30 Day Shred - Ouch!

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I'm on my third day of the 30 day shred and everything hurts!!! Today I managed to do an hour at the gym and a level 1 workout, burning around 600 calories altogether. What I'm wondering (besides when will the pain stop!) is because I've burned that extra 600 calories, do I need to eat that many to avoid 'starvation mode' - I've eaten about 300 more calories tonight. Basically I'm confused about the whole net calories, defects stuff so if someone could put it into simple terms for me, I'd really appreciate that!!xx