Transcript chapter four the human body: from food to fuel

Sports Nutrition
for
Peak Performance
We have been discussing basic concepts of nutrition:
-
Food choices and nutritional guidelines
Digestion
Carbohydrates, lipids, and proteins
Energy balance and body composition
Vitamins
Water and mineral balance
We have been discussing basic concepts of nutrition:
-
Food choices and nutritional guidelines
Digestion
Carbohydrates, lipids, and proteins
Energy balance and body composition
Vitamins
Water and mineral balance
For the rest of this course, we will discuss some specific
applications of those concepts:
-
Sports nutrition
Nutrition in pregnancy and various life stages
Food safety and technology
Global nutrition
As we have discussed many times, maintaining an active
lifestyle is an important part of maintaining energy
balance, normal weight, and healthy eating habits.
As we have discussed many times, maintaining an active
lifestyle is an important part of maintaining energy
balance, normal weight, and healthy eating habits.
Humans evolved for both intensive
short-term (anerobic) exercise such
as sprinting to overtake prey, and
long-term (aerobic) endurance
exercise such as chasing prey over
long distances.
These adaptations include how the body obtains various
nutrients, as well as how the body uses these nutrients
under different physiological conditions.
As we have discussed many times, maintaining an active
lifestyle is an important part of maintaining energy
balance, normal weight, and healthy eating habits.
Thus, nutrition and physical activity
are intricately linked and must be
considered together:
- changes in physical activity result
in changes in nutritional needs
- changes in nutrition are reflected
in changes in physical activity
Nutrition in Exercise and Sports Performance
Unfortunately, in modern life our physical activity and our
our dietary habits have not remained in balance.
Nutrition in Exercise and Sports Performance
Unfortunately, in modern life our physical activity and our
our dietary habits have not remained in balance.
We eat more food and more
types of food, particularly
high-calorie carbohydrates
and fats.
Nutrition in Exercise and Sports Performance
Unfortunately, in modern life our physical activity and our
our dietary habits have not remained in balance.
We eat more food and more
types of food, particularly
high-calorie carbohydrates
and fats.
At the same time, we have become more sedentary,
getting less exercise in both duration and intensity. The
result it that we are becoming increasingly out-of-shape
physically and increasingly obese, and we are
experiencing more health problems because of these.
Nutrition in Exercise and Sports Performance
To combat that, a variety of
recommendations have been
developed through both public and
private organization to encourage us
to get adequate exercise and to
develop eating habits which are
better aligned with modern lifestyles.
Nutrition in Exercise and Sports Performance
Exercise places strong demands on the body to provide
- Energy for strenuous and/or sustained muscle use
- Building blocks for muscle and bone growth
- Pathways to remove waste products of activity
Nutrition in Exercise: Muscle
We need to start out with a review of the structure and
contraction of muscles and muscle cells.
Nutrition in Exercise: Muscle
We need to start out with a review of the structure and
contraction of muscles and muscle cells.
In a muscle such as your rectus femoris
or gastrocnemius (both in the lower limb)
the muscle cells (“myocytes”, “fibers”) are
all arranged in the same direction so
they all pull in the same direction.
Nutrition in Exercise: Muscle
We need to start out with a review of the structure and
contraction of muscles and muscle cells.
In a muscle such as your rectus femoris
or gastrocnemius (both in the lower limb)
the muscle cells (“myocytes”, “fibers”) are
all arranged in the same direction so
they all pull in the same direction.
Within each cell are bundles of
contractile proteins called myofibrils.
There are also many mitochondria.
Nutrition in Exercise: Muscle
Those myofibrils are composed of
thousands of smaller structures called
myofilaments which slide past each
other during contraction. That
requires the release of large amounts
of calcium inside the cell, and it
requires a large amount of energy.
Nutrition in Exercise: Muscle
Those myofibrils are composed of
thousands of smaller structures called
myofilaments which slide past each
other during contraction. That
requires the release of large amounts
of calcium inside the cell, and it
requires a large amount of energy.
You will recall that energy for all cellular processes,
including muscle contraction, is
provided by a molecule called
adenosine triphosphate (ATP).
Nutrition in Exercise: ATP
Muscle cells contain a lot of pre-formed ATP.
