Diabetes is a condition that affects the way the body uses food for energy. Diabetes occurs when the body fails to process sugar correctly. Normally, sugar circulates in your blood where it waits to enter cells to be used as fuel.
Having diabetes means that the body has trouble using sugar for fuel. The body needs insulin to use sugar as fuel. Having diabetes means the body does not make enough insulin or the insulin it does make doesn’t work very well. Blood sugar levels become too high.
There are two main types of full-blown diabetes. People with Type 1 diabetes cannot make insulin at all. People with Type 2 diabetes can produce insulin, but their cells don't respond to it. In either case, the sugar can't move into the cells. Blood sugar levels become high. High sugar levels cause serious complications over time.
You can learn to control your blood sugars. You can do that if you balance the food, insulin shots or other medicines, exercise, and stress in your life. When you have good sugar control you feel better. It also helps you lower your risk of having eye, kidney, and other problems from diabetes.
Source:  Diabetes Care, care.diabetesjournals.org