Energy intake and expenditure

Mariam Abdul Latif & Dr Yasmin Ooi 20 July 2008

26 September 2013

School of Food Science and Nutrition

Learning outcomes After completing this module, students should be able to:

•  explain, differentiate and measure energy intake, energy expenditure and energy requirements.

•  understand the concept of energy balance and apply it in explaining body weight gain and biased reporting of energy intake (practical)

•  Describe factors that influence energy expenditure

Next semester Nutrition throughout the lifecycle

•  Energy balance in various conditions: –  Infancy and childhood – Adulthood – Aging

•  Energy requirements in: – Physically active groups – Pregnancy and lactation – Disease and trauma (in detail in Dietetics)

Introduction

•  The average human consumes close to 1,000,000 calories (4,000 MJ) per year.

•  Consider this: 500 MJ is approximately the explosive energy of 100 kg of TNT.

•  We eat the same amount of energy from 800 kg of TNT in a year.

•  Yet, for most people, we manage to achieve energy balance, neither losing weight or putting on weight.

Recap

•  1 kcal = 1000 calories = 1 Calorie •  1 kcal = ? kJ •  1 kcal = 4.1868 kJ •  1 kcal = 4.2 kJ

Terminology

•  Energy intake •  Energy storage •  Energy expenditure •  Energy requirement •  Energy balance •  Metabolisable energy intake

Energy “the capacity to do the work”

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Energy intake •  Human consumes plants and animal products –

breaking down CHOs, fats & protein (during digestion) releasing energy & nutrients

•  The body makes use of the energy from the macronutrients (CHO, fats, protein).

•  Energy intake = caloric or energy content of food as provided by the major sources of dietary energy:

– carbohydrate (16.8 kJ/g), – protein (16.8 kJ/g), –  fat (37.8 kJ/g) and – alcohol (29.4 kJ/g)

Digestive Process

Calculating Food Energy •  Bomb calorimeter •  Weighed food sample

ignited with an electric spark –burned in an oxygenated atmosphere

•  The container is immersed in a known volume of water

•  The rise in the temperature of the water after igniting the food is used to calculate the heat energy generated

1000 calories = 1 kilocalorie = 1 kcal = 4.2 kJoule the energy it takes to raise the temperature of 1kg of water by 1°C.

Energy value of food

•  Not all energy in foods &

alcohol is available to the

body cells

•  Processes of digestion &

absorption are not

completely eficient

•  Fiber : 2 kcal/g –

‘unavailable carbohydrate’

that resists digestion and

absorption (Guenther &

Jensen 2000)

Calculation •  How much is the energy value of a 50

gm butter cake with icing calculated in terms of weight is derived from protein (15%), fat (11%) and carbohydrate (3%).

•  Protein: 15% x 50 gm = 7.5 gm X 4 kcal/g = 30 kcal •  Fat : 11% x 50 gm = 5.5 gm =5.5 gm X 9 kcal/g

= 49.5 kcal •  Carbohydrate: 3% x 50 gm = 1.5 gm X 4 kcal/g

= 6 kcal •  Total energy: 85.5 kcal = 359.1 kJ

Energy storage •  Energy storage = the energy consumed can be: •  Stored

–  Fat (major energy store) –  Glycogen (short-term energy or carbohydrate

reserves) –  Protein (rarely used except in severe cases of

starvation or wasting conditions) •  Used

–  To fuel energy-requiring events

Components of Energy Expenditure

ENERGY  EXPENDITURE  

Basal  metabolic  rate  (BMR)  

~  60-­‐75%  

Thermic  effect  of  food  (TEE)  ~10%  

Energy  expended  in  physical  acMvity  (PAL)  

~  15-­‐30%  

Energy expenditure •  The energy intake (consumed in the form

of food) is used by the body for metabolic, cellular and mechanical work (e.g. breathing, muscular work).

•  Energy expenditure can be divided into: – Basal metabolic rate (BMR) / resting metabolic

rate – Thermogenesis / thermic effect of food (TEE) – Physical activity / thermic effect of exercise – Others

Other energy expenditure – Growing in individuals (negligible except

within the first few months of life) – Adaptive thermogenesis (e.g. exposure to

reduced temperatures, rarely occurs in human except during the first few months of life, fever, other pathological conditions)

– Other activities contributing to thermogenic effects – nicotine (smokers may have a 10% higher energy expenditure), caffeine, capsaicin (in hot chillies)

Back

Resting metabolic rate (RMR) •  RMR : the energy expended in the activities necessary

to sustain normal body functions & homeostasis •  Incl. respiration & circulation, synthesis of organic

compounds, pumping of ion across membranes, energy required by central nervous system, maintain body temp.

•  Approximate energy expenditure of organs in human adults Organ Percentage of RMR

Liver 29 Brain 19 Heart 10 Kidney 7 Skeletal Muscle (at rest) 18 Remainder 17 Total 100

Factors Affecting RMR

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Basal metabolic rate

•  The largest use of energy by the body. •  BMR = the energy expended to maintain basic

physiological functions (e.g. heart beat, muscle contraction and function, respiration).

•  BMR is the amount of energy expended while at rest in a neutrally temperate environment

•  BMR is the minimum level of energy expended by the body to sustain life in the awake state.

