What are the 4 components of energy expenditure?

Direct measurement of total energy expenditure:

Following methods are used to measure the energy needs of individuals;

Direct calorimetry

Indirect calorimetry

Energy required by living organism for the survival and to carry out daily activities. To produce energy , continuous supply of primarily glucose, fatty acid and oxygen is required.

Energy in the from of ATP is produced through oxidative phosphorylation, yielding carbon dioxide (CO2) and water (H2 O).

For the estimation of energy expenditure, direct and indirect calorimeter method are used. In direct calorimeter method, heat production is measured while indirect calorimeter measure the heat exchange i.e. oxygen consumed, and carbon dioxide produced.

Direct calorimetry

Direct calorimetry is used to assess energy expenditure by measurement the body's heat production in a calorimeter. Of the total energy loss in body, approximately 80% are attributed to connective and radiative heat losses, while the remainder is the consequents of evaporative heat loss.

In humans, conductive heat loss is negligible. There are three, principal type of direct calorimetry: heat sink, isothermal, convection system. Following are some of the limitation of direct calorimeter methods:

Excessive time consumption(often conducted over 24hr)

Does not reveal free- living energy expenditures

Very expensive, technically difficult and rarely used

Indirect method

Indirect calorimetry is the usual and more reliable method to measure energy expenditures. Moreover, it is commonly used for measuring RMR and TEE. It is based on the principal of measuring energy expenditure by accounting respiratory gases exchange.

Energy metabolism is dependent on oxygen consumption (VO2) and carbon dioxide production (VO2), thus, expired air contains more CO2 and less O2 than inspired air.

If the volume of expired air and the difference between O2 and CO2 concentration in inspired and expired air is known , energy expenditure can be calculated. Total caloric output is based on measurement of respiratory gases exchange.

This method offers a more reliable estimate of RMR than predictive equation based on anthropometry, sex, and age. It is particularly useful for estimate energy needs of morbidly obese individuals, elderly, patients recovered from illness or injury and, people having recent weight loss or weight gain.

Prediction of RMR by weir equation;

RMR (kcal per day) = [(V02 multiply 3.914)+(VC2 multiply 1.11)] multiply 1440

Respiratory Quotient(RQ)= Ratio of VCO2/VO2

VO2= Oxygen uptake(L/min)

VCO2=Carbon dioxide output(L/min)

RQ varies with different nutrients and affected by clinical conditions, under- or over- feeding.

Nutrients. RQ value

Carbohydrate. 1.00

Fats. 0.71

Proteins. 0.82

Ethanol. 0.67

Mixed fuel diet. 0.85

Methods for indirect calorimetry:-

a. Metabolic cart

b. Portable or hand-held devices (mostly only measure oxygen consumption)

Metabolic cart:-

The subject breathe into a canopy, mask or mouthpiece connected to metabolic cart. Gas analyzer measure the air flow breath-by-breath along with O2 and CO2composition. It has automated flow and gas consumption analysis is accompanied with a monitor for live reading 📖.

It is accurate and well accepted in clinical or research settings. It is used to directly measure energy ⚡ expenditures of hospitalized 🏥 patients (does not require injury factors assumptions). It can also be used to measure energy expended during physical activity 🏃‍♂️.

However, instrumentation has limited mobility and is expensive. It requires skilled personnel and is effective in lab 🔬 setting. It involves calibration with a test durations ⌚ of 30 minutes.

b. Portable devices :-

Portable devices (bodygem, fitmate) are small, lightweight, cost-effective and generate results with in 10-15 minutes. They may be used by personnel fittness trainers, dieticians 👨‍⚕️, or in community settings.

However portable devices show significantly variability and often measure O2 consumption only as against metabolic carts which measure both O2 and CO2. They assume RQ of 0.85 or allow users to enter as estimated RQ.

Others tools ⚙ for energy ⚡ estimation :-

a. Heart ♥ rate monitoring :

Heart rate monitor can measure minutes of rest, activity and heart rate during activity. These monitors can also measure the intensity of physical activity. If calibrated for O2 consumption using metabolic cart, heart rate monitors may be utilized to estimate energy ⚡ expenditure.

The relationship between O2 consumption and heart rate change when subject are at rest vs engaged in physical exertion. Energy ⚡ expenditure during activity is approximately linear with heart rate.

b. Pedometer :-

Pedometer measures steps taken and distance covered while walking 🚶 and running 🏃.

c. Accelerometer :-

Individual wear the device on their ankle, wrist, upper arm or belt and get their body acceleration measured on 3 axis. Information is downloaded, stored and processed into computer 🖥.

Mobile 📱 pedometer applications :-

The free software are either downloaded or installed or are built in features of smart phones. They can be used to measure the distance traveled by foot through recording the steps taken and calories burnt🔥 during the day by measuring the level of physical activity through accelerometer.

It also helps to monitor weight loss goals and is comfortable to use by placing phones in pockets. Moreover, it does not need internet connection once installed.

e. Runner fitness tracker with pedometer :

Mobile 📱 health applications have witnessed tremendous growth in the last decades. Prospects of mobile technology ⚙ integration in health care are promising.

One particular interest for mobile fitness tracker is wrist-worn device capable to monitor variety of parameters including energy ⚡ expenditure, heart ♥ rate, distance traveled 🚶, steps taken and possibly oxygen saturation, blood glucose levels and cardiac arrhythmia.