What is metabolism?

Metabolism has two sides: catabolism, which breaks molecules down to release energy, and anabolism, which uses energy to build molecules such as proteins and DNA. The energy the body uses at rest to keep breathing, circulating blood and maintaining temperature is called the basal metabolic rate. For most adults, this resting rate accounts for roughly 60 to 70 percent of total daily energy use. The brain alone uses about 20 percent of the body's resting energy despite being around 2 percent of body weight. Metabolic rate is influenced by age, body size, muscle mass, genetics and hormones such as thyroid hormone.