By Mukaila Kareem
My recent article, “Obesity Is Stalled Flow and Not a Failure of Willpower,” generated thoughtful responses from readers asking what “flow” really means and how metabolic health can be understood beyond diets and the latest longevity buzzword that have gained attention since COVID-19. The short answer is that walking is the main lever for metabolic health and not because it burns calories, but because it keeps energy moving through an open biological system.
I grew up in a village where lizards often lay still in the sun, and snakes could sometimes be seen stretched across the road on the way to the farm, seemingly “bathing” in the warmth. These are so-called ectothermic animals whose metabolism depends on external heat. Humans are different because we are endothermic. What this means is that we generate large amounts of heat internally from the food we consume, regardless of diet type. Whether one eats carbohydrates, fats, proteins, or some fashionable dietary combination, metabolism produces heat simply to keep us alive.
Apart from the fact that we produce enormous amounts of energy within, our metabolism operates as an open biological system. This means that the energy that enters the body must also move through and then exit back into the environment. We understand this instinctively when it comes to waste. When the bladder is full or the bowels are distended, pressure builds and we rush, sometimes shamelessly, to the nearest bathroom. That urgency is not a moral issue but biology in the public arena not playing nice with self-dignity. Matter accumulation demands release and there is no negotiating it, and as the saying goes, “when you have to go, you have to go”.
However, heat “waste” behaves differently but needs to be exported just like matter “waste”. Every second of life generates heat and if that heat were allowed to accumulate unchecked, normal physiology would fail from overeating. Therefore, the body must continuously move energy outward to maintain internal stability. Unlike urine or stool, heat does not create a sharp sensation of pressure that forces an obvious response like a mandatory run to the bathroom. Instead, its export depends largely on movement.
This is where walking and regular physical activity enter the story and not as exercise prescriptions or calorie-burning strategies but as the mechanism that maintains energy flow. In other words, walking keeps energy moving through the body, rather than letting it accumulate and get stored. In doing so, it often quiets hunger not through willpower but by restoring balance. However, when regular physical activity is reduced, the body adapts. Incoming energy is diverted into fat storage not out of excess or personal failure, but as a protective rerouting away from immediate heat production. Fat storage, however, contributes little to ongoing energy flow. The system still demands movement, and when flow remains inadequate the signal that emerges is hunger, even in the presence of abundant stored calories.
The question is if we have no choice about when we must urinate or defecate to eliminate metabolic waste, how do we manage the large amount of heat we generate every day while maintaining a normal body temperature? The answer is simple and uncomfortable, there is no substitute for regular physical activity. Intake must find an exit, and movement is the primary lever that creates that exit. Therefore, walking keeps energy flowing continuously, like a river, rather than allowing it to pool and stagnate.
Worldwide, obesity rates rise in societies where daily physical activity has been outsourced to energy-saving devices. Yet there are notable exceptions that help clarify the pattern. In the United States, the Amish community, who maintain an agrarian lifestyle with constant walking and physical labor, have obesity rates around 4 percent compared with roughly 40 percent in the general U.S. population. This difference is not driven by dieting, calorie counting, or metabolic optimization. It reflects continuous physical activity embedded into daily life.
In essence, maintaining heat flow through regular physical activity is as fundamental to an open biological system as maintaining matter flow through the bowel and bladder. This is why personal time-scheduled exercise programs lasting eight to twelve weeks, as well as short-term metabolic laboratory studies often fall short. They treat movement as an intervention to be applied temporarily, rather than as physiological infrastructure that must be continuous and inseparable from daily life.
Modern health discourse places overwhelming emphasis on dietary input as if the human body were a sealed container while neglecting energy flow. This oversight helps explain why weight is commonly regained after medications such as Ozempic are stopped.The issue is not personal failure or lack of discipline, but the biology of an open system in which reduced intake without restored flow cannot produce lasting metabolic stability.
Walking, then, is not a fitness trend or a health hack. It is the default condition under which human metabolism evolved. When walking becomes optional, metabolic health becomes fragile. When walking is restored as a daily necessity, energy flows, appetite stabilizes, and health follows, not by force or longevity buzzword but by physics.
Mukaila Kareem, a doctor of physiotherapy and physical therapy advocate, writes from the USA and can be reached via makkareem5@gmail.com
