Why don't runners drink juice?

Firstly, juice is too acidic and upsets the stomach on a run, sometimes even causing heartburn. Secondly, the high sugar content makes me very dizzy and I need a slower burn. You only need to consume a calorie-containing drink if you are running for more than 90 minutes. Otherwise, water is your best bet and even then, don't overdo it. Remember that dehydration and over-hydration are both dangerous. Drink water about a half hour before and sip as you run, don't gulp. Drink lots when you are finished, until you aren't thirsty anymore.