What is fructose? People are consuming more and more fructose these days. Did you know that between 1966 to 2003 fructose consumption rose from one to 8.8 million metric tonnes worldwide? It is not only fruit and vegetables that contribute to this – the food industry mainly uses artificially produced fructose as a sweetener.
Parallel to this, the incidence of fructose intolerance has also increased. This is when fructose cannot pass through the mucous membrane of the small intestine of those affected and causes gastrointestinal complaints. However, this does not mean that you have to avoid fruit forever.
Read our article about fructose intolerance – otherwise known as fructose malabsorption. First things first, find out about fructose, which foods contain fructose and fructose intolerance symptoms.
What is fructose?
The sugar fructose, also known as fruit sugar, is found in various different forms, such as:
- free – as found in fruit, vegetables and honey
- together with glucose as a component of sucrose
- as fructans (fructose in bound form) in Jerusalem artichokes and yogurt
Which foods are high in fructose?
Fructose is found in every type of fruit and vegetable – but not always the same amount. The food industry uses fructose because of its strong sweetening quality in diet foods, soft drinks, ready-made foods and sweets. Foods that are particularly rich in fructose are:[2, 3]
- apples, pears, pomegranates, kiwis
- strawberries, raspberries, currants
- dried fruit (apricot, date)
- maple syrup, agave syrup
You can find out if fructose is found in industrially produced foods by looking at the list of ingredients. If a food or drink contains fructose, you might find the following ingredients listed on the packaging:
- fructose syrup
- glucose-fructose syrup
- sugar substitute
- starch syrup
- artificial honey (invert sugar)
- sorbitol (E 420)
- mannitol (E421)
- isomalt (E 953)
- maltitol (E 965)
- lactitol (E966)
- xylitol (E967)
- sugar alcohol
Fructose intolerance: is it digestive or hereditary?
Scientists distinguish between two forms of fructose intolerance: digestive fructose intolerance (DGI) and hereditary fructose intolerance (HFI), which is very rare. This article primarily explores digestive fructose intolerance.
Table: Differences between intestinal and hereditary fructose intolerance
Digestive fructose intolerance
Hereditary fructose intolerance
Dysfunctional fructose transporter (GLUT-5)
Congenital enzyme defect (aldolase B)
33 per cent
0.01 bis 0.02 per cent
Diarrhoea, bloating, vomiting
Hypoglycaemia, growth disorders, aversion to fruit
H2 breath test
Molecular genetic blood test
Is fructose intolerance hereditary?
One in 25,000 people is born with hereditary fructose intolerance, a congenital enzyme defect. In a healthy person’s liver, enzymes convert fructose into glucose. In people with hereditary fructose intolerance, these enzymes are missing – which is why large amounts of a toxic form of fructose accumulate, damaging liver cells. Even as a child or baby, fructose intolerance symptoms are triggered by any contact with fructose. People affected by hereditary fructose intolerance need to follow a strict fructose-free diet for life, which is not the case with digestive fructose intolerance.
What is digestive fructose intolerance?
With digestive fructose intolerance, also called fructose malabsorption, the intestine can only absorb fructose to a limited extent. The fructose transporter proteins (GLUT-5) in the small intestine do not function properly. When fructose reaches the large intestine, it is broken down by the bacteria that live there.
Fructose serves as food for colon bacteria. After they metabolise the fructose, they form high amounts of gases and fatty acids, including:
- carbon dioxide and hydrogen, which inflate the stomach
- methane, worsens the breath
- short-chain fatty acids, which thin the stool
These gases and fatty acids then cause discomfort in the gastrointestinal tract, such as flatulence, diarrhoea and vomiting.
What are the two forms of intestinal fructose intolerance?
Primary fructose intolerance: The fructose transporters cannot do their job and transport fructose through the mucosa in the small intestine. Even an amount of less than 25 grammes of fructose can lead to digestive discomfort.
