Energy Expenditure

What are components of energy expenditure (EE) ?

How much of EE do they use?

1. Basal metabolic rate 

• Consumes about 50-70% of total EE

2. Physical activity 

• Consumes about 20-40% of total EE

3. Thermic effect of food

• Consumes about 10% of total EE

4. Thermoregulation

What is basal metabolic rate (BMR)?

Such as?

Energy used to sustain basic life functions at rest

Respiration, heat beat, renal function, blood circulation, remain awake

What organs are more and less metabolically active?

How much EE do they use from BMR?

1. Lungs, liver, brain, kidneys

• 60-80%

2. Muscle

• </= 25%

When BMR is measured, its gonna be under standardized conditions

What are the standardized conditions for BMR measurements?

1. Being in a postabsorptive state (12-14 hrs)

2. After waking up 

3. Lying down

4. Relaxed, motionless, awake

5. Comfortable temp 

BMR is converted to units of — to determine —

kcal / 24hrs

basal energy expenditure (BEE)

What is resting metabolic rate (RMR)?

This is similar measurement concept as BMR, expect REE required only no food intake or exercise to occur 4-5hrs before rest (so no need to be in post-absorptive state)

RMR is —% higher than BMR

Why?

10

It also includes energy for digestion, slight muscle activity, thermoregulation, nervous system activation, which are processes that are minimized under strict BMR testing

RMR is —% of daily total EE

65-80

RMR is converted to units of — to determine —

kcal / 24hrs

resting energy expenditure (REE)

Both BMR and RMR are measured the same. What are we measuring?

Why is — measured?

Requires measuring O2 consumed and CO2 produced

CO2

As CO2 is produced when macronutrients are oxidized during metabolism, which indicates energy use and fuel source

— CO2 molecules are formed per TCA cycle

2

Factors that influence BMR and RMR includes:

1. Age and body composition

2. Sex differences

3. Physiological state

BMR is highest during what stage of life? Then it decreases as one —

infancy

Maturates/gets older

REE greater in — than — as —

infants

children

children will have an increase of bone and muscle tissues

REE of children is greater than REE of —

Adults

Adults have decreased — and increased — during aging

active tissue (fat-free mass)

fat mass

Which gender will have a higher BMR?

By how much?

Why?

Males

10%

Males have 1kcal/kg/hr while females have 0.9kcal/kg/hr because of different body composition

What are examples of physiological states that influence BMR and RMR?

1. Fever

2. Fasting

3. Pregnancy

4. Hyperthyroidism

5. Menstrual cycle

What is thermic effect of food?

This is energy used for metabolic response to food ingested, including digestion, absorption, active transport, metabolisn, storage

Thermic effect of food will increase in — after —

heat production

food consumption

After eating, the EE by thermic effect of food will increase —% above BMR

5-30

What influences thermic effect of food?

How so?

By how much?

Type of macronutrient consumed

• Protein causes greatest effect, increasing EE by 20-30%

• Carbs causes intermediate effect, increasing EE by 5-10%

• Fats causes smallest effect, increasing EE by 0-5%

What is thermoregulation?

This is change in metabolism by altering EE, to maintain/restore body’s core temperature

Normal body temperature in —

37℃

How does the body temperature change throughout the day?

1. Lowest in the morning 

2. Highest in the evening

Body temperature maintained in the —, which includes:

Central core

• brain

• central nervous system

• vital organs

Temperature varies in — compared to the central core, so the — can have — temperature while the central core —

outer shell

outer shell

different

must remain the same temperature

What regulates the core body temperature?

1. Skeletal muscle

2. Skin arterioles

3. Sweet glands

What happens when environmental temperature is below the thermoneutral zone?

What action can occur here?

The body generates heat, increasing EE, to maintain core temperature

Shivering

How does shivering affect BMR?

Shivering increases BMR

Does cold exposure always increase energy needs significantly?

No unless shivering occurs

What is hypothermia?

A medical emergency where body temperature falls below 35 °C.

What does hypothermia cause in the body?

What does this result in?

Slows down metabolic processed

Fatigue, disorientation, low heart + lung activity

What happens when environmental temperature is above the thermoneutral zone?

This can occur when?

Reduce muscle tonus and start sweating

Overeating, experiencing trauma or burns

How does a hot environment affect BMR?

Why?

BMR increases

Due to increased blood circulation and sweat gland activity

What is hyperthermia?

when body temperature is above 37℃ and can be medical emergency at extreme temperature elevation

What causes hyperthermia?

