Transcript Energy Release From Macronutrients

Energy Release From
Macronutrients
The Concept of Energy Balance
What Is Energy Balance and Why Is It
Important?
• Energy balance is achieved when the kilocalories
consumed equal the kilocalories expended
Foods and their conversion to energy
• Food is consumed =chemical energy converted
into mechanical energy (muscular contractions &
movement)
• Carbohydrates, fats and protein are the only sources
of food energy and fuel.
Energy (ATP) is stored in small amounts,
therefore the rest is stored as:
•Glucose = Glycogen (muscle & liver)
•Fatty Acids = Body fat
•Amino Acids = Growth,
repair or excreted
as waste
Carbohydrates
• Sugars and starches = body’s preferred source of fuel 
esp. during exercise.
• Carbohydrates = primary energy source during anaerobic
exercise of high intensity and short duration.
• Carbohydrates are broken down and stored as glucose in
the blood and glycogen in the muscles and liver.
• Excess carbs are stored around
the body as adipose tissue (fat tissue)
CARBOHYDRATE SOURCES
• Carbohydrates come in two sources:
– Simple sugar glucose
– Storage form of glucose  glycogen
• Glycogen is stored in
– Muscles
– Liver
– Blood (smallest % in blood)
• Liver = only tissue that can release stored glycogen in the form of
glucose
• Liver = maintain blood sugar levels by releasing glucose through
gluconeogenesis & glycogenolysis
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Carbohydrates
• All carbohydrate converted to glucose
– Primary ATP substrate for muscles, brain
• Glycogen converted back to glucose when
needed to make more ATP
• Glycogen stores
limited (2,500 kcal) =
must rely on dietary
carbohydrate to replenish
Energy from Carbohydrates
• Glucose is absorbed from the intestines into
the blood and broken down by glycolysis
• Excess glucose intake stimulates storage as
glycogen and fatty acids
Energy Release From Carbs
• Carbs primary function to supply energy for
cellular work
• Carbs = only macronutrient whose stored energy
generates ATP anaerobically
 NB for maximal exercise that requires rapid
energy release
 intramuscular glycogen stores supplies most of
the energy for ATP resynthesis
Energy Release From Carbs
• During light & moderate aerobic exercise  carbs
supply 1/3 of body’s energy requirements
• Breakdown of carbs for energy supply occurs more
rapidly than breakdown of fats.
= depletes glycogen reserves significantly
= reduces exercise power output
• Prolonged exercise (marathon runners) = muscle &
liver glycogen depletion
Energy from Carbs and Physical
Activity
• Carbs provide QUICK ENERGY.
• They supply energy for both
AEROBIC & ANAEROBIC
physical activity
• Used for physical activity of a comparatively
SHORT length of time and HIGH INTENSITY
Fats
• Fats = butter, oils, nuts.
• Fat = body’s preferred source of fuel at rest.
• More oxygen is required by the body to use fat as a
fuel than to use carbs to produce ATP.
FAT SOURCES
• Fat for fuel is in the form of free fatty acids
– Two sources of these fats are:
• Peripheral fat stores
– Rolls of fat on the
stomach, glutes…
• Intramuscular fat
– Triglyceride stored
in the actual muscle
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Most Body Fat Is Stored in Adipose
Tissue
• Two types of fat make up total body fat:
Essential fat
• Found in bone marrow, heart, lungs, liver, spleen,
kidneys, intestines, muscles, and central nervous
system
• Women have 4x more essential fat than men
Stored fat
• Found in adipose tissue
• Subcutaneous fat – located under the skin
• Visceral fat – stored around the organs in the
abdominal area
Fats
• Fats have the capacity to produce much more
ATP than carbs
BUT: the conversion rate is much less efficient
 require much more oxygen to produce the
same amount of ATP.
