Understanding IBS and Food Intolerances: What You Need to Know

This transcript has been edited for clarity.

Irritable bowel syndrome (IBS), the most common condition diagnosed by gastroenterologists, is a gut-brain disorder where patients experience abdominal pain and change of bowel habits. 

Unfortunately, IBS symptoms can wreak havoc on patient quality of life and sometimes become quite debilitating. Because certain foods can exacerbate IBS symptoms, it's important to take a detailed history and to educate patients. 

This video will explore food intolerances related to IBS, recent research discoveries, and opportunities for future study. 

Diagnosing IBS

Gastroenterologists diagnose IBS using the Rome IV criteria, which assess specific symptoms and their duration. 

Patients must experience abdominal pain on at least 1 day per week over the past 3 months. In addition, the abdominal pain must be associated with two or more of the following: (1) related to having a bowel movement; (2) associated with a change in frequency of bowel movements; and/or (3) associated with a change in appearance of the stool or stool form. 

Although bloating is a symptom that IBS patients experience, it is not a requirement to make a diagnosis. 

Anywhere from 5%-10% to 10%-20% of the world's population has IBS, depending on the study, with the numbers increasing over the past decade. Another study also estimated the global prevalence of IBS to be approximately 10%-20%, with an incidence of approximately 1.4%-1.5% found in long-term studies with a duration of 10-12 years. The prevalence of IBS in the United States, Canada, and the United Kingdom is approximately 4.4%-4.8%; in Mexico, it ranges from 4.4% to 35.5%, according to a study. Interestingly, we are seeing a higher prevalence in younger adults, females, and smokers. 

In untreated IBS, patients may be more likely to miss work due to debilitating symptoms and cut down on participation in social activities, which can have a detrimental impact on their quality of life. 

Approximately 85% of patients report worsening of IBS symptoms after eating certain foods. As a result, gastroenterologists have focused some of their management attention on dietary control. But it's important to use the Rome IV criteria to distinguish patients with IBS from those who simply have a food intolerance. 

Recommendations for Managing IBS

Taking care of patients with IBS is one of the most satisfying things we do as gastroenterologists, because it gives us the opportunity to help patients get their quality of life back. 

Patients with symptoms should be evaluated for celiac disease using serologic blood testing, especially in those experiencing diarrhea. It is also recommended to check fecal calprotectin to help rule out inflammatory bowel disease.

In the American College of Gastroenterology's 2020 clinical guideline on managing IBS, the expert panel offered a consensus recommendation against “testing for food allergies and food sensitivities in all patients with IBS unless there are reproducible symptoms concerning for a food allergy.” 

The panel gave a strong recommendation for using chloride channel activators or guanylate cyclase activators to treat global IBS constipation symptoms. 

A strong recommendation was also given to use rifaximin, a non‒systemically absorbed antibiotic, to treat global IBS diarrhea symptoms. 

In addition, the authors provided a strong recommendation for using low-dose tricyclic antidepressants to treat global symptoms of IBS.

A conditional recommendation was given for treating patients with mixed opioid agonists/antagonists, and to use a limited trial of a low‒fermentable oligosaccharides, disaccharides, monosaccharides, polyols (FODMAP) diet to help improve global symptoms for patients with IBS. 

The Toll of Food Intolerances and Sensitivities 

It should be noted that food allergies are exceedingly rare in patients with IBS. However, patients do experience food intolerances and sensitivities. 

It has been demonstrated that particular foods can precipitate symptoms in up to 84% of patients with IBS. In many patients with IBS, eating gluten and high-FODMAP foods can cause symptoms to flare.

Unfortunately, these food triggers are associated with a decrease in quality of life. In a recent study performed by researchers at Indiana University School of Medicine and the Cleveland Clinic, food intolerances led large numbers of participants to miss work (36.1%), schedule a doctor's appointment (17.5%), and be hospitalized (15.1%). 

Such results highlight the importance of working with patients to identify specific food triggers.

FODMAP Foods

The term "FODMAP" was initially coined in 2005 by researchers at Monash University in Australia. 

Adopting a low-FODMAP diet has since become an important treatment for patients with IBS. Patients on this diet eliminate foods that contain fermentable oligosaccharides, disaccharides, monosaccharides, and polyols to help prevent bloating and abdominal pain. 

Commonly consumed high-FODMAP foods that tend to exacerbate symptoms include onions, garlic, apples, pears, watermelon, ripened banana, avocados, Brussels sprouts, cabbage, broccoli, cauliflower, cheese, milk, chocolate, yogurt, beans and legumes, high-fructose‒containing sodas, teas including chamomile and chai, artificial sweeteners such as sorbitol and mannitol, asparagus, mushrooms, wheat, flour, tortillas, rye, and processed meats. 

