When sick, especially with a fever, the body burns more calories due to an increased metabolism as the immune system works to fight the illness. For each degree Celsius increase in body temperature, the body’s energy expenditure increases by about 10-13%, leading to higher calorie burn. Even without a fever, the immune response and inflammation cause a slight increase in calorie burn, though the effect is more modest. However, sickness often leads to reduced appetite, which combined with increased calorie use, can result in weight loss. Muscle breakdown can also increase during illness to meet energy demands, making it important to maintain nutrition, especially protein intake, while sick.
Why More Calories Are Burned When Sick
- Fever increases metabolism to fight infection.
- Immune system activation requires extra energy to produce immune cells.
- Inflammation from illness speeds up metabolism.
- Symptoms like coughing and sneezing add minor calorie burn.
- Reduced appetite and physical activity can create an energy deficit.
Effect of Illness Severity
- The amount of calories burned depends on illness severity and presence of fever.
- Short-term illnesses cause a slight increase in calorie burn.
- Long-term or severe illnesses may lead to muscle loss and changes in metabolism.
In summary, sickness increases calorie burning to some extent, especially with fever, but overall energy balance depends on appetite, activity level, and illness severity.
