Chapter 4- Energy Flashcards
what is energy ?
work capacity
what is work ?
force * distance
what is power ?
work/time
what is energy expenditure?
energy/time
what are the two energy expenditure unit ?
calorie and joule
what is a calorie ?
energy needed to raise the temperature of 1g of water by 1 degree Celsius
what is the difference between Cal and cal ?
Cal = 1 kcal cal = 1 cal
what unit is on food labels for energy expenditure ?
it is written in cal, but actually represents kcal
how to convert cal into joules ?
1 cal = 4.186 J
in energy produced in humans, what is the proportion of it used for movement ? what happens to the remainder ? what does this show ?
20% for movement
80% for maintaining homeostasis
shows that body is not efficient at using energy
how is energy conserved in the human body
in the chemical bonds between proteins, fats, CHO
how do you determine the energy content of food ?
bomb calorimetry
explain the process of bomb calorimetry
combust food of a known weight (usually 1g) with high pressure oxygen tank
heat is produced and transferred through metal walls, heating up water bath in which the sealed food tank is in
rise in water temperature reflects the energy content
what is the main drawback of bomb calorimetry ?
it measures the gross yield, but not what we would necessarily absorb, therefore overestimates actual calories, and also no distinction is made between the different macromolecules
what measurement does bomb calorimetry give ?
gross energy value (yield)
in bomb calorimetry, if 2g food increase the temperature of 3L water by 4 degrees Celsius, how many calories ?
1 cal - 1g - water 1 deg C
here, 3L x 4 deg C=12
12/2g = 6kcal/g
what does energy content of carbs depend on ?
the carb type and its structure
what does energy content of fat depend on ?
structure of TG or FA, a long chain may have more
what does energy content of protein depend on ?
type of protein and nitrogen content
nitrogen does not provide energy, so the denser the protein the more energy per gram
the denser the nitrogen the less energy per gram
what are the Atwater factors ?
correction factors for energy content that take into account differences in digestibility.
what is the coefficient of digestibility ?
the percentage of food absorbed
what is the coef of digestibility of carbs ?
97%
what is the coef of digestibility of fat ?
95%
what is the coef of digestibility of protein ?
92%
in an avg diet, what is the energy content of carbs ?
4 kcal/g
in an avg diet, what is the energy content of fat?
9 kcal/g
in an avg diet, what is the energy content of protein ?
4 kcal/g
what is the direct way of measuring energy expenditure in humans ?
direct calorimetry
all biochemical processes end up in heat production. true or false ?
true
how is direct calorimetry similar to bomb calorimetry ?
in both cases, measuring heat production. in humans: all biochemical processes result in heat production. in food: you combust it to measure.
in both you will measure the change in water (found in top of chamber) temperature
describe direct calorimetry
closed chamber with coils with known amount of water flowing. increase of water temperature as person is in room will indicate to us energy expenditure
how does air travel through chamber in direct calorimetry ?
carbon dioxide and water are filtered out before it reenters the chamber, and there is a constant oxygen supply
what is the disadvantage of direct calorimetry ?
expensive and requires trained personnel
why is it not ok to use direct calorimetry in sport ?
usually unsuitable
what is closed-circuit spirometry ?
a way to measure energy expenditure in resting conditions
breathe through mouthpiece into a spirometer with 100% oxygen (nose clamped)
measure the difference in volume of CO2 and difference in O2
what does indirect calorimetry count on ?
the energy for all biochemical reactions depend on O2 supply
what is the formula for RER ?
VCO2/VO2
what is a respiration chamber ?
measurement of complete energy balance. similar to chamber in direct calorimetry but without coils to measure heat exchange. carefully monitor flow of O2
CO2 produced is recorded
how is a respiration chamber installation different from direct calorimetry ?
can be bed, etc
without coils to measure heat exchange
why is the respiration chamber ideal to calculate energy balance ?
because food intake can be controlled and urine/ fecal matter collected
what is the advantage of the respiration chamber
allows to control for everything, including energy loss through feces
what is the disadvantage of the respiration chamber
expensive, not suited for vigorous exercise, and usually needs 24hrs so disruptive to life of participant
how does canopy calorimetry work ?
