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The question

Is it true that you should "feed a cold"? What foods I should eat when I'm sick? Is there a supplement I can take to recover faster?

The answer

It's an axiom that dates back hundreds of years: Feed a cold, starve a fever. Yet its origin is vague and its scientific basis is tenuous.

It's believed the age-old adage stemmed from an obsolete belief that eating food warmed the body during a "cold" while fasting cooled it down when it was overheated from fever.

The evidence to feed a cold and starve a fever, however, is in short supply.

I could find only one small study (six healthy young men) that was published in 2002. When the volunteers drank a 1,200-calorie liquid meal after a night of fasting, immune cells that combat cold viruses were increased. But when they drank water only, the immune response to influenza viruses was enhanced. Hardly convincing.

Forgoing food isn't a recommended treatment for any illness. When the body is fighting infection – a cold or flu virus – it needs extra calories to support a higher metabolic rate.

More important, though, is to drink plenty of fluids. If you have a fever, a common flu symptom, drinking hot and cold beverages replaces fluids lost through increased sweating.

Staying hydrated also prevents the mucus in your nose, throat and lungs from becoming thick; thinner mucus is more easily cleared from your upper respiratory tract. And by keeping the lining of your upper respiratory tract moist, fluids can help ease sore throat symptoms.

Your body also relies on a steady supply of nutrients to respond to attacking viruses quickly and efficiently. Protein, omega-3 fatty acids, vitamins A, C and E, folate, selenium and iron, for example, are essential for a strong immune system.

Yet, there's no evidence that certain foods can treat the common cold. The question hasn't been studied.

Studies have evaluated the impact of various supplements and turned up mixed results. Variations in dose and formulations and different study populations (e.g., adults versus children) likely contributed to inconsistent findings.

Even so, the following foods, beverages and supplements are worth adding to your diet when you have a cold. As always, speak to your doctor before taking any supplement if you are pregnant, have a medical condition or take a medication that may interact with certain natural health products.

Fruit (and green) smoothies. Smoothies made with whole fruit (not juice) provide all-important fluids to keep you hydrated. Plus, they're easy to stomach if you don't feel like eating solid food.

Smoothies made with fresh or frozen fruit and vegetables also deliver plenty of immune cell-protective antioxidants such as vitamins C and E, beta-carotene and flavonoids. (When fighting infection, white blood cells release free radicals to kill viruses but, in the process, free radicals damage white blood cells themselves.)

Antioxidant-rich smoothie additions include strawberries (vitamin C, flavonoids), raspberries (vitamin C, flavonoids), kiwifruit (vitamin C), frozen mango (vitamin C, beta-carotene), spinach (vitamin C, beta-carotene) and peanut and almond butter (vitamin E).

Blend your fruit with kefir, a fermented milk that's packed with probiotics, so-called friendly bacteria that stimulate the immune system.

Green and white tea. Drinking hot liquids helps ease nasal congestion by improving mucous flow. It also, of course, provides much-needed hydration.

But green and white tea have another benefit – they're excellent sources of catechins, potent antioxidants thought to prime the immune system to fight infection.

Add a teaspoon or two of honey to your tea. Studies conducted in children suggest it acts as a mild cough suppressant.

Chicken (and vegetable) soup. Your grandmother's advice to eat a bowl of chicken soup to ease cold symptoms wasn't misguided. A 2000 study from the University of Nebraska revealed that chicken soup reduced the activity of white blood cells that cause inflammation, a result that could ease the cold symptoms and shorten upper respiratory tract infections.

The soup studied wasn't your basic canned chicken soup, though. The remedy was made with chicken, onions, sweet potatoes, parsnips, turnips, carrots, celery stems, parsley and salt and pepper. It's thought that the combination of ingredients work together to have anti-inflammatory effects.

Zinc. Most studies, but not all, have found that taking zinc lozenges reduces the severity and duration of symptoms in adults. Zinc is thought to block rhinoviruses from replicating. (More than 200 viruses can cause colds; the rhinovirus is responsible for 30 per cent to 50 per cent of colds.)

Lozenges of zinc gluconate or zinc acetate should be taken every two to three hours while awake, starting within the first 24 to 48 hours of the onset of symptoms. Don't take more than 50 mg of zinc (five lozenges) a day. Zinc lozenges may cause a dry feeling and metallic taste in the mouth.

Vitamin C. The nutrient plays an important role in immune function and there's evidence that taking 2,000 mg of vitamin C a day, in divided doses, can reduce the duration of cold symptoms by 24 to 36 hours.

Vitamin C seems to be most effective in children, people under physical stress, and those who consume little vitamin C from their diet.

Vitamin D. A vitamin D supplement (1000 international units) should be part of your daily nutrition regime, whether you're sick or not. Beyond its benefits to bone health, vitamin D is also needed for a strong immune response.

Research has connected low blood levels of vitamin D to a greater risk of upper respiratory tract infections. A 2012 review of clinical trials also found that taking a vitamin D supplement significantly reduced the risk of such infections in children.

Most experts recommend 1000 IU (international units) of vitamin D each day for adults and 400 IU for children.

Leslie Beck, a registered dietitian, is based at the Medisys clinic in Toronto.