Fuel Homeostasis
Energy Content of Foods and Energy Requirements
Content created and narrated by: Jiyan Ma PhD
Molecular and Cellular Biochemistry
For more information contact:
Charles E. Bell PhD
Associate Professor, Dept. of Molecular and Cellular Biochemistry
Primary Learning Objective
Integrate the metabolic pathways leading to ATP production to those
involving biosynthetic pathways leading amino acid, lipids, nucleic
acids and correlate with their changes in diseases
Secondary Learning Objective
• Define calorie, respiratory quotient, and daily energy
expenditure, and describe how these values are measured or
calculated
• Define and differentiate direct and indirect calorimetry; identify
the reasons why a direct calorimetry may give different values
than animal or human calorimetry
• Define basal metabolic rate (BMR), thermic effect of food (also
called Diet-induced thermogenesis, DIT), daily energy
expenditure, and described how these values are measured or
calculated
Content
1. Units Used to Measure Energy
2. Energy Content of Food
— 2.1 Direct Calorimetry
— 2.2 Indirect Calorimetry
— 2.3 Respiratory Quotient (RQ)
— 2.4 Energy Density
3. Energy Needs of Human Body
— 3.1 Basal metabolism
— 3.2 Physical activities
— 3.3 Thermic effect of food
— 3.4 Calculating daily energy expenditure
1. Units Used to Measure Energy
1000 calorie
= 1 kilocalorie (kcal)
= 1 Calorie
= 4180 joules
= 4.18 kilojoules (kj)
2. Energy content of food
• 2.1 Direct Calorimetry
e.g.
CHO + O2
CO2 + H2O
Heat
Question:
Is the energy content determined by direct calorimetry
the same as that measured inside the body?
2.2 Indirect Calorimetry
Indirect calorimetry estimates caloric yield in
the body by measuring the oxygen consumed,
carbon dioxide produced, and nitrogen
eliminated.
Carbohydrates
Fats
Proteins
Direct calorimetry
3.7-4.3
9.5
4.0-4.3
Metabolic (average)
4.1
9.3
4.1
O2 consumed (L/g)
0.75-0.83
2.03
0.97
CO2 produced (L/g)
0.75-0.83
1.43
0.78
kcal/ O2 consumed (L)
5.0
4.7
4.5
Kcal/CO2 produced (L)
5.0
6.6
5.6
Energy content (kcal/g)
2.3 Respiratory Quotient (RQ)
Respiratory quotient (RQ) is defined as the
ratio of the volume of CO2 produced (exhaled)
to that of O2 utilized (inhaled) in the process
of metabolism of a substance.
RQ for Major Fuels
Carbohydrate
1
Protein
0.8
Fat
0.7
RQ is used to determine the energy contribution
from one type of nutrient in a mixed diet.
Fuel usage in a Marathon runner
In this study, a well-fed runner ran for 25 minutes at a given rate, stopped for 5
minutes so tests could be run, then continued with the next rate for 25 minutes
and so on for a total of six hours. All the results are given at the table below.
Protein metabolism accounted for only 2% of the total energy production and
has been neglected. (Edwards, et al., Am. J. Physiol. 108:203 (1934))
Measurements
Running
Rate
Body
Weight
Blood
Sugar
O2
Use
km/hr
kg
Mm
moles
0
59.61
5.6
11.3
59.32
4.6
2.75
9.3
59.03
4.9
11.3
58.82
9.3
11.3
~P Energy Production
RQ
Total
From
CHO
From
Fats
moles
moles
moles
0.97
17.1
15.5
1.6
2.34
0.96
14.5
12.7
4.8
2.71
0.94
16.6
58.65
58.25
4.4
4.6
2.31
2.76
0.88
0.86
9.3
58.15
4.5
2.40
11.3
57.93
4.2
9.3
57.78
11.3
Fraction
From
Fat
Wt. of Fuels
Glycogen
Fats
g
g
0.09
67
3
1.8
0.12
55
4
13.5
3.1
0.19
58
6
13.8
16.5
8.5
9.0
5.3
7.5
0.38
0.45
37
39
11
15
0.82
14.1
5.7
8.4
0.60
25
16
2.85
0.82
16.7
6.8
9.9
0.59
29
19
4.3
2.44
0.79
14.1
4.2
9.9
0.70
18
20
57.48
3.8
2.85
0.82
16.7
6.8
9.9
0.59
29
19
9.3
57.30
4.1
2.49
0.79
14.3
4.3
10.0
0.70
19
20
11.3
57.55
3.7
2.88
0.81
16.9
6.3
10.6
0.63
27
21
9.3
57.35
3.2
2.48
0.77
Total
14.3
185.5
3.2
96.5
11.0
89.0
0.77
14
415
22
175
Fuel Consumption During Exercise
Duration
Fuel types
~ 10 minutes
Glycogen
~ 10 -20 minutes
Glycogen
Glycogen
> 20 minutes
Glycogen
Glycogen
> 2 hour
Vigorous activity
(>75% VO2max)
Continue for a short time
If continue…
Fatty acid
Glycogen depletion
Fatty acid
“hitting the wall”
Gluconeogenesis
Blood glucose
hypoglycemia
Halt CNS function
Fatty acid
2.4 Energy Density
Energy Density (or calorie-density) is the
number of calories per gram of a food item.
