The old saying, "feed a cold, starve a fever," may be only partially good advice, according to experts.

Starving a fever by eating fewer calories may actually make it more difficult for your body to fight off the flu virus. "'Starve a fever' has been medical folklore for hundreds of years because some medical historians believe that doctors in the 1500s and 1600s thought fever meant that your metabolism was in overdrive or working overtime, which is true to some degree," says Mark A. Moyad, MD, MPH, Jenkins/Pokempner director of preventive and alternative medicine at the University of Michigan Medical Center in Ann Arbor, Mich.

The Origin of Feed-or-Starve for Colds and Fever

People thought that eating would activate digestive processes which could lead to more fever, according to Dr. Moyad. "They believed less of the body's energy would be able to fight fever because it was expending energy for digestion," adds Moyad. The origin of the saying may date back to 1574, when writer John Withals suggested that fasting would cure a fever. At the time, colds were blamed on a drop in body temperature, which could be helped by eating and drinking. Eating less, on the other hand, was believed to stop stoking the heat of a fever.

The Truth Behind Feed-or-Starve for Colds and Fever

The truth, according to researchers, suggests that eating less during the early stages of an infection can actually be dangerous. "The body requires large amounts of energy to create and assemble the large number of immune cells necessary to fight the enemy. Good nutrition and calories provide this energy," says Moyad. Most experts dismiss starve-a-fever as folklore. In addition, fevers often decrease appetite naturally as part of the body's defense system, so your immune system can focus its energy on fighting the cold and flu pathogens.

As with other types of infections, individuals with less robust immune systems (such as very young children, the elderly, and people with co-existing illnesses like diabetes, cancer, or immune disease) may suffer more serious colds and infections by an inadequate intake of high-quality calories in the early stages of an infection. And the body requires additional fluids above the norm in the presence of illness, including colds or flu. Water, juice, and hot liquids along with food will help fight cold infections by keeping the body well-hydrated and nourished.

Physicians and experts stand by traditional recommendations for colds and flu over the starve-a-fever adage: Drink plenty of fluids to replace lost electrolytes and eat if you're hungry. Drink water or drinks with added electrolytes, such as Gatorade or Pedialyte.

"We now know that the cold and flu are caused by viruses," says Curt Gingrich, MD, associate program director of the Riverside Methodist Hospital Family Medicine Resident Program in Columbus, Ohio. "Starving a fever is not helpful. In addition to making sure you are drinking plenty of fluids during an illness, be sure to also get plenty of rest," says Dr. Gingrich. "If you have a high fever or a fever lasting more than two to three days, you will need even more fluids to keep from getting dehydrated."