Energy Expidenture

What is energy expenditure?

rate of energy use

How are energy requirements estimated?

can be estimated based on energy expidenture assuming that energy expended/day = energy required/day

What is energy balance?

energy intake = energy expended

• body stores are stable

What happens when one’s energy intake < energy requirement?

• reduction in physical activity

• reduced growth rate in children

• mobilization of tissue energy reserves (primarily adipose tissue)

What happens when one’s energy intake > energy requirement?

• weight gain may occur

• increased risk of chronic disease

What are the different components of total energy expidenture (TEE) in individuals?

TEE = Basal Metabolic Rate (BMR) + Physical Activity (PA) + Thermic Effect of Food (TEF)

• BMR = 60-70% (directly correlated with FFM as the bigger the body, the more energy needed to function and vice versa)

• PA = 20 - 30%

• TEF = 10%

What is the difference between resting metabolic rate (RMR) vs Basal Metabolic Rate (BMR)?

BMR: the minimum rate of energy expenditure necessary to maintain basic physiologic functions, and this is typically measured during deep sleep, typically during the night or early morning hours

RMR: the rate of energy expenditure when at rest, and this is measured after an 8-12 hour fast and after a 30 minute rest, this can be ~3-10% higher than BMR

What are BMR and RMR closely related to?

body size, especially FFM

• the amount of FFM explains ~70-80% of variance in RMR among individuals

What is the most variable component of TEE between individuals?

physical activity

Describe how different levels of activity contribute differently to TEE of individuals?

• sedentary people = ~20-30% of TEE

• very active people = 50% of TEE

• athletes and heavy laborers = > 50% of TEE

Describe energy costs during and after an activity.

• there is an immediate rise in energy expended during the activity

• see a small increase in energy expenditure after the activity (but this is dependent on intensity of activity and can contribute ~15% of expenditure that occurred during the activity overall)

What is the thermic effect of food (TEF)?

energy expended to digest, transport, metabolize, and store nutrients

• differs depending on what type of food is eaten

How do different macromolecules contribute differently to our TEF?

• carbs = ~ 5-10%

• fats = ~ 0-5%

• proteins = ~ 20-30% (high metabolic cost in processing amino acids)

• mixed diets = 10%

What is thermoregulation?

process by which mammals regulate their body temperature within narrow limits

How does thermoregulation influence our TEE?

• 2-5% increase in TEE in low normal environmental temps (68-82ºF vs 82-86ºF)

• under cold stress that triggers shivering, RMR may increase by 2.5%

  • in most conditions people can regulate their clothing and environment to maintain a comfortable body temp therefore temperature variations contribute very little to TEE

Describe energy requirements for growth during infancy and childhood.

• infancy: energy requirement for growth is low except for the first few months

  • 1 month = 35% of energy

  • 12 month = 3%

  • puberty = 4%

What is the difference between what the BMR is mostly dedicated for in infants (0-2) versus in adults?

in infants, a larger % (~60-70%) of BMR is dedicated to support brain function and growth compared to adults

What more than BMR, PA, and TEF can module TEE?

pregnancy, lactation, age, and injuries

How does age impact TEE? Why?

TEE declines to age

• due to loss of FFM (lowers metabolism), decline in physical activity, and decline in organ-level metabolic rates (BMR)

How does pregnancy impact TEE?

• BMR increases due to increased metabolism of the uterus, fetus, heart, and lungs, and by the end of pregnancy this increase in BMR is due to the fetus

  • physical activity tends to decline but as weight gain continues, activities tend to require more energy

What are the different additional energy requirements during the different trimesters of pregnancy?

• 1st = 0 kcal/day

• 2nd = 340 kcal/day

• 3rd = 452 kcal/day

How does lactation impact TEE?

BMR tends to increase 4-5% in order to support milk production

• milk energy output ~400-500kcal/day

• energy mobilization from tissues can support some of the energy required for milk production (this supports postpartum weight loss)

• in general physical activity levels tend to decline so any changes aren’t due to this

  • physical activity may return to normal by 2-3 months

What are four factors that decrease energy expenditure?

1. hypothermia

2. hypothyroidism

3. prolonged fasting

4. decreased FFM (muscle atrophy)

What are five factors that increase energy expenditure?

1. fever (13% increase per ºC)

2. hyperthyroidism

3. burns (can double injury needs)

4. recovery from major surgery

5. sepsis

How do you measure kcal needs during injury or illness?

kcal need = BMR x activity factor x injury factor

• activity factor: confined to bed OR seated/little movement

How you measure energy expenditure from estimation?

make use of prediction equations

What are the different physical activity levels found in prediction equations?

1. inactive

2. low active

3. active

4. very active

What is considered an inactive physical activity level?

activities of daily living

• ex: 30 minutes walking + ~90 minutes of light-moderate activity (household task, dishes, raking the lawn, etc)

What is considered a low active physical activity level?

activities of daily living +

• 60-80 min of moderate activity (ex: walking 3-4 mph)

What is considered an active physical activity level?

activities of daily living +

• 30-50 min of moderate activity + 85 minutes of vigorous activity (ex: jogging/cycling)

What is considered a very active physical activity level?

activities of daily living +

• > 2 hours of vigorous physical activity

Energy expidenture requirement equation for children

younger ages dont have physical activity accounted for bc it is assumed that they are active or that their activity levels are negligible

Energy expidenture requirement equations for those who are pregnant.

Energy expidenture requirement equations for those who are lactating.

What is RMR positively correlated with?

positively correlated with FFM

• this is what mostly causes the inter-individual variation amongst RMR (FFM differences)

What are two ways that RMR can be estimated/measured?

1. prediction equations (make use of weight, height, age, and sex)

2. can be measured using indirect calorimetry

What are two prediction equations used for estimating resting metabolic rate?

1. Mifflin-St Jeor (1990s)

2. Harris-Benedict Equations (1910s and revised 1980s)

What are characteristics associated with the Mifflin-St Jeor equation?

• developed from normal weight, overweight, and obese individuals in 1990

• is the overall equation that is recommended

• found to predict RMR ±10% in 82% normal weight individuals and 70% of obese individuals

• formula does not work well for elderly (> 80 years)

What are three different ways to assess energy expidenture?

1. estimation

2. direct measurement

3. factorial method

Why can’t TEE be calculated from a single sample taken over a few hours after a dose of doubly labelled water?

• because measuring TEe requires observing isootpic