However, in exercise they quickly deplete all of that
stored ATP. They have a related molecule called
creatine phosphate (CP) which can be used to quickly
make more ATP, but that too will be used up in just a few
seconds of strenuous
exercise.
(Your book calls this the “ATP-CP Energy System”)
Nutrition in Exercise: ATP
Once ATP and CP are depleted, your muscle cells begin
to break apart glycogen to release
glucose molecules.
Nutrition in Exercise: ATP
Once ATP and CP are depleted, your muscle cells begin
to break apart glycogen to release
glucose molecules.
Through glycolysis, each molecule
of glucose is converted to two molecules
of pyruvate, forming two molecules of ATP in
Glucose
the process. This does not require oxygen,
ATP that is, it is anaerobic.
ATP
2 Pyruvate
Nutrition in Exercise: ATP
Once ATP and CP are depleted, your muscle cells begin
to break apart glycogen to release
glucose molecules.
Through glycolysis, each molecule
of glucose is converted to two molecules
of pyruvate, forming two molecules of ATP in
Glucose
the process. This does not require oxygen,
ATP that is, it is anaerobic.
ATP
2 Pyruvate
2 Lactic
Acid
In the absence of oxygen, pyruvate is
converted to lactic acid, which interferes
with contraction. It must be removed from
the muscle cells and sent to the liver.
(Your book calls this the “Lactic Acid Energy System”)
Nutrition in Exercise: ATP
This anaerobic system of glycolysis can produce a small
amount of ATP quickly, so it is sufficient for short periods
of exercise. However, it can not produce enough to
sustain long-term exercise. For that, oxygen is needed.
Oxygen is delivered to the muscle cells in the blood, and
some was stored by attachment to the molecule
myoglobin.
Nutrition in Exercise: ATP
In the presence of oxygen, the pyruvate is converted to a
molecule called acetyl CoA. Within the mitochondria, this
is sent into a series of reactions called the Kreb’s Cycle
or Tricarboxylic Acid Cycle, which generates
another 18 molecules of ATP from
Glucose
each acetyl CoA, or 36 molecules of
ATP
ATP from each glucose molecule.
ATP
2 Pyruvate
2 Acetyl CoA
6 O2
36 ATP
6 CO2
Nutrition in Exercise: ATP
In the presence of oxygen, the pyruvate is converted to a
molecule called acetyl CoA. Within the mitochondria, this
is sent into a series of reactions called the Kreb’s Cycle
or Tricarboxylic Acid Cycle, which generates
another 18 molecules of ATP from
Glucose
each acetyl CoA, or 36 molecules of
ATP
ATP from each glucose molecule.
ATP
2 Pyruvate
2 Acetyl CoA
6 O2
36 ATP
6 CO2
(Your book calls this the “Oxygen Energy System”)
While that produces
a lot more ATP
than glycolysis
alone, it is much
slower
Nutrition in Exercise: ATP
Another advantage of the Kreb’s Cycle is that it can also
be used to produce energy from fats (and, if absolutely
necessary, proteins) through acetyl CoA.
Glycogen
Triglycerides
Glucose
Fatty Acids
(Proteins)
(Amino Acids)
Pyruvate
Acetyl CoA
O2
ATP
CO2
Nutrition in Exercise: ATP
Another advantage of the Kreb’s Cycle is that it can also
be used to produce energy from fats (and, if absolutely
necessary, proteins) through acetyl CoA.
Glycogen
Triglycerides
Glucose
Fatty Acids
Pyruvate
Acetyl CoA
O2
However, it takes a
(Proteins)
longer time for the
body to mobilize fats
(Amino Acids)
and send them to the
muscle cells, so at
least the early stages
of exercise depend on
ATP
the muscle cells’ store
CO2
of glycogen.
Nutrition in Exercise: ATP
During exercise, of course, all of these systems of
producing energy (in the form of ATP) are used by
muscle cells as long as glycogen is available.
Nutrition in Exercise: ATP
During exercise, of course, all of these systems of
producing energy (in the form of ATP) are used by
muscle cells as long as glycogen is available.
Eventually, the stored
glucogen will be
depleted and muscle
fatigue occurs.
The muscle cells can obtain some glucose from the blood,
but this is not enough to sustain prolonged exercise.
