By Mukaila Kareem
A calorie is a unit of energy, specifically a measure of how much stored energy exists in food. However, stored or potential energy is not the same as energy actively flowing through a living system. Much of modern nutrition conversation quietly treats these two ideas as if they were interchangeable, yet they are distinctly different and understanding that difference could gently encourage more movement in everyday life with cumulative metabolic health benefits.
When we eat, we introduce food substrates, which often include a mix of glucose, fats, and amino acids, into a dynamic biological engine. Each of these substrates carries stored possibilities that may either be transformed into movement and heat or remain in storage depending on how the body is being used. In physics, energy quantity and energy flow are not the same thing. Calories measure how much energy exists, while watts measure how fast energy is moving, and one watt simply means one joule of energy being used every second.
At rest, the body is never truly inactive. It quietly operates at roughly seventy to one hundred watts of power to sustain breathing, circulation, temperature regulation, and cellular function, which means energy is continuously flowing through the body whether one is exercising or not. When the body begins to move more frequently, such as walking between rooms, standing instead of sitting, carrying groceries, sweeping, climbing steps, or simply changing position throughout the day, the rate of energy flow rises above that resting baseline. In many cases it can double depending on the level of demand, not because new calories suddenly appeared, but because the existing energy is being moved through the system at a faster rate.
During brief periods of more intense effort, the rate of flow can climb even higher for short intervals before settling again. This reminds us that metabolism is not defined merely by how much energy we store, but by how dynamically that energy circulates through muscles, blood vessels, and organs. This distinction becomes clearer when we think of gathering yams and stacking firewood in the village. The quantity of yams harvested, and the amount of wood gathered tell us how much food could be prepared, yet no meal is cooked simply because ingredients are present unless the fire is lit and carefully tended.
In the human body, skeletal muscle functions much like that flame because it is the largest organ system we can voluntarily activate. When skeletal muscle contracts, it increases energy turnover, draws substrates into active use, enhances circulation, and contributes to the steady release of heat that naturally accompanies metabolic activity.
When regular movement is embedded in daily life, energy flow remains dynamic, heat is safely dispersed, and food substrates are more likely to be used rather than stored. When movement becomes scarce while food intake remains steady, stored energy is more likely to remain in reserve because demand has not meaningfully increased. None of this dismisses calorie science or denies that total energy intake matters over time. It simply reminds us that counting stored energy without understanding energy flow rate offers only part of the picture, because metabolism is not a static warehouse, but a living process shaped by motion.
Calories describe what food could become. Watts describe how quickly energy is being used. Health ultimately depends less on the size of stored energy and more on whether the quiet fire of regular mechanical effort, powered by skeletal muscle contraction, is consistently and gently burning.
Mukaila Kareem, a doctor of physiotherapy and physical therapy advocate, writes from the USA and can be reached via makkareem5@gmail.com
