First, this is an idiom that is no longer considered good medicine. It comes from a culture from long ago before we understood pathogens, disease, and our immune systems.

When you are ill with a cold, other upper respiratory infection, and/or fever, eat sensibly when you are hungry and stop when you are satisfied. Drink plenty of liquids. Rest in bed. You can treat the symptoms with over-the-counter medicines. Ask your pharmacist for product recommendations for your specific symptoms. See more in the related question for how to treat a cold.

Don't rely on this old saying as medical advice.

About the origin of this common traditional saying:

The phrase is from Chaucer in "The Canterbury Tales." In Middle English, the phrase was "Fede a cold and starb ob feber" translated as "feed a cold and DIE of fever." It wasn't medical advice, it was a cautionary statement: If you eat when you're sick, you'll die of fever.

Because so many people didn't eat when they were sick and they died, "starb" became "starve" and the definition was changed from just "die" to "die from lack of food." Considering that people at that time believed bathing caused illness (hence the wearing of perfumed pomanders to hold at your nose to ward of the stench of the person you were talking to), and that they believed many myths about health, such as that Jews were the cause of the Black Plague, and that drinking your urine could cure the plague. Even if they meant it as medical advice, it's not something we should be taking seriously today!

There are other stories about the original phrasing and origin of the idiom that have been handed down over the generations, here are some of those provided by Answers.com contributors:

• The adage is "Starve a fever, feed a cold." It was based on beliefs that don't hold true in today's medical knowlege. Some of those beliefs that led to the idiom were that fighting the flu took a lot of metabolic activity, and that digestion is a demanding task. They reasoned that as a fever is usually short lived (1-3 days), not eating may be a better way of allowing your body to contribute the maximum amount of metabolic activity to recovery. But, if the fever lasted longer, then maintaining adequate available energy to support the immune system may become a problem if not eating your normal amounts and quality of foods. Doctors who practice "Natural" medicine, and many allopathic doctors, too, continue to recommend diluted vegetable juice (preferred) or fruit juice (unsweetened) for energy during an illness. (This is not suggested for a long term or normal diet.)

• The original phrase, back before it was misquoted, was - "Feed a cold, STAVE a fever" - as in "stave off" or "keep away" a fever.

• I'll preface this by saying I am a licensed naturopathic physician and acupuncture physician. Feed a cold: As others have pointed out the common cold tends to last 7-10 days. It is hard/and or dangerous to fast for that long. Avoid sugars/starches, since eating mainly simple carbohydrates like breads, potatoes, and sugars can result in nutritional deficiencies and over production of insulin that is difficult for your body to deal with, especially if you have a concurrent cold. But, do eat healthy nutritional foods from all food groups if you can.

  Starve a fever: Digestion does take a lot of energy. As the temperature increases, metabolism can become less efficient. You may feel bloated if you eat too much at a time. As for keeping your temperature up when you are sick: that is correct, to a point. Your body increases its temperature to fight infection by creating a hostile environment for the pathogens. You can help your immune system do its normal job by not taking medicines that lower the temperature too soon or too often. In an otherwise healthy adult, short bouts of 102-103 degrees F. are acceptable, but if the fever increases or lasts more than a day at that temp, it should be addressed with contact with your health care provider. Depending on the age of a child, it may or may not be a good to let the temperature rise that high and you should consult the pediatrician for advice about fevers in children the age of yours. In all cases the person must keep well hydrated and temperatures checked frequently, because fever is only a part of what is happening.

• Actually, a fever is one of the ways your body fights an infection. The reason you get a fever is because your body is trying to render the biological processes inside the infectious bacteria useless. The proteins inside the bacteria only function within certain temperature ranges, i.e., the normal human body temperature range of 97.5 degrees to 99.5 degrees. When the temperature rises beyond this, the proteins lose their ability to function; they've been denatured. Without these proteins working properly, or at all, the bacteria either dies or is severely weakened enough for your immune system to easily finish it off.

• Unless the fever lasts longer than a week, or isn't too high (higher than 103 degrees in adults can become dangerous), you shouldn't try to lower your body temperature. Your doctor will tell you if that's necessary. Otherwise just bundle up and insulate yourself so that your body can keep up the higher temperature without having to expend a lot of energy. Eat healthy foods and don't physically stress your body too much.

• Eating doesn't really matter. Just drink lots of fluids.

• As I have always understood, this adage applies to temperature. "Feed a fever" means bundle up and sweat it out. "Starve a cold" means bundle up and warm up. (This is not the current understanding, we now know that being cold does not cause or exacerbate a cold.)

• It would seem that both are wrong. Most doctors will tell you that it is important to reduce stresses on your body when sick. Both starving and overeating produce unwanted stress. So, unless you have a stomach disorder, eat moderately to maintain your strength in either case. The saying is not intended to be current medical advice.

• (From Cecil Adam's "Straight Dope") Your version of the proverb is the traditional one, but you can find citations in the literature that have it the other way around. The idea, if not the exact wording, dates back to 1574, when a dictionary maker named Withals wrote, "Fasting is a great remedie of feuer."

