What percentage decline do individuals experience in resting metabolic rate on average per decade after age 25?

The average decline in resting metabolic rate (RMR) is estimated to be between 2% to 4% per decade after the age of 25. This gradual decrease is attributed to several physiological changes that occur as individuals age, including a reduction in muscle mass, hormonal shifts, and changes in overall energy expenditure.

Muscle tissue is metabolically active, meaning that it burns more calories at rest compared to fat tissue. As people age, they tend to lose muscle mass—often due to a sedentary lifestyle, hormonal changes, and a natural decrease in physical activity levels. Because of this loss of muscle, the overall resting metabolic rate declines since there is less muscle to sustain a higher metabolic demand.

Moreover, age-related hormonal changes, including decreased levels of growth hormone and testosterone, also contribute to a slower metabolism. These factors combined result in the observed decline in resting metabolic rate, making the 2-4% range the most accurate estimate. Understanding this decline is crucial for creating effective nutrition and fitness plans, especially for individuals entering their middle and later years.