Managing IBS with FODMAPs

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Understanding IBS

Irritable Bowel Syndrome (IBS) is a functional gastrointestinal disorder afflicting between 10-15% of the U.S. adult population (1). There are no specific tests for IBS, so a diagnosis is made using the Rome IV Diagnostic Criteria (2):

Recurrent abdominal pain (on average, at least 1 day/week in past 3 months) associated with two or more of the following:

  • Related to defecation
  • Associated with a change in the frequency of stool
  • Associated with a change in the form (appearance) of stool

IBS is characterized by constipation (IBS-C), diarrhea (IBS-D), or both (IBS-M), along with abdominal discomfort, gas, and bloating. Importantly, IBS is NOT a physical/chemical disorder, a type of cancer, a precursor to another gastrointestinal disorder, or a result of structural abnormalities in the digestive tract (1). IBS is also not caused by stress or anxiety (although, stress can worsen symptoms), but is believed to result from changes to the nerves and muscles that control sensation and movement in the digestive tract (1).

There are no cures for IBS, but evidence suggests that dietary and lifestyle changes can effectively manage the symptoms of the condition. Of the various dietary approaches suggested, a low FODMAP diet has seen the greatest success in alleviating symptoms of IBS.

What are FODMAPS?

FODMAP is the acronym for ‘F’ermentable, ‘O’ligosaccharides, ‘D’isaccharides, ‘M’onosaccharides, and ‘P’olyols, which are short-chain carbohydrates that are poorly absorbed in the digestive tract. When these carbohydrates are consumed by those with IBS, they may trigger negative digestive symptoms. A low FODMAP diet is an elimination-type diet that can help determine which FODMAPs (and in what dose) are problematic for an individual suffering from IBS.

How to Implement a Low FODMAP Diet


Step 1: Find a FODMAP Professional


Given the complexity of the elimination diet, and the inherent risk of nutrient deficiencies, it’s worth consulting with a Registered Dietitian (RD) skilled in FODMAPs and digestive health (to find an RD in Canada, click here; to find an RD in the U.S., click here). I also highly recommend downloading the FODMAP app by Monash University, whose researchers and scientists are responsible for creating the low FODMAP diet.

Step 2: Identify Sources of FODMAPs (3)

Fructose (in excess of glucose)

Found in: certain fruits, honey, and corn-syrup

Symptoms: diarrhea, abdominal pain, bloating

Fructose is a monosaccharide (carbohydrate made up of just one sugar unit) that is poorly absorbed when consumed in excess amounts in 30-40% of people (3). Absorption can be enhanced by consuming fructose with adequate glucose, which is another monosaccharide found in a variety of foods, such as grains and starches.


Found in: dairy

Symptoms: gas, diarrhea, bloating, abdominal pain

Lactose is a disaccharide (made up of two sugar units) found in dairy products. To absorb lactose, the enzyme, lactase, is needed to break the disaccharide into its individual units. Approximately 65% of the human population (and individuals both with and without IBS) are unable to digest dairy due to a loss of the lactase enzyme (4).

Polyols (Sorbitol, Mannitol)

Found in: some artificial sweeteners, some fruits and vegetables

Symptoms: diarrhea and abdominal pain

Sorbitol and mannitol are both sugar alcohols; a type of artificial sweetener most often found in sugar-free gums and foods. Because they are only partially digested in the intestine, they pass onto the colon where they draw in water and are fermented by the bacteria living there, resulting in uncomfortable gastrointestinal symptoms.

Oligosachharides (Fructans and Galacto-oligosaccharides)

Found in: wheat, rye, onions, garlic, beans and lentils (pulses)

Symptoms: gas, abdominal pain, bloating, altered transit time

What’s interesting to note is that no one absorbs oligosaccharides since humans lack the enzymes to do so. In most, oligosaccharides have a beneficial impact on gut health since they promote the growth of good bacteria. However, because IBS-sufferers have a highly-sensitive digestive tract, flatulence can result in significant pain and bloating.

Step 3: Avoid Foods High in FODMAPs

A low FODMAP is an elimination diet that should only be used for 2 to 6 weeks. During this time, it’s important to keep a detailed food and symptom log in your Cronometer account (which your dietitian can use to identify sources of FODMAPs and determine adherence). It’s also important to ensure that your diet remains balanced and you continue to include foods that will meet vitamin, mineral, protein, and fibre requirements.

Step 4: Challenge Phase and Diet for Life

It’s important to work with your dietitian during the challenge phase to ensure that FODMAPs are being re-introduced in a systematic and structured way. A typical approach to re-introducing FODMAPs is to choose one food from the above FODMAP categories and consume it on two separate days in an amount that you would normally eat (e.g. 1 cup wheat pasta consumed on Monday and Thursday). If there are no negative reactions to the food, it is then added back into the diet and marked as “tolerable”. If digestive symptoms are experienced, the dietitian may suggest re-trialing the food using a smaller amount (e.g. ½ a cup of pasta) or moving on to another food within the same category. Eventually, over a 6 to 8 week period, all FODMAP foods that are commonly consumed in an individual’s diet have been tested and deemed tolerable, intolerable, or tolerable under certain conditions (i.e. consumed in small amounts).

Additional Tips for Managing IBS

In addition to the low FODMAP diet, it’s also important to make lifestyle and dietary changes that facilitate healthy digestion (5):

  • Eat at regular intervals throughout the day
  • Avoid overeating
  • Eat slowly and chew your food extremely well
  • Limit swallowed air by not chewing gum/sucking on mints, avoiding carbonated beverages, wearing proper fitting dentures, and not drinking liquids from a straw
  • Ensure you are consuming adequate fluids (this can be tracked in your account)
  • Meet minimum fibre requirements (can also be tracked in!)
  • Include more soluble fibre (e.g. ground flax, oat bran, chia seeds, etc.)
  • Limit caffeine and alcohol
  • Avoid foods very high in fat
  • Engage in regular physical activity
  • Take a probiotic

If you do not receive benefit from a low FODMAP diet and/or from the changes mentioned above, it’s necessary to work with your physician to determine the cause of your digestive complaints.


  1. American College of Gastroenterology. Irritable Bowel Syndrome. n.d. Available from:
  2. Editorial Team at Irritable Bowel New Rome IV Diagnostic Criteria for IBS. 2016 Dec. Available from:
  3. Monash University. The Low FODMAP Diet. n.d. Available from:
  4. NIH U.S. National Library of Medicine. Lactose Intolerance. 2018 Oct. Available from:
  5. Practice-based Evidence in Nutrition (PEN). Healthy Eating Guidelines for Irritable Bowel Syndrome. 2015 October. Available through subscription only.

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