This document discusses energy, metabolism, and how the body uses food for fuel. It covers the following key points: 1. Energy is measured in kilojoules and kilocalories, and is required for life processes like heart function, organ function, temperature regulation, and muscle movement. Different people need varying amounts depending on age, gender, size, activity level, and genes. 2. Energy comes from carbohydrates, proteins, and fats in food. Carbohydrates and proteins provide 4 calories per gram while fat provides 9 calories per gram, making it the most energy dense. 3. Basal metabolic rate is the minimum energy needed for basic body functions at rest. It can

1. Food and Metabolism

2. Energy is the ability to do work. It is measured in kilojoules (kJ) and kilocalories
(kcals). We all need energy to grow, stay alive, keep warm and be active. Energy is
essential for life, and is required to fuel many different body processes, growth and
activities.
These include:
• keeping the heart beating;
• keeping the organs functioning;
• maintenance of body temperature;
• muscle contraction.

3. Different people need different amounts of dietary energy
depending on the following:
• age;
• gender;
• body size;
• level of activity;
• genes.

4. Energy is provided by the carbohydrate, protein and fat in the food and drink we
consume.
These are known as macronutrients.
The amount of energy that each of these macronutrients provides varies.

5. Definition of terms
Calorie: unit used to measure energy
Kilocalorie is a unit of energy commonly used to express
energy value of food.
Food energy is the amount of energy in food that is a
available through digestion. The energy value of food
indicates its value to the body as fuel.

6. Kilocalories come from foods and beverages
• Bomb calorimeter used in laboratories to measure
kilocalories in foods and beverages
- Results must be adjusted for the physiological fuel
values
• Nutrition analysis software or food composition tables
can estimate energy in
- Carbohydrate and Protein: 4 kcal/gram
- Fat: 9 kcal/gram
- Alcohol: 7 kcal/gram

7. Energy
Energy intake is measured in joules (J) or kilojoules (kJ), but many people
are more familiar with Calories (kcal).
1 kilojoule (kJ) = 1,000 joules
1 megajoule (MJ) = 1,000,000 joules
1 kilocalorie (kcal) = 1,000 calories
To convert from one unit to another:
1 kcal = 4.184 kJ
Therefore, a 2000-kcal diet
provides 8.368 MJ or 8368 kJ
1 MJ = 239 kcal

8. Carbohydrate (starch and sugars) provides 3.75 kcal (16 kJ) per gram (for the
purposes of food labelling this is rounded up to 4 kcal (17kJ) per gram).
Protein provides 4kcal (17kJ) per gram.
Fat is the most energy dense nutrient, providing 9kcal (37kJ) per gram.
Energy intake can be estimated by applying these figures to the amount of
carbohydrate, protein and fat we consume from food and drink.
Alcohol also provides energy at 7kcal (29kJ) per gram.

9. 16
17
29
37
0
5
10
15
20
25
30
35
40
Carbohydrate Protein Alcohol Fat
Energy
(kJ)
per
gram
Energy in food and drinks
Per gram, fat provides
more than twice the energy
of carbohydrate.

10. Which of these foods do you think contributes the most energy per 100g?
Total Energy: 1135.5kJ
Carbohydrate 982.6kJ
Protein 170.0kJ
Fat 66.6kJ
Total Energy: 3696.0kJ
Carbohydrate 0.0kJ
Protein 0.0kJ
Fat 3696.0kJ
Total Energy: 450.9kJ
Carbohydrate 17.0kJ
Protein 312.8kJ
Fat 122.1kJ
Energy in food and drinks

11. How much energy do we need?
Energy requirements vary from person to person,
depending on the Basal Metabolic Rate (BMR) and
Physical Activity Level (PAL).
Total energy expenditure (TEE) =
BMR x PAL

12. What Is Energy Balance and Why Is It
Important?
Energy balance is achieved when the kilocalories consumed
equal the kilocalories expended

13. Energy Balance
Energy balance can be maintained by:
• regulating energy intake through the diet;
• adjusting physical activity levels;
• a combination of both.
Energy in:
food and
drinks
Energy
out:
activity
Energy in = Energy out = Energy balance

