Should you really starve a fever?

There are a number of infectious diseases -- typhoid fever and Rocky Mountain spotted fever, for instance -- that have "fever" in their names. That said, the word fever actually refers to a symptom, rather than a specific illness.

When you get a fever, your body temperature, typically around 98.6 degrees Fahrenheit (37 degrees Celsius), rises by at least 1 degree. A temperature of 100 to 102 degrees F (37.8 to 38.9 degrees C) is considered a low-grade fever. If it rises above 103 degrees F (39.4 degrees C), it's considered a high-grade fever, which is a sign that something really bad may be happening.

A variety of conditions, from cancer and multiple sclerosis to inflammatory bowel disease and heat exhaustion, can cause your temperature to soar, which is why developing a fever is a good reason to see a doctor. But odds are that your body is fighting off some nasty viral or bacterial invader.

The attacking microbes are spotted by the immune system, which sounds the alarm by releasing chemicals called cytokines into the bloodstream. When the cytokines reach the hypothalamus, an almond-sized structure in the brain that acts the body's internal thermostat, they inhibit heat-sensing neurons and excite cold-sensing ones. The hypothalamus is fooled into thinking that the body's temperature is too low. It cranks up the heat by telling the skeletal muscles to generate warmth by contracting rhythmically -- to us, that's shivering -- and constricting the blood vessels in the skin, so that the heat is retained.

While you feel awful, a fever is a potent anti-infection weapon. The heat stimulates white blood cells to produce antibodies to fight the invaders. And some bacteria and viruses can only tolerate a narrow temperature range, so heat can kill them or inhibit their reproduction.

In the next section, we'll look at where the idea of starving a fever came from.

For much of human history, people didn't know that much about infectious diseases and the body's mechanisms for fighting them. Perhaps the first healer to use diet to fight disease was fourth century B.C. Greek philosopher and physician Aristotle, who theorized that nutritional excesses and deficiencies caused various illnesses. Aristotle thought that food was to the body like wood is to a fireplace, and that the more you ate, the higher your temperature would rise. Instead of starving a fever, though, Aristotle instructed fever sufferers to gorge themselves. He thought that would heat up the body so much that it would burn out the fever, the way that a burning forest overwhelms a campfire.

Though Aristotle's medical teachings were followed by Western doctors for many centuries afterward, eventually someone must have realized that gluttony didn't cure fevers. By the 1500s, feverish patients were being advised instead to fast, in the hope that depriving the body of fuel would cool their internal fire. The first published prescription came in 1574, when English writer John Withals observed that "fasting is a great remedie of feuer." Unfortunately, his medical expertise wasn't much more reliable than his spelling.

Nevertheless, by the 1800s, fasting -- in addition to other dubious remedies, such as bloodletting and swallowing castor oil to induce vomiting -- was an established fever remedy. In an 1884 article in the magazine Popular Science, physician C.E. Page confidently concluded that "where the 'fasting-cure' is applied in extensor, with appropriate water and air baths, sunshine and perfect ventilation, the worst forms of fever rarely have a 'run' of ten days -- three or four days will often suffice to insure convalescence."

By the late 1800s, the axiom had evolved into "Stuff a cold, starve a fever." Many people of that time thought that colds were the opposite of fevers and were caused by a drop in body temperature. So, it made sense that colds could be cured by shoveling more fuel in the bodily furnace. In an 1863 sketch, Mark Twain wrote of trying to cure a cold with a hearty meal at a restaurant. (It didn't work, and he got sicker.)

Did any of this fasting do anybody any good? We'll get into that in the next section.

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.

When you've got a fever, you may not feel much like eating. That's because the cytokines, those chemical messengers released by the immune system that trick the hypothalamus into resetting the body's thermostat, also monkey around with your appetite, which the hypothalamus controls. Additionally, some viral infections that cause fevers also attack the stomach and make you want to vomit, which isn't too appetizing.

Even so, most experts agree that your body needs good nutrition when you're sick, so that the immune system can do its job. Having enough calories to run the infection-fighting mechanism is particularly important, which is why dieters should feel free to take a break from low-calorie regimens during the flu season, which lasts from October through January.

So what should you actually eat and drink when you have a fever? Begin with liquids, since your body can become dehydrated, especially if you've been vomiting or had diarrhea. Start small, with a couple of ounces of water or lemon-lime soda (let it go flat first, so that the bubbles don't bother your stomach). Repeat that every 15 to 30 minutes for a few hours, and then start taking larger quantities of water, tea, fruit juice and juice-based drinks, carbonated soft drinks and broth. After that, give solid food a try. You may want to start mild, with something like buttered white toast, but just about any food that doesn't cause nausea is OK.

Once you've graduated to more substantial fare, try foods such as lean meats, fish, poultry, eggs, legumes and nuts and seeds, which are rich in protein and nutrients such as vitamins B6 and B12, selenium and zinc, all of which will help boost your immune system. Other good choices are citrus fruits such as grapefruits, oranges, lemon and lime, which contain anti-inflammatory compounds called bioflavenoids, and watermelon, whose pulp contains a powerful antioxidant, glutathione, that helps curb cell damage.

One food you definitely should consider adding to your flu diet is chicken soup. In a study published in 2000, University of Nebraska Medical Center physician Dr. Stephen Rennard reported that his wife's grandmother's favorite recipe had anti-inflammatory properties that helped stop the movement of neutrophils, the white blood cells that stimulate the release of mucus. That, in turn, can reduce the coughing, sneezing and stuffed-up feeling that accompanies upper respiratory-tract viral infections. It's good for colds, too.

Want to know the truth behind more old wives' tales about your health? We've got links to more articles you'll like on the next page.