Fast food makes the immune system more aggressive in the long term, suggest researchers. According to the University of Bonn study, even after a change to a healthy diet, the body’s defenses remain hyperactive. These long-term changes may be involved in the development of arteriosclerosis and diabetes, diseases linked to Western diet consumption. A previous study said that consumption of fast foods more than three times a week was significantly higher among asthmatics.

The scientists placed mice for a month on a so-called “Western diet”: high in fat, high in sugar, and low in fibre. The animals consequently developed a strong inflammatory response throughout the body, almost like after infection with dangerous bacteria. “The unhealthy diet led to an unexpected increase in the number of certain immune cells in the blood of the mice, especially granulocytes and monocytes. This was an indication for an involvement of immune cell progenitors in the bone marrow,” Anette Christ, postdoctoral fellow in the Institute of Innate Immunity of the University of Bonn explains.

To better understand these unexpected findings, bone marrow progenitors for major immune cell types were isolated from mice fed a Western diet or healthy control diet and a systematic analysis of their function and activation state was performed. “Genomic studies did, in fact, show that the Western diet had activated a large number of genes in the progenitor cells. The genes affected included those responsible for proliferation and maturation”, explains Professor Dr Joachim Schultze

Fast food thus causes the body to quickly recruit a huge and powerful army. When the researchers offered the rodents their typical cereal diet for another four weeks, the acute inflammation disappeared. What did not disappear was the genetic reprogramming of the immune cells and their precursors: Even after these four weeks, many of the genes that had been switched on during the fast food phase were still active.

“It has only recently been discovered that the innate immune system has a form of memory”, explains Professor Dr Eicke Latz. “After an infection, the body’s defenses remain in a kind of alarm state, so that they can respond more quickly to a new attack.” Experts call this “innate immune training”. In the mice, this process was not triggered by a bacterium, but by an unhealthy diet.

The scientists were further able to identify the responsible “fast food sensor” in immune cells. They examined blood cells from 120 subjects. In some of the subjects, the innate immune system showed a particularly strong training effect. In these subjects, the researchers found genetic evidence of the involvement of a so-called inflammasome.

Inflammasomes are key intracellular signalling complexes that recognise infectious agents and other harmful substances and subsequently release highly inflammatory messengers. How exactly the NLRP3 inflammasome recognises the exposure of the body to Western type diets remains to be determined.

Interestingly, in addition to the acute inflammatory response, this also has long-term consequences for the immune system’s responses: The activation by Western diet changes the way in which the genetic information is packaged. The genetic material is stored in the DNA and each cell contains several DNA strands, which together are about two metres long. However, they are typically wrapped around certain proteins in the nucleus and thus many genes in the DNA cannot be read as they are simply too inaccessible.

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