Dr. John Ragsdale is medical director of the Duke Family Medicine Center. Here he explains whether there is any scientific evidence to support this old bit of medical advice. Questions and answers have been edited.
Q. What is the origin of the familiar saying “feed a cold, starve a fever?”
A. This commonly held belief can be traced back to doctors in the 16th and 17th centuries. Back then, doctors believed that colds were caused by a drop in body temperature, and eating would help to warm them up. Conversely, they assumed that with fever, the body was in overdrive and the plan was to “starve” the fever out of them. Happily we have learned a bit since then – although less than one might think.
Q. Is there any truth to that saying? For instance, does research indicate that eating more gives the body the energy it needs to fight off a cold, or conversely that withholding food might lower one’s metabolism and reduce fevers?
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A. I found no evidence in the literature that simply taking in more calories gives the body more energy to fight off a cold. Also, withholding food, and especially liquids, when you have a fever will not make your temperature drop. Instead, our best prescription is rest and plenty of fluids. Especially during a fever when the body is perspiring, those fluids need to be replaced so that organ systems are well hydrated and metabolic processes can continue to work to make one well.
Q. Why is it that appetites often increase during a cold and decrease during a fever?
A. Often your body’s hunger mechanisms are depressed when you have a fever. There is surprisingly little data out there about the causes of this hunger suppression when people get a fever. There is likely a connection between appetite and inflammation, the body’s protective response to an infection. The lack of appetite might simply stem from the body focusing on getting well instead of on eating.
It has been suggested that alterations in the relative amounts of different types of specialized immune cells that are in charge of fighting illness might actually change the levels of hormones in the gut to inhibit hunger. This finding came from a small study, though, and needs to be investigated further.
Q. Are there any immune-boosting foods or liquids people can consume to help them fight off their colds?
A. Bed rest and plenty of fluids remain the cornerstone of therapy for viral illnesses and fever. Supplements such as echinacea, vitamin C and probiotics are very popular, but the evidence has largely been lacking. Echinacea products have not been shown to provide benefits for treating colds, although results of individual prevention trials give relatively weak evidence that they could work to prevent them. Vitamin C is a commonly suggested prevention for the common cold. That might help some people, but large randomized trials do not support this. Probiotics may also give some benefit, but there have not been large randomized trials to uniformly support or endorse their use.