Fructose is a sugar found in fruits and a key ingredient in regular table sugar. For a long time fructose was considered “safer” for diabetics and was recommended as a sugar substitute for weight loss, as it has a lower glycemic index.
However, the modern scientific position boils down to the fact that the human body is able to fully assimilate about 25-50 g of fructose – while exceeding the norm changes the metabolism¹. Specifically, fructose has been shown to lower levels of tryptophan, folate, and zinc.
What is the harm of fructose?
The key misconception associated with fructose is its lower glycemic index – which is three times the GI of regular sugar. But we are talking about an increase in blood glucose levels – and not about the effect on insulin production or other metabolic parameters.
Unlike glucose, which requires a special enzyme to be absorbed, fructose is much easier to convert into energy. It is absorbed in the large intestine and then transported to the liver, where it accumulates. At the same time, the use of a large amount of fructose activates the biosynthesis of fatty acids.
Research in 2020 suggests that fast fat gain from ripe, high-fructose fruits is part of the hibernation mechanism in animals — similar metabolic changes can be seen in humans, triggering obesity, diabetes and hyperten
Fructose syrup in foods
If you do not overeat ripe fruits or consume pure fructose, this does not mean at all that it is not in your diet. Fructose syrup is commonly 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 regular fructose), sweet yoghurts – as well as to all kinds of pastries and desserts.
Fructose syrup allows for an airy texture without having an overly sugary-sweet taste.
Intolerance and malabsorption
Despite all the harm of glucose, the human body copes well with the utilization of sufficiently large amounts of it (with the exception of conditions associated with diabetes). The mechanism for regulating fructose, in turn, works much worse – and has severely limited limits.
Excessive fructose in the colon reduces the osmotic absorption of water and is converted by intestinal bacteria into short-chain fatty acids with the release of hydrogen, carbon dioxide and methane³.
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 assimilate a number of vitamins and minerals.
Primary symptoms:
- flatulence
- bowel dysfunction
Secondary symptoms:
- bad mood and sleep problems (lack of tryptophan)
- decreased testosterone in men (zinc deficiency)
- impaired DNA replication (lack of folic acid)
Maximum doses
The situation is aggravated by two factors. First, the simultaneous consumption of fructose, sorbitol or xylitol (types of sweeteners) can increase fructose malabsorption. Secondly, in practice, it is difficult to estimate the amount of a substance in foods, since some of it is contained in the form of sugar.
Recall that agave syrup is 55% fructose, 50% table sugar, and 40% honey. Plus, the requirements of GOSTs do not imply a mention of the sugar source (that is, even pure fructose and fructose syrup can be designated 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. The real consumption figure among Russians reaches 110 grams per day.
Diet for fructose intolerance
Since fructose is widely used as a substitute for sugar in sweets and sugary drinks, they will have to be eliminated first. One glass of cola (or grape juice) contains about 10-15 grams of fructose – and almost 100% of the daily value of sugar.
Next, ripe fruits containing an excess of fructose – apples, pears, grapes, figs, mangoes, as well as dried fruits based on them – fall under the ban. Citrus fruits (orange, grapefruit, tangerines), apricots, plums, pineapples – and all kinds of berries are acceptable
Also, in case of fructose intolerance, it is better to exclude products from wheat flour – not only sweets, which 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 into fructose during
Unlike glucose, the body cannot process large doses of fructose. Exceeding the figures of 25-50 g can disrupt the intestinal microflora, provoking flatulence and disrupting the absorption of nutrients. The situation is aggravated by the fact that fructose is widely used in the food industry as a substitute for sugar.
Sources of data:
- Review article: fructose malabsorption and the bigger picture
- Fructose metabolism as a common evolutionary pathway of survival associated with climate change, food shortage and droughts
- Modern approaches to the diagnosis and correction of fructose malabsorption
- Fructose Malabsorption and Symptoms of Irritable Bowel Syndrome: Guidelines for Effective Dietary Management