Nutrition in Exercise and Sports Performance
Endurance training increases the number of
mitochondria within the muscle cells, and it increases
their ability to store glucose as glycogen and to store
oxygen attached to myoglobin, so it
- Decreases reliance on anaerobic systems
- Extends availability of glycogen
- Delays fatigue
Nutrition in Exercise: Muscle Cells
In reality, we have been oversimplifying things a bit.
It turns out that not all muscle cells are the same.
All of your skeletal muscles (the organs, such as your
biceps brachii or trapezius) have two types of muscle
cells (“myocytes” or “fibers”)
1. Fast twitch cells have large amounts of
glycogen but few mitochondria and small
amounts of myoglobin. They can generate
ATP quickly by the anaerobic pathway and
contract quickly, but they fatigue easily.
Nutrition in Exercise: Muscle Cells
In reality, we have been oversimplifying things a bit.
It turns out that not all muscle cells are the same.
All of your skeletal muscles (the organs, such as your
biceps brachii or trapezius) have two types of muscle
cells (“myocytes” or “fibers”)
2. Slow twitch cells have moderate
amounts of glycogen, many mitochondria,
and large amounts of myoglobin. They
generate a lot more ATP but do it more
slowly by the aerobic pathway, contracting
more slowly, but fatiguing less easily.
Nutrition in Exercise: Muscle Cells
Exercise training can
change the proportion of
slow-twitch and fasttwitch cells in your
muscles.
Consequently, you can
make your muscles
more efficient for either
short-term or long-term
exercise.
Nutrition in Exercise and Sports Performance
Production of ATP for energy (from creatine phosphate,
through glycolysis, and through the Kreb’s cycle) is
certainly an important part of nutrition for exercise, but of
course it is not the only thing which is important.
Nutrition in Exercise and Sports Performance
Production of ATP for energy (from creatine phosphate,
through glycolysis, and through the Kreb’s cycle) is
certainly an important part of nutrition for exercise, but of
course it is not the only thing which is important.
During exercise you need to:
- consume adequate calories for your energy needs
- consume adequate amino acids to maintain proteins
- consume adequate vitamins and minerals
- maintain fluid balance & avoid dehydration
Long-term, you also need to:
- maintain proper body mass and body fat
- recover from muscle damage from exercise
Nutrition in Exercise and Sports Performance
The most important nutritional concern of exercise and
athletic performance is adequate energy intake from two
primary sources:
- carbohydrates
- lipids
Nutrition in Exercise and Sports Performance
The most important nutritional concern of exercise and
athletic performance is adequate energy intake from two
primary sources:
- carbohydrates
- lipids
These are important both
- short term to provide glucose and fatty acids for
immediate use, and
- long term to provide the molecules needed to
replenish glygocen and triglycerides.
Nutrition in Exercise: Carbohydrate
For most athletes, smaller more frequent meals
containing complex carbohydrates works best.
These take longer to be digested to release
mosaccharides, slowing their absorption from
the intestine into the blood and producing a
more stable level of glucose in the blood.
This helps increase glycogen storage in liver and muscle
cells as well as ensuring that a continuous supply of
glucose is availabe in the blood for immediate energy
needs.
Food with complex carbohydrates have the additional
advantage of often also providing vitamins and minerals.
Nutrition in Exercise: Carbohydrate
If you start early enough, you
can significantly increase the
amount of glycogen stored in
your muscles by a process
called carbohydrate loading in
which you alternate shorter, less
intense periods of exercise with
high carbohydrate meals.
Nutrition in Exercise: Carbohydrate
If you start early enough, you
can significantly increase the
amount of glycogen stored in
your muscles by a process
called carbohydrate loading in
which you alternate shorter, less
intense periods of exercise with
high carbohydrate meals.
Since the muscles of most athletes have enough glycogen
to last at least 60-90 minutes, this is only effective for
periods of activity longer than that.
Nutrition in Exercise: Carbohydrate
Two to four hours before
strenuous exercise, meals
should contain up to 65% of
their calories as complex
carbohydrates with low or moderate glycemic
indices, and 10% to 20% each from lipids and proteins.
