Even when the body is completely still during sleep, it continues to burn energy to sustain life. This energy expenditure fuels the body’s essential, non-stop internal operations. The exact number of calories burned during an eight-hour sleep period is highly individualized, meaning the amount varies significantly from one person to the next.
How to Estimate Your Sleep Calorie Burn
The total number of calories burned during an eight-hour sleep session generally falls within a predictable range, typically between 320 and 600 calories for the average adult. This approximation is based on the fact that an individual burns roughly 40 to 75 calories per hour while sleeping, with the number largely dictated by body weight and composition.
A simple way to estimate this is to use an approximation of 0.42 to 0.5 calories per pound of body weight per hour. For example, a 150-pound person would burn approximately 504 to 600 calories over eight hours. This calculation provides a generalized baseline, as heavier individuals require more energy to maintain their larger body mass. However, this method does not account for many underlying physiological factors.
The Role of Basal Metabolic Rate
The energy expenditure that occurs during sleep is directly related to the Basal Metabolic Rate (BMR), which represents the minimum amount of energy needed to keep the body functioning at complete rest. BMR accounts for around 80% of the body’s total daily calorie usage, even while a person is physically inactive. During sleep, the body’s metabolic rate slows down, often dropping to 85% to 95% of the daytime resting rate.
Energy consumption fuels involuntary processes that sustain life, including the constant circulation of blood, breathing, and maintaining a stable core body temperature. Cellular activities, such as tissue repair, cell growth, and nerve function, also demand energy throughout the night.
The brain is a significant energy consumer, and its activity varies across the different sleep stages. During non-rapid eye movement (NREM) sleep, especially in the deep sleep stages, both heart rate and brain activity slow down, leading to a lower metabolic rate. Conversely, the rapid eye movement (REM) stage, associated with dreaming, is highly energy-intensive. During REM sleep, the brain’s glucose metabolism increases, and its overall energy use can equal or even exceed the energy consumption seen during wakefulness.
What Makes the Number Change
Several biological and environmental factors cause an individual’s actual sleep calorie burn to deviate from the average range. Body weight is a major determinant, as larger bodies possess more tissue that requires energy for maintenance. This means that a person with a higher body weight will naturally have a higher BMR and, consequently, burn more calories during sleep than a lighter person.
Age also plays a role, with metabolism tending to decrease as a person gets older. This reduction is often attributed to a gradual loss of muscle mass, which is metabolically more active than fat tissue. The amount of time spent in each sleep stage modifies the rate, particularly the duration of REM sleep, which, as the most metabolically active stage, burns the most calories.
Environmental factors, such as bedroom temperature, can also influence the number. Sleeping in a slightly cooler environment may cause the body to expend a small amount of extra energy to maintain its core temperature, marginally increasing the calorie burn. Underlying medical conditions or sleep disorders, like sleep apnea, can disrupt the normal metabolic rate, sometimes leading to increased energy expenditure as the body works harder to breathe.