Agave nectar (or syrup) from the agave plant is commonly used by diabetics and health foodies as an alternative sweetener. It is 90% fructose, making it sweeter than table sugar, so less of it is needed. Its use comes with some caution, however: Fructose can elevate triglycerides and trigger metabolic syndrome. So if you already have high triglycerides or other risks of heart disease (which many type 2 diabetics do), it is probably wise to choose a different alternative sweetener.
When sold commercially (in health food stores and some grocery stores), agave nectar is usually clear or translucent golden brown. It mixes well into beverages like hot or cold tea. When substituting as a sweetener in recipes, it usually works well to look at how much sugar is called for and use about 25% less worth of nectar. Then, reduce the liquid in the recipe by about a third and reduce the oven temperature by 25 degrees.
The agave plant comes in many varieties which are indigenous to Mexico. The blue agave plant is what tequila is made from. The least manipulated commercial form of agave nectar is made from extracts of the Salmiana agave plant, and processed with enzymes derived from the mold Aspergillus niger (a process "generally recognized as safe" by the FDA).
One teaspoon of agave nectar contains 5g of carbohydrate and 20 calories.
As a food exchange, 1 teaspoon of Agave nectar equals a free food.
Basciano H, Federico L, Adeli K. Fructose, Insulin Resistance and Metabolic Dislipidemia. Nutrition & Metabolism, 2005,2:5.
FDA GRAS Notification Strain for Asparaginase from a Genetically Modified Strain of Aspergillus Niger. Obtained 5.6.2010. http://www.accessdata.fda.gov/scripts/fcn/gras_notices/grn000214.pdf
Mayes, PA. Intermediary Metabolism of Fructose. American Journal of Clinical Nutrition. 1993,58(5S):754S-765S.