Nutrition in Exercise: Carbohydrate
Two to four hours before
strenuous exercise, meals
should contain up to 65% of
their calories as complex
carbohydrates with low or moderate glycemic
indices, and 10% to 20% each from lipids and proteins.
Just before exercise, eat easily
digestable carbohydrates with
higher glycemic indices.
Nutrition in Exercise: Carbohydrate
Two to four hours before
strenuous exercise, meals
should contain up to 65% of
their calories as complex
carbohydrates with low or moderate glycemic
indices, and 10% to 20% each from lipids and proteins.
Just before exercise, eat easily
digestable carbohydrates with
higher glycemic indices.
During exercise, eat or drink small
amounts (large meals can cause digestive
problems) of foods with high glycemic indices.
Nutrition in Exercise: Carbohydrate
Immediately after strenuous exercise you
should begin eating foods with
moderate to high glycemic indices
to immediately begin to replenish
glycogen, and you should continue
to eat carbohydrates for a few hours.
Nutrition in Exercise: Carbohydrate
Immediately after strenuous exercise you
should begin eating foods with
moderate to high glycemic indices
to immediately begin to replenish
glycogen, and you should continue
to eat carbohydrates for a few hours.
Of course, exercise causes significant loss
of water and minerals, so it is important to
also remain hydrated during exercise to
maintain fluid balance. Without this, your
muscle cells can not effectively use glycogen, produce
energy through glycolysis or the Kreb’s cycle, or remove
waste products such as lactic acid or CO2.
Nutrition in Exercise:
While carbohydrates are critical to peak performance during
exercise, they are not the only important nutrients.
Fats, proteins, vitamins, and minerals are also involved.
Nutrition in Exercise: Fats
At all times, carbohydrates and fats are the two primary
fuels: fats should contribute 20%-30% of calories.
Glycogen
Triglycerides
Glucose
Fatty Acids
Pyruvate
Acetyl CoA
O2
ATP
CO2
Nutrition in Exercise: Fats
At all times, carbohydrates and fats are the two primary
fuels: fats should contribute 20%-30% of calories.
Glycogen
Triglycerides
Glucose
Fatty Acids
Pyruvate
Acetyl CoA
O2
This is particularly true during
exercise. In low-intensity
exercise after glycogen is
depleted from cells, fats often
become the primary fuel
source if carbohydrates
are not consumed.
ATP
CO2
Nutrition in Exercise: Fats
However:
- fat is digested and absorbed more slowly than
carbohydrates with high glycemic indices
- fatty acids are not transported as easily in the blood
as glucose
- fatty acid are not absorbed from the blood into
muscle cells as easily as glucose
Nutrition in Exercise: Fats
However:
- fat is digested and absorbed more slowly than
carbohydrates with high glycemic indices
- fatty acids are not transported as easily in the blood
as glucose
- fatty acid are not absorbed from the blood into
muscle cells as easily as glucose
Thus, fatty acids are more
difficult for muscle cells to use,
but
Nutrition in Exercise: Fats
Like any other times: dietary fats during exercise should
- include monounsaturated &
polyunsaturatedfatty acids
- minimize trans fatty acids
- include omega-3 and
omega-6 fatty acids
- be part of foods that also include
proteins, vitamins, and minerals
Nutrition in Exercise: Fats
A word of caution:
Fat is sometimes erroneously seen by athletes as something
“bad” to be avoided in the diet and removed from the body.
While excess fat is indeed unhealthy,
too little body fat is also unhealthy
Fat: Provides fatty acids for energy
Protects internal organs
Insulates against heat loss
Regulates a number of hormones
Stores some vitamins
Forms phospholipids for cell membranes
Nutrition in Exercise: Fats
The American Dietetic Association recommends that
- men have 15-18% body fat
- women have 20-25% body fat.
but
- healthy male athletes can have 5-12% body fat
- healthy female athletes can have 10-20% body fat
Nutrition in Exercise: Fats
A group of compounds called thermogenics or “fat burners”
are available.
These may include the
stimulant and appetite
suppressant ephedrine or
similar chemicals which
have been linked to high
blood pressure, heart
disease, stroke, and
occasionally death.
Nutrition in Exercise: Proteins
In addition to carbohydrates and fats, proteins are important
for peak performance during exercise.
