When a low FODMAP diet doesn’t work

food plan

Dr. Jane Varney & Dr. CK Yao - Research Dietitians, 20 August 2018

Many, but not all people will experience an improvement in their IBS symptoms during the first 2-6 weeks on a low FODMAP diet. While a poor response to the diet can be disheartening, there are a number of very good reasons to explain this. Working with an experienced dietitian will help you to understand why your symptoms improved less than hoped, and to formulate a management strategy going forward.   

How to assess response to a low FODMAP diet

You can assess your symptom response to a low FODMAP diet using the food and symptom diary in the Monash University low FODMAP App™. This diary allows you to track changes in your IBS symptoms as you follow the diet. 

Alternatively, you can rate the improvement in your IBS symptoms on a simple, 0 to 100 scale. Ask yourself: ‘On a scale of 0 to 100, how much did my symptoms improve since starting a low FODMAP diet?’ Using this method, zero would indicate no improvement at all, and 100 would indicate total symptom relief.

When reviewing your symptom response, it is important to consider that:

  • Symptom response to a low FODMAP diet can be highly individual 
  • Most people find their symptoms do not resolve completely 
  • IBS symptoms tend to fluctuate over time; sometimes they may be very mild and sometimes they may be more severe. 
  • Many factors outside of diet can influence IBS symptoms, including stress, anxiety, gastroenteritis, menstruation (in women), physical activity and other lifestyle factors. 
  • Some symptoms are normal, such as a small amount of wind or bloating. It is important to determine what level of symptoms are ‘normal’ and therefore, acceptable for you (given #2).

If after 2-6 weeks on the diet, you consider that your symptom response was adequate, then it is time re-challenge. However, if not, work with your dietitian to figure out why.

Reasons for a poor response to a low FODMAP diet 

There are a number of reasons to explain a poor response to a low FODMAP diet. 

1. Not sensitive to FODMAPs

A low FODMAP diet is effective in most people with IBS, but not all. In fact, research shows us that around 50 to 80% of sufferers will experience an improvement in their IBS symptoms during phase 1 of the diet, leaving 20-50% of people who will not respond. 

Comparing your symptoms before and after the first 2-6 weeks on this diet will help you to decide whether or not your symptom response was ‘adequate’. 

If you adhered to the low FODMAP diet, but feel that the improvement in your IBS symptoms was inadequate, then FODMAPs should be re-introduced, and other therapies should be considered. Reintroduction of FODMAPs can occur slowly/gradually if you experienced a minor, but inadequate improvement in symptoms (to avoid any flare in your IBS symptoms). By contrast, FODMAPs can be reintroduced all at once if you experienced no improvement at all. 

2. Compliance 

You may have achieved a suboptimal response to the low FODMAP diet if you did not sufficiently reduce your FODMAP intake. This may occur if you unknowingly consumed high FODMAP foods, or if you had trouble implementing the dietary restrictions. An experienced dietitian who is specialised in IBS can assess your low FODMAP diet, and determine whether you implemented the diet properly. Your dietitian may consider:

  • Meal size  – if you ate very large meals, your FODMAP load  may have been quite high
  • Eating out – if you regularly ate out, you may have consumed larger meals and had fewer low FODMAP options
  • Processed foods - many processed foods contain high FODMAP ingredients, such as inulin, chicory root, apple/pear juice concentrate, xylitol, isomalt, erythritol  and fructooligosaccharides (FOS). 
  • Recipe modification – you may need to adapt your usual recipes to lower  their FODMAP content

3. Other conditions with IBS-like symptoms are present

Another possibility is that you have another underlying diagnosed or undiagnosed condition that is contributing to ongoing gastrointestinal symptoms. Conditions with IBS-like symptoms include inflammatory bowel disease, coeliac disease and endometriosis. Although these conditions are relatively uncommon (and usually ruled out when your IBS is first diagnosed), if they have not been ruled out, you may need to arrange screening tests with your GP or a gastroenterologist. 

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