Secondary fructose intolerance: Diseases that harm the mucous membrane of the small intestine, such as coeliac disease or Crohn’s disease, can also damage fructose transporters. Medical professionals often observe people with irritable bowel syndrome, in particular, suffering from this form of fructose intolerance.[3–5]
Did you know that, according to a study in the journal Food Science and Nutrition, digestive fructose intolerance is probably more common because more and more foods contain processed corn syrup. This corn syrup contains very high amounts of fructose and is therefore a popular sweetener.
Please note that fructose intolerance is not a food allergy. An allergy is characterised by immune system reactions, whereas fructose intolerance is due to a defective protein in the small intestine. Allergies can be diagnosed with the help of allergy tests. To find out more about the differences between food allergies and intolerances, head over to our Health Portal article.
What are typical fructose intolerance symptoms?
If your body cannot digest fructose properly, your gastrointestinal tract usually suffers. Whether you experience symptoms may depend on the amount of fructose and the meal you are eating. Even if you do not suffer from digestive fructose intolerance, you may experience symptoms if you consume more than 25 grammes of fructose in one day. This corresponds to about one apple, one banana, one glass of apple juice and two kiwis.
Fructose intolerance symptoms: how do I know I am intolerant?
If you, as someone affected by fructose intolerance, have eaten foods containing fructose, typical fructose intolerance symptoms may appear within 30 minutes. The following symptoms can last up to nine hours:[2, 3]
- abdominal cramps, or
- depressive moods, tiredness
Did you know that people with fructose intolerance often tolerate small amounts of fructose. If you eat fruit together with proteins and fats, you can tolerate fructose better.
Treatment: how do you counteract fructose malabsorption?
The goal of fructose intolerance treatment is being able to avoid fructose intolerance symptoms, which can be achieved by changing your diet.
If you have been diagnosed with fructose intolerance, a change in diet can alleviate your symptoms. You should then eat mostly low-fructose food. In addition to fructose, it is best to avoid the sugar substitute sorbitol and the carbohydrate inulin (fructans). This is because these two substances are converted into fructose in the body, resulting in fructose intolerance symptoms.
How are glucose and fructose linked?
Glucose proves to be a good source of energy for people with fructose intolerance: glucose enters our bloodstream with the help of a different transporter than the fructose transporter. If glucose and fructose enter the small intestine together, fructose can also use the glucose transporter to pass through the mucous membrane of the small intestine. Therefore, people with fructose intolerance often tolerate foods that contain fructose and glucose in equal proportions or more glucose.[3, 6, 7]
These foods have such a glucose–fructose ratio:
- apricots, plums, tangerines, papaya
- bananas, lemons, honeydew melons
- cranberries, sour cherries, mirabelles
- avocado, cucumber, carrots, potatoes, courgettes
Alternatively, you can improve how well you digest certain foods by adding glucose in the form of dextrose.
Sweeteners such as brown rice syrup, brown sugar, maple syrup, molasses and dextrose are usually tolerated.[3, 4]
How can I benefit from an elimination diet?
After diagnosis, you should relieve your gastrointestinal tract and avoid fructose, sorbitol and inulin. Then you can find out how much fructose you can tolerate. Based on this knowledge, you can figure out a longer-term diet. You can discover more about how an elimination diet works in our dedicated Health Portal article.
Phase 1: abstinence
In this phase, you should follow a strictly low-fructose diet for a period of two to four weeks. The following foods should be avoided: fruit, but also dried fruit, fruit products, soft drinks with fructose, honey, invert sugar, ice cream, baked goods and sweets, muesli with dried fruit, fruit yoghurt, fruit curd, semolina porridge with fruit and fruit jelly. In addition, foods that contain sorbitol should be avoided. Sorbitol is converted to fructose in the body.
Phase 2: test
After the abstinence phase, during which you have mostly abstained from fructose, the six-week test phase begins. During this time, you can eat more fructose-containing foods again and test how much fructose you can tolerate.
Tip for you: Keep a food diary: note down the amount of food you eat and enter whether and after how long any complaints occurred.
