The answer to whether you burn more calories when you have COVID-19 is yes; any acute infection significantly increases the body’s energy expenditure. This rise occurs because defending against a virus is an energetically demanding process that temporarily elevates the Basal Metabolic Rate (BMR). The common feeling of lethargy or fatigue, often referred to as “sickness behavior,” is the body’s way of conserving energy to redirect it to the immune response.
The Biological Mechanism of Increased Energy Expenditure
The heightened calorie burn during illness is primarily driven by fever and the systemic immune response. The body shifts into a state of hypermetabolism, where the metabolic rate is elevated above normal resting levels. This state can increase energy expenditure ranging from 10% to 30% or more, depending on the severity of the infection.
Raising the core body temperature to create a fever is an energy-intensive task. For every one-degree Celsius rise in body temperature, the metabolic rate increases by approximately 10% to 12.5%. This process requires constant muscle activity, sometimes manifesting as shivering, to maintain the higher temperature set point.
The immune system consumes vast energy to mount an effective defense. Immune cells must be rapidly mobilized and activated to destroy the invading virus. This requires the synthesis of new proteins, antibodies, and signaling molecules like cytokines, the chemical messengers of the inflammatory response.
This intense demand prioritizes energy delivery to defense systems. If caloric intake is insufficient, the hypermetabolic state often leads to the breakdown of stored energy, including muscle protein catabolism.
COVID-19 and Specific Metabolic Demands
The metabolic demands of a COVID-19 infection relate directly to the severity of the illness and the resulting inflammatory response. In mild cases, energy expenditure resembles a severe cold, driven by fever and initial immune mobilization. The hypermetabolic state is relatively short-lived and less pronounced.
In severe cases requiring hospitalization, systemic inflammation and metabolic demands are greater and more sustained. Severe COVID-19 is associated with a distinct metabolic profile, characterized by alterations in circulating metabolites like glucose, lactate, and amino acids. These changes reflect the body’s attempt to fuel the prolonged immune activity.
Persistent production of inflammatory cytokines sustains the hypermetabolic state for a longer duration. Patients with severe respiratory involvement face an additional energy burden from increased work of breathing. Respiratory muscles must work harder to maintain oxygen levels, further elevating calorie expenditure.
This prolonged hypermetabolism, especially in critically ill patients, leads to significant catabolism and rapid loss of lean body mass. Muscle tissue breakdown provides necessary amino acids and glucose to fuel the immune response, contributing to the muscle weakness seen in recovery.
Supporting the Body: Nutritional Needs During Acute Illness
Supporting the body with adequate nutrition is paramount during the acute phase of COVID-19 to prevent muscle wasting and aid recovery. Sufficient fuel is needed to meet the demands of the hypermetabolic state. Consuming enough calories prevents the body from breaking down muscle and fat stores for energy.
Maintaining adequate hydration is crucial, as fever and increased metabolic activity lead to greater fluid loss. Increased fluid intake prevents dehydration, which can compound the feeling of sickness and stress the body.
Protein intake is important because the immune system relies on amino acids for the rapid synthesis of immune cells, antibodies, and tissue repair. Individuals recovering at home should focus on consistently consuming protein-rich foods to minimize muscle breakdown and support the rebuilding phase.
Supporting the body’s overall nutritional status is beneficial. Micronutrients like Vitamin D and Zinc play roles in immune function and should be consumed at adequate levels to ensure the immune system has the necessary components to operate effectively. Focusing on a nutrient-dense diet helps sustain the energy-intensive processes of fighting the infection and preparing the body for recovery.