Letzte Aktualisierung am 11. December 2023 von Dr. Michael Zechmann-Khreis
Have you just been diagnosed and don’t know your way around? What happens next? What else can you eat? Here we explain the basics of fructose intolerance (fructose malabsorption) to all newcomers. This article is a first introduction to the topic, which should clear up any initial confusion.
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Fructose intolerance / fructose malabsorption
Fructose malabsorption or intestinal fructose intolerance is not a bad thing in principle! The first thing you should do is make an appointment with a state-approved nutritionist who is familiar with food intolerances. You should also clarify whether you have any other intolerances. Around 20% of people with fructose malabsorption also have lactose intolerance, for example. Food allergies should also be clarified by your doctor.
Clarification of the terms used to prevent misunderstandings
- The ending -ose denotes a sugar; sugar is an umbrella term for certain carbohydrates | What is fructose?
- The suffix -ase denotes an enzyme; enzymes are (almost always) proteins, i.e. proteins that control biochemical reactions in the body
- Fructose is the German word for fructose; fructose is a simple sugar, i.e. it consists of only one sugar molecule
- Dextrose is also called glucose; glucose is also a simple sugar
- When the two simple sugars glucose and fructose are combined, this disaccharide is called sucrose (table sugar)
- Sucrose is broken down into the two individual sugars in the intestine by the enzyme saccharase
- Fructose malabsorption is the same as fructose intolerance, or intestinal fructose intolerance!
- Fructose is not broken down by an enzyme, but is absorbed directly into the body via a transport protein(GLUT-5) from the intestine. You can find an explanation of the GLUT transporter here.
- If the GLUT-5s do not function properly or are not formed in sufficient quantities, this is referred to as fructose malabsorption. The fructose then reaches the large intestine, where bacteria “eat it up”. This causes the formation of gases and other substances that trigger the symptoms of fructose intolerance.
Symptom and food diary
If you suspect that you are suffering from fructose intolerance, you should keep a so-called symptom and food diary before going to the doctor. This makes it much easier for the attending physician to narrow down the symptoms. Such a diary is useful because the symptoms can often occur with a time delay (several hours!). As a result, it is often impossible to recognize the correct connection between food and symptoms. In practice, this is a major problem, as many sufferers associate their symptoms with food, which often has nothing to do with their symptoms. Important: In the case of fructose intolerance, symptoms do not occur immediately after eating, but only once the fructose has ended up in the large intestine. This takes between 20 minutes and several hours.
The elimination diet after the diagnosis of fructose intolerance
In the first 2 weeks, you should avoid fructose and sugar alcohols as much as possible to allow the intestines to recover. It is also important to avoid flatulent foods such as pulses, cabbage and too much fiber in the first few weeks. After approx. 2 weeks (maximum 4 weeks, but the recommendation is 2 weeks) these foods can then be slowly reintroduced into the diet. It is important to drink enough fluids (2-3 liters per day) (water, no carbonated drinks, no alcohol).
It is wrong to assume that people with fructose intolerance should no longer consume fructose at all. After the phase of abstinence, you should start with small amounts of fructose – free and bound – and slowly increase the amount. Avoiding fructose or consuming too little fructose worsens fructose intolerance.
The chapter on the elimination diet is very complex and you should definitely seek advice from a nutritionist. We have also written a book about the elimination diet for fructose intolerance, which explains this period in great detail and contains many recipes.
As soon as you feel better (which will be soon!) and as soon as no symptoms occur again, you can end the elimination diet and start the test phase .
The test phase
Depending on your mood, you can start by consuming small amounts of fructose. You should then pay close attention to the body’s reactions. Now you can eat household sugar and long-chain sugars such as inulin or oligofructose in small quantities again. The test phase usually lasts a few months and varies greatly from person to person.
The bottom line is: find out what you can tolerate and don’t let others influence you! Each person reacts differently to different amounts of fructose and each person reacts differently from day to day to the same amounts! However, this does not mean that every bodily reaction is due to fructose! Don’t make the mistake of immediately interpreting every nip and tuck as a symptom! It is completely normal for the bowels to make noises and for you to have bowel movements from time to time.
