What is metabolism?
Metabolism is all the chemical processes in the body that turn food into energy and use that energy to build, repair and run cells. Metabolic rate is how fast the body burns calories.
Metabolism has two sides. Catabolism breaks down food molecules, such as carbohydrates and fats, to release energy. Anabolism uses energy to build new molecules, such as proteins for muscle and stored fat. These processes happen constantly in every cell and are controlled by enzymes and hormones like insulin and thyroid hormones.
Your basal metabolic rate is the energy your body uses at rest to keep vital functions going, such as breathing, circulation and maintaining body temperature. It makes up most of the calories you burn each day. Digesting food and physical activity use the rest.
What affects metabolism
Metabolic rate depends on body size, muscle mass, age, sex, genetics and hormones. Muscle burns more energy than fat, even at rest. A 2021 study found that metabolism stays fairly stable between about ages 20 and 60, then slowly declines, challenging the idea that it drops sharply in middle age.
Did You Know?
Babies have the fastest metabolism relative to body size. In the first year of life, their energy use per kilogram is about 50 percent higher than an adult's.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.