Metabolism is the sum of all the chemical reactions that sustain life: turning food into energy, building and renewing tissues, removing waste. Metabolism is divided into catabolism (the breakdown of molecules with the release of energy) and anabolism (the synthesis of complex molecules using that energy).
The pace of metabolism is set by the basal metabolic rate, and the total spend over a day is reflected by total daily energy expenditure. How efficiently your metabolism works is indirectly shown by metabolic age.
Catabolism and anabolism
In catabolic reactions large molecules — carbohydrates, fats, proteins — are oxidized and broken down, releasing energy that the cell stores as ATP. In anabolic reactions this energy is spent on assembling proteins, lipids and nucleic acids. Both processes run at the same time, and their balance determines whether the body gains mass or loses it.
Enzymes and hormones
The rate of reactions is regulated by enzyme catalysts and hormones. Thyroid hormones set the overall pace of metabolism, insulin switches the body to storing energy, and cortisol and adrenaline to mobilizing it. Most of the cell's energy is produced by mitochondria, and their aging reduces the efficiency of metabolism.
Metabolism and aging
With age metabolism changes: the basal metabolic rate falls, muscle mass decreases, tissue sensitivity to insulin declines. This raises the risk of metabolic syndrome — a combination of abdominal obesity, high blood pressure and disturbances of sugar and lipids. Maintaining activity, muscle and sleep quality helps keep a "young" metabolism.
Calculate using this marker
Calculators where Metabolism is used directly:
Frequently asked questions
Is it true that thin people have a "fast" metabolism?
Not necessarily. Absolute energy expenditure is higher in people with more mass and more muscle. A "fast metabolism" in slim people is more often explained by high everyday activity and a greater share of muscle mass, not by a special gift of nature.
Does metabolism slow down after age 30?
A large 2021 study showed that energy expenditure per kilogram of mass is stable from about 20 to 60 years and drops noticeably only after 60. Weight gain in middle age is due mainly to loss of muscle and a decline in activity, not to a "breakdown" of metabolism.