Your basal metabolic rate accounts for approximately 60-75% of your total daily energy expenditure, representing the calories your body burns simply to maintain essential functions like breathing, circulation, and cellular repair. Research shows that BMR naturally declines by roughly 1-2% per decade after age 20, a process accelerated by loss of metabolically active lean muscle tissue. The Mayo Clinic explains how metabolism affects weight and what factors influence your metabolic rate.
When muscle mass decreases through aging, inactivity, or repeated caloric restriction, your body requires fewer calories to sustain itself. This creates a compounding cycle: fewer calories burned leads to easier fat accumulation, which further displaces metabolically active tissue and drives the metabolic rate even lower.
Hormonal regulation plays a central role in metabolic function. Thyroid hormones, particularly triiodothyronine (T3), directly control the rate of cellular energy production. When thyroid output diminishes or hormone signaling becomes disrupted by factors such as stress, insulin resistance, or sex hormone imbalances, the entire metabolic system downshifts accordingly.
