There is no right or wrong answer to this question. It comes down to two things, whether you like to exercise with food in your stomach or not and how many calories you've consumed vs. how many you've burned in total for the day or in other words getting the weight loss formula right.
The food you eat 30min before exercise won't be metabolised and ready for use by the muscles that quickly. The energy you will be using for your exercise will be from food you ate a day or two ago....not a matter of minutes ago.
The trap can come from eating a snack before working out and then eating a full meal after working out so the snack becomes additional calories that need to be burnt off.
This question only really comes into play for the performance levels of high level endurance athletes and even then each one will have a different personal preference and do things differently when it comes to eating before exercise.
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