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Basal Metabolism

What is Basal Metabolism?

Basal Metabolism
Basal metabolism is a term commonly used in health and fitness, though many people are unaware of its importance and impact on the body. Basal metabolism refers to the process that takes place in our body immediately after waking, when we are at rest and not engaged in any physical activity. It is the minimum amount of energy required by our body to maintain essential physiological functions such as breathing, heart activity, body temperature regulation, food digestion, and nervous system function.

Factors Affecting Basal Metabolism

Understanding basal metabolism requires recognizing that each organism has different energy needs, which depend on factors such as:

  • Age – As we age, our basal metabolism tends to slow down, often leading to weight gain
  • Gender – Men generally have a higher basal metabolism compared to women; they burn more calories at rest due to higher muscle mass.
  • Body weight
  • Body height
  • Activity level

For these reasons, basal metabolism is determined individually for each person.

How is Basal Metabolism Measured?

Basal metabolism is measured under specific conditions:

  • In a wakeful state
  • After 8 hours of sleep
  • After 12 hours of fasting
  • In mental and physical relaxation
  • In a comfortable temperature zone (neither too cold nor too hot)

There are several methods to determine basal metabolism. The most commonly used method is measuring the oxygen used during breathing, a direct method known as calorimetry, performed in laboratory settings. Using specialized devices, such as calorimeters, the amount of oxygen inhaled and exhaled, as well as the carbon dioxide exhaled, is measured. Based on these measurements, an individual’s basal metabolism can be calculated.
A more commonly used practical method is an equation that takes into account gender, age, height, and body weight, using specific tables. For example, basal metabolism can be calculated based on body mass (BM).

Age
(years)
< 3 3 – 10 10 – 18 18 – 30 30 – 60 > 60
Women
(kcal/day)
61.0 x TM -51 22.5 x TM+499 12.2 x TM+746 14.7 x TM+496 8.7 x TM+829 10.5 x TM+596
Men
(kcal/day)
60.9 x ТМ-54 22.7 x ТМ+495 17.5 x ТМ+651 15.3 x ТМ+679 11.6 x ТМ+879 13.5 x ТМ+487

BMR = Body Mass (kg) x 20 kcal
Basal Metabolic Rate (BMR) is typically expressed as the amount of heat in kilojoules (kilocalories) per 1 kg of body weight or per 1 m² of body surface area per hour or per day.
One of the most common formulas for calculating BMR is the Harris-Benedict formula:

Men BMR = 66.4730 + (13.7516 x weight in kg) + (5.0033 x height in cm) – (6.7550 x age in years)
Women BMR = 655.0955 + (9.5634 x weight in kg) + (1.8496 x height in cm) – (4.6756 x age in years)

Alternatively, the modified Harris-Benedict formula (Roza and Shizgal) from 1984 is used:

Men BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
Women BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)

Can Basal Metabolism Increase or Decrease?

Basal metabolism can indeed increase or decrease due to various factors. For example:

  • Increased Basal Metabolism: High environmental temperatures, illness, and stress can raise basal metabolism as the body expends more energy to maintain homeostasis or respond to stressors.
  • Decreased Basal Metabolism: Fasting and inadequate food intake can lower basal metabolism because the body tries to conserve energy.

It’s important to note that basal metabolism tends to decrease with aging, while regular exercise and muscle building can increase it.
Given the significance of basal metabolism, maintaining a balanced diet and regular physical activity is crucial for balancing energy intake and expenditure. Proper nutrition rich in essential nutrients and consistent exercise can help sustain optimal basal metabolism. Understanding basal metabolism is key to maintaining a healthy lifestyle.

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