Carbohydrates are sugars. There are simple sugars and complex sugars. For example, sucrose (common sugar) is made up of two simple sugars called glucose and fructose. Lactose (milk sugar) is composed of glucose and galactose. Your body uses enzymes to break sucrose and lactose down into their simpler sugars to enable the body to absorb them and use them. If your body does not produce enough of the enzymes or if they do not work properly, you are unable to break down sugars properly. This leads to high levels of sugar to build up which is harmful to the body and causes the signs and symptoms of this group of disorders.