The “low-FODMAP diet” has received a lot of attention in recent years. With more people diagnosed with irritable bowel syndrome (IBS) each year, people are turning their attention to different ways to alleviate symptoms. The low-FODMAP diet is one of these approaches. In this article, we will describe what FODMAPs are and their potential health benefits — and why people with IBS might indeed want to avoid them. Finally, we discuss areas of future research regarding the low-FODMAP diet.

What are FODMAPs?

FODMAPs were first defined in a 2005 review positing them as a dietary risk factor for getting Crohn’s disease. The term FODMAP is an acronym that refers to the disparate group of carbohydrate molecules with a set of common traits. The acronym goes as follows:

• FODM stands for Fermentable Oligosaccharides, Disaccharides, and Monosaccharides. Oligosaccharides and disaccharides are sugars that link together into a chain. The fructans and galactooligosaccharides are two kinds of these chains. Monosaccharides are simple sugars that act as building blocks for the oligosaccharides and disaccharides, most notably fructose.
  
  
• A stands for and.
  
  
• P stands for Polyols. These are sugar compounds with multiple hydroxyl (-OH) residues attached. Examples of these compounds include sorbitol, xylitol, mannitol and maltitol.

Foods rich in at least one of these compounds are classified as a member of the FODMAPs, including:

• Grains: Wheat, barley and rye-based products have the most FODMAPs among the grain-based products. They account for a major part of daily consumed FODMAPs and are rich in fructose and fructans.
  
  
• Milk: Milk and milk-based products contain high concentrations of lactate. The inability to produce lactase, an enzyme that provides us the ability to digest lactose in the small intestines, is the key cause of lactose intolerance.
  
  
• Sweeteners: FODMAPs are also readily available for digestion with their increased use in the food industry. Agave syrup, honey, and high-fructose corn syrup each have high concentrations of fructose. Other artificial sweeteners also contain high concentrations of polyols.
  
  
• Fruits and Vegetables: Some fruits and vegetables contain high concentrations of fermentable oligosaccharides, disaccharides and monosaccharides. Legumes, beans and cabbage contain high concentrations of galactooligosaccharides. Onions, shallots, garlic, artichokes and asparagus are also rich in fructans.

Benefits of including FODMAPs in your diet

Foods classified as rich in FODMAPs can provide a range of benefits when you implement them in your diet — assuming your gastrointestinal (GI) tract can tolerate them. Because the small intestine cannot take up as much fructose and other FODMAP compounds into the bloodstream compared with other sugars like sucrose and glucose, most of these compounds make their way into our large intestines, where our gut microbes digest them through a process called fermentation. This process generates compounds called short chain fatty acids (SCFAs) as a by-product. Because our gut microbes can use FODMAPs to grow in the gut, FODMAPs can be classified into a larger group of molecules called “microbiota accessible carbohydrates.”

Many of the benefits from eating foods with FODMAPs come from the production of short-chain fatty acids (SCFAs) in our guts. When these compounds make their way into the bloodstream, they provide us with diverse benefits, including:

• Potential benefits for preventing/managing diabetes: Mice administered with butyrate, the most abundant SCFA in our guts, alongside a high-fat diet, had lower insulin resistance than mice not fed with butyrate. The obese mice used in this study also had reduced fat content when fed a fat-rich diet supplemented with butyrate. The ability to prevent insulin resistance helps reduce the risk of developing type 2 diabetes.
  
  
• Colon cancer prevention: SCFAs can also prevent colon cancer cells from proliferating in the gut and stop excessive cell growth by colon cancer cells.
  
  
• Regulating inflammation: SCFAs also help ensure that our bodies do not damage themselves by constantly keeping the inflammatory response on. For instance, SCFAs can increase effector and regulatory T cell counts to make sure our immune system responds appropriately to diverse stimuli.

The downside, for some people, of ingesting FODMAPS

Many of the nutrients that SCFA-producing bacteria acquire to grow in our guts derive from FODMAPs. Yet despite the benefits that FODMAPs provide, some people benefit from avoiding them. This is particularly true for people with inflammatory bowel syndrome (IBS). Why are FODMAPs so harmful for this group of people when they are beneficial for so many others?

FODMAPs and IBS

IBS is a condition affecting the large intestine. People are diagnosed with IBS when they experience chronic or recurring abdominal pain associated with altered bowel movements. The onset of the following symptoms is closely associated with IBS:

• Bloating
• Gas production
• Stomach pain
• Diarrhea
• Constipation 

IBS patients who eat foods rich in FODMAPs are more likely to experience worsening of the above symptoms. This is because FODMAPs demonstrate two characteristics that cause the symptoms to worsen for IBS patients:

• Fermentative capacity: All FODMAPs act as principle substrates for our gut bacteria to grow in the gut. While this process helps produce beneficial compounds such as SCFAs, the same bacteria also produce gas as a by-product. Too much microbial fermentation results in increased flatulence and bloating in IBS patients.
  