Nutrition in Exercise: Proteins
In addition to carbohydrates and fats, proteins are important
for peak performance during exercise.
However, it is a misconception that a high-protein diet will
significantly enhance performance in most cases.
- Proteins are not a significant source of calories during
exercise
- Excess amino acids must be broken down in the liver
and their amino groups disposed of as urea in the urine.
This increases urine production, pulling water out of the
body and leading to dehydration.
- Excessive protein intake, such as through supplements,
can overload this system and cause kidney failure
Nutrition in Exercise: Proteins
Dietary proteins are needed primarily to
- replace muscle proteins damaged during exercise
- build new proteins as muscle cells grow during training
Note that the key to the latter is the
training: Additional dietary protein
alone will not increase muscle mass
without the stimulus of strength training
or endurance training.
Nutrition in Exercise: Proteins
As noted a couple of weeks ago, the amount of protein in
the diets of most Americans greatly exceeds the amounts
needed, so most people usually get enough protein in their
diets for moderate exercise.
Athletes in training for such
events as marathons, strength
training, elite-level sports, etc.
may need to increase their
dietary protein, up to double
the normally recommended
amounts
Nutrition in Exercise: Proteins
Athletes in training for such events as marathons, strength
training, elite-level sports, etc. may need to increase their
dietary protein, up to double the normally recommended
amounts.
These should come from the
“high quality” protein foods we
discussed earlier:
Lean meats, poultry, fish
Low fat dairy products
Legumes
Grains
Eggs
Nutrition in Exercise: Proteins
Proteins also play an important role after exercise:
Combined intake of carbohydrates and proteins increases
the synthesis of glycogen more than the intake of
carbohydrate alone.
Recommendation: 1 g protein per 2.5 g carbohydrate
As always: foods containing both such as dairy products,
grains, or legumes are more effective than
individual supplements.
Nutrition in Exercise: Vitamins
Many reactions in the body during exercise need vitamins:
-
Vitamin A helps regulate protein synthesis & cell growth
Vitamin D is necessary for healthy bones & muscles
Vitamin K regulates bone growth & blood clotting
Vitamins E and C are antioxidants to remove waste
products of cellular metabolism
- Many B vitamins are cofactors of the enzymes needed
to extract energy from carbohydrates and fats
- Many B vitamins are need for to extract and store the
energy released from carbohydrates and fats
Nutrition in Exercise: Vitamins
Fortunately, the amounts of vitamins in a normal diet are
sufficient to meet the needs of all but the most highly
trained athletes.
Nutrition in Exercise: Minerals
Of more concern to athletes are minerals, since these
are necessary for proper fluid balance and for the health
and normal functions of bones, muscle, nerves, and
blood.
They can also be lost in the
increased amounts of sweat
and urine which can occur
during strenuous activity.
Nutrition in Exercise: Minerals
- Iron is needed for hemoglobin for oxygen transport
- Calcium, potassium, and magnesium regulate nerve
function and muscle contraction
- Calcium and phosporus provide strength to bone
- Sodium, chloride, and potassium regulate fluid
movement among compartments
Nutrition in Exercise: Minerals
As with vitamins, the amounts of minerals in healthy diets
are sufficient to meet most of the needs of all but the most
highly trained athletes.
The most common problem arises from excessive sweating
which can cause the loss of chloride, sodium, potassium,
calcium, magnesium, and smaller amounts of other
minerals.
Nutrition in Exercise: Minerals
As with vitamins, the amounts of minerals in healthy diets
are sufficient to meet most of the needs of all but the most
highly trained athletes.
The most common problem arises from excessive sweating
which can cause the loss of chloride, sodium, potassium,
calcium, magnesium, and smaller amounts of other
minerals.
Fortunately, these can be quickly
replenished from a variety of foods,
and sports drinks are specifically
formulated to provide adequate amounts.
Nutrition in Exercise: Fluids
Although the needs of these various nutrients are important
components of maintaining healthy nutrition during exercise
and strenuous activity, the most critical component for most
athletes is maintaining water and fluid balance.
Nutrition in Exercise: Fluids
Forms
urine
Forms tears,
saliva, CSF,
synovial
fluid, semen,
lymph, etc.
