Celebrating National Sucrose Intolerance week – what is CSID?

Posted on March 31, 2021

The 1-7th of April marks National Sucrose Intolerance week for 2021. This week aims to raise awareness for Congenital Sucrase-Isomaltase Deficiency (CSID). CSID has a complicated name but may be more common than you think. Today we’ll explain what CSID is, as well as the symptoms, diagnosis and treatment for it. We’ll also explore how the low FODMAP diet interacts with CSID and sucrose intolerance.

What is CSID?

To understand what CSID is, let’s break down the acronym. C stands for congenital – which means to exist at or before birth. Those affected by CSID are born with this condition. S and I stand for sucrase and isomaltase – two important digestive enzymes involved in the digestion of sugars and starches. D stands for deficiency – meaning that those living with CSID have absent or low levels of the aforementioned enzymes. When we put this definition altogether, we understand that CSID is a genetic disease acquired at birth that describes a person’s inability to digest sugars and starches due to a deficiency of the enzymes sucrase and isomaltase. The prevalence of CSID is unknown and an ongoing subject of study. For those of European descent, prevalence ranges from 1 in 500 to 1 in 2000. However, more recent studies suggest that CSID is more common than currently estimated.

What are the symptoms associated with CSID?

CSID symptoms are usually brought to the surface after an infant is weaned from breast milk and starts to consume fruits and grains. It is often diagnosed within the first 18 months of life. After someone affected by CSID consumes foods containing sucrose or maltose (such as apples, oranges, carrots and breakfast cereal), they will typically experience watery diarrhoea, bloating, excess gas production and a stomach-ache. They may also suffer from vomiting, nausea or reflux-like symptoms. In some children, their digestive problems will lead to them struggling to gain weight and grow at the expected rate (as growth is an important measure of health for children).

What is the diagnosis and treatment of CSID?

CSID is diagnosed with an endoscopic biopsy – a tissue sample that is taken from the small intestine. Sucrose breath hydrogen tests can also be used – they are less invasive but have a larger margin of error and may provoke symptoms in infants due to the amount of sucrose that must be consumed for a breath test to be performed.

In someone diagnosed with CSID, dietary restrictions may require life-long adherence to a strict sucrose-free diet. However, people with CSID may experience varying severity of symptoms, so some may not have to be as strict as others. Generally, foods high in sucrose and starch should be avoided. Starch is the storage form of carbohydrates and includes cereal, breads, pastas and potatoes. These foods may also need to be excluded, particularly during the first years of life. As people with CSID grow, their tolerance usually grows too.

What is the difference between CSID and IBS?

CSID is a genetic disorder diagnosed in the early years of life, whereas IBS is a functional disorder that tends to develop later in adulthood. However, sucrose intolerance can also be associated with IBS. You can read more about this type of sucrose intolerance here.

Usually, sucrose is broken down in the small intestine by the enzyme known as sucrase. When sucrose malabsorption occurs, the sucrose is not properly broken down by this enzyme and is therefore not absorbed in the small intestine. Instead, the sucrose travels to the large intestine where it is fermented by gut bacteria, producing either hydrogen or methane gas as a by-product of fermentation. This fermentation can result in uncomfortable symptoms such as excessive wind, bloating, cramps and constipation/diarrhoea. We can diagnose sucrose intolerance through a hydrogen and methane breath test. The breath sample will be analysed for hydrogen or methane content to determine if you are able to properly break down lactose, fructose, or sucrose, or if you have bacterial overgrowth.

Does having a sucrose intolerance relate to the low FODMAP diet?

Both CSID and IBS-associated sucrose tolerance involve an inability to fully digest sucrose, also known as table sugar. Sucrose is a disaccharide (the ‘d’ in FODMAP). This is why a low FODMAP diet is also typically low in sucrose. We find sugar added to foods while cooking or baking, sugar added to processed foods such as sweetened drinks, canned fruits, pasta sauces and sucrose that occurs naturally in foods (such as maple syrup, fruits and vegetables).

You’ll notice that many foods that fall within those three categories also contain other FODMAPs. For example, pasta sauce may be high in sucrose due to added sugar and high in fructans (an oligosaccharide – the ‘o’ in FODMAP) due to the addition of onion and garlic. This raises an important point – following a low sucrose diet is not the same as following a low FODMAP diet. The term ‘FODMAP’ encompasses many more short-chain sugars than sucrose alone.

In summary

CSID is a genetic disease acquired at birth that describes a person’s inability to digest sugars and starches due to a deficiency of the enzymes sucrase and isomaltase. Symptoms of CSID include bloating, abdominal pain and frequent diarrhoea, with the treatment being a lifelong low-sucrose diet. However, sucrose intolerance can also be associated with IBS but refers to the unwanted fermentation that occurs in the large intestine as a result of sucrose not being broken down properly in the small intestine, leading to uncomfortable symptoms.

If you believe you may be experiencing sucrose intolerance, a specialised gut health Dietitian can be a great source of help. They will help you establish which exact foods trigger your symptoms and what your individual threshold for sucrose and other FODMAPs are. They can also help you establish whether or not you need to be tested for sucrose intolerance, or whether your symptoms may be attested to other causes.

Written by Charlotte Barber (Student Nutritionist)
Reviewed by Kiarra Martindale (Accredited Practising Dietitian)

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