Metabolism refers to all the chemical reactions that maintain life within an organism and plays a key role in how many calories a person burns in a day. Factors that influence metabolic rate include genetics, age, body composition, gender, health status, and amount of exercise. Infants have the highest metabolism due to growth requirements, while basal metabolic rate decreases with age. Though individuals may lament having a slow metabolism, it’s a more complex issue that includes resting energy expenditure and the energy required for activity.
- Metabolism Basics: Metabolism includes functions like converting food into energy, breaking down food into building blocks, and eliminating wastes. It determines how many calories a person burns in daily activities.
- Variations Among Individuals: Metabolic rate varies based on factors such as genetics, gender, age, body composition, and physical activity. For instance, an overweight woman with 40% body fat will burn fewer calories at rest than a woman with 30% body fat and more muscle mass.
- Influence of Health and Medical Conditions: Medical conditions like thyroid functionality, fever, muscle atrophy, hypoxia, and diabetes can also influence basal metabolic rate. For example, higher thyroid production leads to a higher metabolic rate.
- Age and Metabolism: As people age, they generally lose muscle mass and gain fat tissue, which results in a decrease in basal metabolic rate by approximately 1% to 2% per decade.
- Methods of Estimation: Metabolic rate can be estimated through predictive formulas like the Mifflin-St. Jeor or Harris-Benedict equations, or by indirect calorimetry, where energy expenditure is calculated by measuring oxygen use and carbon dioxide release. Increasing muscle mass and activity level can enhance metabolism.