Williams, @rjwilliams

Mayo Clinic Connect member and volunteer mentor, Teresa @hopeful33250, was recently advised by her GI doctor to start on the FODMAP diet due to her IBS symptoms. She reached out to the Mayo Connect Community, and a robust discussion ensued.

What exactly is the FODMAP diet?  Mayo Clinic gastroenterologist, Dr. Xiao Jing (Iris) Wang explains that “the FODMAP diet is used to eliminate foods with high levels of FODMAP components. Patients who were diagnosed with irritable bowel syndrome and those with functional diarrhea or constipation may benefit from trying the FODMAP diet. However, these diagnoses are often difficult to confirm.”

FODMAPs are certain carbohydrates found in food that do not digest completely and can cause gas, bloating, diarrhea due to the bacteria in the digestive tract causing the FODMAPs to ferment. FODMAPs are carbohydrates that are:

FODMAP chart

Dr. Wang explains that “there are two ways to try the FODMAP diet—one is what is called a ‘Top Down’ approach, which is where all FODMAPs are eliminated from the diet for a full 6 week period. Then, food groups are reintroduced one by one to assess for return of symptoms. Another is the ‘Bottoms Up’ approach, where groups are eliminated one at a time based on prior experience with offensive food (i.e. if milk caused symptoms in the past, start with eliminating lactose). I would recommend the ‘Bottoms Up’ to avoid any unnecessary dietary limitation which can lead to poor nutrition.”

Dr. Wang also recommends that while following the FODMAP diet, patients should monitor themselves “for symptomatic improvement…There should not be any additional or new GI symptoms from dietary elimination of these certain food groups.”

The question was raised in the discussion about patients who have had their gallbladder removed and the role that bile flow has in the digestion process. Mayo Clinic Gastroenterology Fellowship graduate, Dr. Priya Vijayvargiya, who focused her research on bile acids, explains that “Bile is a substance synthesized by your liver and stored in your gallbladder. Upon eating, the gallbladder contracts and releases the stored bile into the small intestine. Its main role is to help absorb fat. Fat is not water soluble which makes it problematic to be absorbed. The bile surrounds the fat to help make it easier to absorb within the intestine.

“Once the gallbladder is removed, the liver will constantly release bile into the small intestine. Having your gallbladder removed typically does not have any significant impairment in fat absorption. Patients may notice some diarrhea, particularly after a high fat meal, but the bile in the intestine is sufficient to absorb most fat.”  Dr. Wang further explains that, “If patients eat a meal with high fat content, there may not be enough bile sent down to the intestines to help digest all of those fats. These fats can then travel down to the colon and cause diarrhea.”

In addition to patients diagnosed with irritable bowel syndrome, Mayo Clinic registered dietician Jaclyn See explains that patients with celiac disease may also benefit from following the FODMAP diet if they are following a strict gluten-free diet and still experiencing symptoms. Patients with celiac disease should discuss this option with their physician who may want to do further testing to ensure their symptoms are not due to uncontrolled celiac disease, a pancreatic disorder, or colitis.

In addition to consulting their physician, Ms. See recommends that patients work with a registered dietician who can make sure they are following the FODMAP diet correctly as well as ensure patients are eating a balanced diet and getting the proper nutrition.

There have been studies that show that people with NCGS (non-celiac gluten sensitivity) may actually be sensitive to FODMAPs rather than gluten. One such study was cited in a 2016 article in The Guardian, “Could sourdough bread be the answer to the gluten sensitivity epidemic?” This article was also shared via Mayo Clinic Connect in April 2016. This study was conducted at Monash University in Australia.  In 2011, this university conducted the study that started the “gluten-free” movement in which patients with IBS were found to feel better when they followed a gluten-free diet. Two years later, in 2013, they did a follow-up study in which patients with NCGS eliminated gluten and FODMAPs from their diet. Once these subjects started feeling better, researchers gave some of them gluten, and there was no adverse reaction. This suggested that FODMAPs may be the cause of their sensitivity rather than gluten. Then why is that so many people believe that gluten is the culprit and have never heard about FODMAPs?  In this same article in The Guardian, Mayo Clinic gastroenterologist and celiac disease expert, Dr. Joseph Murray explains that by the time the 2013 study results were published “it was too late to stop this gluten sensitivity train: it had left the station.”

Connect with other patients talking about FODMAP, digestive health issues, and more:

Following a horrid first bout of Diverticulitis and then an early relapse from eating some raw cruciferous veggies,. I began a FODMAP diet plan. I kept a daily diary of food intake for 2 1/2 months and used the "bottom up" approach which proved effective for me. Re-introducing raw vegetables into my diet was the scariest and longest effort for me. Each of us is uniquely different and our symptoms and problematic food groups will differ as well. I'm just glad my research led me to have discovered a FODMAP diet which worked well for me.

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