You have undoubtedly heard that diabetes is a problem of “high blood sugar”. While it is true that high blood sugar is an important aspect of diabetes, the problem is not “sugar”, it is that the metabolic processes throughout the body are malfunctioning because of insulin resistance. High blood sugar is just one aspect of metabolic dysfunction, we talk about blood sugar a lot because it is easy to measure and understand. But there is a deeper truth to what is causing the problem, and to understand that we need to know a little background about metabolism. Metabolism is all of the chemical reactions that take place in each cell of the body, keeping it alive. There are 2 basic branches of metabolism.

Fuel metabolism

Our bodies extract chemical energy the from the food we eat, and use it as a metabolic fuel to power the cells. Just like a machine, our cells need a constant, uninterrupted source of chemical energy in order function. In fuel metabolism, the cells need to decide which fuel to “burn” and what fuel to store for later use. This is of course a vitally important process, as if a cell runs out of metabolic fuel, it will quickly die.

Structural metabolism 

Our cells build themselves, repair damage, and makes substances to be exported out of the cell for use elsewhere in the body. Sometimes in times of need, the cells can burn some of the built structures to fuel the cell in times of need.

Our bodies have over 37 trillion cells in them, each with their own metabolic processes running constantly. But it is not chaos; rather, there is an exquisite order that allows for coordination of the metabolism of cells. You probably already know that structurally, cells are organised into tissues, tissues are organized into organs, and the organs form the organism.
Metabolically, cells are coordinated by the nervous system (which sends communications by hardwired electrical signals) and the endocrine system (which sends communication by signals spread through the bloodstream). For the purpose of this discussion, we are focused on the endocrine system.

Hormones allow cells to coordinate their metabolisms.

Imaging that you have not eaten in over a day. Every cell in your body has to adapt to this lack of food, and keep the energy flowing to each cell. Some of your cells (which specialize in storing energy) need to be told to mobilize and release energy, while other cells need to be instructed to use less energy. Hormones are what allow coordination like this to happen. Hormones are substances made by endocrine glands, which travel through the blood stream to reach all of the cells in the body and transmit messages to the cells.
Hormones serve many functions, but one of their most important is helping control metabolism. Because of how important metabolism is, there are MANY hormones that help control it. I will not name all of the hormones that control metabolism, but some of the most well known include insulin, glucagon, cortisol, adrenaline, ghrelin, GLP-1, adiponectin, somatostatin, thyroxine, and growth hormone. Of these hormones, insulin is perhaps the most important in controlling metabolism.

Insulin is a key hormone in controlling metabolism

Insulin is an anabolic (growth promoting) hormone. Its function in fuel metabolism is to promote using carbohydrates as a metabolic fuel and to promote storage of any excess consumed carbohydrate.

Metabolic changes that are triggered by insulin:
Insulin increases the storage of glucose in the liver
(by converting it into glycogen)
Insulin increases the conversion of glucose to triglycerides in liver cells.
This is another way of storing glucose as an energy source for later use.
Insulin increases the conversion of glucose to triglycerides in adipose cells.
Insulin increases the uptake of amino acids into cells.
Amino acids are the building blocks that form proteins. Proteins are what form most of the structure of the cell, so this is an example of the anabolic effect of insulin.
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Insulin triggers changes in the metabolism of cells by signal transduction

Signal Transduction is the process that transmits a hormone signal into a cell.

Insulin causes metabolic changes by sending a signal inside of the cell, by a process we call signal transduction. Insulin binds to insulin receptors on the surface of a cell’s membrane. When insulin binds to an insulin receptor, a signal is created and sent into the cell, and this signal causes a whole host of changes in the cell to regulate metabolism.

Diabetes is a metabolic disease caused by malfunction of insulin

If insulin signaling is disrupted, many of the normal metabolic processes in cell throughout the body will not work correctly, resulting in diabetes.