Module 8 Flashcards
Law of Conservation of Energy
• Energy (E) cannot be created or destroyed, but it
can change form. Some forms of energy are:
– Heat energy
– Chemical energy
– Potential energy
• Energy balance occurs when energy consumed
equals energy expenditure
Kilojoules (kJ)
• Unit of work
• Amount of work required to move a 1 kg
object 1 meter under the force of gravity
Kilocalories (kcal)
• Unit of heat
• Amount of heat (energy) required to raise
the temperature of 1 kg of water 1 °C
Calories vs Kcal
• 1000 Calories = 1 kcal
– A calorie is the amount of heat needed to raise
the temperature of 1 g of water by 1 °C
Sources of Energy
Energy is consumed in the diet as: – Carbohydrates (4 kcal/g) – Fats (9 kcal/g) – Proteins (4 kcal/g) – Alcohol (7 kcal/g)
Direct Calorimetry
Obtains a direct measurement of the amount of heat generated by the body within a structure large enough to permit moderate amounts of activity.
Bomb Calorimeter
– Instrument used to measure the energy content of food. – Chamber surrounded by jacket of water – Dried food is burned in chamber – Released heat raises temperature of the water – Increase in water temperature used to calculate the amount of Energy in the food
Heat is generated by metabolic
reactions that
• Convert food energy into
ATP
• Use ATP for body processes
Direct Calorimetry (cost)
• Accurate method for measuring Energy expenditure
• It is expensive and impractical for humans
– Requires an individual to be in an insulated
chamber throughout the measurement
Indirect calorimetry
Catabolic reactions break large molecules into
smaller units
– Energy in chemical bonds is released
– Energy is captured and stored in phosphate
bonds of ATP
• At the same time O2 is consumed and CO2 is
produced in a known ratio
• This is how energy expenditure is usually
measured in animals
• Device measures consumption of O2 and
expiration of CO2
– ATP production can be calculated from the
amount of CO2 expired & O2 inhaled
Mammalian Energy Expenditure Components
- Basal Metabolic Rate (BMR)
- Thermic effect of food (TEF)
- Physical activity (PA)
Basal Metabolic Rate (BMR)
• Energy for metabolism under basal conditions
• Involuntary activities of the body that are necessary for body
maintenance to keep you alive
– For example:
• Regulation of body temperature
• Nerve transmission
• Blood circulation
– Excludes:
• Physical activity
• Food digestion/absorption and processing
• Growth
• Represents 60 to 70% of total Energy expenditure
BMR Measurement
• BMR measurement is taken
– After 12-hr fast
– In an awake, but calm state
– Thermoneutral conditions
Resting Metabolic Rate
- RMR does not require a fasted state
* RMR is ~10% higher than BMR
BMR Determinants
• BMR is directly proportional to lean body mass (LBM) or muscle mass – LBM is affected by • Age • Gender • Body weight • Resistance Exercise • BMR can rise with • Fever • Hyperthyroid function • BMR can decrease as an adaptation to starvation
Thermic Effect of Food (TEF)
• Increase in Energy expenditure after ingestion of food • Causes body temperature to rise slightly for some hours after eating • Metabolic cost of: – Digestion – Absorption – Metabolism – Storage of nutrients • ~5 to 10% of Energy intake • A meal high in fat has a lower TEF
Physical Activity (PA)
• Metabolic cost of external work
– Voluntary movements of the skeletal muscles and
support systems
• 2nd largest component of Energy expenditure
– ~15 to 30% of Energy expenditure
• Varies greatly with each individual
– NEAT (Non exercise Activity Thermogenesis) is the
energy expended for daily activities other than sleeping,
eating or sports-like exercise
– Has the most potential for change
Energy Storage
– Excess Energy stored as Triglycerides (fat)
• Also some glycogen (carbohydrates)
– Energy stores come from macronutrients not used to
meet immediate Energy needs
– Stored energy is used when Energy intake is less than
Energy expenditure
Ways to Estimate Energy Expenditure
• Standard Formulas
– RMR for individuals of same age, sex and
weight are fairly constant
•Weight can be used in a standard equation
– PA can be estimated from adding up energy
required for various activities
– TEF is ~ 10% of Energy intake
Bioelectrical Impedence
A way to estimate energy expenditure. – A method to determine body composition – Uses a weak current to determine % body fat and lean body mass (LBM) – More the muscle or lean body mass, the more the water associated with it – Fat is a poor conductor of electricity, so it offers resistance to the current • Can use LBM to predict BMR
Body Mass Index (BMI)
• Body fat stores can also be estimated by evaluating weight for height – BMI = weight in kg / (height in m)2 • BMI is a standard for evaluating body weight – BMI correlates with body fat in most people – It overestimates fat in people with a high muscle mass
BMI Scale
• Healthy Weight – 18.5 - 25 • Overweight – 25 – 30 • Obese – > 30
Metabolic Hierarchy (Protein)
• Amino acids are used to meet the needs for
the synthesis of body proteins and non-
protein molecules first
• Any excess is then oxidized because there is
no mechanism for storing them as amino
acids or proteins
Metabolic Hierarchy (carbs)
• Carbohydrates are used to maintain blood
glucose and to build glycogen stores
• Once glycogen stores are full, the remaining
Carbohydrates are oxidized for energy
Metabolic Hierarchy (Fats)
• Dietary fat is first put into storage as TAG • Fat is taken out of storage to meet the energy needs – Most fat that is stored in the body comes from dietary fat
Energy In Formula
BMR + TEF + PA +/- storage
Hormone Leptin
• Long-term signal to tell body how much fat (stored
energy) it has
• Hormone produced by adipose tissue
– Produced in proportion to body fat
– Reduces appetite
•Higher fat causes more leptin to suppress appetite
– Increases Energy expenditure
