**1. Introduction**

Historically, the word *diabetes* was coined from the Greek word meaning a *siphon* by the 2nd century Greek physician, Aretus the Cappadocian. He used the word to connote a condition of passing water (urine) like a *siphon*. Later the Latin description *mellitus* meaning *sweetened or honey-like* was added. Put together, the term *diabetes mellitus* was literarily used to denote a disease condition which was associated with *the persistent passage of sweetened urine* (Krall & Braser, 1999).

In 1999, the World Health Organization described diabetes mellitus as a metabolic disorder of multiple aetiology characterized by chronic hyperglycaemia (the fasting blood glucose level equal or above 200 mg/dl taken at least twice, on different occasions) with disturbances of carbohydrate, fat and protein metabolism resulting from defects in insulin secretion, insulin action, or both. In other words, diabetes mellitus is a chronic disease with insidious onset in which the fasting blood glucose is persistently raised above the normal range values, the normal range being between 60 to 120 mg/dl of blood [Krall & Braser, 1999]. It occurs either because of a lack of insulin (the hormone responsible for glucose metabolism), or due to the presence of certain factors opposing the action of insulin on the body tissues that are involved in glucose metabolism, particularly, the liver and the skeletal muscles.

The consequence of insufficient insulin action is hyperglycaemia which may be associated with many associated metabolic abnormalities notably the development of hyperketonaemia resulting from disordered protein metabolism, and derangements in fatty acid and lipids metabolism. If the fasting blood glucose lies between 100 to 130 mg/dl, it is referred to as *Prediabetes* which is associated with an increased tendency or potential of developing *frank* diabetes. A fasting blood glucose of 140 mg/dl or higher is consistent with either type of diabetes mellitus, particularly, when accompanied by classic symptoms of diabetes [Diabetes Control and Complication Trial Research Group, 1997].
