The act of sitting down with a book or screen often leads to a common question: does this mental activity burn any meaningful amount of energy? The reality is that the human body never truly rests its energy consumption, and reading is no exception to this constant need for fuel. Understanding the true caloric cost of reading requires examining the body’s fundamental energy demands.
Understanding Resting Calorie Expenditure
The majority of calories burned during reading are simply the energy required to sustain life, a process measured by the metabolic rate. The basal metabolic rate (BMR) represents the absolute minimum energy expenditure needed to keep vital organs functioning if a person were completely immobile and fasted. Since BMR measurement requires strict clinical conditions, a more practical measure is the resting metabolic rate (RMR). The RMR accounts for the energy used while awake and at rest, supporting processes like breathing, blood circulation, and organ maintenance. When you are reading, the body is operating at this RMR baseline, which means the vast majority of calories burned are for non-reading-specific bodily functions.
The Specific Caloric Cost of Reading
To quantify the energy burned during an activity like reading, scientists use a system called the Metabolic Equivalent of Task (MET). One MET is defined as the energy expended while sitting quietly. Reading while sitting is assigned a MET value of approximately 1.3, placing it slightly above the baseline rest. This value means reading burns 1.3 times the energy expended during complete, quiet rest. To calculate the actual calories burned, you multiply the MET value by your body weight in kilograms, and then by the duration in hours. For example, a 70-kilogram (154-pound) person burns about 91 calories per hour while reading. Individual metabolic rate and body weight are the primary variables that affect this final hourly number.
How Brain Activity Affects Energy Use
Many people assume that intense mental effort, such as focusing on a complex novel, must significantly increase calorie expenditure. The brain is the most metabolically active organ, consuming about 20% of the body’s total energy, despite making up only about 2% of total body weight. This energy is derived almost exclusively from glucose, the body’s primary sugar source. However, the energy consumption of the brain remains remarkably constant across various states of consciousness. Studies show that the energy increase for a demanding mental task is often a negligible change, perhaps only a 1% to 5% increase against the high baseline.
Reading Compared to Other Sedentary Activities
Reading’s calorie burn is best understood in the context of other low-intensity activities, revealing minimal differences among various sedentary states. The 1.3 MET value for reading and desk work is comparable to other non-strenuous activities, such as sitting quietly without a specific task. In contrast, the energy expenditure while sleeping is the lowest, coming in at approximately 0.9 METs, as the body is in its deepest state of rest. Watching television is slightly higher, often measured at 1.0 METs, which is essentially the same as the definition of quiet rest. Therefore, reading burns only a marginally greater number of calories than sleeping, and is nearly identical to other forms of non-physical sitting.