umm...yeah, your body needs energy to function, that energy comes from the food you eat! 1000 calories seems a very low amount to me, but those remaining 800 calories will be needed by your body to do all the stuff we don't think about or notice (like digesting food, organ functions, thinking, blinking breathing etc etc)
If your personal trainer told you that the excess calories will turn to fat I would recommend looking for another trainer. She sounds a bit ill-informed!
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