How Many Calories Do You Burn When You Are Sick

Ever stepped on the scale after a week of being bedridden and wondered, “Did I actually burn calories while I was sick—or just lose water?” If you’ve had a fever, nonstop coughing, or stomach bugs, it’s natural to wonder how illness affects your calorie burn, body composition, and fitness progress.

In this article you’ll get clear, practical answers about how many calories you burn when you are sick, real-world examples and calculations, safe workout variations, nutrition tips to preserve muscle and recover faster, and guidance on when to rest versus when to move.

What happens to your calorie burn when illness hits?

Illness can change your energy expenditure in two opposite ways:

• Increased metabolic rate from fever and immune activation (you may burn more calories at rest).
• Decreased total daily calorie burn because you are less active (sitting or lying down more).

Which effect “wins” depends on the type and severity of the illness. An upper respiratory cold without fever might change your calorie burn very little, while a feverish flu can raise your resting metabolic rate substantially.

How fevers affect calorie expenditure

Fever is the biggest single driver of increased calorie burn during sickness. A commonly used rule of thumb: for each 1°C (1.8°F) increase in body temperature, resting metabolic rate increases by about 10–13%. That means:

• If your BMR is 1,500 calories and you develop a 2°C fever, your resting calories could rise by roughly 20–26% → 1,800–1,890 kcal/day.
• That’s about 300–390 extra calories burned per day at rest.

Real-world example: Anna usually burns 1,600 calories at rest. She catches the flu and spikes a 2°C fever. Her resting energy expenditure increases to about 1,920–1,952 calories—roughly 320–350 extra calories just from the fever, not counting any activity.

Other symptoms and calorie loss

Coughing, shivering, and repair processes also require energy. Severe infections trigger immune system activity (cytokines, white blood cell production) that raises energy needs modestly. On the flip side, if you’re too weak to move, your total daily energy expenditure (TDEE) may drop because you’re burning fewer activity calories.

How many calories do you burn when you are sick: practical calculations

To estimate your calorie burn while sick, follow these steps:

1. Estimate your normal BMR (use a standard BMR calculator or 1,400–1,800 kcal/day for many adults).
2. Add activity calories (your usual TDEE minus BMR).
3. If you have a fever, multiply BMR by the increase percentage: ~10–13% per 1°C (1.8°F).
4. Subtract activity calories you’re not doing because of rest.

Example: Ben has a TDEE of 2,400 kcal (BMR 1,700 + 700 activity). With a 1.5°C fever, his BMR rises by ~20% → 1,700 × 1.20 = 2,040. If he’s resting and cutting activity to 150 kcal/day, his TDEE while sick becomes ~2,190 kcal. Compared to his normal 2,400 kcal, he’s burning ~210 fewer calories despite the fever bump.

Practical fitness tips while you’re ill

When you’re sick, the priority is recovery. But small, smart actions can protect your fitness and speed recovery.

When to rest vs when to move

• Rest: Fever, body-wide muscle aches, chest congestion, shortness of breath, vomiting, or diarrhea → avoid workouts.
• Light movement: Mild cold symptoms above the neck (runny nose, sore throat) without fever → short walks, gentle yoga, mobility work are okay.

Safe workout variations

• 15–20 minute gentle walks — improve circulation without taxing your immune system.
• Mobility and stretching sessions — maintain range of motion and reduce stiffness.
• Low-intensity bodyweight circuits (if symptoms are mild): one or two rounds of push-ups, air squats, and core work; stop if you feel worse.

Tip: Keep sessions short and monitor symptoms. If you get winded more than usual or recovery takes longer, stop and rest.

Nutrition and lifestyle advice to support recovery

Eating well and managing hydration are as important as rest when you’re sick:

• Prioritize protein (20–30 g per meal if possible) to preserve muscle and support immune function.
• Hydrate often — fever and diarrhea deplete fluids and electrolytes; oral rehydration, broths, and electrolyte drinks help.
• Choose nutrient-dense, easy-to-digest foods: soups, smoothies, yogurt, bananas, rice, lean proteins.
• Sleep and stress management are crucial — aim for extra rest and avoid intense mental or physical stressors.

Real-world example: After a week with gastroenteritis, Mark focused on small, protein-rich meals, electrolytes, and gradual reintroduction of walking. He preserved muscle better and returned to training quicker than a past illness when he restricted calories too much.

Protecting muscle and fitness during illness

Significant calorie deficits during extended illness can cost muscle mass more than fat. To minimize losses:

• Aim for adequate protein (1.2–2.0 g/kg if you can tolerate food).
• Resume resistance training gradually as symptoms improve.
• Consider short, light resistance sessions (band work, bodyweight) once fever and major symptoms resolve.

Even when you lose a little weight from being sick, much of the immediate drop is water and glycogen. Rehydration and normal eating often restore weight quickly; sustainable fat loss is unlikely from a short illness.

Frequently Asked Questions

1. Will I lose fat if I’m sick and eat less?

Short-term reduced intake during illness usually leads to water and glycogen loss, not meaningful fat loss. Prolonged calorie deficit can cause fat loss but also muscle loss. Focus on recovery and muscle-preserving protein intake.

2. Can I exercise with a cold?

If symptoms are above the neck (runny nose, mild sore throat) and no fever, light-to-moderate exercise is generally safe—reduce intensity and duration. If you have fever, chest congestion, or systemic symptoms, skip workouts until you recover.

3. How long after a fever can I return to normal workouts?

Wait at least 24–48 hours after a fever subsides before resuming normal training. Start with low-intensity sessions and build back over several days, monitoring for fatigue or symptom return.

Conclusion — How many calories do you burn when you are sick and what should you do?

How many calories do you burn when you are sick depends on the illness: fevers and immune activation raise resting calorie burn, but reduced activity often lowers total daily energy expenditure. Short illnesses rarely produce meaningful fat loss; your focus should be on rest, hydration, adequate protein, and a cautious return to movement.

Ready to build a gentle return-to-training plan or learn what to eat during recovery? Check our workout routines, dive into practical tips in our nutrition guides, or get daily recovery habits from our wellness tips to help you bounce back stronger.

Have a recovery story or a question about your specific situation? Leave a comment or subscribe for weekly health and fitness guides to help you train smarter—especially when life (and illness) gets in the way.