• Fatty acids are stored in the blood,
triglycerides in the muscles
• Excess fats are stored as adipose tissue around
the body
Energy from Fats
• The body stores most fats as triglycerides
• When blood glucose falls, enzymes break
triglycerides into glycerol and fatty acids
– Glycerol enters the energy cycles to be converted
to glucose
• Fatty acids yield more energy (ATP) than carbs
Fat
• Efficient substrate, efficient storage
– +70,000 kcal stored in body
• Energy substrate for prolonged,
less intense exercise
– High ATP yield but slow ATP production
– Must be broken down into free fatty acids (FFAs)
and glycerol
– Only FFAs are used to make ATP
Fat release for energy and physical
activity
• Fats provide SLOW ENERGY
• The energy release from fats is too slow to be used when
used when working hard
•
•
Used for walking and low-impact exercise
Used for exercise of a longer duration, and MODERATE
INTENSITY
•
Physical activity of LONG DURATION and HIGHER INTENSITY
is fuelled more from fat stores in the body because the
glycogen store becomes depleted
Protein
• Protein includes meat, fish, poultry, dairy, eggs &
lentils.
• Protein is used for growth & repair of the body &
as fuel source in extreme situations.
• Body only uses protein as energy source when
glycogen & fat sources have already
been depleted.
 ie. marathon or starvation
Energy from Proteins
• Proteins enter the bloodstream as amino acids
• Amino acids can be used for energy by
removing the amino group (as ammonia)
Energy release from Protein
• Energy yield not easy to determine
– Nitrogen presence unique
– Nitrogen excretion requires ATP expenditure
– Generally minimal, estimates therefore ignore
protein metabolism
Fuel Utilization is Determined by Energy
Output or Intensity Level
• First thing in the morning before you eat
breakfast = energy demands are very low can
be met mainly by fat derived from blood free
fatty acids
• Free fatty acids are released at a low rate by
peripheral fat stores
• This allows the muscles to preserve both
intramuscular fat and glycogen stores
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Exercise Intensity and Duration
• For all energy substrates, carbs and fats,
ultimately ATP is generated in the muscle cell
as the high energy substrate for moving
muscle.
• Carbs can also be broken down in the absence
of oxygen for limited energy production
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Fuel Utilization - Intensity
• Low intensity
– Walking: energy output can be generated entirely
by peripheral fat stores releasing free fatty acids
– Stimulus to increase FFA release to maintain
enough blood concentrations of FFA for uptake by
the working muscles
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Moderate Intensity
• Exceeds the capacity of peripheral fat stores to
supply enough free fatty acids to meet energy
output rates=
– Intramuscular triglycerides are broken down
to provide more fat sources
– Peripheral fat uptake does not stop  it
plateaus
– + another source is provided to makeup the
needed energy…(glucose/glycogen)
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Medium/ Moderate
Intensity
• A medium intensity pace can be maintained
until either your intramuscular fat stores are
depleted or you run out of glycogen
– When the glycogen is depleted then protein
is broken down for energy
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High Intensity
• High Intensity exercise goes above
the limits of energy production
rates that fats can supply and
requires additional energy derived
from glucose
• glucose requires less oxygen per
unit of energy
• At lower intensities, the energy
production rate is low enough that
oxygen is plentiful enough for fat
burning
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Very High Intensity
• At very high intensities the aerobic system reaches
its limitations for energy generation (fat or
glucose)
• The anaerobic system takes over
• Only a little of the potential energy of glucose is
released but is done so in a very rapid manner to
meet short duration and very high energy
production rates
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The Benefits of Exercise At Any
Intensity
• Low intensity exercise is not
the is not the best form for
weight loss
• High intensity exercise can
lead to fat loss  depletion of
glycogen & glycogen stores
must be replenished with
dietary carbs that would
• Intramuscular stores (fat or
otherwise be burned for
glycogen) are depleted
energy
– During the recovery phase
(post exercise) fats and
carbs from the diet will go • While the storage process
occurs = the body will burn
to restoring those levels
extra fat to supply current
energy needs
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