Higher energy density
Taco shell
Bologna
Fried chicken
Fried pork chop
Cheseburger
Hash brown potato
Fried fish
Fried rice
Potato salad
Sweetened Strawberries
(frozen)
kcal/g
4.7
3.1
2.8
2.8
2.7
2.2
2.2
1.6
1.4
1.1
Low energy density
Corn tortilla
Sliced turkey breast
Grilled chicken
Broiled pork chop
Bean burrito
Broiled potato
Broiled fish
Rice
Tossed salad (with dressing)
Fresh Strawberries
kcal/g
2.2
0.9
1.7
2.0
1.9
0.9
1.2
1.3
1.1
0.3
Summary for Energy Content of Food
•
•
•
•
•
The units used to measure energy in Nutrition include calorie,
kilocalorie (kcal) and Calorie.
Direct calorimetry determines the total energy content of a food
by measuring heat released from total physical combustion of a
food.
Indirect calorimetry estimates caloric yield in the body by
measuring oxygen consumed, carbon dioxide produced, and
nitrogen eliminated.
Respiratory quotient is the ratio of the volume of CO2 produced
to that of O2 utilized, which is used to determine the energy
contribution from one type of nutrient in a mixed diet.
Energy density is the number of calories per gram of a food item.
3. Energy Needs of Human Body
The body expends energy to maintain physiological functions,
support physical activity and process food. Collectively, these
components of energy use make up total energy expenditure
(TEE).
3.1 Basal Metabolism
Basal metabolism is the energy expended to
sustain basic, involuntary life function such as
respiration, beating of the heart, nerve function, etc.
Basal Metabolic Rate (BMR) is the most commonly used
measure for basal metabolism. It is measured right after
awakening using indirect calorimetry and requires the
testing subject to be:
• awake (it is 10% less if asleep)
• lying quietly in a room at neutral warm temperature
• in a postabsorptive state (fasting overnight)
• free from strong emotions
3.2 Physical activities
3.3 Thermic effect of food
fats
carbohydrate
protein
Mixed diet
~5%
~10%
~20-30%
~10%
3.4 Calculating daily energy needs
1. Determine BMR and calculate daily (24 hours) energy
requirement for basal metabolism
2. Correct for the 10% decrease in metabolic rate during
sleep
3. Determine the energy requirements for daily physical
activity (using the table provided on handout). The
values are low because they do not include BMR and
they represent an averaging over a long period of time
(waking hours)
4. Correct for thermogenesis (10% for mixed diet)
5. Add all together and that is the daily energy needs
Summary for Energy Needs of Human Body
•
•
•
•
•
The total energy expenditure of human body consists of three
major parts, which are basal metabolism (~50 - 70%), physical
activities (~15 - 30%), and thermic effect of food (~10%).
Basal metabolism is the energy expended to sustain basic
involuntary function, and BMR (Basal Metabolic Rate) is the
most common measure to determine the basal metabolism.
BMR is influenced by many factors, and in adults, BMR is most
closely related to lean body mass.
Physical activities account for ~15 - 30% of total energy
expenditure in the body.
Thermic effect of food is the extra heat produced when food is
ingested, which is estimated as 10% of a mixed diet.
A brief review of terms
Kilocalorie (kcal) A commonly used energy measuring unit, which equals to the energy required
to raise the temperature of 1 kg of water for 1 degree centigrade. 1 kcal = 1000 calorie = 1 Calorie
= 4180 joules = 4.18 kilojoules (kj)
Direct calorimetry A measurement of energy content of food, which meausres the heat released
from total physical combustion of food.
Indirect calorimetry A measurement of energy expenditure obtained by assessing nitrogen
excretion, oxygen consumption and carbon dioxide production.
Respiratory Quotient (RQ) A measurement used to assess the energy contribution from different
types of nutrients. It is defined as the ratio of the volume of CO2 produced to that of O2 utilized in
the process of metabolism of a substance.
Energy density (caloric density) Energy per amount of a food item.
Total energy expenditure (TEE) Total energy expended by the body. It can be divided into three
parts: basal metabolism (50-70%), physical activities (15-30%), thermic effect of food (10%).
Basal metabolism Energy expended to sustain activities related to basic vital body functions.
Basal metabolic rate (BMR) Energy expended for basal metabolism per hour, which is closely
related to lean body mass.
Resting metabolic rate (BMR) A measure of energy expenditure assessed under less striingent
conditions than is BMR.
Thermic effect of food (also called thermogenesis, diet induced thermogenesis (DIT)) Energy
expended for the digestion, absorption, and metabolism of nutrients.
Thank you for completing this
module
I can answer any questions
you may have:
Charles Bell PhD
bell.489@osu.edu
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