How Many Extra Calories When Sick? A Nutritional Guide

October 12, 2025 •

4 min read

When you're sick, your body's immune system is in overdrive, burning extra calories to fight off infection. This raises the common question: How many extra calories when sick? The answer is more nuanced than a single number, depending on the severity of your illness, but understanding your body's energy demands is a key step toward a faster recovery.

Quick Summary

During an illness, your body's metabolism increases to combat infection, raising caloric and nutrient needs. Adequate consumption of calories and protein, along with proper hydration, is critical for supporting the immune system, preventing muscle breakdown, and ensuring a quicker recovery, even when appetite is reduced.

Key Points

Metabolism Increases During Illness: Your body's metabolic rate rises to fight infection, requiring more energy (calories) than normal.
Fever Significantly Boosts Calorie Needs: For every 1°C increase in body temperature, energy expenditure can increase by 10-13%.
Increased Protein is Crucial: Higher protein intake is needed to prevent muscle breakdown and support immune cell production.
Hydration is Key: Staying well-hydrated is essential, especially with fever, to regulate temperature and replace lost fluids and electrolytes.
Small, Frequent Meals Work Best: When appetite is low, eating small, nutrient-dense meals throughout the day is more effective than forcing large ones.
Focus on Nutrient Density: Prioritize nutrient-rich foods like soups, smoothies, and fortified meals to maximize the nutritional benefits of every bite.
Avoid Dieting During Recovery: Restricting calories while sick can hinder your body's healing process and prolong recovery.
Listen to Your Body: Pay attention to your appetite and cravings, but choose nutritious options that are easy to digest to aid your body's natural healing process.

The Immune System's Energy Demands

When you fall ill, your body shifts its resources to prioritize fighting the invading pathogens. This intense immune response is a highly metabolic process that requires a significant increase in energy, which comes from calories. Think of your immune system as a hard-working army; it needs fuel to operate effectively. Without adequate energy, your body may resort to breaking down muscle tissue to meet its energy demands, a process known as catabolism. This can weaken your body and prolong the recovery process.

The Fever Factor: Calorie Needs with Elevated Temperature

One of the most significant factors influencing your caloric needs is a fever. A fever is not an enemy to be feared but rather a natural defense mechanism that makes it harder for pathogens to survive. However, this defense comes at an energy cost. For every increase of 1° Celsius (or approximately 1.8° Fahrenheit) in body temperature, your basal metabolic rate (BMR) can increase by roughly 10-13%.

To put this into perspective, a person with a persistent fever of 101°F (38.3°C) could see their caloric needs jump by as much as 20% compared to their normal resting metabolic rate. While it is not recommended to use fever as a weight-loss tool, acknowledging this increased energy demand is crucial for nourishing your body through recovery.

Hydration and Micronutrients: More Than Just Calories

Beyond a simple calorie count, proper nutrition during illness involves a focus on fluids and micronutrients. A fever can increase fluid loss through sweating, and vomiting or diarrhea can further exacerbate dehydration. Replenishing electrolytes lost during illness is vital. Micronutrients like vitamins A, C, D, and zinc are rapidly depleted during the immune response and are essential for its proper functioning. Relying solely on calorie-rich junk food can impede recovery by causing inflammation and failing to provide these crucial nutrients.

Strategies for Meeting Caloric Needs with Low Appetite

One of the main challenges when sick is a reduced appetite. Symptoms like nausea, congestion, and fatigue can make eating a chore. Instead of forcing large meals, focus on making your intake as nutrient- and calorie-dense as possible throughout the day.

Small, Frequent Meals: Opt for 5-6 smaller meals or snacks rather than three large ones to make eating more manageable and less daunting.
Liquid Nutrition: If solid food is unappealing, liquid calories from nutrient-rich smoothies, broths, and nutritional shakes are an excellent way to get energy and essential nutrients. Adding protein powder, avocado, or nut butter to a smoothie can significantly increase its caloric density.
Easy-to-Digest Foods: Plain, soft foods like bananas, rice, toast, and scrambled eggs are often well-tolerated when your stomach is sensitive. Chicken soup is a classic for a reason; it offers hydration, electrolytes, and easy-to-digest protein.
Fortify Your Food: Incorporate extra calories into your meals without adding bulk. Add cheese to scrambled eggs, butter to toast, or a spoonful of cream to soup.