Phase 3: long-term diet
During the last phase, you can make a plan for how you will eat in the future. You should ensure that you meet your nutritional needs despite these dietary restrictions. Knowing what you can tolerate from the last phase, you can now make a diet plan suited to you. For example, if you eat fruit, divide it into several small portions throughout the day. Avoid fruits with a very high fructose or sorbitol content (for example, sultanas, prunes, grapes) to avoid discomfort as much as possible.
Did you know that steam-cooked vegetables are better tolerated by our intestines. By preparing vegetables this way, they also don’t lose as many nutrients.
Is there medication for fructose intolerance?
Meanwhile, pharmaceutical manufacturers offer tablets that are supposed to facilitate the consumption of foods containing fructose. They contain the enzyme xylose isomerase, which converts fructose into glucose. This process facilitates fructose absorption and can prevent discomfort.
Is fructose intolerance connected with sorbitol intolerance?
If you are fructose intolerant, you should limit your intake of foods containing sorbitol, especially pome fruits such as apples and pears. The reason for this is that sorbitol and fructose share the same transport proteins. If you consume sorbitol as well as fructose, the two compete with each other: sorbitol blocks the mutual transporter. As a result, even more undigested fructose enters your colon and exacerbates the fructose intolerance symptoms you already have.
Moreover, while your intestine breaks down and utilises sorbitol, it also converts it to fructose, among other things. This means that the more sorbitol you consume, the more fructose is produced.
There is no need for people with sorbitol intolerance to worry. People affected by this intolerance can still tolerate foods containing fructose. In this case, the difficulty in changing your diet is to clearly distinguish foods containing sorbitol from foods containing only fructose.
How does fructose contribute to fatty liver?
Fatty liver is a liver disease, which leads to excess fat stored in the liver cells. The disease is also related to fructose. Fructose is converted into energy, glucose or fatty acids in the liver, depending what our body needs. Fatty acids are deposited in the form of stomach fat or in the liver itself. An excess of fructose in the diet can therefore lead to more fatty acids in the liver and thus to non-alcoholic fatty liver disease (NAFLD).
Until a few years ago, the term ‘fatty liver’ was only ever described in the context of excessive alcohol consumption and was hardly perceived as a disease beyond that. It is now clear that it is a disorder that is currently still underestimated.[10–12]
What is the most common test for fructose malabsorption?
Fructose consumption has increased massively in recent years, especially because the food industry uses fructose as a sweetener. Parallel to this, the number of people suffering from fructose intolerance has also increased. If you want to find out whether you might react to fructose, a fructose intolerance test is recommended.
How does a fructose intolerance test work?
The test is often done by family doctors or allergists. First, you drink a solution containing fructose on an empty stomach. At several time intervals, you give breath samples in which the concentration of hydrogen is measured. With digestive fructose intolerance, more hydrogen is produced in the large intestine. You emit hydrogen through the air you breathe, among other things – this is why the breath test can be used to identify an intolerance.
What is fructose & fructose intolerance – at a glance
Which foods are high in fructose?
Fructose is found in its free form in all fruits and vegetables as well as in honey. It is also a component of household sugar. Yogurt and Jerusalem artichokes contain fructose in its bound form. Due to its sweetening power, fructose is often found in industrially produced foods.
What is fructose intolerance?
Hereditary fructose intolerance is a rare enzyme defect that is genetically determined.
Digestive fructose intolerance is a disorder that causes gases and short-chain fatty acids to form in the large intestine.
The consequences are nausea, vomiting, diarrhoea and depressive moods.
How do you treat fructose intolerance?
First of all, you should avoid fructose-containing foods for several weeks until your symptoms have subsided.
Then slowly introduce fructose-containing foods into your diet and find out what quantities of fructose you can tolerate without symptoms. Based on this, you figure out a long-term diet plan.
How do you test for fructose intolerance?
A self-test can tell you whether you suffer from digestive fructose intolerance. To do this, you need to drink a solution containing fructose. After you have given several breath samples, a laboratory measures the concentrations of hydrogen and methane in your breath. If you are intolerance to fructose, both gases are produced more frequently.
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