Feed a cold and starve a fever.
Prov. You should feed someone who has a cold, and withhold food from someone who has a fever.; (or, interpreted differently) If you feed someone who has a cold, that will ward off a fever. Jill: I don't feel like going out to lunch with you. I have a cold. Jane: All the more reason you should get something to eat. Feed a cold and starve a fever, you know.