Episode 131 – Nutrition For CSID

Key Topics Covered

Carbohydrate foods including grains, fruits and vegetables.

What Is CSID?

  • CSID stands for Congenital Sucrase-Isomaltase Deficiency. 
  • It’s a rare genetic disorder that affects the digestive system, particularly the ability to break down certain sugars.
  • It is also known as GSID, sucrase-isomaltase deficiency and disaccharidase deficiency, disaccharide intolerance.
  • People with CSID lack the enzymes sucrase and isomaltase, crucial for digesting sugars in the small intestine.
  • This can lead to digestive issues like bloating, diarrhea, abdominal pain, reflux and vomiting  


  • Sucrose & maltose are both disaccharides which means they are sugars that have two sugar molecules that are linked together.
  • Specific enzymes are required to break down these sugars into single molecules so they can be digested.
  • Note lactose is also a disaccharide.

How Is CSID Diagnosed?

  • CSID usually becomes apparent in infancy when someone is first introduced to fruits and grain foods. 
  • Symptoms can lead to malnutrition in infants and a failure to thrive so having a diagnosis and management strategy as soon as possible is very important. 
  • Diagnosis of CSID can be done using a disaccharidase assay
  • This involves taking a small tissue biopsy from the small intestine to test the levels of sucrase, maltase, and lactase present.

A Case of Misdiagnosis 

  • When CSID is not picked up in infancy, it can go undetected for decades! And misdiagnosed as IBS especially when symptoms are less severe.
  • Due to testing for CSID being rare in adults and many health practitioners not being aware of the condition – it is theorized that it is severely undiagnosed and under-reported.

Primary VS Secondary CSID

  • Primary sucrase-isomaltase deficiency is something you are born with, it is genetic/congenital and cannot be cured. This must be managed with diet.
  • Secondary SID on the other hand, is when these issues develop later in life and much of the time, addressing the underlying cause can resolve the issue long-term.

Common Reasons for Why SID Would Develop Later in Life Are:

  • IBD.
  • Unmanaged celiac disease.
  • Chemo/radiotherapy.
  • Acute infections such as gastro.
  • Use of some medications.
  • SIBO.

How This Occurs

  • This is due to these conditions damaging the cells in the small intestine that are responsible for producing digestive enzymes.
  • Much of the time, treating the underlying cause of the damage to these cells can allow them to heal and produce more digestive enzymes over time.
  • For example, it is not unusual to see some lactose intolerance develop after a bout of gastro but return to normal over the following weeks/months.
  • Commonly my approach is to:
    • a) address symptom management.
    • b) investigate potential underlying causes and treat them if needed.
    • c) focus on gut-specific strategies to assist with healing the gut overall which can result in a higher tolerance to sucrose and starch over time OR completely resolve the issue all together.
  • However, a lot more research needs to be done in this space for more evidence-based care to be able to be provided.

The Best Way to Manage CSID

Low carbohydrate containing foods.

There is no one-size-fits-all approach to CSID. This is because everyone with CSID will have differing levels of enzymatic deficiency and therefore different tolerance levels.

Simple Low-Carb Approach

  • Although not all carbohydrates need to be avoided, by taking a low-carb or keto approach, you will be dramatically reducing your intake of sucrose and starch, and therefore symptoms will be reduced/resolved.
  • This can be a great place to start for instant relief while learning more about different sugars and types of carbohydrates which can be complex.

Reducing Sucrose and Starch

  • Getting more specific you can take a more nuanced approach to carb intake.
  • This could include adding back in some starches (grains and starchy veg) + sucrose in the form of higher sucrose fruit and veg and finding your tolerance (this is going to be different for everybody).
  • You can also play around with non-sucrose sweeteners such as glucose, fructose, dextrose + non-nutritive sweeteners but not sugar alcohols.
  • There are also lower sucrose sweeteners that have a higher component of glucose/fructose such as honey.
  • High levels of sucrose sensitivity may not be able to tolerate things like honey, and may even need to limit the intake of nuts and seeds along with some even lower carb fruit/veg.
  • For this approach, I do highly recommend working with a SID-informed dietitian as it will make the whole process a lot easier.

Digestive Enzymes

  • Sucraid – not available Australia.
  • Intolerance starchaway – for starch and sucrose, in my experience it tends to be less effective for sucrose,
  • Quite expensive.
  • Not an everyday solution but great for when you want to have something that will likely cause symptoms, when you don’t have much control over food, eating out socially etc.

Tips & Tricks

  • Chewing really well.
  • Pairing starches/sucrose with fats and fibre to slow digestion.
    • Eg. higher fibre starch foods such as wholegrain bread VS white.

Co-managing Other Intolerances (A Complex Case)

  • SIBO.
  • Food chemicals.
  • Nourishing the gut microbiome.
  • There are many cases where there are other intolerances to manage – again best to work with a dietitian if possible as this can be difficult.
  • But you may need to do a FODMAP or failsafe elimination diet alongside having a CSID-friendly diet that works for you and then identify other triggers.


There are many nuances and difficulties associated with this condition. Therefore, we strongly recommend you work with someone who is well-informed in this space, as you will likely benefit significantly more by doing this.

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