The lab mice were then infected with the influenza virus and kept on the same diets they had before being infected.

Graphical abstract.
Infected mice who ate highly-processed food died
In a surprising turn of events, the infected mice who were accustomed to eating the highly-processed diet died. Scientists also noted that those who feasted on the processed diet failed to regain the weight lost due to the illness. Meanwhile, all the mice on the grain-based diet began regaining weight within ten days of the initial infection, and all of them recovered.
They also found that those fed the highly processed diet failed to regain weight loss due to the illness. In sharp contrast, all of the mice on the grain-based diet began regaining weight within ten days of the initial infection, and all of them recovered.
What does this mean in a broader context?
The findings, published in Cell Reports, might have broader implications for research with laboratory animals, which are often fed processed or grain-based chow, reported The Scientist.
It could also shed more light on the impact of diet on illness recovery.
Immunologist and study author Carl Feng, along with his colleagues, found that the difference in survival was irrelevant to a lack of immune response to the virus. Previous studies by the team revealed that mice on either diet did not display any difference in health or behavior when not infected.
As per analyses, the ultra-processed diet weakened their recovery phase.