Fuel

Fueling up is a big deal for longer runs--for me, this is anything 10 miles and up.  On longer runs you lose electrolytes, sodium, and of course, water.  It's generally recommended that you don't drink more water than you're sweating, because it can lead to hyperhydration.  (Yup, it's a thing!  But it's hard to achieve.)  Also think about it logically:  You're burning more calories than you've probably taken in, and there can be a point where you hit "the wall."  This is where your mind and body agree and say "Nope. You're done."  Runners typically avoid hitting the wall by fueling correctly, and it can mean everything in a long distance race.

When learning how to "fuel correctly" it is really just a matter of trial and error.  Some people prefer gels, others chews.  For me, I tried just gummy bears first and it did not work well.  Next I tried sucking on chews or eating them with water and that does the trick for me.  It makes me feel like I'm having candy while running since it's a little sweet but helps with giving me a little boost of energy as well.  Meanwhile, my Dad and Brother in Law enjoy gels.    Some people like to have caffeine in their fuel, which can have some positive effects on your performance.  

>Like I said, it is a matter of trial and error.  This is one of the points where running gets gross.  Choose the wrong thing, and it can wreak havoc on your digestive tract during your run.  That being said, do NOT try new fuels on race day (or for that matter, a new restaurant the night before a race.)  When testing out what fuels work for you, I highly recommend either trying it on a treadmill so you know you're close to a bathroom, or an outdoor route where you will be close to restrooms.  Also, don't beat yourself up when you find a fuel that didn't work for you.  It will feel horrible.  You will get over it.  If you feel up for it, keep going but at a pace that you're comfortable with until the feeling passes.