Nutritional Needs: Healthy vs. Ill


Nutritional Aspect	Healthy Individual	Mild Illness (e.g., Cold)	Severe Illness (e.g., High Fever, Infection)
Caloric Need	Varies by age, sex, activity level	Slightly increased to support immune function	Significantly increased by 20-60%
Protein Need	0.8g/kg body weight/day	Slightly elevated to aid tissue repair	As much as 1.2-2.0g/kg body weight/day
Hydration Need	Standard 2.7-3.7 liters/day	Increased to address fluid loss from sweating	Crucial for temperature regulation and replacing lost electrolytes
Nutrient Focus	Balanced diet for maintenance	Focus on immune-supporting vitamins (C, D, Zinc)	High emphasis on nutrient-dense foods to prevent deficiency
Appetite	Normal	May be suppressed; focus on small, nutrient-dense foods	Often significantly reduced; prioritize liquid calories

Sample Meal and Snack Ideas

Breakfast

Oatmeal with Fortified Milk: Cook oatmeal with whole milk and stir in a spoonful of honey for extra calories. Top with sliced banana and a sprinkle of cinnamon.
Scrambled Eggs with Avocado and Cheese: A protein and fat-rich meal that's easy on the stomach. Add shredded cheese for extra calories and flavor.
Nutrient-Dense Smoothie: Blend whole milk, a scoop of protein powder, a handful of spinach, half an avocado, and a banana. This is packed with calories and vitamins.

Lunch/Dinner

Chicken Noodle Soup: A classic for a reason, providing hydration, electrolytes, protein, and carbohydrates.
Mashed Potatoes: Made with butter and fortified milk, this is an easy-to-digest, energy-rich food. Add grated cheese or cream for more calories.
Soft Fish with Vegetables: Poached or baked fish is easy to chew and digest. Pair with soft-cooked vegetables like carrots or sweet potatoes.

Snacks and Desserts

Yogurt or Pudding: Full-fat Greek yogurt is a protein-dense option. Adding honey or cream makes it more caloric.
Crackers with Nut Butter: Simple carbohydrates with protein and fat provide sustained energy.
Ice Pops or Gelatin: These can be soothing for a sore throat and offer light calories and hydration.

Conclusion: Focus on Healing, Not Calorie Counting

The question of how many extra calories when sick doesn't have a one-size-fits-all answer. Your body's needs are dynamic and depend on the illness's severity, particularly the presence of fever. The most important takeaway is not to focus on strict numbers, but to listen to your body and prioritize nutrient-rich foods and consistent hydration. Eating small, frequent meals of easy-to-digest proteins and complex carbohydrates will provide the fuel your immune system needs to do its job, helping you recover faster and preserving muscle mass in the process. For severe or prolonged illness, consulting a healthcare provider or a registered dietitian is always the best course of action.

For more information on nutritional strategies during illness, MedlinePlus offers comprehensive resources on managing appetite and increasing caloric intake.

Frequently Asked Questions

Yes, your body requires more energy when sick because your immune system works in overdrive to fight infection. This heightened immune activity, along with symptoms like fever, increases your metabolic rate and burns extra calories.

The amount varies, but energy expenditure increases by approximately 10-13% for every 1°C (1.8°F) rise in body temperature. For example, a persistent 101°F fever could increase your total daily calorie needs by around 20%.

If you have a reduced appetite, focus on consuming smaller, more frequent meals throughout the day. Nutrient-dense options like smoothies, soups, and broths are excellent liquid sources of calories and nutrients that are often easier to tolerate.

This is a myth. The body needs nourishment to fight any illness, whether it comes with a fever or not. Starving yourself can deplete energy reserves and potentially prolong recovery.

Protein is crucial during illness to prevent muscle tissue breakdown, a process called catabolism. It also provides the building blocks for immune cells and antibodies, making it vital for a robust immune response.

You can add calories to foods without increasing bulk by using full-fat dairy products like milk or cream in soups, adding butter or margarine to potatoes and toast, or mixing in protein powder to smoothies.

Sports drinks can help replenish lost electrolytes if you are experiencing vomiting, diarrhea, or fever-induced sweating. However, many are high in sugar. Oral rehydration solutions are a better choice, or you can opt for healthier fluids like bone broth or coconut water.

Yes, it is possible to lose weight when sick due to decreased appetite and increased metabolism. However, this weight loss is often from a loss of muscle mass rather than fat, which is not ideal for health. It's best to focus on nourishing your body back to health rather than dieting.