• Doctors have been trying to stamp out the above piece of folklore for years. Current medical thinking is that you want to keep an even strain when you're sick with either a cold or a fever, and you certainly don't want to stress your system by stuffing or starving yourself.

• Nobody's sure where the notion of feeding colds and so on arose. (It surely didn't originate with Withals.) One somewhat dubious explanation has it that the proverb really means "If you feed a cold now, you'll have to starve a fever later." A more plausible interpretation is that the feed-a-cold idea arose out of a folk understanding of the disease process, namely that there were two kinds of illnesses, those caused by low temperatures (colds and chills) and those caused by high temperatures (fever). If you had a chill, you wanted to stoke the interior fires, so you pigged. If you had a fever, you didn't want things to overheat, so you slacked off on the fuel.
• When I had sniffles as a kid the feed-a-cold thing was usually good for a few extra Twinkies. So you'll just have to forgive me if, in the delirium of a 99-degree temperature, I used to imagine it was feed a fever too.

• The way it was explained to me was that if you have a cold you usually didn't want to or couldn't eat and needed to, so you "fed" a cold, basically not binging, but simply remembering to eat. However, if you have a fever, you may crave a lot more food, and may need to back off and need more moderation, so you would need to "starve" a fever so as not to make yourself more sick - keep those hunger pangs in check. And that came from a very, very wise old wife, so it must be true!

• The point is when you have fever your body is working to fight something in your system. You should eat light since the body needs energy to digest and it is better to let the body focus on the "fight at hand" and just eat light until the fever breaks. With a cold, your immune system is involved for up to 10 days, and you need to keep those guys fueled (antibody production). So you eat things that encourage their production, such as vitamin C-rich foods and fruit, and soups, and teas, because they add needed fluid, and because warm fluid helps to thin the mucous associated with colds.

• Your body needs energy to fight whatever viral or bacterial infection it has to, so "starving" is not a good idea. Though your body initially uses energy to digest, the digestion process returns more energy than it uses. If you feel cold at night, get up and eat a piece of cheese or some nuts (the oils and proteins will slowly fuel your body and keep you warm while you sleep). Most importantly, stay hydrated and take no fluids that are diuretics (like caffeine in soft drinks, coffee and tea, beer and other alcohol)!

• The way I remember it is feed a cold but starve a flu ("stomach flu"). Gastrointestinal infections cause nausea, vomiting and diarrhea and your digestive tract needs rest with consumption of plenty of fluids. You need energy to get over a cold, so eat soup, hot foods, and cold liquids.

• I've always found that if you freeze a fever and heat a cold, as in very warm or cool showers, it works out pretty well. If I'm sick with a cold I'll stand in a hot shower and take in the steam. It really clears the the nasal cavity. And as for fevers, a lukewarm bath always helps me.

• Regardless of medical reasons, the adage "Feed a cold and starve a fever" was lexically designed to help remember the proposed eating pattern for each sickness...d in feed-cold and v in starve-fever.

• I agree with the furnace analogy and if you want to test this, try this: After a meal (2-3 hours) get a sugar-filled cookie of your choice (probably most anything with simple sugar will work), locate yourself in a comfortable room and in a relaxed position, take your temperature with a digital thermometer, and also just feel (sense) what your body and temperature are like. Now eat that sugar-filled cookie. You should begin to feel your temperature rise within the first few minutes; you might even break a slight sweat. Measure your temperature each minute for the next 10 minutes... I think you will find that your body quickly goes to work converting this cookie into energy and that process slightly raises your temperature... if not measurable at least in some part you may sense the rise. Now it just seems logical that at a time that we are trying to reduce our temperature taking cold showers and baths, and medications that reduce fever... stoking the body's furnace with simple sugars is not very smart. I go with starve a fever. Of course I do not mean to not eat at all, but understanding the concept you might better choose what you eat to minimize the effect.
• For the record, high glucose (sugar) intake could not possibly raise your temperature in 10 minutes for two reasons, 1) your body temperature does not flux based on what foods you eat, and 2) It takes about 30 minutes for your body to begin effectively absorbing anything taken by mouth, this includes meds and food. And your immune system works at its own pace, you can assist it slightly by working with your body, but getting yourself "close to heat stroke" and putting hydrogen peroxide in your ears cannot make your immune system work 10 times faster, the only thing it is likely to do is make you very uncomfortable and annoy any stray harmless bacteria in your ears.

• "Feed a cold, starve a fever" is right on if you are an active fighter, but dead wrong if you are a passive waiter. With a cold, if you are a fighter, eat all of those favorite foods that make your mouth water when you think of them. You need lots of fuel for the fight. The bugs can't handle the fever temperature. [The following advice is controversial today, suddenly changing anything else while you are ill is usually not good medical advice:]

  So, stop eating suddenly, forcing the body to switch to using stored fat. That is very potent fuel! When the fever comes up, supplement it with a hot toddy (heated lemon juice, honey, medicinal brandy or rum), get into a hot bath. Get into bed and sweat. By morning the nasty 14 day head cold will be gone.

