Sugar

Also known as monosaccharides, sugars include fructose, sucrose, glucose and galactose. Sugar is a fast source of energy used by the body for a wide range of processes. For adults with average body mass, the RDA of sugar is 25 grams. Humans have virtually always eaten sugar naturally present in fruits when available.
Several thousand years ago, Southeast Asian peoples domesticated sugar cane and extracted its juices as a sweetener. Indian populations began making sugar crystals from the juice about two thousands years ago, and Latin American and Caribbean regions refined the processes used to make granulated sugar up to today.

Sugar Deficiency

A deficiency of sugar can result from lack of sugar intake or a lack of sugar utilization in the body. Because the body can make glucose, a simple sugar, from protein as well as from complex carbohydrates, a simply insufficient calorie intake can result in low sugar levels.

At the same time, excessive exercise can drive sugar levels too low. Diabetes can also result in a sugar deficiency defined by problems in the body's ability to use glucose.

Finally, hypoglycemia, literally low blood sugar, can occur in some people after consuming carbohydrate-rich foods and beverages in the context of too little food overall.

Sugar Excess

Excessive sugar levels can result from all forms of diabetes. Type 2 diabetes, the most common kind, involves loss of ability for cells to use the glucose available to them. This happens through desensitization of those cells to the effects of the hormone insulin.

Without proper disposal, the glucose piles up in the blood stream to potentially deadly levels. Type 1 and type 1 1/2 diabetes, also called childhood and autoimmune diabetes, respectively, involve very low or absent production of insulin, resulting in the same problem of glucose accumulation in the blood stream.