151.232

Energy Requirements

Wendy O’Brien School of Food and Nutrition

Learning objectives

• To define types and units of energy

• To identify and quantify the food sources of energy

• To explain the components of energy expenditure (EE), their relative size and variability

• To describe the methods of measurement of EE and their validity for different purposes

• To outline the factors that impact on EE

• To describe the respiratory quotient (RQ)

• To outline how energy requirements can be estimated

Terms and definitions

• Energy: the capacity of a system to perform work

• 1st law of thermodynamics: – Energy cannot be created or destroyed

– Only transformed from one form to another

• 1 Joule (J) - amount of energy required to move a mass of 1 kg with a force of 1 N by a distance of 1 m (international absolute unit of energy)

1 m 1 N = 1 Joule

Terms and definitions

• 1 kcal = amount of energy required to heat 1 L water from 14.5°C to 15.5°C

• 1 kcal = 4.186 kJ (4.2 kJ)

• Conversion of food energy not perfectly efficient - ~75% of the original food energy dissipated as heat

Measuring energy in food

• Can be determined in a bomb

calorimeter

• A known weight of food is

combusted (in presence of O2)

inside a sealed chamber, the

amount of heat released during

this process is measured

• Energy measured this way =

gross energy of food

• 1 g of pure fat would release

37.8 kJ during its complete

combustion

Measuring energy in food

• Not all this energy available in the body

– Not all food absorbed by digestive tract

– Nitrogen in protein is oxidised to urea and excreted in the urine

• Digestible energy (DE) – the energy available after the

digestion of food

• Metabolisable energy (ME) – energy available after

losses in feces and urine have been subtracted from the

gross energy; energy available to body

• ME - measured by collecting duplicate food samples and

all feces and urine, and performing bomb calorimetry on

all 3 samples – this is NOT practical!

Calculation of ME

Energy in food

• Atwater - system of predicting the ME of a

food or diet from the sum of the estimated

ME of CHO, fat, protein and alcohol

• Atwater factors - a good approximation to

actual ME content of most food & diets

Atwater factors

• Atwater factors

– Carbohydrate 17 kJ/g

– Protein 16 kJ/g

– Fat 37 kJ/g

– Alcohol 29 kJ/g

• Energy

– Stored in body as fat, glycogen or protein (limited capacity for

storing protein & CHO; fat stores can increase considerably)

– Or used by the body to fuel energy requiring events

Using Atwater factors

1 slice of bread with 1 Tbsp peanut butter

– Contains 16 g CHO, 7 g protein, 9 g fat

• 16 g CHO x 4 kcal/g = 64 kcal

• 7 g protein x 4 kcal/g = 28 kcal

• 16 g fat x 9 kcal/g = 81 kcal

• 64 + 28 + 81 = 173 kcal

• Total = 173 kcal

– Fat as a percentage of total energy

• 81/173 x 100% = 47% fat

Components of energy expenditure

• Basal Metabolic Rate (BMR)

• Diet Induced Thermogenesis

• Physical Activity

0

50

100

Components of daily energy expenditure

physical activity

diet induced ~

adaptative thermogenesis

BMR

• intensity • duration • body weight • genetic factors

amount and composition

• fat free body mass (muscle mass) • age • gender • genetic factors • hormones • activity of sympathicus

components factors of influence

Basal Metabolic Rate (BMR)

• 60-75% (2/3) of the energy expended by the body

• Reflects energy needed for the work of vital functions

• The EE of a subject lying at physical & mental rest in a

comfortably warm environment, at least 12 hours after the

last meal

• Often described as resting metabolic rate – when

conditions for the BMR are not met (likely to be higher

than BMR)

• The majority of heat production is from active organs such

as the liver, kidneys, heart & brain

Contribution of different tissues and

organs to BMR

Diet induced thermogenesis

• 6-10% of the total energy expenditure

• Heat production increases following the

consumption of a meal

• The increase in energy expenditure in

response to food intake - digestion,

absorption, transport & storage of ingested

nutrients

Physical Activity

• 10-15% of total daily expenditure in most individuals

in industrialised countries – up to 70% of daily EE in

some individuals

• Energy expended when skeletal muscles are used for

any type of movement

• The most variable component of daily energy

expenditure - depends on type, intensity and duration

of activity, differences in body size & composition

• To compensate for differences in body size, often

express energy costs as multiples of BMR & RMR

Estimate of cost of various activities (Expressed as multiples of BMR)

