Anxiety is a common human experience characterized by feelings of worry, nervousness, or unease. The body’s response to this psychological state involves a complex biological cascade that necessitates the use of energy. Anxiety does increase a person’s calorie expenditure, but the amount burned is generally small and insufficient to cause meaningful weight loss. The actual caloric impact depends heavily on the intensity and duration of the anxious state, ranging from a slight metabolic boost to a temporary spike during an acute episode.
Anxiety’s Immediate Metabolic Trigger
The physiological mechanism that increases calorie burn during anxiety begins with the activation of the hypothalamic-pituitary-adrenal (HPA) axis. This is the body’s primary system for managing stress, initiating a chain reaction that prepares the body for a perceived threat. The HPA axis prompts the adrenal glands to release stress hormones like adrenaline (epinephrine) and noradrenaline (norepinephrine).
These hormones are responsible for the immediate “fight or flight” response characteristic of acute anxiety. Adrenaline rapidly increases the heart rate and blood pressure, requiring the heart muscle to consume more energy. Respiration rate also accelerates, and muscle tension increases as the body mobilizes for action, all demanding an immediate increase in fuel consumption. The HPA axis also causes the release of cortisol, which signals the liver to break down stored energy reserves, providing the muscles and brain with immediate fuel.
Measuring Energy Expenditure Under Stress
The caloric expenditure from anxiety is directly related to the magnitude of the physiological response. An acute anxiety episode, such as a panic attack, causes a sharp, temporary spike in energy usage due to the intense, short-term work of the cardiovascular and muscular systems. For instance, a panic attack that significantly raises the heart rate for 15 to 20 minutes could burn an additional, though still small, number of calories compared to a resting state. This burst of energy mobilization is akin to a brief period of light physical activity.
Chronic anxiety, which involves sustained low-level worry, results in a slight but continuous elevation in the Resting Metabolic Rate (RMR) rather than a sharp spike. The body remains on a low-level alert, requiring slightly more energy to maintain the elevated baseline functions. While some studies suggest a modest percentage increase in RMR due to chronic stress, this increase is often negligible when measured against the total daily caloric output.
The Systemic Cost of Chronic Anxiety
While anxiety does technically burn calories, the long-term metabolic effects of chronic anxiety are detrimental to overall health and body composition. The constant activation of the HPA axis leads to sustained, elevated levels of cortisol in the bloodstream. This prolonged exposure to the stress hormone forces the body to prioritize immediate survival mechanisms over long-term metabolic health.
Sustained high cortisol levels significantly impair glucose regulation, causing the body’s cells to become less responsive to insulin, a condition known as insulin resistance. This disruption means that glucose struggles to enter the cells for energy, leading the pancreas to pump out even more insulin. The energy that is mobilized is often sourced through catabolism, the breakdown of muscle tissue, which can slow the RMR over time.
Paradoxically, this state of chronic metabolic stress often leads to increased fat storage, particularly in the abdominal area, known as visceral fat. Visceral fat cells possess a higher density of cortisol receptors compared to subcutaneous fat cells, making the midsection a preferential storage site. This type of fat accumulation is associated with a higher risk of cardiovascular disease and metabolic dysfunction. Therefore, the modest increase in acute calorie burn is overwhelmingly overshadowed by the negative physiological consequences.