Is the old adage “feed a cold, starve a fever” true? NorthShore's Robert Mitchell Figura, D.O., puts to rest the truth of this ancient wisdom.

The reason people say “feed a cold” is because the body needs energy when it's fighting illness. This applies to both colds and flu, but for different reasons. For a cold, eating healthy food will provide the body the extra energy it needs to fight illness, but can also help the body generate heat. The cold virus replicates faster in a cold environment so raising your body's temperature along with bundling up can stop cold germs in their tracks, said Dr. Figura.

Fevers have a totally different reason for needing to be "fed." When you have a fever, it's your body's attempt to overcome the virus. This increased heat causes an increase in metabolism, which in turn increases calories burned. You want to take in calories to counteract this. Of course, fevers often come with a loss of appetite. Don’t force yourself to eat if you don’t feel like it.

So it seems that in either case, calories are key in helping the body recover, but that's not actually the most important part of the equation. Fluids, while not technically "feeding" anything, are more important than calories. Fevers dehydrate your system, and colds require mucus to expel all the germs. Dried up mucus can clog up its exit routes and keep those germs inside you. Juice and water are your best go-to fluids. Avoid caffeinated or alcoholic beverages, as these can further dehydrate the body, Dr. Figura said.

This is what makes chicken soup a healthy choice for colds and fevers. It provides both calories and fluids to keep the body fighting illness. There is nothing magical about soup, it's just a combination of the best things for a cold or a fever.

Next time you are trying to remember if it's "starve a cold and feed a fever" or "feed a cold and starve a fever," remember this new adage: Feed them both to keep the body fighting.