What is fructose: how to recognize an intolerance

In this practical tip we have summarized what fructose is and how you can tell whether you suffer from fructose intolerance.

What is fructose?

Fructose or fructose is a simple sugar (monosaccharide) and belongs to the carbohydrates. It occurs naturally in fruits and vegetables, but is also found in table sugar and finished products.

• The term fructose is misleading because it is not only found in fruits and vegetables, but also in many other products such as baked goods, sweets or milk products.
• Especially in industry, fructose is often used as a sweetener because it is cheaper than sucrose (table sugar) and also has a higher sweetening power.
• The main source of fructose is corn syrup, the fructose content of which is increased by means of enzymatic processes.

Fructose intolerance - symptoms

Bitten once in the apple and you get bloating, violent abdominal cramps or even diarrhea? If you are familiar with these symptoms, you may be fructose intolerant. Here, however, a precise distinction between two different forms is required.

• Hereditary fructose intolerance (HFI) is an inherited metabolic disorder that occurs very rarely. Due to an enzyme defect, the fructose cannot be broken down or can only be broken down to a very limited extent. It accumulates in the kidneys, liver and small intestine and, if left untreated, can lead to severe functional disorders in the liver and kidney. Here the complete elimination of fructose from the diet is the only possible therapy.
• In contrast, intestinal fructose intolerance is far more common. This is fructose malabsorption: the fructose is only absorbed to a limited extent in the small intestine.
• The reduced absorption in the intestine can be attributed to a reduced availability of the transport protein GLUT-5. The fructose is not completely absorbed and reaches the large intestine, where it is metabolized by microorganisms. The resulting gases and fatty acids are responsible for the typical symptoms.
• Flatulence and diarrhea are particularly common, but abdominal pain, colic-like cramps or a feeling of fullness are also possible. This varies depending on the amount consumed, the level of enzymes and the person.

Fruit with a lot of fructose - you should avoid these varieties

Various types of fruit and vegetables are a natural source of fructose. However, they differ greatly in their fructose content. Therefore, careful selection is important if you suffer from fructose malabsorption but do not want to do without fruit. Particularly high fructose levels include:

• apples
• pears
• mangos
• grapes
• dried fruit
• fruit juices

Low fructose fruit

Since fruit contains many important ingredients such as vitamins and is healthy, you should not completely refrain from consuming it even with fructose malabsorption. There are some fruits that contain lower amounts of fructose and are therefore easier to eat:

• citrus fruits
• apricots
• berries
• avocado

Nutrition for fructose malabsorption - diet suggestions

Since fructose is present in different proportions in food, you have to reorient yourself in terms of nutrition in order to reduce or even avoid the undesirable symptoms.

• Since the fructose cannot or can hardly be split in the case of hereditary fructose intolerance, the complete therapy without fructose is the only possible therapy.
• In the case of fructose malabsorption, on the other hand, there are some tips and tricks to be able to lead a life that is as symptom-free as possible without having to forego fruit and vegetables altogether.
• It is important to reduce your daily fructose intake (10 g / day). However, complete waiver is not advisable, since fewer transport proteins would then be formed and the rate of uptake would be further reduced. Fruits and vegetables also contain important ingredients such as vitamins.
• You should also pay attention to the ratio of glucose to fructose in the food. With a ratio of 1: 1 (e.g. in kiwi or banana), most people with fructose malabsorption have no complaints. This is because glucose facilitates the absorption of fructose.
• Furthermore, you should avoid foods with sugar substitutes such as sorbitol, xylitol or isomalt, as these block the absorption of fructose in the intestine. Sugar substitutes are often found in sugar-free chewing gums or reduced-sugar sweets.
• Since the symptoms differ from person to person and also occur to different degrees, it is advisable to keep a food diary.
• In a two to four week phase, fructose should be completely avoided. At the same time, keep a list of your complaints, which should be significantly reduced during this time.
• This is followed by a test phase in which you consume low-fructose foods and note your symptoms. So go ahead and slowly but surely find out what your body can take and in what amounts.
• So there is no general principle, you have to find out for yourself what works for you and what doesn't.