Even during the axiom's heyday in the 19th century, there were physicians who thought that withholding food from fever sufferers was a bad idea. Physician Charles Gatchell, in an 1881 article in the St. Louis Clinical Review, advised instead that both cold and fever sufferers should eat frequently, and warned, "No doubt, under the old method of keeping the patient on a low diet for fear of adding fuel to the flames, many poor victims were actually starved to death when recovery would have followed, had they been properly nourished."
Recent research would enable him to say, "I told you so." Animal studies indicate that restricting food intake actually hinders the immune system's ability to respond to an infection, because it deprives key cells of the energy they need to produce proteins that recognize invaders and target them for destruction. In a study published in 2008, for example, Michigan State University nutritional immunology researcher Elizabeth Gardner found that mice with a calorie-restricted diet were more likely to die during the first few days of infection than mice with a normal diet, and they took longer to recover from the illness.
Conversely, there's evidence that eating actually boosts the immune system's ability to fight illness. A 2002 Dutch study found that six hours after human subjects consumed a meal, their levels of gamma interferon increased. Gamma interferon is a chemical messenger that helps trigger the killer T cells that destroy cells invaded by viruses. In a comparison group who drank only water, gamma interferon levels fell slightly. One caveat: The researchers did find that fasting might possibly help the body fight certain types of fevers -- ones caused not by viruses, but by bacterial infections. The human subjects who only drank water had increased levels of another chemical, interlukin-4, which helps B cells produce antibodies that attack bacteria lurking outside cells.
Advocates of starving a fever sometimes argue that digesting food consumes energy that the body needs to fight the infection, but that's not really so: Only 10 percent of the body's energy intake goes to metabolizing food [source: Williams].
So what should you eat when you have a fever, and how much? We'll deal with that in the next section.