energy 2013.ppt

D224N2 Principles of Human Nutrition

Energy Requirements

S Azam-Ali

Summary of the lecture

Revision – BMR, activityIntroduction to the other major components

of energy expenditure

Major Components of Energy Expenditure

Basal Metabolic Rate (BMR)Activity

Postprandial thermogenesis

Pregnancy & LactationGrowthTrauma, Sepsis & Burns

Basal Metabolic Rate

Basal Metabolic RateUsually the biggest single component of energy

expenditureEnergy expenditure of a subject lying at physical

and mental rest in a comfortable warm environment, at least 12 hours after the last meal

BMR normally measured in the morning before any physical activity and 12h after stimulants such as tea, coffee or cigarettes

Heavy physical activity should be avoided the day before.

Energy Expenditure

Resting Metabolic Rate

Diet-Induced Thermogenesis

Physical Activity

Energy expended by use of skeletal muscle for any type of physical activity

Digestion, metabolism and storage of ingested macronutrients

Maintenance of basic physiological function

Greatest source of variation

Duration

Type

Intensity

Energy Expenditure

Resting Metabolic Rate

Diet-Induced Thermogenesis

Physical Activity

Average daily energy

expenditure (ADEE)

60-70 %

10 %

30-40 %

Quantity and quality of

macronutrientsBody composition

Gender

Activity level

What affects BMR?

What affects BMR? Body size

accounts for half the variability in BMR in adult humans Body composition

adipose tissue has a lower metabolic rate than lean tissue Age

in adults BMR tends to decline with age as lean tissue is lost and adipose tissue is gained

Sex Differences in body size and composition result in

differences between the sexes.

Energy Expended in Activity

Activity is the work of the musclesWork can be measured (force x distance)Since work and heat are equivalent you can

measure energy expended as heat produced above basal

As heavier bodies require more energy to move than lighter ones this can be expressed as a multiple of BMR.

Physical Activity Ratios (PAR)(energy cost of physical activity as a ratio of BMR)

PAR 1.2 Lying, sitting or standing at rest

PAR 3.7 mopping floors, gardening, cleaning windows golf bricklaying

PAR 6.9 jogging, swimming, skiing.

Estimates of BMR in adult humans

Age range Male Female 10-17 0.074(wt)*+2.754 0.056(wt) + 3.434

18-29 0.063(wt) + 2.896 0.062(wt) + 2.036

30-59 0.048(wt) + 3.653 0.034(wt) + 3.538

60-74 0.0499(wt) + 2.930 0.0386(wt) + 2.875

75+ 0.0350(wt) + 3.434 0.0410(wt) + 2.610

FAO/WHO/UNU 2004

Postprandial Thermogenesis

Metabolic rate remains increased up to 5h after a meal The size of the effect depends on the quantity of food

eaten and it’s composition Overall it is normally assumed to be about 10% of the

energy ingested Has been suggested that more energy is utilized in

processing protein and carbohydrate than fat Postprandial thermogenesis is included in calculations of

Physical Activity Ratios (PARs) so no need to make further adjustments

Estimated Average Requirements for Energy in Adults (MJ/d)

Age (y) Males Females

19-50 10.60 8.10

51-59 10.60 8.00

60-64 9.93 7.99

65-74 9.71 7.96

75+ 8.77 7.61

Additional Energy Needs

Pregnancy

For a well-nourished women of between 60-65kg, producing an infant of 3.4kg, it has been estimated that they would gain approximately 12.5kg in body weight Nutrition & Metabolism (Gibney,

Macdonald & Roche) Chapter 6

Components of weight gain in pregnancy(as described by Hytten & Leitch in 1960s)

Products of Conception

Foetus

Amniotic Fluid

Placenta

4850g

Maternal TissuesFat Stores

Extracellular Fluid

Uterus & Breasts

Blood

7650g

Total Weight gain 12500g



Foetus

Amniotic Fluid

Placenta

4850g

3400g

800g

650g


Extracellular Fluid

Uterus & Breasts

Blood

7650g




Foetus

Amniotic Fluid

Placenta

4850g

3400g

800g

650g


Extracellular Fluid

Uterus & Breasts

Blood

7650g3345g

1680g

1375g

1250g


Energy requirements in Pregnancy

Average extra energy cost of such a pregnancy was estimated to be 350MJ over 9 months Increased fat stores = 150MJ Foetus, placenta & other maternal tissues = 50MJ Energy requirements of new tissue = 150MJ

More recent studies

Since the 1980s several “longitudinal” studies of pregnancy have been performed

These have included more careful measurements throughout pregnancy and more accurate determination of fat & lean tissue.

These suggest early studies over-estimated maternal fat gain which may be more like 100MJ (rather than 150MJ)

Energy Cost of Pregnancy in Different Countries (MJ)

Component Scotland Gambia

Foetus 34.0 29.9

Placenta 3.05 2.34

Lean Maternal Tissues

12.1 10.4

Maternal Fat 106 27.6

BMR 126 7.9

Total 281 78

Change in BMR during pregnancy in different countries

-1

-0.5

0

0.5

1

1.5

0 10 20 30 40

weeks

chan

ge in

BM

R (

MJ/

day) scotland

gambia

Energy Intakes During Pregnancy

Energy Cost of pregnancy is approximately 300MJ or 1.1MJ/day

This is equal to about 10-15% above pre-pregnancy intake

Can we detect equivalent increase in intake?

