Turns out that ancient phrase is half right.

The thinking started in the 1500s, explains Sharon Bergquist, M.D., assistant professor of medicine at Emory University. There was a belief that a person had a cold because their body temperature was low, and feeding could increase their temperature and help fight the illness, she says. A fever meant the body temperature was high, and starving a person would slow down metabolism, bring down body temperature, and could stop stoking the fires.

Turns out feeding a cold is good practice. But so is feeding a fever, says Dr. Bergquist. Your body needs nutrients to help the immune system mount a strong response.

What should you feed your cold or fever?

As you can imagine, no doctor is going to say doughnuts and bacon. Heres what to swallow, according to Dr. Bergquist:

• Liquids are more important than solids. When youre sick, your appetite decreases because your body diverts so much of its energy to fighting infection and it has less energy for digestion, she says. Liquids are easier to take in, especially when your nose is stuffy. Plus, you need extra hydration when you have a fever, since a higher body temperature means more sweat. And more sweat means you lose electrolytessodium, chloride, potassium, and magnesium. You can replace those through liquids like broth or a sports drink.
• Warm liquids are better than cold ones. Vapor from hot liquids can moisten your sinus passages and your throat, she says. That helps break down the mucus so you can expectorate itexpectorating mucus is our first line of defense in getting rid of germs.Is chicken soup the king of all warm liquids? It has a lot of advantages, she says. Its hot, has electrolytes, and if it has vegetables, it contains antioxidants that help support your immune system.

Feed your body to prevent a cold or fever next time

Theres no magic food that prevents colds, but if a person has certain habits, the immune system in general is stronger, says Dr. Bergquist. That means you would get sick less frequently and youd get over the cold or fever sooner.

Seventy percent of the immune system is in the gut, she points out. So gut bacterial balance is a key part of your immunity. While its not clear exactly which bacterial strains will give you the best balance of good and bad bacteria in your gut, diversity seems to be important. So you want to feed your gut not just the probiotics everyone talks about; you want prebiotics that feed those probiotics. All prebiotics are fiber, but not all fiber is a prebiotic, she says. Aim for a diversity of fibers from foods including fruits, vegetables, legumes, nuts, and seeds.

Familiar advice, yes. But are you doing it? You don't have to live on walnut-studded kale salad (although thats not a bad choice). Check out this Mediterranean Roasted Red Pepper Chicken with Lemony Garlic Hummus , or discover how to eat a days worth of healthy greens in 14 minutes (its actually amazing, trust us).