Do You Burn Extra Calories When Sick? A Nutritional Guide for Illness Recovery

October 9, 2025 •

5 min read

When fighting an infection, your body's energy demands skyrocket, with some studies showing a metabolic rate increase of 10-13% for every 1°C of fever. So, do you burn extra calories when sick? Yes, and understanding why is crucial for choosing the right nutrition diet to support your recovery.

Quick Summary

Being sick raises your metabolic rate as your immune system works harder. Fever and inflammation increase your calorie needs, making proper nutrition vital for recovery and energy.

Key Points

Metabolism Increases: Your basal metabolic rate (BMR) goes up when sick, especially with a fever, as the immune system requires more energy to fight infection.
Fever Fuels Calorie Burn: A fever raises your body temperature, which directly increases metabolism. For every 1°C increase, energy expenditure rises by approximately 10-13%.
Immune System is Energy Intensive: Immune cells demand a massive amount of energy to activate, proliferate, and produce inflammatory mediators, leading to increased calorie consumption.
Prioritize Hydration and Nutrition: Despite potential appetite loss, it's crucial to stay hydrated and eat small, frequent, nutrient-dense meals to prevent muscle breakdown and support healing.
Avoid Sugary and Greasy Foods: Processed foods high in sugar or fat can increase inflammation and are difficult to digest, hindering the recovery process.
Protein is Vital: Consuming enough protein from sources like lean meats, broths, and yogurt is important to preserve muscle mass, which can be broken down for energy during illness.

The Energetic Battle: Why Your Body Burns More Calories When Ill

When you're under the weather, your body is engaged in a complex and high-energy battle against invading pathogens. This heightened state of activity, known as "immunometabolism," demands a significant increase in energy, which is why your metabolic rate rises and you burn more calories. This calorie expenditure isn't a passive process but an active, necessary function to fuel your immune system's response.

The Immune System's High-Energy Demands

The immune system is a highly active and energy-intensive system. When it detects a threat, its cells, such as T cells and macrophages, must proliferate and function at a rapid pace. This process requires a metabolic shift, often favoring glycolysis to generate energy quickly, even though it's less efficient than other metabolic pathways. This is why you often feel fatigued—your body is prioritizing energy resources to combat the illness, diverting energy away from other activities. For example, the total energy demands of an activated immune system can account for 25–30% of your basal metabolism. This energy reallocation is a survival mechanism, ensuring the resources are available where they are needed most.

The Role of Fever and Inflammation

Two of the most common and energy-intensive responses to illness are fever and inflammation. A fever is a deliberate strategy by your body to fight infection by raising your core temperature. Many viruses and bacteria struggle to survive at higher temperatures. This increase in body temperature, in turn, accelerates your metabolic rate. Research indicates that for every 1°C increase in body temperature, your energy expenditure increases by approximately 10–13%. Inflammation also increases your energy needs. When your body is inflamed, it releases chemicals called cytokines, which help fight off the illness but also heighten your metabolic rate. This inflammatory response requires more calories to sustain the body's defense mechanisms effectively.

The "Sick Metabolism" and Muscle Breakdown

While your metabolism increases during illness, particularly with a fever, it's important to consider other factors. Illness often leads to reduced physical activity and increased bed rest, which decreases your overall daily calorie burn. For short-term illnesses, this is a minor effect. However, during prolonged or severe illness, especially if your appetite is suppressed, your body may start breaking down muscle for energy. This is why it's so important to eat enough, even if you don't feel like it, to prevent significant muscle loss and aid recovery. Consuming enough protein is especially crucial to preserve muscle mass.

The Old Adage Debunked: "Feed a Cold, Feed a Fever"

For generations, the wisdom of "feed a cold, starve a fever" has been passed down. However, modern medical science has debunked this advice, emphasizing that your body needs nutrients and energy to fight any illness. Restricting food during a fever deprives your immune system of the fuel it needs most to function effectively. A better approach is simply "feed a cold, feed a fever," focusing on nutritious and hydrating options.

What to Eat to Support Your Recovery: Key Nutrients and Food Choices

Choosing the right foods when you're sick is essential for a quicker and more comfortable recovery. Focus on nutrient-dense, easy-to-digest options.

Nutrient-Rich Foods for When You're Sick

Chicken Soup and Broths: These provide hydration, electrolytes, and are gentle on the digestive system. The warmth can also help with congestion. Chicken soup offers cysteine, an amino acid with antiviral effects.
Hydrating Fruits: Bananas, watermelons, and citrus fruits are easy to eat, provide fluids, and offer essential vitamins and minerals like potassium and Vitamin C.
Oatmeal: A bland, soft, and easy-to-digest source of calories, vitamins, and minerals. It can also aid digestion.
Yogurt and Fermented Foods: These contain probiotics, which support a healthy gut microbiome, and about 70% of the immune system resides in the gut.
Salmon: An excellent source of high-quality protein and omega-3 fatty acids, which have anti-inflammatory effects and support immune function.
Leafy Greens: Packed with vitamins, minerals, and antioxidants, leafy greens like spinach and kale help fight inflammation.
Ginger: Known for its anti-nausea effects, ginger can help soothe an upset stomach.
Garlic: Has been shown to have antibacterial, antiviral, and antifungal properties.

