Opposing Effects Of Fasting Metabolism On Tissue Tolerance In Bacterial And Viral Inflammation

When you're sick, you naturally lose your appetite - a phenomenon scientists call "anorexia of illness." This Yale University study investigated whether this loss of appetite actually helps or hurts your body's ability to fight different types of infections. The researchers tested this using laboratory models of both bacterial infections (like sepsis) and viral infections (like influenza).

The results revealed a surprising split: fasting and avoiding food was protective against bacterial infections, while eating glucose (sugar) made bacterial infections worse. However, the opposite was true for viral infections - animals needed glucose to survive viral illnesses, and blocking glucose utilization was deadly during viral infections like the flu.

The researchers discovered this wasn't because fasting affected the amount of bacteria or viruses in the body, or because it changed the overall inflammatory response. Instead, the different metabolic states - fasting versus fed - helped protect brain cells through different cellular mechanisms. During bacterial infections, ketone bodies (produced during fasting) protected neurons from damage caused by reactive oxygen species. During viral infections, glucose was essential to prevent a harmful cellular stress response that would otherwise damage neurons.

This research provides scientific backing for the old saying "starve a fever, feed a cold" and suggests our natural loss of appetite during illness may be an evolved protective mechanism. For clinical practice, this highlights how metabolic interventions during illness should potentially differ based on whether someone has a bacterial or viral infection, though more human studies are needed before changing medical recommendations.