14. The Concept of Energy Balance

15. A person is said to be in positive energy balance when the
diet provides more energy than is needed to meet energy
demands of the body. Energy is stored as fat and the
person puts on weight over time.
People who achieve a positive energy balance over an
extended period of time are likely to become overweight
or obese.
Being overweight or obese is associated with an increased
risk of developing certain cancers, cardiovascular disease
and type 2 diabetes.
Positive energy balance
Energy in:
food and
drinks
Energy
out:
activity
Energy in > Energy out = Weight gain

16. A person is said to be in negative energy balance when
there is insufficient energy from the diet to meet energy
demands of the body. Energy is derived from energy
stores and the person loses weight.
People who achieve a negative energy balance over an
extended period of time are likely to become
underweight.
Being underweight is associated with health problems,
such as osteoporosis (low bone mass), infertility
(difficulty to conceive) and even heart failure.
Negative energy balance
Energy
in: food
and
drinks
Energy
out:
activity
Energy out > Energy in = Weight loss

17. Experts have estimated the average requirements for energy for
different types of people.
These figures are known as Estimated Average Requirements (EAR)
for energy.
It is also recommended that:
• about 50% of our energy intake should come from carbohydrate;
• no more than 35% of our energy intake should come from fat.
That means around 15% of our energy intake should come from protein.
Dietary reference values

18. Estimated average requirements (EARs) vary throughout life.
Babies, young children and teenagers need more energy in
relation to their size to grow and be active.
After the age of 18, energy requirements decrease and remain
the same until 50, but actual needs depend on people’s activity
levels.
Energy requirements for older adults decrease as activity levels
fall, and there is a reduction in the basal metabolic rate.
Estimated average requirements

19. The Scientific Advisory Committee
on Nutrition (SACN) has published
reference values for daily energy
requirements as follows:
EARs - children Breast-fed
Months Boys (MJ) Boys (kcal) Girls (MJ) Girls (kcal)
1-2 2.2 526 2.0 478
3-4 2.4 574 2.2 526
5-6 2.5 598 2.3 550
7-12 2.9 694 2.7 646
Years Boys (MJ) Boys (kcal) Girls (MJ) Girls (kcal)
1 3.2 765 3.0 717
2 4.2 1004 3.9 932
3 4.9 1171 4.5 1076
4 5.8 1386 5.4 1291
5 6.2 1482 5.7 1362
6 6.6 1577 6.2 1482
7 6.9 1649 6.4 1530
8 7.3 1745 6.8 1625
9 7.7 1840 7.2 1721
10 8.5 2032 8.1 1936
11 8.9 2127 8.5 2032
12 9.4 2247 8.8 2103
13 10.1 2414 9.3 2223
14 11.0 2629 9.8 2342
15 11.8 2820 10.0 2390
16 12.4 2964 10.1 2414
17 12.9 3083 10.3 2462
18 13.2 3155 10.3 2462

20. EARs - adults
Years Men (MJ) Men (kcal) Women (MJ) Women (kcal)
19-24 11.6 2772 9.1 2175
25-34 11.5 2749 9.1 2175
35-44 11.0 2629 8.8 2103
45-54 10.8 2581 8.8 2103
55-64 10.8 2581 8.7 2079
65-74 9.8 2342 8.0 1912
75+ 9.6 2294 7.7 1840
Why do you think there is a difference in requirements for males and females?
What effect would increasing activity levels have on the energy requirements?

21. Metabolic Rate
• It is the rate of energy production within the body.
• ATP molecules are the unit of biologic energy. ATP is converted to ADP to
release energy, which is needed for all bodily functions, such as cell division,
contraction of muscles, maintaining body temperature, movement of fluids
etc.
• ATP can be synthesized from energy molecules (carbohydrate, protein and
fat) aerobically or anaerobic ally.
• The rate of ATP production (to perform the bodily functions) is closely
coordinated with cardiovascular response.
• Higher ATP consumption rate higher is oxygen consumption rate and higher
the cardiac output.