How to measure BMR •  BMR is the minimum amount of energy a body requires when lying in physiological

and mental rest •  Subject fasted for 12 hours (post-absorptive

state, meaning the digestive system is inactive)

•  Subject is awake, but rested physically and mentally in a thermoneutral, quiet environment, throughout the measurement. (not too hot or cold)

•  Use direct calorimetry or indirect calorimetry. Note: If one of these conditions is not met (e.g. shorter time interval for fasting) the measurement is usually termed resting metabolic rate (RMR).

BMR or RMR?

•  RMR = Resting Metabolic Rate •  RMR is ≈ 3% higher than BMR, but it is

very difficult to measure BMR. •  RMR is measured instead, and the two

terms and values are used interchangeably.

Measuring energy expenditure

•  Doubly labelled water measurements •  Respiratory quotient (RQ) or

respiratory coefficient

Estimating BMR •  Several equations exist •  The earliest: Harris-Benedict equation (1919)

Original Harris-Benedict (1919)

•  where P is total heat production at complete rest, m is the weight, h is the stature (height), and a is the age, and with the difference in BMR for men and women being mainly due to differences in body weight.

Men

Women

Currently used formula

•  Harris-Benedict estimation formula –  males: RMR = 66.5 + (13.75 x wt) + (5 x ht) – (6.8 x age) –  females: RMR = 655 + (9.6 x wt) + (1.8 x ht) – (4.7 x age)

•  Mifflin-St. Jeor (1990) estimation formula –  males: RMR = (9.99 x wt) + (6.25 x ht) – (4.92 x age) + 5 –  females: RMR = (9.99 x wt) + (6.25 x ht) – (4.92 x age) – 161

Harris-Benedict equation –  Males: BMR = 66.47 + (13.5 x wt) + (5 x ht) – (6.76 x age) –  Females: BMR = 655.1 + (9.56 x wt) + (1.85 x ht) – (4.68 x age)

–  wt = weight (kg), ht = height (cm), age (years)

–  Total calorie need = BMR X activity factor X injury factor –  Injury factor : 1.0 (no illness or non stress) –  Activity factor or physical activity (PAL)

•  Bed rest = 1.0 – 1.1 •  Very light= 1.2 – 1.3 (sit, stand, drive, sew, iron, cook) •  Light = 1.4 – 1.5 (house cleaning, child minding, golf) •  Moderate = 1.6 – 1.7 (gardening, cycling, dancing, tennis) •  Heavy = 1.8 – 2.1 (manual labour, climbing, soccer, basketball) •  Strenuous = 2.2 – 2.4

Currently used formula •  WHO/FAO/UNU (1985)

Males –  18-30 years (MJ/day) = 0.0640 W + 2.84 –  30-60 years (MJ/day) = 0.0485 W + 3.67 Females –  18-30 years (MJ/day) = 0.0615 W + 2.08 –  30-60 years (MJ/day) = 0.0364 W + 3.47

•  Henry & Rees (1991) Males –  18-30 years (MJ/day) = 0.0560 W + 2.800 –  30-60 years (MJ/day) = 0.0460 W + 3.160 Females –  18-30 years (MJ/day) = 0.0480 W + 2.562 –  30-60 years (MJ/day) = 0.0480 W + 2.448

Estimating BMR for Malaysians

Ismail et al., 1998

•  Basal metabolic rate for Malaysians •  The present study shows that the BMR in

adult Malaysian is lower than that predicted by the FAO/WHO/UNU(1985) and Henry and Rees (1991) equations and should not be dismissed as an artifact. There is a good reason to believe that the capacity to low down metabolism in a hot and humid climate experienced throughout the year as a genuine phenomenon in Malaysia besides body size and composition and metabolic economies in response to energy deficit.

Ismail et al., 1998

Thermic effect of food

•  The energy required to digest food. •  10% of total energy expenditure.

Physical activity

•  Dependent on lifestyle: sedentary or physically active.

•  Sedentary = 1.2 PAL •  Active: ≈ 1.9 PAL

Metabolisable energy intake

•  Each food item has a specific metabolisable energy intake.

•  For a normal human this value is obtained by 85% of kcal or kJ in a food item

•  = the amount of energy actually obtained by a human after the digestive processes have been completed.

Energy balance

•  Remember Form 5 Physics? •  The First Law of Thermodynamics? •  That energy can be neither destroyed nor

created. •  Therefore, EI = EE, body energy stores

must remain constant.

Energy balance

•  EI = EE + δ in body weight.

Energy Requirement (WHO 1985) •  The energy requirement of an individual is the level of

energy intake from food that will balance energy expenditure

•  when the individual has a body size and composition, and level of physical activity consistent with long-term good health

•  and that will allow for the maintenance of economically necessary and 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 at rates consistent with good health

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Energy balance •  Refers to the relationship between energy in (food consumption)

and energy out (physical activity). –  Positive balance –  Negative balance

•  Storing Fat as Energy •  Historically, the body’s ability to store energy as fat was

extremely useful. •  Fat stores are still important today, as they help us to

–  Maintain body temperature –  Build and maintain body tissue and cells –  Protect internal organs –  Fuel muscle movement

•  Easy to over-consume food and store an excess of energy and have systematically reduced physical activity in our daily lives through all the conveniences available