How is the increased energy requirement met?

Increase intake? Most studies indicate only minor increases that account

for no more than 25% of the extra requirementDeceased activity?

Increased body weight might be expected to increase the energy cost of activity

However, women might reduce pace or intensity of exercise?

No evidence to suggest this is trueFurther studies needed to explain how pregnant

women balance energy requirements and intake

Energy Costs of Lactation

Major Determinants are volume and energy content of milk

A well-nourished women will produce approx 750ml of milk/day for the first 4-6 months of full lactation

Energy content of milk is 2.8kJ/ml so approx 2.09MJ/day are secreted

The actual cost of synthesizing milk may add another 0.150-0.523MJ/day

Use of Stored EnergyA well nourished women may have stored an

additional 2-2.5kg of adipose tissueEstimated that if this represents 147MJ and is

mobilized steadily for 6 months then would offset energy cost of lactation by 0.84MJ/day

This reduces full cost of lactation from 2.2-2.62MJ/day down to 1.36-1.78MJ/day

If women does not breastfeed then she will not necessarily lose excess adipose tissue

Additional EAR for energy during lactation

Period Additional energy (MJ/day)

1 mth +1.90

2 mth +2.20

3 mth +2.40

4-6mth (group 1) +2.00

4-6 mth (group 2) +2.40

>6 mth (group 1) +1.00

>6 mth (group 2) +2.30

Group 1: progressively wean babies after 3 monthsGroup 2: maintain milk as primary source of nourishment for 6mths or more

Energy & nutrient inadequacies in lactation

Lactating women are considered as high risk, particularly

Complete vegetarians & women who avoid dairy produce

• Vitamin D, Calcium, Vitamin B12 Women who diet to lose weight

• For women with adequate reserves milk energy output will be maintained even if they are losing 0.5kg/week.

Women on low income


Basal Metabolic Rate (BMR)ActivityPost- Prandial thermogenesis Pregnancy & Lactation

GrowthTrauma, Sepsis & Burns

Basal Metabolic Rate Changes with Age

050

100150200250300350400450500

0 10 20 30 40 50

Age (y)

BMR(kJ/kg BW/day)

Contribution of different organs to BMR is different in infants & young animals

Reason for decrease in BMR as get olderAs increase in age, muscle and adipose tissue

increase in proportion of body weightBoth these tissues have a low resting energy

requirement Internal organs (Brain, Liver, Kidneys, Heart)

have a high resting energy requirement In a young child (1-5y) these organs contribute

approx 18% of body weight while in adult (21-30y) this represents approx 6%

Thus on a kg BW basis the child has a higher BMR

Growth

Infants and children have an increased requirement for energy to maintain growth

Growth often considered to have 3 phases: infant, childhood and pubertal

These phases not distinct but can merge into a continuum

Male & Female Growthweight (50th percentile)

010

2030

4050

6070

80

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

age (y)

wei

ght

(kg)

malefemale

infant childhood pubertal

Male & Female Growthheight 50th percentile

020406080

100120140160180200

0 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21age (y)

hei

ght

(cm

)

malefemale

infant childhood pubertal

Infant growthCharacterised by a rapid, but decelerating rateFoetal & new-born growth is primarily nutrient-

led and insulin regulated. This changes towards growth-hormone regulated over the the first 2-3 years

In first 12-18 months growth velocity will vary considerably between individuals as they seek to attain their genetic potential

Those growth-restrained in utero may show rapid (catch-up)_ growth while those over-nourished (e.g. maternal diabetes) may show slow growth

Infants and Young Children Very Vulnerable

Dependent on CarerHigh Growth PotentialHigh demands but low storesPhysiological immaturity reduces ability to

respond to over- and under –supply of nutrients

In 1998 11.6 million under-fives died from malnutrition

Childhood Growth

Relatively slow and growth hormone ledWill normally grow along a genetically-

predetermined “centile” (size relative to the age-specific population

Deviation from the centile usually suggests illness, over- or under-nutrition

This is why children’s growth is normally carefully monitored

Pubertal Growth

Changes occur in both physical size and body composition

Growth velocity and nutrient requirements vary greatly because age of onset of puberty varies

Delay may be due to illness or severe undernutrition

Estimated Average Requirements for Children(MJ/d)

Age Males Females

0-3mth 2.28 2.16

4-6mth 2.89 2.69

7-9mth 3.44 3.2

10-12mth 3.85 3.61

1-3y 5.15 4.86

4-6y 7.16 6.46

7-10y 8.24 7.28

11-14y 9.27 7.72

15-18y 11.51 8.83


Basal Metabolic Rate (BMR)ActivityPost- Prandial thermogenesis Pregnancy & LactationGrowth

