ELI5 Metabolism - How does it work?

What makes your metabolism faster and what makes it slow down? In my day to day cycle what happens to it? How big of a factor is metabolism in losing weight? Can I overcome a slow metabolism with exercise? Is it going to totally mess up a diet?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community, and specifically the following reddit users whose questions and responses formed the basis of this conversation: takingbackmychem & vijchti   To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected] ... we love hearing from you!