Insulin is a hormone produced by the pancreas. Its job is to convert glucose from food (sugar, carbohydrates) just eaten into glycogen to be stored in the liver if it is not needed or to deliver the glucose to cells as energy.
If the food just eaten is simple sugar or food with high glycemic index (GI), the glucose content is very high, causing pancreas to release high amount of insulin (insulin spike) to transport glucose to cells as energy. Extra glucose will be delivered to the liver or muscles for storage. During the spike, you may feel tired or hungry as it uses a lot of energy.
Relation between insulin and obesity
But what happens if the liver is already full of glucose/glycogen? Well, the insulin will store the extra glucose in your cells as fats. You may call insulin as hoarders. They just keep storing your extra glucose, causing obesity.
The liver can store a limited amount of glycogen. If the liver is full, extra glucose can be forced to be stored here as fats. You will then have fatty liver.
If the extra glucose cannot be stored anywhere else, it will go into the bloodstream. When this amount of glucose is high, you will have diabetes.
Why glucose in bloodstream is dangerous
Trying to pump blood full of sugar is like pumping sledge through tiny opening. This causes your body to have high blood pressure, your organs (kidneys, brain, eyes, heart) may not be able to receive enough blood, causing failures.
*hormone - a substance produced in an organism and transported in tissue fluids such as blood or sap to stimulate specific cells or tissues into action. A hormone is just like a policeman ordering the inmates/prisoner to do specific work.
So, how not to let insulin store glucose in the cells?
Simple, eat more good fats and protein food. Good fats are converted into energy first, hence they will not be stored in our body. Protein will use stored fats from cells as energy. If you are still short of glucose as energy, protein will be converted to energy. Eventually, you will use up all the fats stored in your body, resulting in loss of weight and less glucose in your bloodstream.