You loved downing orange juice at the breakfast table growing up. However, there's a time and a place to sip the sweet stuff. "Fresh pressed juice can be beneficial but not with food," said Joe Holder, performance specialist and Nike master trainer. "Instead of being utilized as quick fuel when you need an extra boost, it just becomes extra calories and more stress on the digestive system." Instead, stick to lower-sugar juice varieties, on an empty stomach, and if your main goal is fat oxidation during workouts, don't have it too close to your sweat, Holder suggests.