Failure of thermoregulation

Total EE will — in both cold and hot environments due to —

Increase

• contribution from thermoregulation and BMR

• adjustment in metabolism to maintain body’s core temperature

Physical activity is the most — out of all EE components and it’s — altered

variable

easily

Factors of physical activity impacting EE includes:

1. Intensity 

2. Duration 

3. Frequency of activity

EE can remain — after completing a physical activity for a short period

elevated

Energy expenditure is energy used to burn — and producing — + —, while producing — and — as byproducts

calories

ATP

heat

CO2

H2O

Energy can be lost in different forms, such as:

1. Heat

2. feces (undigested macronutrients)

3. urine (as urea)

How is energy intake measured?

1. 25 hour recall

2. Food record

What method is used for measuring body heat loss to determine energy expenditure? What are the types?

calorimetry

1. Direct calorimetry

2. Indirect calorimetry

• Respiratory quotient (RQ) method

• Doubly labelled water method

What is direct calorimetry?

A method that measures heat produced by the body in a controlled, closed chamber, and body heat lost is measured by change in air temperature

What principle is direct calorimetry based on?

isothermal principle

How is measured heat in direct calorimetry method converted to energy expenditure?

Temperature change in the chamber is converted to kilojoules; 1 kcal raises 1 kg of water from 15–16 °C.

What is an application of direct calorimetry used in real-life?

What can we determine?

The goal?

Measuring heat stress and energy requirements in miners 

Impact of mining activities and underground temperatures on the miner body heat

To prevent heart stress in miners and design an efficient ventilation infrastructure in mines

Limitations of direct calorimetry includes:

1. Expensive 

2. Laborious 

3. Causes discomfort in patient

What is respiratory quotient (RQ)?

A method that estimate heat produced by the body by measuring O2 consumed and CO2 produced

Exchange of O2 and CO2 is proportional to —

metabolism

Formula of RQ?

CO2 / O2

RQ is used to identify —

Type of fuel that the body is used to produce energy

What does an RQ of 1.0 indicate?

Meaning?

What is occurring?

carbohydrates metabolism

amount of CO2 produced equals amount of O2 consumed

lipogenesis

What does an RQ of 0.8 indicate?

Meaning?

This also includes producing —

protein metabolism

amount of CO2 produced is greater than amount of O2 consumed

Urea [CO(NH2)2]

What does an RQ of 0.7 indicate?

Meaning?

fat metabolism

amount of CO2 produced is less than amount of O2 consumed

What does an RQ of 0.82 indicate?

mixed diet thus mix of carbs, fats, proteins metabolism

— have a minimal effect on RQ as its contribution to EE is small compared to — + — which makes sense since they are —

(carb, fat, protein)

Proteins

fats

carbs

Not used for energy production until fasting/starvation

A RQ < 0.8 indicates —

individual being underfed

A RQ < 0.7 indicates:

1. individual being starved

2. Low carb diet

3. high alcohol intake

A RQ > 1.0 indicates:

1. Hyperventilation

2. Acidosis after an excessive exercise

How to calculate calories burnt based on the RQ?

Ex. C6H12O6 + 6 O2 —> 6 CO2 + 6 H2O

1. Since O2 consumed is equal to CO2 produced, RQ = 1.0

2. Gas exchange (either consider CO2 or O2), 6 x 22.4 L = 134.4L

3. Since O2=CO2, then this means carbs are metabolized and 1 mol glucose = 673 kcal (i think this number will be given in exam but idk)

4. Energy equivalent for gas, 673 kcal / 134.4L = 5.047 kcal/L at RQ = 1.0

What is double labelled water method?

A method that includes consuming stable isotope labelled water, waiting for couple hours for it to distribute, then for couple of weeks, we measure the isotope disappearance in blood and urine

By measuring disappearance rates of isotopes, researchers can measure total — produced, which is a indicator for EE, providing an estimate of —

CO2

total EE

Diet records collected during study period serve to calculate — which is — thus allows us to use — to measure — and assess —

Food quotient

A value that equals RQ

RQ = CO2/O2 formula

O2 consumed

EE

Limitations of double labelled water method includes:

1. Increasing risk of underreporting (from patient) due to using food records

2. Expensive as calculation of O2 consumption from food quotient requires labelled O2, clinical staff, analytical infrastructure, duration of participant involvement  

What is estimated energy requirement (EER)?

Required dietary energy intake that is predicted to maintain energy balance in a healthy adult of a defined age, sex, weight, height, level of physical activity consistent with good health