22. What is basal metabolic rate?
Basal metabolic rate (BMR) is the rate at which a person uses
energy to maintain the basic functions of the body when it is at
complete rest, such as:
• breathing;
• keeping warm;
• keeping the heart beating

23. Unit of energy production (metabolism)
• Basic unit of energy = Force x distance = 1N x 1m = 1 Joule
• Energy content in food is given in terms of Kcal (commonly referred as
Calorie).
• Kcal is the amount of energy needed to raise the temp of 1 kg of water by 10
C.
• 1 Joule = 0.000239 kcal
• 1 kcal = 1/0.000239 J = 4184 J
• Rate of energy consumption = 1 Joule/sec = 1 watt
• 1 kcal/hr = 1/3600 Kcal/sec = 4184/3600 J/sec = 1.16 watt

24. Basal Metabolic rate
Energy metabolism needed to maintain body temperature
and body functions (regeneration of cells, respiration,
circulation etc) at rest.
– 1.28 W/kg for males,
– 1.16 W/kg for females (higher percent of fat do not need
metabolism).
– Children have higher surface to volume ratio more heat loss,
also higher growth rate so they have higher basal metabolic
rate.

25. Factors that Affect Basal Metabolic Rate
Exercise: This is one of the biggest factors
that influence BMR.
BMR is higher in people who exercise
regularly

26. Hormones: an increase in thyroid hormones increases
BMR, decreased levels of the hormone lower BMR
Body Temperature: Excessive heat or cold raise BMR

27. Gender: Males tend to have higher basal metabolism than
females due to an abundance of hormones such as
testosterone ad elevated levels of muscle mass compared to
females
 Age: as we get older basal metabolic rate becomes
increasingly slower.

28. Surface Area: Taller individuals have a higher BMR
compared to shorter individuals. More surface area
means more heat lost from the body, which causes the
metabolism to speed up in order to maintain body
temperature.

29. Stress and Illness: increase in hormone activity due to
physical or physiological stress increase BMR.
Starvation: Fasting for more than 48 hrs. will lead to a
decrease of 50% of Basal Metabolic Rate.

31. Body mass index (BMI)
Body Mass Index (BMI) can be used to
identify if an adult is a correct weight for
height.
BMI can be calculated as follows:
BMI = weight (kg)
(height in m)2
Recommended BMI range (adults)
Less than 18.5 Underweight
18.5 to 25 Desirable or healthy
range
25-30 Overweight
30-35 Obese (Class I)
35-40 Obese (Class II)
Over 40 Morbidly or severely
obese (Class III)

32. www.foodafactoflife.org.uk © Food – a fact of life 2019
BMI calculation
Calculate the BMI. Click the colour blocks to reveal the answers.
51kg 82kg 78kg
1.7m x 1.7m 1.95m x 1.95m 1.63m x 1.63m
= 17.6 BMI = 21.6 BMI = 29.4 BMI
Underweight healthy weight overweight
1. Samantha
Height: 1.70m
Weight: 51kg
2. Dale
Height: 1.95m
Weight: 82kg
3. Ruth
Height: 1.63m
Weight: 78kg

33. Health Risks Associated with Body Weight and Body
Composition
Being overweight increases health risks
• Overweight and obesity associated with increased risk of
heart disease, hypertension, stroke, hyperlipidemia,
gallstones, sleep apnea, and reproductive problems
• Increases risk of certain cancers including colon, breast,
endometrial, and gallbladder cancer
• More than 80% of people with type 2 diabetes are
overweight
• Metabolic syndrome is associated with central obesity

34. Health Risks Associated with Body Weight and Body
Composition
Being underweight also increases health risks
• Symptomatic of malnutrition, substance abuse, or disease
• Higher risk of anemia, osteoporosis and bone fractures,
heart irregularities, and amenorrhea
• Correlated with depression and anxiety, inability to fight
infection, trouble regulating body temperature, decreased
muscle strength, and risk of premature death
• May be unintentional and due to malabsorption
associated with diseases such as cancer, inflammatory
bowel disease, or celiac disease

