Episode 44 – How and How Not to Identify Food Intolerances (FODMAPs, RPAH, Food Sensitivity Testing)

Key Topics Covered

What is a Food Intolerance

  • Many people confuse allergies with intolerances.
  • Allergy – involves an immune response
  • Intolerance – does not invole any immune response.

Food Intolerance Symptoms

  • Stomach pain
  • Bloating
  • Gas/flatulence
  • Diarrhoea
  • Irritable bowel syndrome (IBS)
  • Rashes, hives and mouth ulcers
  • Fatigue
  • Headaches

How Not to Identify Food Intolerances

Blood tests /  IgG food antibody testing

  • Immunoglobulin G antibody testing is commonly used. But IgG is really a memory antibody.
  • This test is really just a measurement of exposure to particular foods. 

It is not an accurate test. The false-positive rate is so high that it is not worth looking at.  

  • I can see why people buy into it though.
  • It sounds legit, plus it also gives you a list of foods you normally eat. If you normally get symptoms, it has to be something you normally eat that is causing it. If you cut out the foods it says to cut out, there can be improvements.
  • But you are also often cutting out other foods unnecessarily. 
  • The Australasian Society of Clinical Immunology and Allergy – “IgG antibodies to food are commonly detectable in healthy adult patients and children, whether food-related symptoms are present or not. There is no credible evidence that measuring IgG antibodies is useful for diagnosing food allergy or intolerance, nor that IgG antibodies cause symptoms.” 

IgE testing can be done for allergies, and even that has issues with accuracy – so needs a thorough history. But that is a separate topic to IgG testing. 

Other tests

  • Hair analysis
  • Kinesiology
  • Vega tests
  • ALCAT – There just isn’t strong evidence to support other options.  

Outside of lactose intolerance, all other reliable testing options require systematic elimination and reintroduction.  

How To Identify Food Intolerances

Lactose intolerance

  • Can be diagnosed by hydrogen breath test. Also can be pretty easy to trial and error. 
  • They provide 25-50g lactose (1 cup milk 12-13g lactose) and test your breath to see any is malabsorbed.
  • Not many people get it because it’s pretty easy to trial yourself.

Fructose intolerace

  • Fructose malabsorption can be diagnosed by a breath test too.
  • But this can be a false positive in a way for a lot of people, since it is pretty common to be a fructose malabsorber but rarely actually get symptoms in practice 
  • One study identified that 30-80% of people have incomplete absorption of 50g of fructose.   
  • A breath test usually tests 25-50g.  
  • The average consumption of fructose is ~ 16g per day. Heavy consumers might get up to 60-100g per day.  
  • But the point of this is in practice, a lot of people might never get symptoms – which is why systematically testing via an elimination style diet could make more sense 


  • FODMAPs are a group of foods that commonly contribute IBS symptoms. They are short chain carbohydrates and sugar alcohols.   
  • The low FODMAP diet significantly improves IBS symptoms in 50-80% of cases. 
  • Eliminate all FODMAPs for a short period of time, if symptoms resolve, it’s probably FODMAPs. Then systematically reintroduce them.  


  • RPAH or FAILSAFE diet to asses Food Chemical intolerances  
  • There are food chemicals such as salicylates, amines, glutamates and other things like food colours that can contribute to a wide variety of symptoms.  
  • This can include IBS symptoms like FODMAPs, but it also covers other symptoms like headaches and rashes unlike FODMAPs. 
  • Similar protocol of eliminating these foods – then systematically reintroducing to identify what causes symptoms.  

CSID (congenital sucrase isomaltose deficiency) 

  • Rare condition where someone is lacking disaccharidase enzymes (sucrase, isomaltase and sometimes lactase as well) – malabsorption of these sugars leading to chronic diarrhoea, bloating and abdominal pain  
  • Can be identified through a disaccharide free diet  
  • But usually identified through biopsy of the small intestine and typically identified in infancy but not always  

Keep an open mind

  • Less clear options are becoming available as more research is being done in this area.
  • e.g. A2 protein as an example – even people with diagnosed lactose malabsorption have been reported to have less symptoms after switching to A2 milk with the same lactose content – this is just one of many examples for options beyond the stuff mentioned here. 

Other considerations 

  • Always rule out other options e.g. coeliac disease, IBD, bowel cancer.  
  • Also consider other options playing a role e.g. stress. 
  • Listen to your body, if it disagrees it may be useful cutting that food out. In saying that though, if it’s a large range of foods this can lead to malnutrition and should be investigated with a health care professional.

Useful Links/ Resources

Studies Mentioned

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