In this "trigger happy" state, certain immune cells are less discerning, resulting in inflammation, more severe infections and even new food intolerances or sensitivities.

Researchers from the Department of Nutritional Sciences at the University of Vienna have shown how when fructose comes into contact with free-roaming immune cells (monocytes) in the blood, they become far more sensitive and reactive. But far from this "boosting" the immune system, this state of hypervigilance works against the body.

Most of us probably know fructose is naturally found in fruit and some vegetables, as well as being added to many processed foods and drinks as high fructose corn syrup (HFCS). While a natural sugar like sucrose (albeit refined as table sugar) and glucose, the body processes it differently, primarily in the liver. But unless you have a fructose sensitivity, the 6 g in an average apple is not going to trouble you.

However, if you eat a general Western diet in the US, chances are you're consuming much more. For context, a 355 ml can of Coca-Cola has around 39 g of HFSC. While this study doesn't specifically target HFCS, it's come under scrutiny in the scientific community in the last few decades, with researchers linking it to various metabolic diseases including gastrointestinal issues, obesity and type 2 diabetes mellitus.

Prior to the 1970s, most processed foods were primarily sweetened with cane sugar, however, the invention of HFCS – a liquid made from corn starch – flipped that. Because it was more stable, cheaper to produce (thanks in part to high government subsidies for corn growers), it's now commonly found in everything from sodas to sauces. (Since 2000, its popularity has been steadily declining.)

In this new study, researchers set out to find the biochemistry behind the link between high fructose intake and inflammation. In two randomized studies with otherwise healthy adults, the initial trial saw 10 adults given a diet high in fructose – three serves of a Jello-like substance per day, totalling 110 g of the sweetener. Blood samples were collected before and after the 3.5-day fructose diet. In the second study, monocyte cells were isolated from a different cohort of adults and the immune cells exposed to glucose, maltodextrin and fructose to investigate cellular activity.