填空题.This past year, we became aware of the dangers of energy drinks. Amid allegations linking these popular beverages on various illnesses and even 1 death, the Food and Drug Administration has launched an investigation. However, the ongoing probe hasn't seemed to have dampened enthusiasm for energy drinks. In fact, consumption is skyrocketing—sales top $8 2 billion last year in the US alone, nearly 15% increase from two years ago. 3 What's more, the success of energy drinks has inspired the launch of "energy" versions of popular snacks as popcorn, potato chips, jelly beans, 4 and even sunflower seeds. We have become obsessed with the concept of "energy" and yet display a profound misunderstanding of what energy is. On a purely biological level, it's molecules that help cells do the work they need to do—the carbohydrate, protein and fat we get them from food that feeds our 5 muscles and brain. By contrast, the active ingredient in "energy" drinks is not energy but a chemical stimulant: caffeine. Most energy drinks contain at least one and a half times the amount of caffeine in a single cup of coffee—and some contains more. Caffeine 6 works by blocking adenosine, a molecule that helps us slow down. Our energy obsession isn't all bad. On surface, we are working harder, 7 performing better and are more productive. Furthermore, this makes us 8 vulnerable to the belief which we just need more "energy" to be able to 9 keep up. But until we reckon with our susceptibility to this sales pitch, and have a better understanding of what energy really is, we will not simply be 10 running on a treadmill with no end in sight.