Metabolism and diet

Role of Metabolism in Nutrition

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.

Role of Metabolism in Nutrition

Definition: the sum of all biochemical changes that takeplace in a living organism.

Group these reactions into two types:

anabolic catabolic

Reactions: require energy release energy

Produce: more complex more simple compoundscompounds

ModusOperandi: Occurs in small steps, each of which is controlled by specific enzymes.

Examples of each type of metabolism:

Anabolic Pathways Catabolic Pathways

Protein Biosynthesis GlycolysisGlycogenesis TCA (Krebs cycle)Gluconeogenesis ß-oxidationFatty Acid Synthesis Respiratory Chain

What you need to know is that Catabolic Pathways take sugars and carbs to turn them into ATP which is our major energysystem. The anabolic pathways then allow your body to usethe energy released by Catabolic pathways.

ATPGeneratedProvidesEnergy

FOR

Metabolism: Who Needs It?

Average American consumes ~ 1450 lbs ( 600kg) of foodeach year.

Assuming that 98.2% of this energy is metabolizable, 1424 lbs ( 590kg) is used to supply ourneeds.

Supplies roughly 1 x 106 kcals/ year

How do we employ energy?

• MECHANICAL- muscle contraction

• ELECTRICAL- Use of internal organs.

• CHEMICAL- transformation through catabolic and anabolic processes.

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: 17 kJ or 4 kcal/g CHO: 17 kJ or 4 kcal/g

Fat: 37 kJ or 9 kcal/g

Fuel KJ/g Kcal/g

Fat 38 9

Alcohol 29 7

Carbohydrates 17 4

Protein 16 4

Measurement of Energy Intake

Energy needs

Metabolic Energy Yields

Food Total energy content of

serving (kJ)

% Energy from

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

Energy needsMeasurement of Energy Intake% Energy from carbohydrates, protein and

fat

Energy Balance: Input vs Output

Energy Balance

• Energy In = Energy Out– Weight Maintenance

• Energy In > Energy Out– Weight Gain

• Energy In < Energy Out– Weight Loss

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”

Energy In

• Food and Beverages– Food composition tables– Bomb Calorimetry

• Complex social, environmental, physiological control

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

BMR > Activity > Dietary Thermogenesis

Energy OutputEnergy of food ATP + Heat Loss• 50% efficiency

ATP “Work “+ Heat Loss• 50% efficiency

“Work “ Heat

Energy needsMeasurement of Energy Output

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

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

Factors affecting BMR

• 5) Growth BMR– Children, pregnancy

• 6) Fasting/starvation: BMR

• 7) Fever/stress BMR

• 8) Smoking/caffeine: BMR