Activity Men Activity Women

Sitting 1.2 Sitting 1.2

Standing 1.4 Standing 1.5

Walking 3.2 Walking 3.4

Carpentry 3.5 Light cleaning 2.7

Mining with

a pick

6.0 Hand-threshing

grain

5.0

(James & Schofield, 1990)

Different classification systems

for rating the intensity of PA

Factors that increase BMR

• Higher lean body mass

• Greater height (more surface area)

• Younger age

• Elevated levels of thyroid hormone

• Male gender

• Pregnancy and lactation

• Certain drugs such as stimulants, caffeine and

tobacco

• Genetics - BMR varies by +10% between individuals of

the same age, sex, BW and FFM

Effects of under and over nutrition

on EE

• Under nutrition – decrease BMR

– Loss of body weight

– Energy conservation resulting from increased

efficiency of metabolism

• Over nutrition – leads to gain in body

weight which is often less than predicted

due to compensatory increases in EE

Estimation of energy requirements

• Energy requirement = ‘the energy intake which will

balance energy expenditure when the individual has a

body size, composition & level of physical activity

consistent with long term good health; & that will allow

for the maintenance of economically necessary &

socially desirable physical activity.

• In children & pregnant or lactating women, the energy

requirement includes the energy needs associated with

the deposition of tissues or the secretion of milk

consistent with good health” (FAO/WHO/UNU 1985)

Estimation of energy requirements

• An individual maintaining his or her weight is in

energy balance (EI = EE)

• In theory can base estimates of energy

requirements on measures of either EI or EE

• EI measures – less reliable – vary widely, under

reporting

• Therefore estimates based on measures of EE

Measurement of energy

expenditure

• Direct calorimetry

• Indirect calorimetry

• Non – calorimetric methods

Direct calorimetry

• Gold standard

• Measure energy expended over a given period by

measuring the heat emitted from the body

• Enclosed chamber

• Expensive & impractical

• Technically difficult – walls, floor & roof need to be

sensitive to heat transfer; need to exclude anything

(other than subject) from chamber that will produce

heat

• Measurements made over periods of several hours

or more

Indirect calorimetry

• Measures energy production via respiratory gas analysis

• Measure O2 intake and CO2 output (VO2, VCO2) that occurs during the combustion (or oxidation) of protein, fat, carbohydrate and alcohol

• When foods are oxidised in the body, O2 is used and CO2 is produced in proportion to heat generated

C6H12O6 + 6O2 6H2O + 6CO2 + Heat (the combustion of a simple molecule of glucose)

• Heat released (energy expended) by metabolic processes can be calculated from rate of O2 consumption

• Equipment ranges from simple (field conditions) to sophisticated whole body chambers

Values for oxidation of major

nutrients

Energy Requirements

The most widely used formulae for calculation of human

energy expenditure are those developed by Weir in 1949!!!

EE (kJ) = 16.489 VO2 (L) + 4.628 VCO2 (L) - 9.709 N (g)

If urinary nitrogen excretion is not measured but protein

oxidation is assumed to represent around 15% of total

energy expenditure, the same formula becomes:

EE (kJ) = 16.318 VO2 (L) + 4.602 VCO2 (L)

The Respiratory Quotient (RQ)

• Defined as the ratio of the volume of CO2 produced to the volume of O2 used on oxidation of a given amount of the nutrient

• RQ = amount CO2 produced / amount O2 consumed

– Carbohydrate 1.0 (all O2 consumed used to oxidise C & H in the CHO) – Fat 0.7 (takes more O2 to catabolise lipids to CO2 and H2O) – Protein 0.81 – Alcohol 0.66

• Useful guide to mix of nutrients being oxidized: – if protein oxidation determined from urinary nitrogen & little alcohol in the diet, amounts of fat

& CHO oxidised can be calculated

• Over 24 hours the RQ should reflect diet composition of an individual in

energy balance

• Normal Western diet (35% energy as fat, 15% energy as protein – 24 hour

RQ should be ~ 0.87)

IC - Douglas Bag Technique

• Subject breathes through valve which separates

inspired & expired air, expired air collected into a

non-permeable bag (up to 150L capacity), duration

of collection noted

• Volume of expired air measured & adjusted to

conditions of standard temperature & pressure

• Concentration of O2 & CO2 is measured in a

sample of air from the bag (chemical Haldane

method or gas analysers)

