We talk about metabolism like it’s something we can manipulate by gulping a pill, downing some green tea, or running faster. You’ve seen the articles headlined “Boost your metabolism” or “Try this high-metabolism diet to lose weight.”

But this obscures many truths about this essential, yet still somewhat mysterious, biological process.

Here are nine facts to help you understand metabolism, and how to think about it in the context of weight gain and weight loss.