Blood Sugar Regulating Gormones: Insulin and Glucagon
Normal blood sugar levels are maintained in your body with the help of hormones, regulating chemicals that signal to your body organs and tissues to start or cease certain processes. Insulin is the best known hormone produced by the pancreas. Your body needs it to absorb sugar from the blood stream and use it for energy, at the same time lowering blood glucose levels to normal. And the inability of one's body to respond to insulin properly is called insulin resistance.
Insulin and Glucagon
The amount of glucose in your blood is not fixed all the time, it fluctuates: rises after having meals and lowers after a lengthy fasting period as we don't consume food 24/7, and so no glucose at all enters our blood to provide the energy. But the body and the brain in particular need the energy all the time, regardless of eating or fasting, otherwise one may feel feeble, faint or one's brain may me unable to perform vital functions normally, like breathing, regulating the work of the heart and other vital controls you are not conciously aware of. On the other hand, unadequately high blood glucose may cause epileptic seizures or nerve damage. Insulin and glucagon are 2 major hormones invloved in maintaining the right glucose balance (glucose homeostasis), or, in other words, maintaining proper levels over time. These hormones produced by your pancreas work by counterbalancing one another by menas of negative feedback loop, the term widely used in scientific world.
The concentraion of glucose in your blood during fasting periods while the brain still functions normally is 0.001%. Insulin is secreted by the pancreas when blood glucose levels rise above 0.001%, which happens after meals, and enables body cells to absorb glucose. In order to provide glucose supplies in fasting periods, your liver reacts to insulin as well and starts producing glycogen, a sugar type that your liver can temporarily store. Muscles are also able to store some glycogen. This process is called glycogenesis. Glycogenesis stops when your blood stream stops getting glucose from food and glucose concentration returns to 0.001%. In response to that, the pancreas starts producing glucagon, which makes the liver release the stored glycogen into the blood stream as small portions of glucose to maintain the 0.001% concentration and support the brain becuase the brain does not need insulin in order to use glucose. Glycogen breakdown happens until another rise of blood glucose above 0.001% and and onset of insulin production, when the liver starts another loop of glycogenesis.
Please note that the liver is able to store just about 200-300 g of glycogen and the surplus sugar will be used to form the fat tissue. This 200-300 g amount in the liver is able to support the functions of one's brain for about 2 days without serious issues. The reason is simple: the brain works actively all the time regulating vital functions, like breathing, heartbeat, temperatue and blood pressure controls and numerous other functions. Only when your body runs out of glycogen supplied, breaking down of fat starts to provide the required energy. This is the reason why 1-2 days fasting periods shifting into the same periods of overeating don't help with fat loss. More than that, losing fat rapidly and starving may be is dangerous. The best approach is moderate calory consumption in 5-6 meals a day and using low-glycemic foods.
How to check the effectiveness of Insulin and Glucagon?
You can do a Glucose Tolerance Test to check how well these hormones counterbalance each other. In the process, a patient is injected a certain amount of glucose and then blood samples are taken to esitmate how quickly one's glucose lowers and to which levels.