The human body burns calories continuously, even during sleep, though the amount is significantly less than during waking hours. Calorie burn measures the energy expenditure necessary for the body to perform its fundamental functions. Sleep is not a state of metabolic shutdown; rather, it is a period of necessary energy use to maintain life and perform essential restorative processes. While you are at rest, your body still requires a steady supply of energy to keep its internal systems running smoothly.
The Energy Baseline: Understanding Resting Metabolic Rate
The energy expenditure during sleep is closely tied to the Resting Metabolic Rate (RMR). RMR is the total number of calories the body burns at rest to sustain basic functions, such as breathing, blood circulation, and brain activity. The term Basal Metabolic Rate (BMR) is similar, but it represents the absolute minimum energy required for survival under strict, clinically controlled conditions. RMR is a more practical measurement for estimating the calories burned during an average day’s rest, including sleep.
The body uses this resting energy for crucial “housekeeping” tasks that cannot be performed efficiently while awake. This includes cellular growth and repair, which is active during certain sleep stages to mend the wear and tear of the day. A significant portion of this energy is also devoted to the brain, which remains highly active, consolidating memories and clearing metabolic waste products. These constant functions ensure that metabolism never truly stops.
Calculating Calorie Expenditure During Sleep
The number of calories burned while sleeping is a direct reflection of your RMR, with a small reduction to account for the body’s subdued state. On average, a typical person burns approximately 0.4 to 0.5 calories per pound of body weight per hour during sleep. For example, a 150-pound adult equates to roughly 60 to 75 calories burned every hour. This rate results in an expenditure of about 480 to 600 calories over an eight-hour sleep period.
To estimate this more precisely, predictive formulas like the Mifflin-St Jeor or Harris-Benedict equations calculate a daily RMR based on weight, height, age, and sex. This daily RMR figure is then adjusted downward by about 10 to 15 percent to account for the reduced metabolic activity while sleeping. This adjustment reflects the body’s lower energy demand compared to the waking rest state. This sleep burn rate is dramatically lower than even light physical activity, such as walking slowly, which can burn two to three times as many calories per hour.
Physiological Factors That Influence Sleep Metabolism
An individual’s sleep metabolism is not static; it is influenced by several biological variables, primarily body composition. Muscle tissue is metabolically active even at rest, requiring more energy to maintain than fat tissue. Therefore, a person with a higher percentage of lean muscle mass will have a higher RMR and burn more calories during sleep than a person of the same weight with less muscle mass.
Age is another factor, as RMR decreases by 1 to 2 percent per decade after the age of 20, largely due to age-related muscle loss. Biological sex also plays a role, with males having a naturally higher RMR than females due to a greater average body size and a higher proportion of muscle mass. Hormonal differences contribute to these variations in resting energy needs.
The stages of sleep also cause fluctuations in the hourly calorie burn. During non-rapid eye movement (NREM) sleep, which includes the deepest, most restorative phases, heart rate, breathing, and body temperature all decrease, leading to the lowest metabolic rate of the 24-hour cycle. In contrast, Rapid Eye Movement (REM) sleep is characterized by high brain activity, similar to wakefulness, and an increased heart rate. This heightened neural activity requires more glucose, making REM sleep a phase where energy expenditure slightly increases compared to NREM sleep.
Actionable Steps to Optimize Your Resting Metabolic Rate
Since RMR is the primary determinant of calories burned during sleep, the most effective strategy for optimization is to increase your body’s baseline resting energy needs. Building lean muscle mass through resistance training is the most direct way to achieve this. Each pound of muscle tissue requires a consistent supply of calories to sustain itself, a need that continues around the clock.
Another strategy involves maintaining consistent sleep quality, which helps regulate metabolic hormones. Insufficient sleep can disrupt the balance of leptin (the hormone that signals fullness) and ghrelin (the hormone that signals hunger). When sleep is restricted, leptin levels drop while ghrelin levels rise, increasing appetite and leading to increased caloric intake the following day. Poor sleep also elevates cortisol, the stress hormone, which can promote fat storage, especially in the abdominal area.
Prioritizing sufficient, high-quality sleep stabilizes these hormonal signals, which supports a more efficient metabolism. Focusing on increasing muscle mass and ensuring restful sleep implements lifestyle changes that raise your body’s overall energy demands. These strategies effectively increase the number of calories your body burns, both during the day and while sleeping.