L29 energy balance, metabolic rate..

Question 1

Define the term” energy balance” and explain the difference between positive and negative energy balance

Answer 1

energy balance = dynamic balance exists between energy input and output

Positive energy balance

• When the rate of energy assimilation is > greater than energy output (gain weight, as fat)

Negative energy balance

• When the rate of energy assimilation is < less than energy output (loss weight)

Question 2

Energy used for? (heat, work, tissue)

Answer 2

• Transport -movement of molecules across membranes
• Mechanical -use of intracellular fibers and filament to create movement (e.g. skeletal muscle contraction)
• Chemical- for growth, maintenance and storage of information and energy
• Subdivided into synthesis (tissue) and storage ( fat and glycogen)

*lost heat no “wasted”, maintain endothermic condition

Question 3

Define terms “gross energy”“c”“metabolizable energy” “ net energy“and”specific dynamic action” *diagram

Answer 3

Gross energy= total energy content of a food

digestible energy = energy contained in nutrient absorbed from digestive tract (after faces , GE subtract indigestible energy)

Metabolizable energy (ME) = chemical energy available

Net energy (NE) = represents TRUE amount of energy available for maintenance, work, growth & reproduction (ME-energy converted to heat during digestive processes)

Specific dynamic action (SDA)= the amount of energy expenditure above the basal metabolic rate due to the cost of processing food for use and storage

Question 4

Define metabolic rate, affected by?

Answer 4

Metabolic rate is the measure to total body metabolism

Linked to body temperature and activity

Question 5

Describe and explain the relationship between metabolic rate and body mass (size)

Answer 5

Metabolic rate(or mass-specific metabolic rate) is non proportional to body mass

Mass specific metabolic rate declines with increasing body mass

Smaller animals usually have higher metabolic rates per unit body mass than larger animals

Question 6

What is Kleiber’s law? What it indicated?

Answer 6

Slope(0.75)give prediction of body mass and metabolic rate

In mammals, the metabolizable energy requirement at maintenance

(MEM) = aW^0.75(KJ/day)

a = constant ( 525 average) W = body mass

Question 7

Describe the process of direct calorimetry

(how do we measure energy content of food; amount of energy released from food)

Answer 7

Calorie ( C )= approximates the energy required to increase the temp of 1 g of water by 1 ℃(2.184 Joules)

Kilocalorie (kcal) = approximates the energy required to increase the temp of 1 kg of water by 1 ℃ (4.183 kilojoules)

Question 8

In human what is the generally RMR/BMR? Affected by (3 factors) ？

Answer 8

In human: RMR/BMR is generally 20-25 kcal (80-105 kJ) per kg body mass

But affected by:

1) Age and gender

Higher in males than females, usually 5-10% less than male of same ag and SA (more adipose) ( more muscle/ less fat in males)

Decrease with age

Ratio of BMR to surface area highest in infancy (more energy need for growth) and lowest at senescence

2) Body composition

Fat-free mass (FFM)

i.e. total mass of body that is not fat, e.g. organs, muslce

Explains 60-80 % of the variation in RMR between individuals

BMR/RMR increase with body mass

Muscle consume more O2 than fat at rest → increase muscle mass to increase BMR, lose weight

3) Diet- diet induced thermogenesis associated with digestion and absorption

An increase in energy expenditure (via increased metabolic rate) occurs in response to food intake

Thermic effect of a meal (meal-induced thermogenesis); ~10% of energy content of the meal consumed

Fat cause relatively little diet-induced thermogenesis compared to proteins and dietary fiber

Question 9

Explain what is meant by indirect calorimetry and the respiratory quotient * An animals’ metabolic rate

Answer 9

indirect calorimetry = consumption of O2 and/or production of CO2 is measured

Average figure for a mixed-diet is 20.2 KJ/L of oxygen

Ration of CO2 produced : O2 consumed = respiratory quotient (RQ)

Respiratory quotients can be used to determine the metabolic substrate used by an animals *carbohydrate 1, lipid 0.7.

Question 10

Understand the concepts of basal metabolic rate (BMR), resting metabolic rate (RMR),and maintenance energy requirement

Answer 10

basal metabolic rate (BMR)= the amount of energy expended while at rest in a neutral temp environment, in the post-absorptive state( 12 h fasting in humans)

BMR quiet restrictive, it assumes that the sympathetic nervous system is not stimulated

Resting metabolic rate = is related, less restrictive measurement

BMR / RMR constitutes ~ 66 % (2/3) of total daily energy expenditure, but variable