HOW DO NUTRITIONISTS MEASURE TOTAL ENERGY EXPENDITURE?

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HOW DO NUTRITIONISTS MEASURE TOTAL ENERGY EXPENDITURE?


Energy must be supplied regularly to meet needs for the body’s survival. Although all energy eventually takes the form of heat. Knowing these facts can help us in the measurement of total energy expenditure. To measure total energy expenditure, we need learn more about energy requirements

ENERGY REQUIREMENTS

Energy requirements are the dietary energy intake that is required for growth or maintenance and physical activity. In children and pregnant or lactating women, energy requirements include the needs associated with the deposition of tissues or the secretion of milk. In ill or injured people, the stressors have an effect by increasing or decreasing energy expenditure.

 

COMPONENTS OF ENERGY EXPENDITURE

We divide the TEE into three parts. Energy is expended by the human body in the form of basal energy expenditure (BEE), thermic effect of food (TEF), and activity thermogenesis (AT). These three components make up a person’s daily total energy expenditure (TEE).

Basal and Resting Energy Expenditure (BEE & REE):

BEE, or basal metabolic rate (BMR), is the minimum amount of energy expended that is compatible with life. An individual’s BEE reflects the amount of energy used during 24 hours while physically and mentally at rest in a thermoneutral environment that prevents the activation of heat-generating processes.

Resting energy expenditure (REE), or resting metabolic rate (RMR), is the energy expended in the activities necessary to sustain normal body functions and homeostasis.

As you can see there are some differences between BEE & REE & BMR & RMR but in clinical measurements these differences can be ignored.

Factors Affecting Resting Energy Expenditure

1)      Body composition

2)      Age

3)      Body size

4)      Climate

5)      Gender

6)      Hormonal status

7)      Temperature

 Thermic Effect of Food 

The thermic effect of food (TEF) is the increase in energy expenditure associated with the consumption, digestion, and absorption of food. The TEF accounts for approximately 10% of TEE (Ireton-Jones, 2010). 

 

Activity Thermogenesis

Beyond REE and TEF, energy is expended in physical activity, either exercise-related or as part of daily work and movement. This is referred to as activity thermogenesis. Activity thermogenesis (AT) includes nonexercise activity thermogenesis (NEAT), the energy expended during activities of daily living, and the energy expended during sports or fitness exercise. (Levine and Kotz, 2005).

 Measurement of Energy Expenditure

 The standard unit for measuring energy is the calorie, which is the amount of heat energy required to raise the temperature of 1 ml of water at 15°C by 1°C. Because the amount of energy involved in the metabolism of food is fairly large, the kilo calorie (Kcal), 1000 calories, is used to measure it and nutritionists use Cal (with a capital C) which means Kcal. 

various methods are available to measure human energy expenditure

  1. Direct Calorimetry:

    This method is the most expensive one and it is only used for some experiments. Direct calorimetry provides a measure of energy expended in the form of heat, but provides no information on the kind of fuel being oxidized. In this method individuals are kept in a room which is actually a big calorimeter. . Therefore the measurement of TEE using this method is not representative of a free-living individual in a normal environment, because physical activity within the chamber is limited.

  2.  Indirect Calorimetry:

    you can actually measure the TEE by measuring the volume of  CO expired and the O2 which consumed. Also in this method we can guess the fuel which was used in the body using an Indicator called RQ.

    RQ = volume of CO expired/volume of O2 consumed 

     RQ values: 

    1 carbohydrate

    0.85 mixed diet

    0.82 5 protein 

    0.7 5 fat   

     

    As you can see these methods are not very good and easy for clinical use. So what do we do really? I will talk about the other ways in the next part. let me know what do you think of these methods.


     

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