Health. How does fructose increase the risk of inflammation?

Metabolic diseases such as type 2 diabetes are associated with higher rates of infections, which are more complex to treat, as well as more mortality.

But what's the connection with fructose? A team led by Ina Bergheim, from the Department of Nutritional Sciences at the University of Vienna (Austria), has shown for the first time that monocytes, key cells in the immune system, react more strongly to bacterial toxins after ingesting fructose.

Unfortunately, not in a positive way: fructose consumption leads to an increase in the number of monocyte receptors for certain toxins, which makes the body more vulnerable to inflammation.

In two randomized trials (high-level studies) in healthy adults, researchers investigated the impact of consuming fructose-sweetened beverages on the immune response, compared to glucose-containing beverages. They also conducted laboratory experiments on isolated monocytes and cell culture models to study molecular mechanisms.

Scientists have observed that fructose consumption, unlike glucose consumption, leads to an increase in the concentration of a certain type of receptor (Toll-like 2) in monocytes. Its function, among others, is to regulate the immune response.

This higher receptor concentration is accompanied by an increased sensitivity of monocytes to a bacterial toxin: lipoteichoic acid. "The concentration of receptors for these toxins then increased in the body, which means that the inflammatory response intensified," explains Ina Bergheim. Specifically, pro-inflammatory messengers (interleukin-6, interleukin-1β, tumor necrosis factor alpha) were released en masse.

"These results contribute greatly to our understanding of the influence of certain food components, and fructose in particular, on the immune system," she says. "Even high fructose consumption over a short period of time in healthy people can influence the immune system and increase inflammation."

Future studies will need to clarify the long-term effects of high fructose consumption on the immune system and susceptibility to infections, particularly in people with type II diabetes or those with fatty liver disease (hepatic steatosis) associated with metabolic dysfunction (MASH).

Many common beverages contain fructose, either naturally or in added form, primarily through high-fructose syrups used in the food industry (such as glucose-fructose syrup or high-fructose corn syrup).

This is the case with industrial sodas and iced teas (colas, orange drinks, lemon drinks, etc.), which are almost always sweetened with glucose-fructose syrup (so-called "invert" sugar).

Industrial fruit juices also contain it: even without added sugar, they are naturally rich in fructose, and when they are made from concentrates, they may also have added sugars, also in the form of glucose-fructose syrup.

Highly sweet energy drinks are also enriched with fructose or glucose-fructose syrup. The same goes for sports drinks rich in glucose, fructose, or maltodextrin. Fruit drinks and non-alcoholic cocktails, whether still or sparkling, also contain fructose, both naturally occurring and added.