Trauma, Sepsis & Burns

Energy requirements during injury, sepsis & burns

Clinical Nutrition (2005) Chapter19: Nutrition in Surgery & Trauma. Eds. Gibney, Elia, Ljungqvist & Dowsett

Injury increases the energy requirements due to the energy used for defence and repair

In recent years it has been recognised that the extra-energy required has been over-estimated

Burns elicit the most pronounced effect with increases in resting energy expenditure and loss of lean and fat body tissue

If a burns victim loses more than 30% of their body weight they are likely to die

Energy Requirements in Sepsis & Trauma

Serious injury or illness can often be accompanied by starvation because the patient either can’t or won’t eat

Starvation has evolved to allow the body to survive in periods when food is not available. Thus, energy use is minimized

Injury & illness often requires the mobilization of energy and other nutrients for defence and repair

This mechanism tends to take priority even in the presence of starvation

Comparison of Injury & Starvation

Starvation Injury

Metabolic Rate Decreased Increased

Weight Slow loss, primarily from fat stores

Rapid loss. 80% fat, rest protein

Nitrogen Losses reduced Losses increased

Hormones Early small increase in catecholamines, cortisol, GH then slow fall in glucagon & cortisol. Insulin decreased

Increases in catecholamines, glucagon, cortisol, GH

Relative insulin deficiency

Water & Na Initial loss Retention

Phases of Response to Injury

The Ebb PhaseThe Catabolic or “Flow” PhaseThe Anabolic Phase

The Ebb Phase

Lasts for a few hoursDepression of metabolic function and a

reduction in energy expenditure

Endocrine Response in the Ebb Phase

Increase in secretion of adrenaline & cortisol from the adrenal gland

Increase in glucagon/decrease in insulin from the pancreas

Metabolic response in Ebb Phase

In response to hormonal changes Glycogen breakdown in muscle for energy Glycogen breakdown in liver releasing glucose

into blood Triacylglcerol breakdown in adipose tissue

releasing free fatty acids into circulation

The Flow Phase

“Hypermetabolic” phase which may last for several weeks

Magnitude of changes reflect the severity of the trauma

Physiological Features of the Flow Phase

Increased Heat Production Increased resting metabolic expenditure Increased respiration rate Increased pulse rateAll lead to an increased energy

requirement

Effect of injury on resting energy expenditure

Injury Increase in requirement

Uncomplicated surgery

Multiple fractures

Major surgery + sepsis

Major Burns



Uncomplicated surgery +10%

Multiple fractures


Major Burns




Multiple fractures +10-20%


Major Burns





Major surgery + sepsis +25-50%

Major Burns





Major surgery + sepsis +25-50%

Major Burns +50-100%

Determine approx BMRAdjust for stress according to nomogramAdd a combined factor for activity andDiet induced thermogenesis

Bedbound immobile +10%Bedbound mobile + 15-20%Mobile on Ward + 25%

Energy Requirements of AdultHospital Patients

Glucose metabolism

Glucose required by damaged tissues as an energy supply during repair

However, insulin resistance is common during the Flow Phase

Antagonistic effects of cortisol and growth hormone Increase plasma Free Fatty Acids.

Therefore, although plasma glucose is raised it is not necessarily available to tissues

Protein MetabolismA recent study suggests that 16% of total body protein can

be lost following severe trauma or sepsis over 21 days Moderate trauma- protein synthesis Severe trauma- protein synthesis & protein degradation

Major site of loss is skeletal muscleCardiac muscle largely sparedLiver may actually increase synthesis of proteins

associated with an inflammatory response (e.g. fibrinogen, C-reactive protein) while reducing others (e.g. albumin)

Protein Metabolism

Skeletal Muscle Protein

Essential AAs

Liver & damaged tissuesfor protein synthesis

Branched chain AAs

alanine glutamine

Protein Metabolism


Essential AAs


Branched chain AAs

alanine glutamine

Liver forGluconeogenesis

Protein Metabolism


Essential AAs


Branched chain AAs

alanine glutamine

Liver forGluconeogenesis

Damaged tissuesSource of N for purine & pyrimidine synthesis for DNA/RNA

Fat Metabolism

Body fat becomes the major source of energy

Increase in adipose tissue lipogenesis and plasma free fatty acids

Not normally associated with an increase in ketogenesis (levels of insulin might be high enough to prevent this)

The anabolic phase

Catabolism declines and enter an “anabolic” phaseOften associated with return of appetiteUnless there are specific reasons, normal feeding

should be resumed as soon as possible Nutritional therapy should aim to restore muscle

mass and increase protein synthesisRecent evidence suggests that insulin treatment to

reduce hyperglycaemia may reduce risk of infection

Consequences of over-feeding

In patients suffering from malnutrition it is important to avoid overfeeding, as it can have a number of complications Too much protein can cause uraemia,

dehydration and metabolic acidosis To much carbohydrate can cause

hyperglycaemia and hypertriglyceridaemia To much fat can cause hypertriglyceridaemia

and fat-overload syndrome

energy 2013.ppt

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