Basal metabolic rate

The Basal Metabolic Rate (BMR) refers to the number of calories your body needs to maintain basic bodily functions, such as heartbeat and respiratory functions, while at rest. These physiological functions account for the majority of your body's energy expenditure, around 60-75%, even without any physical activity.

Determining Factors

BMR varies significantly among individuals due to several factors:

• Body Composition: Muscle tissue burns more calories at rest than fat tissue, so people with a higher muscle to fat ratio generally have a higher BMR.
• Sex: Men typically have a higher BMR than women due to their larger muscle mass.
• Age: BMR decreases with age as muscle mass typically decreases and fat mass increases with age.
• Genetics: Genetic differences can contribute to variations in BMR.
• Thyroid hormone Levels: Higher amounts of thyroid hormones increase BMR.
• Body temperature: An increase in body temperature, such as during fever, also raises the BMR.

Measurement and Calculation

BMR is usually measured in a controlled environment, after an overnight fast, and while the subject is fully at rest (both physically and mentally). Various formulas, such as the Harris-Benedict equation or the Mifflin-St. Jeor equation, can estimate BMR. However, direct measurement using indirect calorimetry is more accurate.

Clinical Relevance

Understanding BMR can aid in weight management and dietary planning. It also has medical implications; a significantly higher or lower BMR may indicate certain health conditions, such as hyperthyroidism or hypothyroidism.

See Also

• Metabolism
• Thermogenesis
• Body Composition

References

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