Is it better to eat or fast when you have a virus?

December 19, 2025 •

4 min read

While the centuries-old saying "feed a cold, starve a fever" persists, modern medical understanding reveals it's not entirely accurate for viral infections. The nuanced relationship between nutrition and the immune system suggests the best approach depends less on the specific illness and more on what your body needs to fight off the virus.

Quick Summary

Modern science debunks the 'feed a cold, starve a fever' myth, revealing the complex relationship between eating, fasting, and the immune system during a viral infection. Staying hydrated and providing your body with necessary nutrients and energy are generally recommended for recovery.

Key Points

Debunking the Adage: The old myth "feed a cold, starve a fever" is not supported by modern science; your body needs fuel to fight any viral infection.
Prioritize Hydration: Staying well-hydrated is the most critical aspect of managing a viral illness, especially if you have a fever.
Fuel Your Immune System: Eating nutritious, easily digestible foods provides the energy and nutrients your immune system needs to function optimally.
Listen to Your Appetite: It's okay not to force yourself to eat full meals if you aren't hungry, but focus on getting fluids and small, bland food portions when you can.
Avoid Intentional Fasting: Fasting can deplete your body's energy and essential nutrients, potentially hindering your recovery and increasing the risk of dehydration.
Seek Professional Advice: For persistent or severe symptoms, or if your appetite does not return, consult a healthcare provider for guidance.

Decoding the 'Feed a Cold, Starve a Fever' Myth

The enduring phrase "feed a cold, starve a fever" dates back centuries, but advances in science reveal a more complex picture of the body's response to viral infections. While a loss of appetite is a common response to being unwell, the blanket advice to fast during a fever can be counterproductive. The modern medical consensus emphasizes providing the body with the fluids and energy it needs to power a robust immune response, regardless of whether a fever is present.

The Immune System's Energy Demands

When your body is fighting a virus, its energy requirements increase significantly. A fever, for instance, elevates your metabolic rate, causing you to burn more calories. Depriving your body of this much-needed fuel can hinder your immune system's ability to mobilize and function effectively. Conversely, consuming nutrient-dense foods gives your body the resources it needs to produce immune cells, fight off pathogens, and repair damaged tissue.

The Critical Role of Hydration

Whether you have a cold or a fever, adequate fluid intake is non-negotiable. Fever, vomiting, and diarrhea can all lead to dehydration, which further weakens the body's ability to fight infection. Dehydration can exacerbate symptoms like headaches and fatigue, making recovery longer and more difficult. Fluids also help moisten the respiratory tract, helping to clear mucus and soothe sore throats.

Fasting vs. Eating with a Virus: A Deeper Look

The Case for Eating (When You Feel Like It)

Replenishes Energy Stores: Eating provides glucose, the primary fuel for your cells, including the energy-hungry immune cells working to combat the infection.
Provides Essential Nutrients: Food delivers critical vitamins (like C and D), minerals (like zinc and iron), and proteins that directly support immune function.
Supports Cellular Repair: The amino acids from protein are vital for building and repairing tissues damaged during the immune response.
Boosts Mood and Comfort: Simple comfort foods like warm soup can have a soothing psychological effect, which supports overall well-being during illness.

The Nuance of Fasting

While prolonged fasting can offer some health benefits when healthy, the research on its effect during an active viral infection is complex and debated. Some studies in animal models suggest that fasting might help the body tolerate bacterial infections by producing ketones, while eating may be better for viral infections by providing glucose. Other research indicates that short periods of fasting could potentially support some aspects of immune function, such as autophagy (cellular renewal), but the overall effect on an active viral illness is not yet fully understood.

It's important to note that many studies on fasting during illness are conducted in animals and may not directly translate to humans. Additionally, fasting during a viral infection can carry risks, including low blood sugar, severe fatigue, and nutrient deficiency. Given the energy demands of fighting a virus, most medical professionals advise against intentional fasting.

