Stevia is a genus of native South American plants which have been known for over 1,500 years as a sweet herb, whose leaves have traditionally been eaten as a sweet snack as well as being employed to sweeten medicines and teas. It is currently used as a sweetening food additive and sugar substitute, as a replacement for the less safe saccharin and cyclamate. Stevia extract is vastly sweeter than sugar; the taste takes longer to develop but also lasts longer.
The main properties of stevia reside in its active steviol glycoside compounds, mostly rebaudioside and stevioside, which have very little effect on glucose levels in the blood, making stevia a good sugar substitute for diabetics and those on a low carbohydrate diet.
Some stevia extracts contain only the super-sweet rebaudioside, while others contain also the more healthful, though more bitter-tasting stevioside element of the leaf. It is the whole leaves, dried and ground, which are traditionally used, both in South America and, more recently, in Japan.
As a nutrient, stevia is used in such small quantities that nutritional value is negligible, but the whole plant boasts antioxidant flavonoid compounds as well as some protein, minerals, dietary fibre and vitamins.