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8 Important things to know before starting the low FODMAP diet

Thinking about starting the low FODMAP diet?  Who isn’t these days? Before you dive in, there are a few things we need to discuss first.  The more you know, the smoother your FODMAP journey will go.

*Trigger warning: #8 in this post briefly discusses eating disorders

1. FODMAPs are in A LOT of foods

FODMAPs are types of carbohydrates that are poorly digested, and as a result, they can cause bloating, gas, pain and altered bowel habits.

Because FODMAPs are carbohydrates, they are found in dairy, plants and foods made from plants – vegetables, fruits, soy and tofu, grains, nuts, seeds, beans, legumes, and milk. As carbohydrates, they are not found in meat, poultry, fish or eggs.

FODMAP is an acronym for the different types of carbohydrates.

F = Fermentable

  • FODMAPs are not fully digested and absorbed so they end up in the large intestine where bacteria feast on them and produce gas.

O = Oligosaccharides

  • There are two types: 1) Fructans, 2) Galacto-oligosaccharides (GOS).
  • Fructans are found in garlic, onion, wheat, dates.
  • GOS are found in lentils, chickpeas, black beans, soy, soy milk, cashews, pistachios, green peas.

D = Disaccharide

  • Lactose is the disaccharide in this group.
  • Lactose is found in milk, yogurt, sweetened condensed milk.
  • There is no to little lactose in cream (whipping) and hard cheeses like cheddar, mozzarella, parmasean.

M = Monosaccharide

  • Fructose – specifically large amounts – is the monosaccharide in this group.
  • Excess fructose is found in apples, figs, asparagus.

A = and

P = Polyols

  • Polyols are “sugar alcohols” (no, there’s no alcohol in them).
  • There are two types we’re watching out for: 1) Sorbitol, 2) Mannitol.
  • Sorbitol is found in apples, peaches, blackberries, coconut milk.
  • Mannitol is found in mushrooms, cauliflower, celery.

2. The low FODMAP diet is not forever

Contrary to common belief, the low FODMAP diet is not meant to be a long term diet. 

The low FODMAP diet can be pretty restrictive so there’s risk of nutrient deficiencies, inadequate fibre, and a negatively altered gut microbiome if it’s not done right. Dietary restrictions can also put a big dent in your social life.

The purpose of the low FODMAP diet is to improve IBS symptoms and identify which FODMAPs you’re sensitive to so you can reduce them.  The ultimate goal is to achieve balance between good symptom control and the fewest dietary restrictions possible.

Phase 1: Elimination

In the elimination phase, you replace all moderate and high FODMAP foods with low FODMAP alternatives. This phase lasts 2-4 weeks, depending on your response.

Phase 2: Reintroduction

In the reintroduction phase, you systematically reintroduce high FODMAPs and monitor your gut symptoms to determine which FODMAP groups you tolerate and which trigger symptoms. This phase lasts about 6 weeks, depending on how smoothly the process goes.

Phase 3: Personalization

In the personalization phase, you expand your diet to include the FODMAPs you tolerate. You may also experiment with FODMAP groups you didn’t tolerate in the reintroduction phase to see if there’s a small portion you DO tolerate. This serves to minimize unnecessary dietary restriction.

Ultimately you end up on your own individual FODMAP diet, rather than following the low FODMAP diet indefinitely.

3. You should speak to your doctor before starting the low FODMAP diet

You should work with your doctor to diagnose your gut condition. IBS symptoms overlap with other more serious gut conditions, like colon cancer, celiac disease, and inflammatory bowel disease.  

Your doctor needs to assess for these conditions because, unlike IBS, they can be life threatening.  Once they’re ruled out, your doctor can diagnose IBS with the Rome IV Diagnostic Criteria and advise you on whether the low FODMAP diet is appropriate.

If you assume you have IBS but haven’t been formally assessed, you risk delaying an accurate diagnosis.  As a result, you may end up spending a lot time, money and effort chasing the right treatment, which only prolongs your pain and suffering. 

Each gut condition has its own causes and interventions.  You wouldn’t fix a flat tire with an oil change, would you?  So know which gut condition you truly have before starting the low FODMAP diet in order to get the result you want.

4. The Monash University FODMAP App is a MUST

Screenshots of Monash University FODMAP app
Monash University FODMAP app

Online FODMAP food lists are unreliable because the FODMAP content of foods can change depending on ripeness, location where the food was grown, storage time, even selective breeding of crops for desired characteristics.