It’s been reported that 52%-86% of patients with IBS experience improvements in their symptoms by simply removing these FODMAPs from their diet. 

Unfortunately, FODMAP foods are poorly absorbed in the intestines and can be quickly fermented by bacteria into hydrogen (H2) and methane gas. These gases increase intraluminal tension and act on the intestinal wall, causing symptoms such as abdominal bloating and pain. FODMAP foods might also cause a low-grade inflammatory response and an increase in intestinal permeability. 

FODMAP foods cause bloating by producing short-chain fatty acids such as acetate, butyrate, and propionate during the fermentation of certain fibers by gut bacteria.

Many patients complain that their IBS symptoms worsen after meals. It should also be noted that some patients with IBS experience dysbiosis with decreased amounts of fecal microbiota, bifidobacteria, and lactobacilli. 

Incorporating the low-FODMAP diet requires three phases of lifestyle modifications.

First, patients substitute high-FODMAP foods like onions, garlic, avocados, and watermelon for low-FODMAP foods. I always counsel patients that this doesn't mean that the high-FODMAP foods are bad for them, but that they simply tend to cause more bloating symptoms in certain people. 

In the second stage, patients slowly reintroduce high-FODMAP foods while monitoring whether specific foods provoke symptoms. This will help determine which high-FODMAP foods they are sensitive to and can avoid in the long term.

Finally, in the third stage, we help patients personalize their diet and add back the high-FODMAP foods that they do not seem to be sensitive to, so they can eat more easily at restaurants and at home. 

It's important for gastroenterologists to give patients and their families the confidence and tools to better understand the importance of these long-term dietary adjustments. Frequently, patients begin to avoid putting themselves in social situations where they might be served food out of their control. I try to counsel patients not to be anxious about these situations, like going over to a friend's house for dinner. If you avoid high-FODMAP food triggers over 90% of the time, that can still make a huge quality-of-life difference, with significant symptom improvement.

It's important to teach patients about these three stages because those who over-restrict their diets can wind up with nutritional deficiencies or worsening eating disorder behaviors. 

Apps and Other Educational Tools

There are several new low-FODMAP diet smartphone apps that can help many patients in conjunction with a dietician or as standalone therapy. 

A 2022 study performed in Belgium in conjunction with the Rome Foundation Research Institute demonstrated that using a low-FODMAP diet smartphone app was superior to using a musculotropic spasmolytic agent when treating IBS symptoms. Additionally, the authors reported that it could be used as a first-line treatment by primary care physicians. 

Patients seem to enjoy using the Monash University FODMAP app that was created in Australia. It allows patients to educate themselves about which foods to eat and avoid, which is helpful when grocery shopping or dining at a restaurant. 

The mySymptoms Food Diary & Symptom Tracker is an app that helps patients identify high-FODMAP food triggers. 

Gutly is a new artificial intelligence‒empowered FODMAP and IBS tracker. 

Finally, Spoonful is an app that helps patients go grocery shopping for low-FODMAP foods.

Educational websites, such as MyGInutrition.com, created by the University of Michigan, and monashfodmap.com, from Monash University, are fabulous, interactive, and up-to-date resource tools for teaching patients about the low-FODMAP diet. 

These innovative web-based initiatives are game changers because they provide easy access to FODMAP information and tracking on the go. 

As a slightly more straightforward option, I personally provide two copies of color-coordinated low- and high-FODMAP food guide handouts to patients, one to keep in their kitchen and one to keep in their car when going grocery shopping. My patients love that. 

Additional Treatment Options

Another helpful food treatment for patients with IBS is to avoid gas-producing foods in their diet. To quote a 2017 review paper on the topic, “Foods associated with an increase in intestinal gas and flatulence include alcohol, apricots, bagels, bananas, beans, Brussels sprouts, caffeine, carrots, celery, onions, pretzels, prunes, raisins, and wheat germ.”

Alternatively, there is a diet called NICE, created by the National Institute for Health and Care Excellence and the British Diabetic Association (BDA), for patients with IBS diarrhea. Patients adopting the NICE diet avoid alcohol, spicy and fatty foods, coffee, caffeine, cabbage, and beans, carbonated drinks like soda or beer, and foods containing the sweetener mannitol, which is found in gum. The NICE diet also encourages patients to eat three meals per day with snacks. The goal of this diet is to help patients with IBS establish a good relationship with food again. 

However, it should be noted that a 2022 meta-analysis published in Gut, examining 13 randomized controlled trials, showed that the low-FODMAP diets are “significantly more efficacious than NICE-BDA dietary advice for abdominal bloating or distension.”

A dietary approach for the treatment of IBS constipation is fiber supplementation. The American College of Gastroenterology’s 2020 guidelines encourage soluble fiber supplementation to treat IBS global symptoms, rating it as a strong recommendation. 

