What Metabolism Does
Your metabolism is like a chemical factory inside your body. When you eat food, your digestive system breaks it down into smaller parts. Your body then converts these parts into a form of energy called ATP that your cells can actually use. This energy powers everything from your heartbeat to your thinking to running and playing sports.
The Two Main Processes
Metabolism has two opposite processes. Anabolism is when your body builds new tissues and stores energy, like when you grow muscle or build new bone. Catabolism is when your body breaks down molecules to release energy, like when you exercise and burn calories. Both processes work together to keep your body functioning.
Metabolic Rate
Your metabolic rate is how fast your metabolism works, measured by how many calories your body burns in a day. Your basal metabolic rate is the amount of calories you burn just to keep your body running at rest, like breathing and pumping blood. Things that affect your metabolic rate include your age, gender, muscle mass, genetics, and activity level.
Factors That Influence Metabolism
Several things can speed up or slow down your metabolism. Having more muscle mass increases your metabolic rate because muscles burn more calories than fat tissue. Exercise and physical activity temporarily boost metabolism. Age plays a role too, as metabolism generally slows down as people get older. Hormones, sleep quality, and stress levels also affect how fast your metabolism works.
Common Misconceptions
You cannot completely stop your metabolism, even when dieting, because your body always needs energy to function. Eating small frequent meals does not necessarily speed up metabolism more than eating regular meals. While you can influence your metabolism through exercise and building muscle, you cannot drastically change your basic metabolic rate just through willpower. 
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