Starve a fever, feed a cold.

Microbes Monthly: A recent research paper found that eating during a listeria infection resulted in a more fatal infection in mice, but eating during a viral infection enabled a speedy recovery. So the old adage of "starve a fever, feed a cold" still stands!

Source: https://naturemicrobiologycommunity.nature.com/channels/303-journal-club/posts/12145-starve-a-fever-feed-a-cold-or-die?