Insulin Metabolism
Insulin is perhaps the most well-known of all hormones, and in the halls of health, fitness and fat loss it is mostly maligned and drastically misunderstood. As with many things in health and fitness there is more to the simple story told about insulin.
Insulin Basics
Insulin functions very much like your hands when you are eating. Just as it would be extremely difficult to eat without hands, insulin fees the tissue of the body in the same way. Insulin is required to facilitate nutrient uptake in the cells. Without insulin, your cells would literally starve and die.
Insulin is made in the beta cells of the pancreas and is released into the bloodstream in response to food. It assures these nutrients get into the cell. Insulin’s primary job is to make sure the cells have enough glucose, and therefore it has a strong impact on blood sugar levels.
In fact, glucose is the primary stimulator of insulin release. In response to food and/or stress blood glucose levels will rise. And, as a result of that, insulin is used to balance things back out.
The body can only operate in a very narrow range of blood sugar. Glucose acts as a chief cellular fuel, but it can also do damage to tissues if left sitting around in the blood in high amounts. By the same token you don’t’ want blood sugar levels too low, which can occur if insulin secretion is too strong. This will force the blood sugar to drop dangerously low and therefore starve the brain.
Insulin Resistance
Insulin works by increasing the amount of glucose receptors on the membranes of cells. So when insulin interacts with cellular physiology it results in an increased ability for the cell to take in glucose, thus lowering the glucose concentration of the blood and feeding the cells.
When insulin is secreted in large quantities repeatedly over time, the cells become less sensitive to its message. This is analogous to walking into a room with a strong smell. When you first enter, you are acutely aware of the odor and may cover your nose in response. After several minutes, however, the odor becomes diminished and you no longer smell it.
This is what happens to the cells when they become insulin resistant. They no longer respond the same way and the glucose has difficulty entering the cell. This has consequences for cellular energy since the cell does not get fed. It also has consequences for health since the blood sugar levels become higher.
The liver is a major site of dysfunction in insulin resistance. Insulin signals the liver to increase its production of glycogen, the body’s source of stored sugar. It also suppresses the liver’s capacity to make new sugar, a process called gluconeogenesis. When the liver loses its ability to sense and respond to insulin, this results in decreased sugar storage and an overproduction of glucose by the body.
Insulin resistance has profound consequences for energy, performance and health. The cells of the body are not getting “fed”, lack of a quick energy source in the form of glycogen is no longer as available, and self-made glucose is flooding the bloodstream.
This results in the body doing the only thing it can to balance things out: store all this extra sugar as fat. So long as the fat cells retain their sensitivity to insulin, the body can stay protected by storing all the sugar away for a rainy day.
It is important to understand that insulin resistance is not an all or nothing thing. Some tissues can remain sensitive to insulin while others lose their sensitivity. The muscle, fat and liver all will have their own response to insulin.
In other words, you can remain sensitive in one tissue while being resistant in another. When the liver loses its ability to sense and respond to insulin, it creates the most problems for metabolic fat burning and health.
Insulin and Stress
What many people don’t realize is that insulin is utilized even when sugar is not eaten. When the body is under stress (e.g. emotional, lack of sleep), it will release stress hormones including adrenaline, noradrenaline and cortisol whose chief functions are to raise blood sugar. This supplies energy to power the fight or flight response.
Historically this stress response was a chief means of survival. In modern times, however, this ancient physiology can be damaging, since rather than fighting or fleeing, we instated sit and seethe. This causes the large amounts of stored sugar to flood the bloodstream and sit there. If the blood glucose is not used for action, insulin has to be called in to adjust the blood sugar back to normal.
Insulin and stress hormones are not a great mix for the body. When this seesaw battle of stress hormone secretion and insulin release happens too frequently, the body begins to lose it metabolic sensitivity.
In other words, it begins to treat both these hormones like the boy who cried wolf, and no longer responds to their signals. This is a key reason for insulin resistance.
This is perhaps the most insidious metabolic disturbance of the modern day. It plays a role in almost every major disease because of its strong impact on obesity. While many blame the hormone cortisol for storing belly fat, the combination of cortisol and insulin is the actual culprit.
