There is often a feeling of disappointment at the end of a walk, a run, or what seems to be an eternity of a session on the treadmill. After all the huffing and puffing and sweating that genuinely feel as if we have done something substantial, we look at the calorie counter only to discover that the machine says we have burned about 250 calories for a whole hour.
This can be particularly discouraging because many people set out to exercise with the hope of burning calories. Burning only 250 calories can seem surprisingly small in a world where foods that can be eaten in only a few minutes may contain as many calories or considerably more. A donut can disappear before the coffee beside it has cooled, while a dessert containing even more calories can be eaten without much effort after a full meal. Understandably, someone looking at the treadmill after all that effort might wonder whether exercise is really accomplishing very much.
“You cannot outrun a bad diet” is one of the most popular sayings used to express the frustration many people feel in conversations about food, exercise, weight and health. It has been used by scientists, health professionals, news reporters and fitness experts, while social media personalities have turned it into graphics comparing foods with miles of running. Unsurprisingly, ordinary people have absorbed the same idea simply because the comparison appears to make so much common sense.
If a donut contains several hundred calories and running a mile appears to burn far less, the numbers seem to settle the matter before much physiology needs to be discussed. Eating is quick, but exercise requires time and effort, and the calorie number attached to food can easily overwhelm the number displayed on the treadmill after what feels like a substantial amount of movement. Once food and exercise have been placed beside each other in this way, it becomes almost inevitable that exercise will appear to be the weaker participant. Therefore, the familiar frustration of seeing only 250 calories after a long walk seems perfectly reasonable.
There is, however, something missing from comparing the energy expenditure of food and exercise. The comparison suspends the simple fact that the person about to step onto the treadmill is already very much alive and therefore did not begin from an energetic zero. Being alive is not an energetically neutral condition, because maintaining the organized biological state that makes exercise, eating, thinking, sleeping, and everything else possible requires a continuous expenditure of energy.
Before the shoes were tied and the treadmill was switched on, trillions of cells were already continuously at work, and all the physiological processes required to keep us alive were already underway. Physiologists describe this background energy expenditure using concepts such as basal metabolic rate and resting metabolic rate. The old Latin saying “first live, then philosophize” seems particularly appropriate here, because a dead person does not step onto a treadmill. What seems to happen when we talk specifically about exercise is that we often put this familiar knowledge on the shelf and construct a new visual and mental picture around what our measuring devices show us.
For example, when someone steps on the treadmill and presses START, the clock, distance and calorie counter begin at zero, after which the person watches all the numbers gradually climb until, after an hour of walking, the display reaches 250 calories. Does the 250-calorie display mean that this person’s energetic expenditure during that hour somehow began from zero simply because the machine’s counting did? Of course not! We have mentally substituted the machine’s zero-calorie starting point for the human starting point, utterly discounting the background energy expenditure of life that got us onto the treadmill in the first place. The zero belonged to the counter rather than to the human being. The treadmill went from an inactive state to an active one when it was switched on, but the human being did not undergo the same transition because the human organism arrived already operating.
Once the machine’s zero is separated from the human starting point, exercise is less like the beginning of energy expenditure and becomes the amplifier of an energetic process that was already underway. The resting body was already expending substantial energy to remain alive, and walking simply increased the demand placed on that living system as skeletal muscles began contracting and the rest of the body responded to support the additional work.
The language we use to describe the body’s background energetic activity may not help us fully appreciate the physiological processes of being alive. This energy expenditure is the difference between life and death, and yet we commonly refer to it as resting metabolism, which naturally creates an image of very little activity. Someone sitting in a chair may appear almost inactive from across the room, while someone sleeping in bed may appear to be doing even less, but external stillness tells us surprisingly little about the biological activity continuing beneath the surface. What looks like idling from the outside is an extraordinarily active state from the perspective of the living organism. Remarkably, idle is expensive. Life therefore arrives at exercise with an energy bill already being paid.
An idling engine provides an imperfect but useful analogy because it continues consuming fuel even while the vehicle remains stationary. Pressing the accelerator does not create fuel consumption from nothing but instead increases the operating rate of an engine that was already consuming fuel. The human body is vastly more complex than an engine, but the distinction between starting a system and amplifying the activity of a system that is already running helps us recover something that the treadmill display tends to hide. Therefore, when we begin walking, we are not switching the body from OFF to ON because life was already ON. In other words, we are moving from one physiological state of energetic demand to another.
This brings us back to the donut that disappeared before the coffee had cooled, because the donut did not arrive in a body that was starting from zero either. It entered the same living system with existing substantial background energy expenditure before consumption. This means that the familiar zero reference comparison between the calories in food and the exercise calorie counter removes the living organism from the middle, leaving us staring at two isolated numbers. The donut becomes several hundred calories eaten, the treadmill becomes 250 calories burned, and because the food number may be larger, exercise appears to have lost the contest.
This is where the familiar saying that “you cannot outrun a bad diet” becomes less helpful because it turns food and exercise into competitors simply because both can be expressed in calories. The ease with which food can be eaten and the effort required to exercise make the comparison even more persuasive, but the comparison also encourages us to judge movement by how successfully its calorie number cancels the calorie number attached to food.
The problem is that exercise was never merely the opposite side of eating. Food enters an already-living system, while exercise increases the energetic demand of that already-living system. Therefore, reducing both events to two calorie numbers leaves much of the physiology between them invisible. A donut may still contain more calories than the number displayed after a long walk, but that does not turn the walk into a failed attempt to catch the donut, because during that walk skeletal muscle contraction increased the operating demand placed on a body that was already spending substantial energy simply to remain alive.
This may also explain why food has become such a powerful part of our mental picture of weight and health, because food is remarkably easy to see, measure and manipulate. We can hold it in our hands, weigh it, photograph it, read the calories on its package, reduce the amount on the plate, or decide not to eat it at all, while the enormous increase in physiological activity that occurs when skeletal muscles begin contracting remains largely hidden from view. We see the donut entering the mouth and we see the 250 calories on the treadmill display, but we do not see the change in energetic throughput occurring inside the living system between those two visible events.
Bringing that organism back into the picture does not require us to make the 250 calories larger or to pretend that a long walk somehow erases whatever we choose to eat. It simply allows us to understand what exercise actually did. The body was already energetically active before the walk began, and exercise amplified that activity by increasing the demand placed on the living system for as long as the movement continued.
This is why the disappointment we felt when we first looked at the treadmill deserves another look. The machine showed 250 calories because that was the exercise session it had been asked to count, but the human being standing on it had arrived with the expensive energetic work of life already underway. Exercise did not start that process. It amplified it.
The next time we hear that a donut contains more calories than we can burn during a long walk, we should resist the temptation to ask which one won. The 250 calories displayed on the treadmill may still look meager beside the calorie number attached to food, but the comparison becomes very different once we remember that exercise did not begin from an energetic zero. It amplified the energetic activity of a living system that was already operating long before the first step was taken.
The treadmill needed a zero because it needed somewhere to begin counting, but the human being standing on it had no such beginning. The heart was already beating, trillions of cells were already at work, and the substantial energetic cost of remaining alive was already being paid before the machine was switched on.
The machine started at zero. We never did!
Mukaila Kareem is a doctor of physiotherapy and founder of metabolichealthliteracy.com
