Feed a cold, starve a fever

"Feed a cold, starve a fever" is an adage or a wives' tale which attempts to instruct people how to deal with illness. The adage dates to the time of Hippocrates when fever was not well understood. His idea was the fever was the disease, and starving the sick person would starve the disease.

Source: https://en.wikipedia.org/wiki/Feed_a_cold%2C_starve_a_fever