Sugar Intolerance

Intolerance to Sugar

Sugar intolerance , sugar intolerance symptoms and what causes an intolerance to sugar . 

In this blog post we are going to deep dive and hopefully shed some light on the matter .

Sugar is a big part of our diets – refined sugar (like table sugar) or natural sugar found in fruits, vegetables, grains, and dairy. Our bodies use sugars to fuel our brain and create energy. However, certain sugars can be poorly digested and cause sugar intolerance. This article will look at what sugar intolerance is, how to tell if you have it, what sugars can cause intolerance, and how to test for sugar intolerance

What is an intolerance to sugar?

An intolerance to sugar is an adverse reaction to eating foods that contain sugars. It is caused by an inability to digest the sugar properly. 

An intolerance to sugar does not involve the immune system as an allergy does. Instead, an intolerance has to do with your digestion and how well you break down and absorb the different sugars.

How do I know if I have an intolerance or an allergy?

A true allergy to sugar is basically non-existent. This is because an allergy is usually a reaction to a food protein, not sugar. For example, a milk allergy is caused by a reaction to the protein in milk. The allergy happens when your immune system mistakenly thinks that the milk protein is a toxin or harmful invader (like a virus or bacteria). 

Having a reaction to sugar is relatively common. An example of this is lactose intolerance, which is an intolerance to the lactose sugar in dairy. The intolerance happens because your body has trouble digesting the lactose. Lactose intolerance affects approximately 65% of the world’s population.

What causes an intolerance to sugar?

A sensitivity to sugar can be inherited and caused by altered genes, or it can develop at any age and be caused by conditions that affect the gut. 

When the intolerance is inherited, it is often because you’re born with genes that don’t allow you to digest the sugars. The genes don’t produce the digestive enzymes needed to break down and absorb sugars like lactose. If lactose intolerance is genetic, you will either not produce the enzyme lactase, or your body’s production of lactase will gradually decline as you age. This type of sugar intolerance is usually permanent and lifelong.

If the intolerance develops over time, it may be because of a gut condition like food poisoning, coeliac disease, an infection, or inflammatory bowel disease. In these cases, the intolerance needs to be managed but may be reduced if handled correctly (this requires the guidance of a practitioner like a dietician, nutritionist or naturopath). 

All children are born with an underdeveloped gut lining that makes them susceptible to intolerances, like lactose intolerance. As our guts develop, our digestion improves, and the intolerances often resolve around the age of three. This is often seen as ‘out-growing food intolerances. This intolerance is obviously not permanent but is why many children have food intolerances that disappear with time.

What sugars can cause intolerance?

We’ve mentioned one of the common sugar intolerances, which is lactose intolerance. However, there are a lot of different types of sugars that can cause intolerance. These include:

  • Fructose – found in foods like honey, table sugar, agave nectar, high-fructose corn syrup, fruits, and fruit juices.
  • Glucose – the most abundant sugar – high amounts are found in fruits (like grapes, dates, and persimmons), honey, agave nectar, molasses, and starchy foods (like corn, potatoes, and rice). 
  • Sugar alcohols (known as polyols) like sorbitol, mannitol, xylitol – found in some fruits and vegetables or synthesised for use as sweeteners (in gums and soft drinks).
  • Fructans – found in foods like grains (like wheat and barley), garlic, chicory, beans, cashews, pistachios, fruits (like watermelon, bananas, and plums), and vegetables (like onion, leek, Brussels sprouts, and cabbage).
  • Galactooligosaccharides (GOS) – found in foods like beans, peas, legumes, artichoke, broccoli, and beetroot.

Lactose – found in all dairy and dairy products.

These sugars are collectively known as FODMAP sugars. The FODMAP sugars have identified by Monash University as a trigger of irritable bowel syndrome (IBS). They poorly absorbed in the intestines, and as a result, they draw water into the intestines (which can cause distension and diarrhoea). They also get eaten by gas-producing bacteria, which leads to increased production of gas, frequent or smelly flatulence, and bloating.

The term FODMAP is an acronym for: 

Fermentable (meaning the bacteria feed on them and produce gas)
Oligosaccharides (the fructans and GOS)
Disaccharides (lactose)
Monosaccharides (fructose and glucose)
Polyols (the sugar alcohols – sorbitol, mannitol, etc.

What are sugar intolerance symptoms?


  • digestive discomfort
  • bloating
  • gas
  • nausea
  • vomiting
  • abdominal pain or cramps
  • diarrhoea
  • fatigue
  • restlessness
  • poor focus

As we saw above, intolerance to FODMAP sugars has been shown to cause symptoms of IBS, which can involve bloating, gas, and abnormal bowel habits (like alternating diarrhoea and constipation).

Testing for an intolerance to sugar

Sugar intolerance symptoms are similar to those of other conditions and other food intolerances. This is one reason why it’s important not to go off symptoms alone and to test for which exact food (or group of foods) you’re reacting to. It’s also important to note that you could be reacting to a range of seemingly different foods that contain a similar sugar.

Our food intolerance test looks at over 350 different foods that you could be reacting to, including various sugars. To do the test, all you need to do is order it HERE and send us a sample of your hair. Once our lab receives your sample, we will send you the test results within three days. Overall, this means that you can complete a comprehensive test (looking at over 350 foods and 350 non-food items), in the convenience of your own home. The test is easy and provides quick results.


Today we explored an intolerance to a food that makes up one of the biggest parts of our diet – sugar. We looked at what it means to have an intolerance to sugar and how it differs to a sugar allergy. We learnt that an intolerance to sugar could be caused by mutated genes (that don’t produce the digestive enzymes you need to absorb the sugar) and conditions that affect the gut (like coeliac disease). It is an in-depth review of the different types of sugars and what foods they’re in. Then we looked at the sugar intolerance symptoms and what you can do to test for it. We learnt that a food intolerance must be tested for, and that our food intolerance test can be ordered online and easily completed from your home.


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