You can slow down your metabolism, but it's not safe.

AKA Starvation. That basically kills your metabolism cuz the body goes into starvation mode and your metabolism will slow down to the point where it barely uses any calories, which is why you are so tired when you don't eat a lot. Your body is trying to preserve your calories so you can survive. Then once it runs out of its storage, it starts eating itself. You gain all that weight back though.

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