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NUTRITION AND
EXERCISE
FOOD FUELS
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Food is the source of energy for all
cellular activity in the body.
When we eat, food travels to the
stomach and intestines to be digested.
The digestive system breaks down the
foodstuffs, absorbs the nutrients and
transports wastes to the bowel.
Our food intake consists of 3
basic nutrients….
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Carbohydrates (CHO) – fruits cereal, bread, pasta
and vegetables. The body’s preferred fuel source
during exercise.
Fat – eg butter , margarine, cheese, oil, nuts. The
body’s preferred fuel source at rest.
Protein – eg meat, fish, poultry. Makes little
contribution to energy production during exercise.
Mainly used for growth and repair.
Nutrients are carried, via the bloodstream
surrounding the digestive system, to cells of the
body.
Other essential dietary
ingredients
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Water, minerals and vitamins are also
essential in the diet.
However, CHO, Fats and Proteins are
the ONLY nutrients from food that form
fuel for ATP resynthesis.
ATP resynthesis
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Only a small amount of ATP exists at the
muscles.
ATP must be continually rebuilt or
resynthesised so that energy can be provided
for longer periods of time.
This process occurs through the energy
systems
The three energy systems
There are 3 pathways in the body that
resynthesise ATP.
There is the Aerobic System and two
anaerobic systems called the Lactic Acid
System and the ATP-PC System.
Fuels for each energy system
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The ATP-PC system requires phosphocreatine (PC), which occurs and
replenishes naturally with appropriate rest
PC will not increase with dietary
supplementation
A balanced diet and healthy body will
maintain PC levels
Fuels for each energy system
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The Lactic Acid system requires glucose
The muscles (and liver) store glucose in
the form of glycogen
Carbohydrates in food breakdown to
glucose for blood transport
The Lactic Acid system may draw glucose
from the blood or stored glycogen
Fuels for each energy system
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The Aerobic system can use
glucose/glycogen, fat or protein as fuel
Which System
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At rest, our demands for ATP are low and can be met
aerobically with little input from the anaerobic systems
As we exercise the demand for ATP increases and our
oxygen intake cannot always keep up. This is where the
anaerobic systems become more involved
For any sub-maximal activity of longer duration the
aerobic system will supply most of the energy…
…But higher intensity efforts, required during that
activity, will call on the anaerobic systems to be
dominant
Food Fuels at rest.
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At rest about two thirds of food fuel is
contributed by Fats and about one third by
carbohydrates (glucose). The contribution
of protein is negligible.
The aerobic system is the major energy
system at work because sufficient oxygen
is available to the organs and muscles.
Food Fuels during exercise
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For exercise of short duration and high intensity
the anaerobic systems supply most of the energy
and the food fuel used by the Lactic Acid System is
the stored form of carbohydrate, glycogen.
For exercise of longer duration, at intensity below
85% of max effort, the aerobic system is the main
supplier, with carbohydrates generally being the
preferred fuel. If CHO stores are depleted, fats
become the main fuel source for aerobic energy
production.
Carbohydrate contribution
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Energy from muscle contraction stems from muscle and liver
glycogen.
An average 80kg person can only store 100 grams of glycogen
in the liver and 400 grams in muscles around the body. This is
enough to fuel a 25km run at moderate pace.
It is important to eat a CHO rich diet if preparing for an
endurance event, to increase these glycogen stores.
Even though fats will produce more ATP per unit during
aerobic energy production, CHO (glycogen) is preferred over
fats as a fuel source during exercise. It requires less oxygen
and still produces a high amount of ATP.
Fat Contribution
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Fats are stored throughout the body in
adipose tissue and in skeletal muscles as
triglycerides.
Fats are transported in the blood as fatty
acids
Fat contribution (cont)
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One fat molecule can produce up to 100 ATP (compared to one
glycogen molecule producing just 38 ATP), but its breakdown
requires a lot more oxygen than glycogen.
