In the simplest terms, “Metabolism is the process by which your body turns what you eat into energy,” Casey Kelley, M.D., ABOIM, functional physician and founder of Case Integrative Health, tells mbg.

This energy (i.e., calories) is used, or “burned,” to fuel your most basic bodily functions—such as breathing, blood circulation, and nutrient absorption.

It also provides energy for complex physiological reactions (including DNA synthesis, RNA transcription, and neuronal cell signaling in the brain), as well as actions that require more energy, (like immune function, healthy inflammatory responses, and physical activity).

Needless to say, your metabolism affects a lot.

Metabolism is closely related to metabolic rate, or the energy/calories you use, or “burn,” every day. Metabolic rate also depends on: