A study revealed that fasting before and during exposure to salmonella intestinal bacteria protected mice from developing a full-blown infection, in part due to changes in the animals’ gut microbes.

When people or animals become infected, they often lose their appetite. However, there is still debate about whether fasting protects the host from infection, or increases its susceptibility to infection. In the new study, published in PLOS Pathogens by Bruce Vallance and colleagues at the University of British Columbia in Canada, mice fasted for 48 hours before and during oral infection with Salmonella enterica serovar Typhimurium, a common cause of foodborne illness in humans.

Fasting reduced signs of bacterial infection compared to the fed mice, including eliminating all intestinal tissue damage and inflammation. And when the fasting animals were fed for one day after they had fasted, there was a significant increase in salmonella numbers and invasion of the intestinal walls, although the associated inflammation was still weak compared to the normal infection.

These findings were not confirmed when mice were exposed to salmonella intravenously instead of orally, and analyzes of mice microbiomes showed significant changes associated with fasting and protection against infection.

Moreover, the fasting did not fully protect the germ-free mice, which were raised to lack the normal microbiome, from Salmonella, suggesting that some of the protection was due to the effect of fasting on the microbiome.

Experiments using Campylobacter jejuni confirmed that the effect of fasting was not limited to salmonella, with similar results observed.

The authors conclude, “These data suggest that therapeutic fasting or caloric restriction has the potential to beneficially modulate infectious and non-infectious gastrointestinal diseases.”

The researchers add: “Our research highlights the important role that food plays in regulating interactions between host, intestinal pathogens, and the gut microbiome.

When food is limited, the microbiome appears to trap remaining nutrients, preventing pathogens from gaining the energy they need to infect the host. While more research is needed, fasting or modifying food intake can be used therapeutically to modify infectious diseases in the future.