Fructose intolerance (malabsorption) - symptoms.

Fructose intolerance (malabsorption) - symptoms.

Fructose intolerance (malabsorption) - symptoms.
Fructose intolerance (malabsorption) - symptoms.

Fructose is a sugar in fruits and a key ingredient in regular table sugar. Fructose has long been considered "safer" for diabetics and is recommended as a sugar substitute for weight loss because it has a lower glycemic index.

However, the current scientific position comes down to the fact that the human body is able to fully absorb about 25-50 g of fructose - while exceeding the norm changes the metabolism. In particular, fructose has been shown to lower tryptophan, folic acid and zinc levels.

//  What is the harm of fructose?

What is the harm of fructose

The main misconception about fructose is its lower glycemic index - which is three times the GI of regular sugar. But we are talking about raising blood sugar levels - not the effect on insulin production or other metabolic parameters.

Unlike glucose, which requires a special enzyme to absorb, fructose is much easier to convert into energy. It is absorbed in the colon and then transported to the liver, where it accumulates. At the same time, the use of large amounts of fructose activates the biosynthesis of fatty acids.

Studies in 2020 show that the rapid accumulation of fat from ripe fruits with high fructose content is part of the mechanism of hibernation in animals - such metabolic changes can occur in humans, causing obesity, diabetes and hypertension.

Fructose syrup in food

If you do not eat ripe fruit or do not consume pure fructose, it does not mean that it is not in your diet. Fructose syrup is often used in the food industry as a substitute for sugar.

Fructose syrup is added to sweet carbonated drinks, reconstituted fruit juices in a bag (natural ones contain ordinary fructose), sweet yoghurts - as well as to all kinds of cakes and desserts.

Fructose syrup gives an ethereal texture without having too sweet-sweet taste.

Intolerance and malabsorption

Despite all the damage from glucose, the human body copes well with the absorption of large enough amounts of it (except for conditions associated with diabetes). The fructose regulation mechanism, on the other hand, works much worse - and has very limited limits.

Excessive fructose in the colon reduces the osmotic absorption of water and is converted from intestinal bacteria to short-chain fatty acids with the release of hydrogen, carbon dioxide and methane.

As a result, we are talking about faster bacterial fermentation and changes in the intestinal microflora - as well as the formation of a layer of bacteria on the intestinal mucosa, which makes it difficult to absorb a number of vitamins and minerals.

//  Primary symptoms:

  • flatulence
  • bowel dysfunction

//  Secondary symptoms:

  • bad mood and sleep problems (lack of tryptophan)
  • reduced testosterone in men (zinc deficiency)
  • impaired DNA replication (lack of folic acid)

Maximum doses

The situation is exacerbated by two factors. First, concomitant consumption of fructose, sorbitol or xylitol (types of sweeteners) may increase fructose malabsorption. Secondly, it is practically difficult to estimate the amount of a substance in food, as some of it is contained in the form of sugar.

Remember that agave syrup is 55% fructose, 50% sugar and 40% honey. In addition, the requirements of GOST do not mean mentioning the source of sugar (ie, even pure fructose and fructose syrup can be labeled simply as "sugar" in the product).

In the case of sugar, the maximum dose is 6-10% of the total caloric intake - or about 30-50 grams per day, including added sugar. Actual consumption among Russians reaches 110 grams per day.

Diet for fructose intolerance

Diet for fructose intolerance

Because fructose is widely used as a sugar substitute in cakes and sugary drinks, they will first need to be eliminated. One glass of cola (or grape juice) contains about 10-15 g of fructose - and almost 100% of the daily value of sugar.

Then the ban includes ripe fruits containing excess fructose - apples, pears, grapes, figs, mangoes, as well as dried fruits based on them. Citrus fruits (orange, grapefruit, tangerines), apricots, plums, pineapples - and all kinds of fruits are acceptable  4  .

Also, in case of fructose intolerance, it is better to exclude wheat flour products - not only pastries that contain fructose in the form of syrup, but also white bread and pasta. They contain fructans (1 to 4% dry weight) - which can be converted to fructose during digestion³.


Unlike glucose, the body cannot process large doses of fructose. Exceeding the figures of 25-50 g can disrupt the intestinal microflora, provoke flatulence and disrupt the absorption of nutrients. The situation is exacerbated by the fact that fructose is widely used in the food industry as a substitute for sugar.

Data sources:

  1. Article review: fructose malabsorption and the bigger picture,  source
  2. Fructose metabolism as a common evolutionary path to survival related to climate change, food shortages and droughts,  source
  3. Modern approaches for diagnosis and correction of fructose malabsorption,  pdf
  4. Fructose malabsorption and symptoms of irritable bowel syndrome: guidelines for effective diet management,  pdf