Movement
among
Nutrition in Exercise: Fluids
Water = more than 60% of total body mass
3 major compartments:
Plasma ~8% of body water
Interstitial ~25% of body water
Intracellular ~65% of body water
Many smaller compartments: ~ 2%
Urine, Lymphatic fluid, Cerebrospinal
fluid, Saliva, Synovial fluid, Digestive
system contents, Semen,
Respiratory system fluids, Peritoneal
fluid, Tears, Occular fluids,
Pericardial fluid, Pleural fluid, etc.
Nutrition in Exercise: Fluids
These fluid compartments are in equilibrium with each other
Nutrition in Exercise: Fluids
Water intake is primarily through food
and drink. Some water is gained from
metabolic processes like the synthesis
of proteins, lipids, and carbohydrates.
Water output is primarily through urine,
sweat, transcutanous loss, respiration,
and feces. These are obviously
affected by such things as temperature,
exercise, humidity, etc.
Nutrition in Exercise: Fluids
During exercise, additional
water is lost through sweating
and must be replaced.
Nutrition in Exercise: Fluids
During exercise, additional
water is lost through sweating
and must be replaced.
Sweating is necessary to cool
the body and remove the extra
heat produced by the muscles.
Nutrition in Exercise: Fluids
The water in sweat is pulled from the
plasma, which pulls water from all
other compartments.
It must then be replaced through the digestive system.
Nutrition in Exercise: Fluids
Sweating starts early in exercise
and continues well after you
finish exercising, so you should
consume water before, during,
and after exercise. The goal
should be to drink fluids at the
same rate you are losing them.
Nutrition in Exercise: Fluids
Sweating starts early in exercise
and continues well after you
finish exercising, so you should
consume water before, during,
and after exercise. The goal
should be to drink fluids at the
same rate you are losing them.
Since minerals such as sodium, chloride, and
potassium are also lost through sweat, in
prolonged exercise you should also take in
minerals to replace those.
Nutrition in Exercise: Fluids
Nutrition in Exercise: Fluids
Inadequate fluid intake can lead to dehydration
Nutrition in Exercise: Supplements
Supplements to enhance athletic performance, or
ergogenic supplements, are a multi-billion dollar
business in the United States
-
Provide energy, both short-term and long-term
Provide carbohydrates, vitamins, minerals
Build muscle mass
Strengthen muscles
Strengthen bones, joints, ligaments, tendons
Enhance post-exercise recovery
Nutrition in Exercise: Supplements
Supplements to enhance athletic performance, or
ergogenic supplements, are a multi-billion dollar
business in the United States
-
Provide energy, both short-term and long-term
Provide carbohydrates, vitamins, minerals
Build muscle mass
Strengthen muscles
Strengthen bones, joints, ligaments, tendons
Enhance post-exercise recovery
Some are beneficial, some are not.
Nutrition in Exercise: Supplements
Common ergonomic supplements include:
1. Antioxidants such as ascorbic acid (vitamin C)
tocopherols (vitamin E)
carotenoids (vitamin A)
glutathione
melatonin
lutein
Nutrition in Exercise: Supplements
Common ergonomic supplements include:
2. Amino acids and proteins
- muscle mass
- muscle repair
Nutrition in Exercise: Supplements
Common ergonomic supplements include:
3. Caffeine
- stimulant
- endurance
Nutrition in Exercise: Supplements
Common ergonomic supplements include:
4. Carnitine
- fat transport
- enhanced nerve function
Nutrition in Exercise: Supplements
Common ergonomic supplements include:
5. Co-enzyme Q
- enhanced aerobic performance
- antioxidant
Nutrition in Exercise: Supplements
Common ergonomic supplements include:
6. Ephedrine
- stimulant
- weight loss
Nutrition in Exercise: Supplements
Common ergonomic supplements include:
7. Androgens (hormones related to testosterone)
such as androstenedione
dehydroepiandrosterone
dihydrotestosterone
Nutrition in Exercise:
In general, however, nutrition in exercise boils down to a
eating a healthy diet with four essential priorities:
1.
2.
3.
4.
Adequate fuel intake (carbohydrate, lipid)
Adequate protein intake
Adequate vitamin and mineral intake
Adequate fluid intake
x