35. Digestion Metabolism
• Energy needed to digest food
• Approximately 10% of the total metabolic demand.

36. Activity Metabolism
Activity Metabolism increases with physical
exertion level. This is due to increase demand of
ATP from muscle contraction, increase work of
ventilation, increased work by the heart muscle.
Population values for Activity Metabolic Rates for
various industrial tasks are available or can be
predicted for job design purposes.
Kcal/hr kcal/min
Light 0-189 0-3.15
Moderate 189-300 3.15-5
Heavy over 300 over 5

37. RESPONSE TO EXERCISE
To match the energy demand for work, adjustment occurs in
1. Heart Rate – varies from resting 70 bpm to maximum (220-age)
2. Stroke Volume – increases gradually up to 40% for Maximal Voluntary Contraction.
3. A-V difference in O2 concentration –
resting arterial 19 mL/100 mL, venous 15 mL/100 mL
In extreme situation venous O2 concentration can drop to 6 mL/100 mL
4. Blood redistribution
5. Blood Pressure
6. Breathing rate
7. Ventilation
Each of these physical responses can be used to measure physical work load.

38. Heart rate and
activity metabolism rate
• Oxygen uptake rate during exercise provides good estimator of ATP use,
hence the metabolic rate.
• In normal physical work, cardiac output (amount of blood pumped per
minute) also matches the oxygen supply needed for a workload.
• Cardiac Output = Heart Rate (/Min) *Stroke Volume (liters) liters/min.
• For an individual Stroke Volume is affected by the intensity of exercise. SV
increases with exercise intensity and reaches its maximum level for an
exercise of about 40% of ones maximum aerobic capacity. For an individual,
it also changes with body posture.
• Heart Rate is an excellent predictor of workload or cardiovascular load for
moderate to heavy intensity physical work.

39. Heart rate and
level of work intensity
• Heart Rate is effected by:
– (i) Emotions especially at low metabolic level.
– (ii) Ambient temperature
– (iii) Exercise intensity
• When using heart rate for light work, other factors needs to be
controlled appropriately.
• For lighter type of tasks also HR is often used to compare exertion
levels of two tasks.
• Heart rate measurement is comparatively easy and often used in
Ergonomics studies to compare physiological costs of work.

40. Classification of physical work intensity
Type of
work
Kcal/Hr Kcal/min
O2 uptake
L/min
HR
(bpm)
Light 0-189 0-3.15 .5 90
Moderate 189-300 3.15-5 .5-.99 90-110
Heavy 300+ 5+ 1-1.49 110-130

41. MEASURMENT OF CARDIOVASCULAR LIMITS OF AN
INDIVIDUAL
• VO2 max in mL/kg- min is a determinant of ones cardiovascular
capacity or fitness level.
• It can be measured in laboratory
• Type of task to determine VO2max also has an influence on VO2
max. Larger muscle group used, produces larger values of VO2
max.
• VO2 max varies with fitness level and age

43. Effect of mental workload on HR
• Response to mental workload, Heart Rate variability
(sinus arrhythmia) is reduced with higher mental
workload.

44. 2009
Energy Imbalance
Effects in the Body
 Excess energy is stored in fat cells, which enlarge or multiply.
 Enlargement of fat cells is known as hypertrophy,
whereas multiplication of fat cells is known as hyperplasia.
 With time, excesses in energy storage lead to obesity.
Fat cells
J La State Med Soc .2005; 156 (1): S42-49.

45. 2009
Fat Cell Enlargement
Hypertrophy
 Enlarged fat cells produce the
clinical problems associated with obesity,
due to the following:
 The weight or mass of the extra fat
 The increased secretion of free fatty acids
and peptides from enlarged fat cells.
J La State Med Soc .2005; 156 (1): S42-49.

46. 2009
 Obstructive sleep apnea
 Osteoarthritis
 Cardiovascular disorders
 Gastrointestinal
disorders
 Metabolic disorders
 Endometrial, prostate
and breast cancers
 Complications of pregnancy
 Menstrual irregularities
 Psychological disorders
Individuals who are obese are at a greater risk of developing:
Morbidity
Associated with Obesity
CDC