Know the Downsides
Here are some facts to keep in mind when it comes to food bars or energy drinks:
They contain excessive sugar and calories. Did you know that some energy bars and drinks contain hundreds of calories? That may be OK for athletes who burn lots of calories in high-intensity activities, like competitive cycling. But for many teens the extra sugar and calories just contribute to weight gain, not to mention tooth decay.
Energy drinks are often full of caffeine. Caffeine may be legal, but it is a stimulant drug. It can cause side effects like jitteriness, upset stomach, headaches, and sleep problems — all of which drag you down, not power you up! Large amounts of caffeine can have even more serious side effects (including fast or irregular heartbeats, high blood pressure, hallucinations, and seizures), especially for people who have certain medical conditions or who take medications or supplements. Energy drinks are not the same as sports drinks. They should not be used to rehydrate because they contain so much caffeine.

Food bars don't make good meal replacements. You never really see someone eat an energy bar for dinner and then sit back with a satisfied grin. Nothing beats a real meal for both that well-fed feeling and the nutritional satisfaction your body needs.
Although many nutrition bars have vitamins and minerals added, they can't give you all the different nutrients your body needs to grow, develop, play sports, and handle all the other stuff on your schedule. The only way to get that is through eating a balanced diet and not skipping meals.
They may contain mysterious ingredients. In addition to caffeine and sugar, some brands of energy drinks and food bars can have ingredients whose safety and effectiveness haven't been tested — things like guarana (a source of caffeine) and taurine (an amino acid thought to enhance caffeine's effect). Some contain herbal supplements that are not regulated by the U.S. Food and Drug Administration (FDA), such as ginseng.
These kinds of ingredients may cause problems, especially for people who are taking certain medications or have a health condition. So play it safe. Always check the label carefully before you eat or drink any kind of energy supplement.
They're expensive. Though energy bars and drinks are everywhere these days, they don't come cheap. At about $3 a pop, you can get a better (and cheaper) energy boost by eating a whole-wheat bagel with cream cheese. And you can get better hydration by drinking 8 ounces of tap water. Other on-the-go foods that provide plenty of nutritional bang for the buck include trail mix, fresh or dried fruits, and whole-grain cereals.