  
•  Increased water retention: People who eat a high-FODMAP diet also have increased water content in their stool. The sugars draw water into the small intestine through a process called osmosis, resulting in more water entering our guts. The increased water content increases the risk of diarrhea for people with IBS. 

The adverse consequences of eating foods rich in FODMAPs for IBS patients stem from how their guts respond to these compounds. It’s because of these symptoms that IBS patients have to resort to the low-FODMAP diet. Fortunately, not all patients have to avoid all foods that are sources of FODMAPs. After a period of elimination, the low-FODMAP diet actually reintroduces foods one at a time to see which ones can be tolerated and which can’t. Then, patients can specifically avoid those problem foods while enjoying everything else.

How well does a low-FODMAP diet work for IBS patients?

The low-FODMAP diet features limiting foods that are rich in FODMAPs. Formerly, people with IBS tried to alleviate their symptoms by self-limiting the foods they believed made their guts react poorly. These efforts led to a 2013 pilot study which found that reducing FODMAPs in their diets reduced abdominal pain, flatulence, bloating and diarrhea for a cohort of 90 IBS patients. However, the low sample sizes and the difficulties in creating a control group made it difficult to prove that a low-FODMAP diet was beneficial for treating IBS. 

Subsequent clinical trials, however, have provided more support for adopting a low-FODMAP diet to treat IBS symptoms. A 2016 meta-analysis of six randomized control trials (RCTs) showed that a low-FODMAP diet alleviates symptoms among IBS patients. A subsequent meta-analysis performed the year after, which included 10 RCTs, showed similar results: reduced bloating, flatulence and diarrhea among patients adopting a low-FODMAP diet.

The future of low-FODMAPs

The low-FODMAP diet has provided an opportunity for people with IBS to manage their symptoms. However, some questions about this now-mainstream diet remain, and as medical providers learn more, hopefully they can help maximize the benefits of this treatment approach for this patient population:

How long do the benefits of a low-FODMAP diet last for people with IBS?

It remains uncertain whether IBS symptoms could return after a patient has been on a low-FODMAP diet for a long duration. Scientists and clinicians are also still studying whether gastrointestinal distress symptoms could remain at bay even after a low-FODMAP diet  is curtailed, or whether symptoms are likely to return immediately upon stopping the diet.

How should the low-FODMAP diet be implemented?

With so many diverse carbohydrates sharing similar functions, one might assume that FODMAPs should be considered as a whole as opposed to individual items. For example, if a patient with IBS was found to have fructose intolerance and lactose malabsorption on breath hydrogen testing, dietary restriction would involve attention to free fructose and lactose intake, as well as the additional restriction of fructans, galactose, and polyols. However, while a broad, restrictive approach may work well, in other cases it’s possible that limiting specific sets of FODMAPs could incur similar benefits. However, this possibility requires further study.  

How helpful is a low-FODMAP diet for treating other GI diseases?

FODMAPs were first identified as a potential risk factor for developing Crohn’s Disease. Despite this, few studies have examined the effects of a low-FODMAP diet for GI diseases other than IBS.

How does a low-FODMAP diet impact the gut microbiome?

IBS patients adopting a FODMAP diet have reduced Bifidobacteria, a result corroborated in other studies. These changes to the gut microbiome could have detrimental effects on our gut health, although more research is needed to determine if the consequences are significant or concerning.  

Foods good for a low-FODMAP diet

While we wait for more data shedding light on FODMAPs, there are many great food alternatives compatible with a low-FODMAP diet. For instance, why not try some sourdough bread? Not only is it a source of beneficial bacteria that can produce bioactive peptides and polyamines, it is already partially digested during the fermentation process, making it is less likely to trigger the fermentation-related gas and bloating that make IBS symptoms worse. 

Other fermented foods — such as kefir, kombucha and sauerkraut — could also be beneficial for people with IBS. However, studies are small, and some fermented foods can actually make symptoms worse. Some fruits and vegetables (including grapes, berries and certain citrus foods) as well as eggplant, potatoes, tomatoes, cucumbers and zucchini also contain low levels of FODMAPs and are usually fine for people with IBS. Nutrition is highly individualized, so the best thing you can do is work with your doctor and consider the low-FODMAP diet to identify foods you can tolerate comfortably.

Key takeaways

FODMAPs are a group of carbohydrates found in fruits, vegetables, wheat and milk-based products. Because FODMAPs are poorly absorbed by the small intestine, they act as a nutrient source for the microbes in our large intestines. When gut microbes ferment FODMAPs, they produce SCFAs, which are associated with diverse health benefits. However, FODMAPs are also linked with worsened IBS symptoms — including stomach discomfort, diarrhea, constipation and/or bloating. The low-FODMAP diet has emerged as a popular method to mitigate IBS symptoms, and it does appear to have efficacy if it is individualized in its approach. While more work needs to be done to determine the long-term benefits of low-FODMAP diets, the current clinical trial data supports the potential for this diet-based approach to treating IBS. (Also worth considering are low-FODMAP alternatives.) Whether the diet would be beneficial for individuals having other GI disorders remains under study.