Comparison Table: Eating vs. Fasting During a Viral Infection


Feature	Eating While Sick	Fasting While Sick
Energy Supply	Provides direct glucose and calories for immune function and increased metabolism, especially with fever.	Depletes available glucose, potentially forcing the body to rely on ketones, which may not be ideal for fighting viral pathogens.
Nutrient Intake	Ensures a steady supply of vitamins, minerals, and protein crucial for immune cell production and function.	Can lead to nutrient deficiencies that weaken the immune system and prolong recovery.
Immune Support	Directly supports the energy-intensive process of producing and deploying immune cells.	Complex and debated. Some theories suggest potential benefits like autophagy, but the overall effect on an active viral infection is not well understood.
Hydration Status	Often encourages fluid intake via soups, broths, and juices, helping to prevent dehydration.	Can increase the risk of dehydration, especially with a fever, vomiting, or diarrhea.
Associated Risks	Low risk, provided healthy foods are chosen. Overeating can lead to discomfort but is generally not harmful.	Potential risks include low blood sugar, prolonged fatigue, nutrient deficiency, and reduced immune function.

The Best Approach: Listen to Your Body

The most practical and safest advice is to listen to your body's signals. Loss of appetite is a natural symptom of illness, and there's no need to force yourself to eat full meals if you aren't hungry. However, intentionally starving yourself or avoiding all food is generally not recommended.

Prioritize Fluids: Focus on staying well-hydrated with water, broths, and electrolyte-rich drinks. Herbal teas can also provide comfort and hydration.
Eat Small, Bland Meals: When your appetite returns, opt for easy-to-digest foods. Broths, plain toast, crackers, bananas, and rice are good choices.
Embrace Nutrients: Incorporate foods high in vitamin C (citrus, berries), zinc (nuts, seeds), and protein (lean chicken, yogurt) to aid your immune system.
Rest: Remember that rest is arguably the most critical component of recovery. Using the energy saved by not preparing large meals can be better directed toward healing.

Conclusion

While the concept of fasting during a viral illness may seem appealing to some, it is not a medically supported strategy. In most cases, the body needs a consistent supply of nutrients and energy to fuel the immune system and repair itself. Relying on the old adage of starving a fever is not just inaccurate but potentially harmful, especially due to the risk of dehydration. The safest and most effective strategy is to prioritize hydration and consume a balanced, nutrient-rich diet as your appetite allows. When in doubt, always consult a healthcare professional for personalized medical advice.

Note: This article is for informational purposes only and does not constitute medical advice. Consult with a doctor or other qualified health professional for any medical concerns.

YaleNews research on the effects of fasting and eating on different types of infections provides a scientific look into the body's metabolic responses to illness.

Frequently Asked Questions

No, you should not force yourself to eat large meals if you have no appetite. It is more important to focus on staying hydrated with fluids like water, broth, or tea. When you start feeling hungry, you can begin with small, bland, easily digestible foods.

Eating provides your body with the energy (calories) and essential nutrients it needs to fuel your immune system. Your metabolism increases when you have a fever, so consuming food helps replenish that lost energy to support the fight against the virus.

Intentionally fasting while sick with a virus can lead to dehydration, fatigue, and a weakened immune response due to a lack of necessary calories and nutrients. The body needs fuel to fight the infection effectively.

Some studies, often in animal models, suggest that fasting might have different effects on bacterial versus viral infections. For instance, it may help with certain bacterial infections but not necessarily viral ones. The overall effect on an active viral infection is not fully understood, and intentional fasting during illness is not medically recommended for humans.

Water is always a great choice. Other good options include clear broths, herbal tea, and electrolyte-rich beverages. These fluids help prevent dehydration and can help soothe a sore throat or clear mucus.

When your appetite returns, opt for gentle foods like broths, bananas, rice, and toast. Foods rich in Vitamin C (citrus, berries) and zinc (yogurt, nuts) can also support your immune system.

While milk doesn't cause phlegm, some people find that dairy can temporarily increase mucus production and worsen congestion. It's often recommended to reduce dairy if you feel congested, but it is not harmful.