Examples of foods that contain soluble fiber include oat bran, psyllium, beans, and barley. Basically, you want to eat fibers that cause laxative effects and improve the water content of the feces while resisting fermentation by bacteria in the colon. 

If fiber is used to treat IBS constipation, psyllium should be started at low doses so that patients don't experience bloating side effects.

Patients can take peppermint oil to treat global IBS symptoms, which received a conditional recommendation in the American College of Gastroenterology’s guidelines. 

Peppermint oil works via several mechanisms, including via the L-menthol contained within it blocking calcium channels. Peppermint oil also helps patients feel better through analgesic properties by activating kappa opioid receptors and inhibiting the 5-HT3 receptors.

Lactose Intolerance

In patients who don't improve on the low-FODMAP diet, physicians should consider lactose intolerance. 

Lactose intolerance is a food intolerance where patients lack lactase enzymes. Consequently, dairy items containing lactose can cause discomfort and poor digestion. Many patients with lactose intolerance complain of bloating, diarrhea, gas, and abdominal pain.

Some patients are genetically insufficient in the lactase enzyme, whereas others acquire a deficiency. When patients malabsorb lactose, a troublesome amount of fermentation can occur and worsen IBS symptoms. 

Trying a lactose-free diet by avoiding dairy or supplementing with inexpensive, over-the-counter lactase enzymes can help with the diagnosis while simultaneously improving symptoms. Alternatively, a physician can diagnose lactose intolerance by measuring H2 levels in patients’ breath after they ingest 25 grams of lactose. Fortunately, patients with this condition can dramatically improve their symptoms simply by replacing the deficient lactase enzyme. It's amazing how inexpensive and widely available lactase enzymes have become at pharmacies.

Here's a clinical pearl. When consuming dairy, some patients undertreat by taking just one lactase enzyme replacement pill. This can lead to improvement, but not complete resolution, of symptoms. They probably take just one pill because they come in individual packages. However, many patients have better symptom prevention when taking two to three lactase pills prior to eating dairy. I encourage patients to have pills available when at home or work or when they go out to eat.

So, it’s relatively easy to treat lactose intolerance. Patients can either avoid dairy or take lactase enzymes. Several companies even produce lactose-free milk now. The flavor is sometimes a little sweeter, so it’s perfect to consume with cereal in the mornings or to pour in a coffee. 

There are a small number of patients who experience mild sucrose malabsorption that presents in adulthood. To evaluate for this, physicians can perform a test of enzyme activity from a duodenal biopsy via esophagogastroduodenoscopy, or they can have patients undergo H2 sucrose breath testing, which can be performed at home and sent to an external lab for analysis. 

There are some patients with IBS but not celiac disease who experience symptomatic improvement by avoiding gluten, especially those with IBS diarrhea who have failed dietary therapy by avoiding high-FODMAP and gas-producing foods.

Avenues for Future Research

There is some evidence in animal studies that food additives might influence IBS symptoms, but research needs to be conducted on humans. Other research has shown that noncaloric sweeteners are associated with changes in gut microbiota, with increases in Bacteroides and decreases in Firmicutes. Researchers should also examine whether emulsifiers and processed foods are having an impact on IBS. Emulsifiers and food additives have become increasingly common in stored foods on shelves over the past two decades. These are areas that deserve lots of future attention.

Genetic research is an important area for future research. Patients with sucrase-isomaltase hypomorphic variants have been shown to have reduced response to the low-FODMAP diet. Investigating additional digestive enzyme mutations that might be exacerbating symptoms could better predict food intolerances.

Hopefully, future clinical trials will help us identify which foods should be avoided by patients with IBS. We need more research about the precise pathophysiology regarding how FODMAPs trigger visceral hypersensitivity and their role in gut fermentation and gas production. Our goal should be to successfully predict and personalize low-FODMAP diets so that patients can enjoy eating again.

Research into the altered fecal microbiota might provide important clues. Future research should also hone in on the collective impact of stress, anxiety, and diet on IBS symptoms. 

Over time, we need to better assess the effectiveness of FODMAP and food symptom‒tracking apps.

Finally, we should address the low-FODMAP diet’s long-term impact on micronutrient intake and how long-term adherence to it might affect the microbiome and overall health. 

Benjamin H. Levy III, MD, is a gastroenterologist at the University of Chicago. In 2017, Levy, a previous Fulbright Fellow in France, also started a gastroenterology clinic for refugees resettling in Chicago. His clinical projects focus on the development of colorectal cancer screening campaigns. Levy, who gave a TEDx Talk about building health education campaigns using music and concerts, organizes "Tune It Up: A Concert To Raise Colorectal Cancer Awareness" with the American College of Gastroenterology (ACG). He frequently publishes on a variety of gastroenterology topics and serves on ACG’s Public Relations Committee and FDA-Related Matters Committee.