The human immune system treats a fast food diet in much the same way as it does to a bacterial infection, raising questions about the damage we're doing to ourselves by hitting the burger drive through so often.

Researchers from the University of Bonn in Germany fed a "Western diet" high in saturated fats, sugar, and salt to lab mice for a month - no fresh fruit, vegetables, or fiber was included.  At the end of the month, the mice had elevated levels of immune cells, just as they would have had if they were subjected to an infection.

"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 research team member Anette Christ.

Increased levels of white blood cells led to the identification of genes containing progenitor cells, which are responsible for raising up an immune cell army to battle bacterial infections.  Previous research showed that progenitor cells have a kind of "memory" which remember how the body fights off a biological attack and "reminds" it the next time the infection appears.

When the mice went back to their regular cereal diet, the inflammation they suffered as a result of the "Western diet" disappeared, but the genetic reprogramming of its immune system remained.  "After an infection, the body's defences remain in a kind of alarm state, so that they can respond more quickly to a new attack," said Eicke Latz from the University of Bonn.

The researchers say the results suggest even more evidence linking an unhealthy diet and health problems such as type II diabetes, obesity, and cardiac issues.