It has been written that agave nectar may not be a  healthy natural sweetener substitute.  Instead it may be a highly refined form of fructose, that can contribute to disease.  Agave may be found in foods labeled “organic raw” such as health fo0d bars and health drinks.  Agave plants are in the lily family and for thousands of years natives to central Mexico used different species of agave plants for medicine.  But the natives would allow this agave plant to ferment naturally, and they also boiled the plant for several hours to make a sweetener.  But the agave nectar purchased in ths stores is neither one of these foods.  The agave is a created sweetener, whose  principle constituent is starch, (such as corn or rice).  The process to make the agave starch into fructose and then sold as agave nectar is through a chemial conversion that alters the nonsweet starch into refined fructose. 

And fructose is not what is found in fruit.  Fructose has adverse effects on insulin action.  It can actually have a decline in insulin sensitivity in the liver and later in peripheral tissues.  Considering there is an increase in obesity and type 2 diabetes in the United States, this may well be because of the substantial increase in the amount of dietary fructose consumption from high intake of sucrose (Sucrose is made up of 50% fructose )  and high fructose corn syrup.  Numbers of animal studies show: high fructose diets induce hypertension in animals; promotes atherosclerosis; raises triglycerides; raises LDL and VLDL. Fructose has also been reported to increase glycosylated hemoglobin more than any other sugar.  

Warning :  Many supplements do  contain fructose.   This added sweetener may be a health concern and not appropriate for diabetics.  The new MicroMiracles chewable digestive enzyme does not contain fructose, it contains the natural alcohol sugar  Erythritol   as does the BioSET Chewable Digestive Enzyme

If you would like to read more about this, here are some references:

Science Daily. http://www.science daily.com/releases/2008/10/081016074701.htm;

http://healthnews.uc.edu/news/?825/;Bray Ga, Nielsen SJ, Popkin BM

Am J Clin Nutr. 2004;79(4):537-543.

I would also recommend reading more on Agave in the Townsend Letter May 2009 Issue #310 Agave nectar by Rami Nagel  P 69-73