A disturbing new study led by scientists at the University of Bonn suggests that the immune system responds to a fast food-style Western diet in much the same way as it would react to a bacterial infection. As well as stimulating widespread inflammatory activity, the study claims that switching to a healthy diet may not fully reverse the long-term damage once initially triggered.

The study began by feeding mice a "Western diet" for one month. This diet is roughly defined as high in saturated fats, sugar and salt, while mostly devoid of fresh fruit, vegetables and fiber.

"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," says Anette Christ, one of the authors on the study. "This was an indication for an involvement of immune cell progenitors in the bone marrow."

What this suggested to the researchers was that the diet had not only stimulated an acute inflammatory response in the animals, but it also activated certain genes in progenitor cells. These progenitor cells are responsible for the proliferation of immune cells in the body and they have been found to have a sort of memory.

"It has only recently been discovered that the innate immune system has a form of memory", explains Eicke Latz, Director of the Institute for Innate Immunity of the University of Bonn. "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."

In this instance, that innate immune system programming process was instigated by a fast food-dominated diet and not by a virus or bacterium. Examining the animal's blood cells closely revealed the key presence of inflammasomes, the multiprotein oligomers that are responsible for recognizing infections and activating immune inflammatory processes.

"The inflammasome triggers such epigenetic changes", explains Latz. "The immune system consequently reacts even to small stimuli with stronger inflammatory responses."

These kinds of inflammatory responses have been linked to diabetes, heart disease and a variety of autoimmune disorders. This isn't the first study to associate the unhealthy Western diet with autoimmune and inflammatory disease, and it did only concentrate on animal models, but the potential long-term implications of these results are undeniably disturbing. With increasing rates of obesity and diabetes in Western countries, the growing body of evidence is making it clear that processed and fast foods can be incredibly damaging to our bodies.

The study was published in the journal Cell.