Despite medical advances, infectious diseases caused by bacteria and viruses are still among the most common causes of death worldwide. What role could fructose play in such diseases? A research group led by Ina Bergheim from the Department of Nutritional Sciences at the University of Vienna has now been able to prove for the first time that monocytes, important immune cells in the blood, react more strongly to bacterial toxins after fructose consumption - but not in a positive way. Specifically, the concentration of receptors for certain bacterial toxins increases, making the body more susceptible to inflammation. The study was recently published in the journal Redox Biology.

In two independent randomised studies with healthy adults, the researchers investigated how the consumption of fructose-sweetened beverages affects the immune response compared to beverages with glucose. In addition, they conducted experiments with isolated monocytes and cell culture models to investigate the molecular mechanisms.

More receptors for bacterial toxins are produced

The scientists were able to observe that the intake of fructose, in contrast to the intake of glucose, led to an increase in the concentration of Toll-like receptor 2 in monocytes. Toll-like receptor 2 regulates the immune response, among other things. The higher concentration was accompanied by an increased sensitivity of the monocytes to lipoteichoic acid, a bacterial toxin. "The concentration of receptors for such toxins in the body increased, which means that the inflammatory response increased," explains study leader Ina Bergheim from the University of Vienna. Specifically, pro-inflammatory messengers such as interleukin-6, interleukin-1β and tumour necrosis factor-alpha were increasingly released.

"These findings make an important contribution to understanding how individual food components and fructose in particular can influence the immune system," says Bergheim. "They indicate that even short-term, high fructose consumption in healthy people can influence the immune system and increase inflammation."

Influence of fructose on metabolic diseases

Future studies should clarify the long-term effects of chronically increased fructose consumption on the immune system and susceptibility to infection, particularly in risk groups with, for example, type II diabetes mellitus or fatty liver disease, which is associated with metabolic dysfunction. "Sugar, especially the fructose in sugary drinks and sweets, has long been suspected of increasing the risk of developing metabolic diseases - this needs to be investigated," says Bergheim.