• It must be pointed out that contributors to this answer are probably NOT doctors. Taking some of the advice given above may harm your health. If you are thinking of trying any of the less-orthodox ideas above, you should probably seek the advice of your doctor first.

• When you have a fever your body uses certain strategies like altering your metabolism and binding iron to slow the pathogens down. That said, although I wrote this after the disclaimer, I'm not a doctor either :)

• Admittedly, I'm not a doctor either, but I am a working nurse and some of these suggestions alarmed me. For minor illnesses you should maintain moderate intake. Gorging or starving yourself for several days will only put added stress on the body. The most common recommendations for oral intake with a fever is to take in plenty of fluids, eat when you're hungry, and try to keep as comfortable as possible. If it's a high-grade fever (above 102 or 103 in adults) you can take whichever NSAID (tylenol, motrin, alleve etc.) you prefer to bring the fever down, since high-grade fevers can be damaging to your own tissues. (Be sure that you do not take any OTC medicines differently than the package directions say. Many cold preparations contain Tylenol and other fever reducers so if you take more than one that does, you risk getting too much acetaminaphen which can be very dangerous and damaging to the liver. Children under 16 should not take aspirin due to the risk of Reyes' syndrome.)

• Feed a cold and starve a fever. This was from the olden days of yore when we did not know much about medicine - when people contracted some bad fevers, they usually died with a few weeks. The general consensus at that time was to not waste good food on a person that was going to die. Of course this is no longer true today... Our knowledge of medicine is far greater and keeps improving almost every week.

• This is definitely not a good idea in either case. You need more fluids than usual when you have the flu AND a cold. Drink plenty of water and juice, eat enough food to satisfy your appetite, and drink hot fluids to ease your cough and sore throat.

• Neither, actually: It's "Feed a cold & STAVE a fever." - as in "stave away" or "stave off."

• You should feed a cold to keep a fever away. If you have a fever you should feed that too, although you are unlikely to feel like eating.

• Firstly, do NOT medicate to lower fevers unless medically necessary (and the target temperature for that in adults varies from source to source - I use 103-104 F as my range, but mostly gear it on how you feel. For infants and children the point at which fever becomes dangerous is dependent on their age and general health status, you should ask your pediatrician in advance what the maximum temperature of your infant or child should be and when to contact the provider for care). You will feel uncomfortable letting your temperature rise above normal, but the goal is not to suppress the body's ability to fight the invader (it was mentioned above about the body's heat). Whether to provide food to the body for a fever/flu can vary depending upon your life-style. If you are prone to eating unhealthy foods or are a regular-heavy drinker/drug user, your body is already lacking in many of the elements that are necessary to fight infection. Nonetheless, my studies have led me to believe that it is warranted to consume nutritional foods while with a fever. However, the best intake would be that of warm fluids such as vegetable (preferred) or fruit juice. I usually drink about 4oz. low-sodium, organic vegetable juice when I 'feel' the need - which tends to be about once per hour. Drink much water, particularly if you have diarrhea. Although typically mentioned, water consumption is so easily neglected, yet has profound effects on the body, both healthy and ill. The same applies to a cold. The bottom line is that providing heavy foods or unhealthy foods will tax your system unnecessarily while not yielding much in the way of nutrients. Eliminating toxins (caffeine, nicotine, alcohol, etc.) and adding substantive [liquid] foods will aid your body in doing its job.
• No, you should be getting proper nutrition and hydration all the time regardless if you are sick. When you starve a fever you are basically denying your body what it needs to get better.
• I disagree with most of the information above. I was brought up to believe it's "starve a cold and feed a fever" which refers to medication when tackling an illness. There is no medication to cure the common cold, only to suppress it or make you more comfortabe while your immune system works, so it's best to let a normal common cold run its course without medication. However, in case of a fever, medication can be taken upon medical advice in order to lower the temperature. This is true and makes more since. It has nothing to do with food. Of course you should encourage food and liquid as much as tolerated in any case.

People often think of it as the 'Golden Rule', saying 'Do unto others as you would have them do unto you'. According to different Bible translations, this scripture at Matthew 7:12reads:

"...Therefore all things whatsoever ye would that men should do to you, do ye even so to them: for this is the law and the prophets..."(KJB)

"In everything, therefore, treat people the same way you want them to treat you, for this is the Law and the Prophets. "(NASB)

This was part of Jesus 'revolutionary' teachings....LOVE your enemies, PRAY for those persecuting you, TREAT OTHERS with LOVE, the way you want to be treated, instead of paying back bad for bad.(Matthew 5:39, 44; 7:12)

If only God would give me some clear sign! Like making a large deposit in my name in a Swiss bank.

Woody Allen, in Without Feathers (1975)

God will not place a burden on a man's shoulders knowing that he cannot carry it.

Muhammad Ali

I know God will not give me anything I can't handle. I just wish that He didn't trust me so much.

Mother Teresa