The saying is backwards, or at best, outdated nonsense. You should eat when you’re sick with either a cold or a fever, as long as you have an appetite. Your body needs fuel to mount an immune response, and deliberately withholding food during a fever can slow recovery and worsen dehydration. The original advice traces back to a 1574 dictionary by John Withals, which stated that “fasting is a great remedy of fever.” The logic at the time was that eating generates body heat (helpful for a cold) while fasting cools the body down (helpful for a fever). That reasoning doesn’t hold up.
Why Your Body Needs Fuel During a Fever
A fever is one of the most energy-expensive things your body does. Research on energy expenditure during fever found that metabolic rate rises roughly 11 to 16 percent for every degree Celsius of temperature increase. That means a moderate fever of 101°F is burning significantly more calories than your body uses at rest on a normal day. Starving yourself during this process forces your body to break down its own muscle and fat stores to power the immune response, which isn’t ideal when you’re already weakened.
At the same time, fever dramatically increases fluid loss. For a 154-pound adult, baseline fluid needs sit around 2.5 liters per day. Each degree of fever above 98.6°F adds roughly an extra 175 milliliters (about 6 ounces) of invisible water loss per day through sweat and respiration. That may not sound like much, but over two or three days of fever, especially combined with reduced drinking, it adds up quickly.
Why You Lose Your Appetite When Sick
If eating during illness is helpful, why does your body suppress your appetite in the first place? Your immune system releases signaling molecules that, among other things, reduce hunger. This appears to serve a few purposes. It eliminates the need to search for food, saving energy and reducing heat loss from moving around. It also limits the availability of certain nutrients in the bloodstream that invading bacteria or viruses need to multiply.
So there is a kernel of biological logic behind reduced appetite during infection. But “your appetite naturally dips” is very different from “you should deliberately fast.” The appetite suppression is a side effect of immune activation, not a treatment strategy. Your body still benefits from whatever nutrition you can comfortably take in.
What to Eat When You Have a Cold or Fever
The best approach is simple: eat what you can tolerate. You don’t need to force down a full meal, but getting some calories and nutrients in helps your body do its job. Good options include bananas (easy on the stomach and energy-dense), applesauce or whole apples for vitamin C and antioxidants, broth-based soups, and toast or crackers if your stomach is unsettled. Ginger can help with nausea and may support your body’s antiviral defenses. If you can manage it, garlic in soup or broth may help with congestion.
The priority, more than solid food, is fluids. Water, broth, diluted 100 percent fruit juice, herbal tea, and electrolyte drinks all count. Small, frequent sips work better than trying to drink a large glass at once, especially if nausea is an issue. Avoid alcohol and heavily caffeinated drinks, which can worsen dehydration.
Dehydration Is the Real Danger
The actual risk of not eating or drinking during illness isn’t starvation. It’s dehydration. Fever, sweating, vomiting, and diarrhea all drain fluids fast, and the signs of dehydration can sneak up on you. In adults, watch for dark-colored urine, urinating much less than usual, extreme thirst, dizziness, confusion, or skin that stays “tented” when you pinch it instead of flattening back immediately.
In young children, the warning signs include no wet diapers for three hours, no tears when crying, sunken eyes, a sunken soft spot on the skull, rapid heart rate, and unusual crankiness or lethargy. Severe dehydration can lead to dangerously low blood volume, which causes a drop in blood pressure and oxygen delivery throughout the body. This is a medical emergency.
The Bottom Line on the Old Saying
Whether you have a cold or a fever, the advice is the same: eat what you can, drink plenty of fluids, and rest. There is no benefit to deliberately starving a fever. The 450-year-old saying was based on a misunderstanding of how body temperature works, and modern evidence points clearly in the opposite direction. Your immune system runs on energy, and it needs you to keep the supply coming.