Foods to Avoid When You're Sick: Hindering Your Healing Process

Just as some foods can help, others can hinder your recovery. Avoid items that can increase inflammation, disrupt digestion, or cause dehydration.

Foods and Drinks to Limit

Sugary Foods and Drinks: While they offer a quick energy boost, added sugars can cause inflammation and suppress the immune system. This includes many traditional sick-day staples like sugary soda and candies.
Greasy and Fried Foods: These are difficult to digest and can worsen symptoms like nausea, indigestion, and diarrhea.
Alcohol: A dehydrating substance that can weaken the immune system and interfere with your sleep.
Caffeine: A stimulant and diuretic that can disrupt sleep and cause dehydration.
Spicy Foods: While they can help clear congestion for some, they can irritate a sensitive stomach, especially if you're nauseous.

Meal Timing and Hydration: Best Practices During Illness

Staying properly hydrated is perhaps the single most important aspect of nutrition when sick. Fevers, sweating, vomiting, or diarrhea can quickly lead to dehydration. Drink plenty of fluids like water, herbal teas, and broths. Electrolyte drinks or coconut water can be beneficial if you've been vomiting or have diarrhea. Instead of large meals, try eating small, frequent meals throughout the day. This is easier on your digestive system and helps maintain steady energy levels for the immune system to use.


Nutrient Focus	During Illness	During Health
Calorie Goal	Higher energy needs, often with reduced appetite. Focus on nutrient density rather than volume.	Balanced intake based on activity level. Focus is on maintaining weight and overall health.
Primary Goal	Fuel the immune system, prevent muscle loss, and maintain hydration.	Fuel daily activities, support muscle growth, and maintain overall wellness.
Protein Source	Easy-to-digest sources like broth, soups with shredded chicken, or soft fish. Key to preserve muscle mass.	Wide variety of sources to support muscle growth and repair, including red meat and legumes.
Hydration Needs	Critical to replenish fluids lost from fever, sweating, or vomiting. Electrolytes are paramount.	Consistent intake for basic bodily functions and metabolic processes.
Dietary Approach	Soft, bland, and easily digestible foods are often preferred due to reduced appetite and sensitive stomach.	Wide variety of foods, textures, and flavors for optimal nutrition.

Conclusion

In conclusion, your body does burn extra calories when sick, primarily driven by the intense energy demands of your immune system. While fever and inflammation contribute to a higher metabolic rate, the focus should not be on weight loss but rather on properly fueling your body for a swift and effective recovery. By prioritizing proper hydration, consuming nutrient-dense and easy-to-digest foods, and avoiding substances that hinder healing, you give your immune system the best chance to win the battle and get you back on your feet. For more detailed information on specific nutrients, you can consult reputable sources like the National Institutes of Health.

Frequently Asked Questions

Most illnesses that trigger an immune response, especially those involving a fever or inflammation, cause an increase in your body's metabolic rate and thus burn more calories. Milder illnesses like a common cold may cause a minor increase, while severe infections and fevers lead to a more significant rise.

The amount varies based on individual factors, but research shows that for every 1°C increase in body temperature, your energy expenditure increases by roughly 10-13%. This adds a notable number of calories to your daily burn, which is why fueling your body is so important.

Loss of appetite during illness is a natural response. Your body prioritizes energy to the immune system and reduces appetite, potentially as an evolutionary mechanism to conserve energy that would be used for digestion. Inflammation can also reduce appetite.

While a few days of reduced intake is generally fine, it is best to consume small, frequent meals of nutrient-dense food. Eating helps prevent muscle loss and gives your body the energy needed for recovery. Focus on easy-to-digest options like soups, broths, and soft fruits.

No, this is a myth. Both a cold and a fever require energy for your body to fight the illness. Restricting calories for either condition can weaken the immune response and delay recovery. It is important to stay hydrated and eat nutritious foods for both.

Focus on nutrient-dense, easy-to-digest foods that also aid hydration. Excellent choices include chicken soup, broths, hydrating fruits like bananas and watermelons, oatmeal, yogurt, lean proteins, and leafy greens.

Hydration is crucial for recovery because it helps replace fluids lost through fever, sweating, vomiting, or diarrhea. It also helps keep mucus membranes moist and allows your immune system to function optimally.

While your metabolic rate increases, any resulting weight loss is often undesirable, consisting of fluid loss and muscle breakdown rather than fat loss. Prioritizing recovery by providing your body with the necessary nutrients is far more important than focusing on calorie burning for weight loss.