This is why CHO is the preferred source of fuel during exercise
– as intensity increases, oxygen is in more demand.
Approximately 50% of the body’s everyday energy production
comes from fat. It becomes a very important source of energy
when glycogen levels are low.
Endurance athletes train to improve their capacity for oxygen
uptake so they can use fat more as a fuel source. That way
they can “spare” glycogen for the anaerobic glycolysis required
during high intensity efforts like surges and sprint finishes.
Protein contribution
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Protein forms the building blocks of tissue growth
and repair.
All enzymes which speed up chemical reactions
are proteins.
Protein is generally not required for aerobic
energy production under “normal” sporting
circumstances
Protein is only used more for energy in extreme
circumstances, such as high stress endurance
events and starvation.
The Glycemic (GI) index
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The GI index is a ranking of carbohydrate based on how
quickly they breakdown to glucose and enter the blood
stream.
CHOs that break down quickly have the highest GI index.
The blood glucose response is fast and high.
CHOs that break down slowly, releasing glucose gradually,
have the lowest GI index.
Low GI leads to a slower rise in blood glucose levels after
meals and can prolong endurance performance.
Nutrients from food
Pre-exercise food
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The ideal meal before exercise should
provide carbohydrates that sustain
blood glucose levels while minimising
increases in insulin levels.
Consuming High GI foods immediately
before exercise results in rapid surges
in blood sugar and insulin - both detract
from endurance performance.
Pre-Exercise food
A good preparatory meal 2 to 3 hours before
competing will focus on Low GI foods and might
include…
Muesli with
yoghurt
Baked Beans
on whole grain toast
OR
Low Fat milk or water would be good fluid intake
During Exercise food
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High GI food is best during competition
It helps to maintain normal blood sugar levels
and prolongs the availability of muscle glycogen
Unless the event is continuous for at least 90
minutes OR a field/court sport lasting at least 60
minutes nutrition during is largely unnecessary.
Hydration should be maintained though at around
200mls per 15-20 minutes
During Exercise food
During the event you need High GI intake
Recovery from exercise
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After exercise an athlete should intake 1.2
gram of High GI carbohydrate per kg of body
mass each hour for at least 4 hours post
exercise.
For at least the first 3-4 hours of recovery,
this CHO intake will accelerate muscle
glycogen recovery from the normal 5% to 78% per hour
Hydration needs to be also maintained
Food for Recovery
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1.2 gram of High GI carbohydrate per
kg of body mass each hour for at least 4
hours post exercise.
Other Food Nutrients
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Vitamins are important as they assist chemical
reactions in the body (and help release energy
from food)
Also particularly important for athletes are
minerals, known as “electrolytes” (eg: sodium,
potassium), which help maintain muscle
contraction, nerve transmission, fluid balance
and enzyme activity
Vitamins
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There are 14 vitamins divided into fat soluble
vitamins and water soluble vitamins.
Although not an energy source in themselves,
they assist chemical reactions in the body
that help break down food fuels.
They are also involved in red cell production,
tissue repair and protein synthesis
Minerals
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There are 10 main minerals needed in various
amounts by the body.
Minerals such as sodium and potassium play an
important part in muscle contraction, nerve
transmission, fluid balance and assisting enzymes
in energy production.
Iron (carrying of O2 in red blood cells) and Calcium
(bone density and strength) are also important
considerations in a well balanced diet.
Fibre
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Fibre is the part of the plant that is not
digestible.
It helps ensure a slow release of energy by
slowing the release of sugar from the
blood.
It helps the feeling of being full without
extra kilojoules and regulates bowel
motions
Fluid
Over 70% of your body mass is water.
 Each day the body has to replace at least two litres of
water to replace what is lost (not including sweating)
 Fluid serves many functions such as:
- transporting energy waste, hormones and antibodies
- diluting waste products
- lubricating joint surfaces and membranes
- helping to regulate body temperature
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