Is it better for us to eat before or after work out.......?

I used to eat few hours before working out but my friend just told me that it's better not to eat before workout.I checked out few articles about this and several studies suggest exercising while your body is low on food may be a good way to trim excess fat. I tried not eating before work out and my body get so weak and tired tho.I just need some foods before working out.What is your opinion on this?
Is it better for us to eat before or after work out.......?
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