• O2 & CO2 content of inspired air 20.95% and

0.03% respectively

• Can calculate O2 consumed, CO2 produced, &

energy expended over time of collection

IC - Portable systems

• Can weigh <800 g, powered by rechargeable

batteries, real time data monitoring, downloadable

• Connected to face mask

which continually

measures pulmonary

ventilation

IC - Ventilated hood system

• Avoids discomfort of mask, or breathing valve &

nose clips

• Maintain a high, one directional flow through the

enclosed area into which the subject breathes

• Can use during rest or stationary periods over

several minutes to 24 hours

• Dilution of the expired air means

more accurate gas analysers are

needed – moderately expensive

IC - Whole body indirect calorimeters

(respiration chambers)

• Operate on same principle as ventilated hood

• Provide a small ventilated room for the subject in

which they can carry on normal activities

• O2 and CO2 are monitored continuously and

subject follows fixed routine – meals, exercise,

recreation, sleep

• Can obtain a value for 24 hour EE

Non-calorimetric methods

• Doubly–labeled water technique

• Accelerometers

• Heart rate

• Activity diaries

Doubly-labeled water technique

• Total energy expended by a free-living subject for periods of 10-20 days – reflects individual’s normal energy requirements

• Reference technique - validating estimates of energy requirements

• Subject takes an oral dose of water containing stable isotopes (2H (deuterium) and 18O), which mix with the normal hydrogen and oxygen in body water within a few hours

• As energy is expended, CO2 and water are produced

• As 18O is contained in both CO2 and water, it is lost more rapidly than 2H (in water only)

Doubly-labeled water technique

• Difference between rate of loss of 18O and 2H reflects the

rate of CO2 production. Can be used to estimate EE using

indirect calorimetry formulae, if RQ value is assumed

• Assumptions made for water lost by evaporation and

extent of incorporation of 2H and 18O into body tissues are

required for the calculation of EE

• Total error – 5% or less

• Can be used in babies, young children, athletes, pregnant

women and hospital patients

• High cost, specialized expertise required for analysis of

isotope concentrations in body fluids by mass spectometry

Accelerometers

• Can measure multiple dimensions of PA – frequency, duration,

intensity of movement

• Advantages

– Real time data stored over many days

– Can measure magnitude of movement

– Can detect intermittent PA and incidental PA

– Small and unobtrusive – no electrodes or chest straps

• Disadvantages

– Insensitive to some forms of movement (cycling, lifting)

– Uncertainty related to EE predictions or cut points (large errors in

measuring TEE) best to assess time spent in different intensities of PA)

– Variability in ease of use & downloading

Heart rate

• During exercise - increase heart rate, increase EE

• To allow for individuals’ variation in fitness, a calibration

curve based on simultaneous measures of HR & EE in a

variety of subjects must be made for each subject

• Compounding factors affect HR more than EE – eg.

eating meals, variations in posture, smoking

• 24 hr EE estimated from HR may have errors of up to

30% in individuals – average for a group likely to be

within 10% of the true value

• Can provide information on amount of time spent in high

intensity exercise

Activity diaries

• Subject’s physical activities are logged over the time

period of interest

• Energy equivalent of these activities is measured or

estimated using a calorimeter or tables

• Time spent in each activity is multiplied by the energy

equivalent for that activity

• Values are summed to derive an estimate of energy

expenditure

• May be combined with BMR to estimate total daily

energy expenditure

Activity diaries

• Potential sources of error

– Inaccurate recording of activities

– Inaccurate determinations of the energy cost of

activities

Factorial method

• BMR and PA estimated separately

• For adults BMR may be measured or estimated from regression

equations based on age, sex and body weight

• Equations based on detailed statistical analysis of some 11,000

published measures of BMR - 95% CI of the BMR predicted from

these equations is +15%

• Energy expended by PA can be added to the BMR by estimating the

total time spent in each activity in the day, and multiplying the

measured or predicted BMR by the energy cost of physical activity

• The values of the energy cost of activity are assumed to include the

effects of meals and other thermogenic processes

• Total EE of healthy adults 1.4 – 2.5 x BMR – mainly due to the

variation in PA