But not ALL agave nectar brands are as pure as they indicate. For instance, through a little research I discovered that Madhava brand is NOT pure blue agave, but adds fillers like maltose, among other things, which raises it's glycemic index to 46. Compare that to the GI for PURE agave which is an amazingly low 27 (using a glucose reference scale for both). Not surprisingly, Madhava does not list it's ingredients on the label.
The only brand I know of that really is PURE blue agave sold in the U.S. is by a company called Blue Agave (also called Volcanic).
Their web site is very informative:
From what I've read, the biggest problem with getting a pure product to market has to do with supply. There just isn't enough agave being produced to meet demand. Hence the fillers.
That said, all of the products on the U.S. market that I'm aware of have a lower GI than honey, which is somewhere around 65.
One important thing I found in my research about using fructose-based sweetners (like agave) is this:
Fructose has a low glycemic value. However, according to some experts, if fructose is consumed after eating a large meal that overly raises the blood sugar or with high glycemic foods, it no longer has a low glycemic value. Strangely enough, it will take on the value of the higher glycemic food. So exercise restraint, even with this wonderful sweetener. It is a good policy to eat fructose-based desserts on an empty stomach, in between meals or with other low-glycemic foods. Use it for an occasional treat or for a light touch of sweetness in your dishes.