Energy Drinks comparison

What is it?: Sugar. Sucrose, another ingredient you'll often see on energy drink labels, is a combination of fructose (the natural sugar found in fruit) and glucose. Many energy drinks contain 50 to 60 grams (g) of glucose or sucrose in a 16-ounce can.

Does it work?: Your body runs mainly on glucose, so topping off your tank with the sweet stuff should theoretically provide an instant boost. And in fact, a recent study in the Journal of Applied Physiology found that men who guzzled a 6 percent glucose drink were able to bicycle 22 minutes longer than those who went sans the extra sugar.

Where glucose won't help, however, is with the fog of fatigue from too little sleep. A 2006 British study determined that sleep-deprived people who drank liquid glucose exhibited slower reaction times and more sleepiness after 90 minutes.

Is it safe?: Dumping empty calories down your gullet is never a great idea, and some energy drinks contain nearly as much sugar as a 20-ounce soda. Then there's the fact that a sudden infusion of glucose can cause your blood sugar and insulin levels to skyrocket, signaling your body to stop incinerating fat. A 2006 New Zealand study reveals that caffeine combined with even the 27 g of sugar in, say, an 8.3-ounce Red Bull may be enough to temporarily inhibit your body's ability to burn lard.
http://www.menshealth.com/mhlists/effectiveness_of_energy_drinks/Glucose.php