patient lie down relaxed on a bed or on a comfortable couch, with the head under a transparent hood connected to a pump, which applies an adjustable ventilation through it. Exhaled gas dilutes with the fresh air ventilated under the hood and a sample of this mixture is conveyed to the analysers, through a capillary tube and analysed. Ambient and diluted fractions of O2 and CO2 are measured for a known ventilation rate, and O2 consumption and CO2 production are determined and converted into Resting Energy Expenditure
what is canopy calorimetry used for ?
measuring resting energy expenditure
what is a Douglas Bag ?
used for example in exercise tests, collect expired air at final minute of each stage
expired respiratory gases are collected on an inflatable airtight bag. After completion of any test using Douglas Bags, gas collected must be analysed for volume and composition
what is substrate utilization ?
use of inherent differences between CHO, fat, and protein in order to obtain info about fuel utilization
RER= VCO2/VO2 and from there you can determine what fuel is being used mostly
what are the assumptions in substrate utilization indirect calorimetry? (4)
- protein is not an important energy fuel
- all gas exchange occurs across the lungs, and what is expired represents oxidation processes in the tissues
- O2 and CO2 are ideal gases
- complete oxidation of CHO, fat, and protein needs different amounts of oxygen and different amounts of CO2
what would be the RQ for a metabolism using 100% fat ?
0.7
what is RQ?
respiratory exchange ratio
what would be the RQ for a metabolism using 100% CHO?
1.0
what are the 2 assumptions of RQ?
- exchange of O2 and CO2 at mouth are equivalent to processes in tissues
- valid at rest and during light to 85% VO2max exercise
what is the formula of RQ ?
CO2 produced / O2 consumed
how is the formula of RER (>1) different from RQ?
RER takes into account CO2 produced unrelated to metabolism (due to buffering or hyperventilation for example)
what are 3 cases where you will see an RER (>1) that therefore differs from RQ?
- hyperventilation: CO2 extracted from body
- high intensity exercise: buildup of lactic acid, lactate binds to sodium bicardbonate and becomes carbonic acid ejected from lungs as CO2
- lipogenesis (RER up to 5.6)
explain the doubly labeled water technique
bolus dose of two stable isotopes of water (2H and 18O), used as tracers. 2H is lost from body in water, and 18O is lost in water and at C18O2 in breath. Therefore the difference between the two tracer excretion rates represents the CO2 production rate, and with knowledge of fuel mixture oxidized, you can calculate energy expenditure
explain the technique of labeled biarbonate
infusion of labeled bicarbonate. any change in body’s CO2 production will result in change of the labeled CO2 isotope, so the change will indicate total CO2 production
what are one pro and 2 cons of labeled bicarbonate
pro: inexpensive
con: needs fancy equipment and personnel
explain the reliability of HR monitoring technique
HR has linear relationship with oxygen uptake at submax exercise, but not reliable at low or supramax levels
what are the cons of HR monitoring technique ?
a lot of factors like temperature, anxiety, etc can influence it + not accurate
why can’t HR monitoring technique work well at rest ?
bc emotions can easily influence HR without much change in oxygen uptake
how do you use HR monitoring technique ?
figure out relationship at different stages between HR and VO2 and calculate
generally what kind of bad calculation does the accelerometer do ?
underestimate energy ependiture
what is a quick way to calculate energy needs per day (for BMR, no physical activity)?
23-24 kcal/kg/day
how many kcal will very strenuous activities burn?
13 kcal/min
what is the largest component of daily energy expenditure ? (60-75%)
resting metabolic rate
what is basal metabolic rate
rarely used, developed to test over several hours lying down and not eating the lowest O2 uptake in resting conditions
what is diet-induced thermogenesis ?
increase in energy expenditure above RMR for several hours after meal, as a result of digestion, absorption, etc
what is the thermic effect of exercise ?
variable component of energy expenditure, voluntary component (exercise) and involuntary (shivering, fidgeting)
what are the three components of energy expenditure ?
BMR
diet induced thermogenesis
thermic effect of exercise
which variable of energy expenditure varies the most in sedentary or very active people ?
thermic effect of exercise
what is energy balance ?
energy intake = energy expenditure
what kind of energy balance does someone who wants to lose weight wish ?
negative
what is a positive energy balance ?
intake > expenditure
what are 6 things affecting energy balance ?
weight, body composition (lean mass more bioactive), sex, age, activity level, genetics
what technique for energy needs do you use on an unlimited budget ?
direct calorimetry ?
what technique for energy needs do you use on a budget ?
equations
