Insulin resistance is a term, which is nowadays used in articles concerning metabolic health, body aesthetics or lifestyle more often than it used to. However, it is sometimes wrongly described, and you can even notice that it is overused in reference to individual health parameters. In order to systematize the knowledge concerning this matter, in this article I will focus on explaining the issue of insulin resistance and I will try to answer the questions of what it is and how it works from the physiological point of view.
Insulin resistance – definition
Insulin resistance is the condition which reveals itself with clear disorder of glucose balance, which is caused by lower sensitivity of the target tissues to insulin (hormone, which transports glucose to the cells), despite its proper or increased concentration is blood serum. What's important, insulin resistance may have different froms and concern only insulin, or the insulin receptor, or sometimes glucose transporters, or enzymatic elements of the insulin tract. As you can see, this matter seems quite complex, and it's not all, because insulin resistance may concern various tissues and organs.
Pre-receptor insulin resistance
As I mentioned before, insulin resistance may be various. For example, it may be connected with the irregularities in the structure of insulin. As a result, the insulin receptors do not read the signals sent by the mentioned hormone in the right way. This condition may be compared to a wrongly copied key, which does not match well into the lock, but the lock works properly (what can be noticed by giving the exogenous insulin in a form of a pharmaceutical product). This disorder has its origin in genetics and it does not depend on the nutrition factors (it is the so-called pre-receptor insulin resistance).
Receptor insulin resistance
Other situation than the one described above is the condition when the insulin receptor works wrongly. In order to understand such pathology, it's good to know that, under the influence of insulin, the insulin receptor moves to the inner part of a cell and initiates a cascade of biochemical reactions, which stimulates various enzymes (protein kinase), and then it comes back to its primal place to the cell membrane, where it may come into the reaction with insulin again. There are many possible irregularities concerning the structure of the receptor, which cause that it doesn't react properly on its influence, or it, e.g. is stimulated by the mentioned hormone, but it doesn't move into the cell. It is the receptor insulin resistance and it may be compared to the situation when your key matches your door, but the lock is broken. The base of such disorder are genetic factors.
Post-receptor insulin resistance
The last type of insulin resistance is the post-receptor insulin resistance. It may be connected with the disorder of the signalising processes responsible for sending the information in a cell, which concern attaching insulin to the receptor, or with the disability of the functions of glucose transporters. In other words, in such situation both, the lock and the key work well, but the door is closed from the inside. Such condition is often connected with nutrition factors, low physical activity, and most of all – with excess amount of body fat, especially that inside abdominal cavity. I will describe the mechanisms, which are the base of this kind of insulin resistance, in further parts of this article.
Circumference and liver insulin resistance
The type of insulin resistance may be also considered on the level of tissues and organs it concerns. And so, using the location, there are two types of insulin resistance: circumference and liver. The first one concerns muscle and fatty tissue, the other – according to its name – concerns liver. The circumference insulin resistance reveals itself by disabling catching and blocking the possibility of “burning” glucose by skeletal muscles and – attention – by increased lipolysis within fatty tissue, which leads to increased release of free fatty acids. The liver insulin resistance causes stronger process of the liver glycogen breakdown and starts gluconeogenesis. As a result, despite increased glycemia, liver releases additional amount of glucose to blood. Additionally, the processes of the syntheses of very low density lipoproteins (VLDL) and triglycerides are also increased.
As you can see, insulin resistance may have various forms, depending on the fact, if the disorder concerns insulin itself, insulin receptor, or the transduction of the insulin signal. What's more, insulin resistance may also concern various tissues and organs. In my next articles I will explain the matter of diagnosing this ailment and its connections with the lifestyle, as well as with the body mass and composition.