If you're in the middle of a 10-mile training run or a full-fledged marathon, you can't really stop and order a salad at the local café. That's where energy bars and drinks come into play. Not only can they fuel your race (before you even take the first step), but they offer a handy way to sustain your energy as you run. Just don't opt for a bar coated in chocolate or dotted with chocolate chips -- unless you don't mind flashing a messy grin as you cross the finish line.
Energy bars offer more than convenience, though. High in carbohydrates, they are easy to digest and convert to energy. Low in protein and fat, they don't slow the digestive process (or cause a "cookie-toss" on mile nine). Energy gels contain similar ingredients and offer the same benefits, just in a viscous liquid form. Both should be ingested with plenty of water; this will make it easier for your body to absorb the nutrients.
Likewise, sports drinks have a high carbohydrate count, but also help replenish lost fluid and electrolytes. Some sports drinks even include small amounts of protein, which helps your body absorb more of the liquid [source: Dada].
Low-tech sources of fuel during endurance runs include pretzels (carbohydrates and salt) and bite-size sugary snacks, such as gummy bears. A whole banana, which is high in sugar and potassium (although admittedly more difficult to store in your pocket than a few sugary bears) is another option. There are even jelly bean-style snacks specifically made for endurance athletes because they contain higher concentrations of electrolytes than a mass-market candy. Keep in mind, though, you'll want to stay away from the gel or bar form of any snack if you're prone to nausea during a long run; these take longer to digest than a sports drink. If you're looking for an immediate energy infusion, you should stick to liquids.
The basic ingredients for an energy boost are carbohydrates laced with small amounts of protein and/or fat. But, you can also look for energy gels or sports drinks with added caffeine to help fight fatigue, as well as sodium to combat sweat loss during hot and humid conditions. Sports drinks also have minerals, known as electrolytes, designed to help you combat fatigue.