Should you eat before or after a workout? Both? Neither?

I'm sure this has been debated before, but I workout late afternoons (1 hour high intensity boxing class) and struggle with a lack of energy. Based on my HRM, I burn 625 in the class. Can/should I eat some energy chews 15-30 minutes before class? I've used ProBar organic chews in the past and liked them. I've been going with a banana and tbsp of peanut butter and hour before and it just doesn't seem to be cutting it for me anymore.

As most of my workouts start around 4:30, I generally eat dinner after. But, on days I don't, should I "replenish" with something?

My goal, even if I add these pre/post workout snacks, will still be to stay within my 1550 calorie/day allowance. So, it wouldn't necessarily be adding calories, just distributing them differently.

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