Metabolism is the sum of all the chemical processes that turn food into energy and keep your body running. Most of it is your resting metabolic rate; the rest comes from digestion and activity. Body size and muscle largely set the rate.
- Metabolism converts food into energy for everything.
- Resting rate is the biggest chunk.
- Body size and muscle largely set it.
- Activity is the part you most influence.
The parts of metabolism
Your total daily burn is mostly resting metabolic rate (keeping you alive at rest), plus the energy to digest food, plus movement — both exercise and everyday fidgeting. Resting rate dominates for most people.
What sets your rate
Body size, muscle mass, age, sex and genetics set most of it. More muscle raises resting burn modestly. The Harvard Nutrition Source has accessible background.
What you can change
You can't dramatically 'reset' metabolism, but you can build muscle, stay active and avoid the slowdown that comes with crash dieting. Supplement ingredients like green tea extract are studied for modest support — emphasis on modest.