Monash University created an app with accurate, up to date food lists so you know which foods contain which FODMAPs and what portions you should eat.  The scientists who keep this app updated use rigorous techniques for sampling foods and analyzing their FODMAP content, and retest food on a regular basis.

At the time of writing, Monash added 7 new foods to the list earlier this year.  They also recently re-tested red and green bell peppers, tomatoes, grapes and strawberries and had to adjust their traffic light ratings based on new results (green for low FODMAP, yellow for moderate, and red for high).

5. Symptoms improve in 70% of people

The low FODMAP diet is not a cure for IBS but it’s a highly effective dietary approach to symptom control.  

  • Roughly 70% of people on the low FODMAP diet see improvement in bloating, abdominal pain, gas and stool consistency (3).
  • People generally experience anywhere from moderate to major symptom improvement (4).
  • When compared to the eating pattern in the NICE Guidelines (considered first-line diet therapy), the low FODMAP diet comes out on top as the superior treatment with the best results (5).

Symptoms don’t improve in everyone for a variety of reasons:

  • Misdiagnosis – you don’t actually have IBS
  • A component in food other than FOMDAPs is triggering symptoms (eg. histamine)
  • The diet wasn’t followed properly
  • Psychological issues are your primary trigger – stress, anxiety, depression

Although general advice is to follow the elimination phase of the low FODMAP diet for anywhere from 2-6 weeks, most of the studies that found improved symptoms had a 3-4 week elimination phase.  One study even found that people closely adhering to the low FODMAP diet felt significantly better after 1 week (3)!

6. It takes 1-4 weeks to feel better

General advice is to follow the elimination phase of the low FODMAP diet for 2-6 weeks.  This is likely because most of the studies that have found symptom improvement on the low FODMAP diet had a 3-4 week elimination phase (7). 

FODMAPs clear your system in about 72 hours so it’s no surprise that one study found that people who closely adhered to the low FODMAP diet felt significantly better after 1 week (1).

If you’re not feeling better by week 3, you need to do a little investigating:

  • Are you diligently keeping a food and symptom journal?
  • Are you using the Monash FODMAP app?
  • Are you following the green-lit portion sizes in the Monash app?
  • Are you FODMAP stacking? (eating too many of one type of FODMAP group at a meal – this is especially relevant to vegetables)
  • Are you eating out?
  • Are you unusually stressed (eg. bad week at work)?
  • Did you start something else during the elimination phase (eg. new medication or supplement)?

If you answer ‘yes’ to the first 3 items on this list, and ‘no’ to the bottom 4 items, then the low FODMAP diet may not be right for you.

7. Plan to spend about 3-4 months on the process

The elimination phase doesn’t have to last long.  As soon as you feel better, you can graduate to the reintroduction phase.

Reintroducing FODMAPs and testing your triggers takes the bulk of the time when it comes to the low FODMAP diet. Expect this phase to take about 8-10 weeks so you can test each major fructan (garlic, onion, fruit & veg with fructans, grains with fructans) and each major polyol (mannitol, sorbitol) in addition to fructose, lactose and GOS.

There are a few different schedules you can employ to carry out the reintroduction phase. For people with a lot of anxiety about starting phase 2, these various schedules offer reassurance. Check them out in my Reintroducing FODMAPs post, where I’ve mapped out the schedules and provided sample calendars.

Overall, you’ll move through the low FODMAP diet quicker if you:

  • Follow the diet properly and consistently
  • Are careful when eating out or buying pre-made meals
  • Stick to a schedule during the reintroduction phase
  • Avoid doing the diet during atypical upheavals in your life – Christmas, vacation, moving house, etc

8. Disordered eating and eating disorders

IBS sucks.  There’s no cure, symptoms fluctuate – seemingly without cause, and searching for a treatment can feel like looking for a needle in a haystack.

Therefore, it’s hardly surprising that in the attempt to cope with unrelenting discomfort, many people with IBS develop disordered eating behaviours.   Such behaviours include food avoidance driven by fear, chronic under eating, skipping meals and not eating when hungry. 

If severe enough, disordered eating can turn into a eating disorder (6).  And for those with an eating disorder history, the restrictions inherent to the elimination phase of the low FODMAP diet can trigger relapse.

This doesn’t mean all hope is lost.  Not at all!  There are other diet and non-diet strategies for calming IBS symptoms that can and should be explored.

11 ways to relieve IBS symptoms without the low fodmap cover image

Confused? Got Questions? Feel free to drop me a line in the comment section 🙂

xoAndrea, RD

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