1. Role of Metabolism in Nutrition

2. Metabolism
• Metabolism – people aquire and use free
energy to carry out actions
• Catabolism (degradation)
– Nutrients and cell constituents are broken
down for salvage and/or generation of energy
• Anabolism (biosynthesis)
- The process of releasing the energy that is consumed.

3. Role of Metabolism in Nutrition
Definition: the sum of all biochemical changes that take
place in a living organism.
Group these reactions into two types:
anabolic
catabolic
Reactions:
require energy
release energy
Produce:
more complex
compounds
more simple compounds
Modus
Operandi:
Occurs in small steps, each of which is controlled
by specific enzymes.

4. Examples of each type of metabolism:
Anabolic Pathways
Protein Biosynthesis
Glycogenesis
Gluconeogenesis
Fatty Acid Synthesis
Catabolic Pathways
ATP
Generated
FOR
Provides
Energy
Glycolysis
TCA (Krebs cycle)
ß-oxidation
Respiratory Chain
What you need to know is that Catabolic Pathways take sugars
and carbs to turn them into ATP which is our major energy
system. The anabolic pathways then allow your body to use
the energy released by Catabolic pathways.

5. Metabolism:
Who Needs It?
verage American consumes ~ 1450 lbs
each year.
(± 600kg) of f
ssuming that 98.2% of this energy is
etabolizable, 1424 lbs (± 590kg) is used to supply
eeds.
upplies roughly 1 x 106 kcals/ year

6. How do we employ energy?
•
MECHANICAL- muscle contraction
•
ELECTRICAL- Use of internal organs.
•
CHEMICAL-
transformation through catabolic
and anabolic processes.

7. International Unit of Energy: Joule
: energy used when 1 Kg is moved
1 meter by a force of 1 Newton
: kJ = 103 J; MJ = 106 J
: 1 kcal = 4.184 kJ
: Protein:
CHO:
Fat:
17 kJ or 4 kcal/g
17 kJ or 4 kcal/g
37 kJ or 9 kcal/g

9. Energy needs
Measurement of Energy Intake
Metabolic Energy Yields
Fuel
KJ/g
Kcal/g
Fat
38
9
Alcohol
29
7
Carbohydrates 17
4
Protein
4
16

10. Energy needs
Measurement of Energy Intake
% Energy from carbohydrates, protein and fat
Food
Total energy
% Energy
content of
from
serving (kJ) carbohydrate
% Energy
from
protein
%
Energy
from fat
Chocolate
1195
43
6
51
Peas
230
47
35
18
Chicken Breast
1138
0
75
24
Potato boiled
535
89
10
1

11. Energy Balance: Input vs Output

12. Energy Balance
• Energy In = Energy Out
– Weight Maintenance
• Energy In > Energy Out
– Weight Gain
• Energy In < Energy Out
– Weight Loss

13. Energy Balance
• Sources of fuel for energy
– Input from diet: carbs, fat, prot, alcohol
– Stored energy: glycogen, fat, muscle
• Energy outgo from:
– Basal metabolism
– Physical activity
– “Dietary thermogenesis”

14. Energy In
• Food and Beverages
– Food composition tables
– Bomb Calorimetry
• Complex social, environmental,
physiological control

15. Energy Out
• Energy of food = Body Energy = ATP
– Overall efficiency 25%, 75% released heat
• Energy out:
• 3 main components:
– Basal Metabolic Rate
– Thermic Effect Food
– Physical activity

16. BMR > Activity > Dietary Thermogenesis

17. Energy needs
Measurement of Energy Output
Energy Output
Energy of food
• 50% efficiency
ATP + Heat Loss
ATP
• 50% efficiency
“Work “+ Heat Loss
“Work “
Heat

18. Basal Metabolic Rate
• BMR = number of calories would need daily
simply to stay alive if were totally inactive, in bed,
awake for 16 hours & slept for 8 hours
• Harris-Benedict Equation:
• Women: 661+(4.38 x weight in pounds)+(4.38 x
height in inches)-(4.7 x age)=BMR
• Men: 67+(6.24 x weight in pounds)+(12.7 x
height in inches)- (6.9 x age)=BMR

19. Factors affecting BMR
• 1) Body Size & Composition
↑Lean tissue ↑BMR
– Body weight ↑wt ↑lean tissue (but also ↑fat)
• 2) Age:
↑age ↓Lean tissue
• 3) Sex: Men ↑lean
• 4) Activity: Exercise ↑lean tissue

20. Factors affecting BMR
• 5) Growth ↑BMR
– Children, pregnancy
• 6) Fasting/starvation: ↓BMR
• 7) Fever/stress ↑BMR
• 8) Smoking/caffeine: ↑BMR