The impact of unhealthy diets
A typical Western diet includes high levels of fat, salt and sugar

The body's immune system responds to the so-called 'Western diet' in a similar manner to how it fights off dangerous bacterial infections, according to a new study conducted by researchers at the University of Bonn (UB) in Germany.

For the study, mice were placed on the equivalent of a Western diet – which is high in fat, sugar and salt, and low in fibre – for one month. The scientists found that the animals' defences became more aggressive, developing a strong inflammatory response of the type that can accelerate the development of diseases such as stroke, heart attacks and diabetes.

The new findings are published in the journal Cell.

"The unhealthy diet led to an unexpected increase in the number of certain immune cells in the blood of the mice," said Anette Christ, from UB.

This observation allowed the scientists to discover that the Western diet had activated large numbers of genes inside so-called progenitor cells, which direct the body's immune response. Essentially, the Western diet was causing these cells to rapidly raise a powerful army of immune response units.

Intriguingly, even when the mice were switched back onto their regular cereal diet and the initial state of inflammation had disappeared, the innate 'memory' of the mammalian immune system meant that many of the genes that had been switched on during the fast-food diet remained active.

"It has only recently been discovered that the innate immune system has a form of memory", explains Eicke Latz, also from UB. "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."

This suggests that getting rid of the aggressive state of alarm may be a difficult task. As a result, inflammation could be more easily triggered in the future, raising the risk for associated problems.

At present, this inflamed immune response to the Western diet has only been observed in mice, however, if confirmed in humans, the findings will have important societal implications, the researchers say.

"The foundations of a healthy diet need to become a much more prominent part of education than they are at present," said Latz. "Only in this way can we immunise children at an early stage against the temptations of the food industry. Children have a choice of what they eat every day. We should enable them to make conscious decisions regarding their dietary habits."