This test phase should also be accompanied by a nutritionist/dietician, especially to prevent deficiency symptoms and one-sided eating.
A few more helpful everyday tips
- Fructose is less well tolerated on an empty stomach than on a full stomach.
- Many sufferers tolerate fructose better in the afternoon than in the morning.
- High-fat meals slow down the intestinal transit, which means that more fructose can be absorbed.
- Exercise reduces intestinal transit, so you tolerate less fructose before exercise than after exercise.
The three-phase program
|1. elimination diet
|2nd test phase
|3. permanent nutrition
|Strictly low-fructose diet, “fructose fasting”
|Testing individual tolerance
|Fructose-reduced, but not fructose-free diet!
|Avoid sugar, fruit and vegetables.
|Test a new food every 2 days, test sugar alcohols!
|Always push your own limits; also do not avoid sugar alcohols completely.
|Duration: 2-4 weeks, no longer!
|Duration: approx. 6 months
|Fructose fasting once a year for approx. 2 weeks
Some FAQs about fructose intolerance
Do I have to pay attention to the exact amounts of fructose in grams?
No! The exact calculation of fructose and glucose contents is not expedient and is not recommended. During the test phase, you can learn to listen to your body and assess the tolerance of foods. Our tables and lists with the sugar content are useful for this. The same goes for our “Ask Ingrid!” app. However, they should not be used to calculate exact amounts of fructose or glucose and then live according to these amounts! Anyone who does this runs the risk of worsening their own fructose tolerance!
Is fruit compatible with fructose intolerance?
Theoretically, you can eat any fruit that contains more glucose than fructose but less fructose in total. Papaya, banana or tangerine are usually well tolerated. You can find a detailed list in the form of a table here or in our “Ask Ingrid!” app.
Can you eat ready-made products and sorbitol?
Certain sugar alcohols presumably block the transport system in the intestine, which functions poorly in people with fructose intolerance. These substances should therefore be avoided. These include sorbitol (sorbitol), mannitol and other, but not all, sugar alcohols. These substances are often found in chewing gum, sweets and ready meals, but must be declared in the list of ingredients on the packaging.
What about the sugar?
Normal household sugar can be consumed in small quantities by most patients on a permanent diet without any problems!
Table sugar (sucrose) is a disaccharide. It consists of one molecule of fructose and one molecule of glucose. As glucose facilitates the absorption of fructose, household sugar is usually well tolerated in moderation (after the elimination diet).
Can I drink alcohol?
Lager beer can be tolerated well, wheat beer (cloudy beer) is often less well tolerated. Lager beer can also be diluted with soda water like a spritzer (“sour shandy”). Dry wines are usually relatively well tolerated in small quantities, sweet wines usually less so. As a general rule, the sweeter an alcoholic drink is, the less well tolerated it is. Alcohol irritates the intestines and makes them more permeable. An irritated bowel should therefore not be additionally burdened with alcohol.
Can I eat everything again with enzyme preparations?
No. These preparations convert fructose (no sugar alcohols!) in the digestive tract into glucose. They should only be used in exceptional cases and are not intended for continuous use.
Which diagnostic methods are reliable?
Currently, the only way to test is via the H2 breath test (with 25g of fructose dissolved in water; to be carried out at the doctor’s, not at home). Home tests or other diagnostic methods such as bioresonance, spit test, hair analysis, pendulum or the like cannot detect fructose intolerance.
Stryer, L., Biochemistry, Specktrum Akademischer Verlag, 4th edition
Zechmann, M.; Masterman, G.; “Nahrungsmittel-Intoleranzen: First aid in diagnosis”, Berenkampverlag, 2012;
Drozdowski L, Thomson A.; “Intestinal sugar transport”, World J Gastroenterol 2006 March 21; 12(11):1657-1670