By Mukaila Kareem
For many years, metabolic diseases have been explained mainly through laboratory numbers. High blood sugar defines diabetes. High cholesterol raises concern about heart disease. Abnormal thyroid tests suggest thyroid problems. Each condition appears to have its own marker and its own explanation. Physicians measure glucose, cholesterol, triglycerides, insulin, and hormones with increasing precision. These measurements are valuable and often lifesaving. But numbers alone can sometimes distract us from a simpler physiological question.
What is the body actually trying to do? To answer that question, it helps to step back and look at metabolism in its most basic form. Metabolism is not simply a collection of chemicals in the bloodstream. It is a continuous process of movement. Nutrients move through pathways, through cells, and through organs. Energy is transferred from one molecule to another. Carbon atoms are constantly entering and leaving metabolic pathways. Life depends on this constant motion thus reinforcing the fact that metabolism abhors stagnation.
Therefore, inside the body, nutrients are always moving. Glucose travels from the bloodstream into cells where it is used to produce energy. Fatty acids move from circulation into tissues where they are burned as fuel. Amino acids move into cells where they help build proteins and enzymes. Hormones move through the bloodstream delivering instructions that coordinate these activities. In a healthy system, this movement is continuous and coordinated. Nutrients are delivered, used for energy, stored when necessary, and cleared from circulation. Essentially, the body functions best when these processes move smoothly.
Problems begin when this movement slows or becomes mismatched with supply. When metabolic flow slows, substances begin to linger in the bloodstream. In type 2 diabetes, glucose remains elevated because tissues are not clearing it efficiently. Glucose is entering the bloodstream through food, but the pathways responsible for processing it are not keeping pace. The result is lingering glucose in circulation.
A similar pattern appears in heart disease. Lipid particles carry cholesterol and other fats through the bloodstream to deliver them to tissues that need them. But when lipid metabolism slows or becomes overwhelmed, these particles remain in circulation longer than they should. Over time, this increases the chance that cholesterol will accumulate within the walls of arteries. In hypothyroidism, the situation is slightly different but follows the same principle. Thyroid hormones normally help regulate the pace of metabolic reactions throughout the body. When thyroid hormone activity declines, metabolic reactions slow. Energy production becomes less efficient, and the overall pace of metabolism decreases.
Seen from this perspective, these conditions share a common feature. It is not simply that glucose or cholesterol numbers are abnormal. It is that metabolic flow has slowed or become disconnected from the body’s ability to process nutrients efficiently. Yet modern medicine often focuses on measuring the lingering signals rather than asking a deeper physiological question. Why did the metabolic flow slow in the first place?
Entire research fields have developed around these signals. Scientists study insulin resistance. Others specialize in lipid metabolism. Some physicians focus on obesity medicine. These disciplines have produced important discoveries and valuable treatments that have helped millions of patients. But sometimes they examine the traffic jam without asking what slowed the highway. To understand that highway, we must look at one of the most important drivers of metabolic flow in the human body.
Enters the skeletal organ. Skeletal muscle is the largest energy using organ in the body. Muscles require energy to contract. Every time a muscle fiber shortens during walking, lifting, climbing, or working, it consumes fuel. To meet this demand, muscle cells draw nutrients from the bloodstream. Glucose enters muscle cells and is used for energy. Fatty acids are oxidized inside mitochondria to produce ATP. Blood flow increases to deliver oxygen and remove metabolic byproducts. In this state, metabolism moves efficiently because tissues are actively demanding fuel.
For most of human history, daily life naturally created this demand. People walked long distances, gathered food, farmed, carried loads, and performed manual work. Movement was not considered exercise. It was simply part of living. In these conditions, the body’s largest energy consuming organ was active for many hours each day. However, modern environments have quietly changed this relationship. Today food is readily available in ways that would have been unimaginable in earlier times. At the same time, physical activity has declined in many daily routines. Work that once required physical effort is now performed while sitting. Transportation replaces walking. Machines perform tasks that once required muscle. As a result, nutrients continue to enter the system through regular meals and snacks even when muscular demand is low.
When movement declines but nutrient supply remains constant, metabolic traffic begins to slow. Glucose, lipids, and other metabolic signals start to accumulate in the bloodstream because the largest pathways for burning those nutrients are not fully engaged. This creates a paradox of modern life. Our ability to measure metabolic signals has become extremely precise. We can monitor blood glucose, cholesterol, insulin, and hormones with remarkable accuracy. Yet the simple physiological engine that helps keep these signals moving often receives far less attention. In the end, metabolism still follows a basic principle. It runs on flow, but when flow slows, metabolic signals begin to accumulate. However, when movement restores demand, metabolic pathways begin moving again.
Which brings us to a simple but important question. What is driving your metabolic bus?
Muscle or menu?
Mukaila Kareem, a doctor of physiotherapy and physical therapy advocate, writes from the USA and can be reached via makkareem5@gmail.com
