I. The six nutrient classes (Visit the American Dietetics Association, and the Tufts University Nutrition Navigator.)
A. Carbohydrate
1. Functions
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a) Serves as a major energy source, especially during high-intensity exercise.
b) Regulates fat and protein metabolism.
c) Exclusively provides energy to the nervous system.
d) Synthesized for muscle and liver glycogen.
2. Carbohydrate consumption and glycogen storage
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a) Excess carbohydrate is stored as glycogen in muscles and the liver.
b) Carbohydrate consumption directly influences muscle glycogen storage.
Key Point: Carbohydrate is the primary fuel source for most athletes and should constitute at least 50% of total caloric intake. For endurance athletes, the percentage of carbohydrate should range from 55% to 65%.
3. Carbohydrate type
4. Ergogenic properties of carbohydrate
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a) Muscle glycogen is a major energy resource during exercise.
b) Muscle glycogen depletion is a major cause of fatigue.
c) Carbohydrate feedings during exercise do not spare muscle glycogen, but they might preserve liver glycogen.
B. Fat
1. Functions
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a) Serves as an essential component of cell membranes and nerve fibers.
b) Serves as a primary energy source.
c) Supports and cushions vital organs.
d) All steroid hormones in the body are produced from cholesterol.
e) Transports fat-soluble vitamins through the body.
f) Serves as an insulating layer to preserve body heat.
2. Fat consumption
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a) Americans consume an average of 33% of their total daily calories from fat.
b) The recommended fat consumption is no more than 30% of total calories.
Key Point: The typical American diet includes a percentage of fat well above that which is recommended and that which may be essential in disease prevention and optimal athletic performance.
3. Ergogenic properties of fat
a) The use of fat for energy production can delay exhaustion.
b) Dietary attempts to elevate plasma FFA have been relatively unsuccessful.
C. Protein
1. Functions
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a) Serves as the major structural component of the cell.
b) Used for growth, repair, and maintenance of body tissues.
c) Used to produce hemoglobin, enzymes, and many hormones.
d) Maintains normal blood pressure.
e) Forms antibodies.
f) Can be a source of energy production.
2. Protein consumption
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a) Protein composes approximately 5% to 15% of daily total calories.
b) The upper limit of this range may be 2 to 3 times the amount actually needed.
Key Point: In general, an appropriate amount of protein is 0.8 g per kg of body weight for adults.
3. Ergogenic properties of protein
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a) Protein is essential for growth of body tissues.
b) Protein is essential for development of body tissues.
D. Vitamins and their functions
1. Vitamin A
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a) Is essential for normal growth.
b) Is essential for development.
2. Vitamin D
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a) Is essential for intestinal absorption of calcium and phosphorus.
b) Is essential for bone development and strength.
3. Vitamin K
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a) Functions as an intermediate in the electron transport chain.
b) Is important for oxidative phosphorylation.
4. B-complex vitamins-essential in cellular metabolism
5. Vitamin C
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a) Plays an important role in the formation and maintenance of collagen.
b) Functions in the metabolism of amino acids.
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(1) Functions in the synthesis of some hormones.
(2) Promotes iron absorption from the intestines.
6. Vitamin E
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a) Enhances the activity of vitamins A and C.
b) Acts as an antioxidant.
E. Minerals and their functions
1. Calcium
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a) Builds and maintains bone.
b) Is essential for nerve impulse transmission.
c) Plays a role in enzyme activation and regulation of cell membrane permeability.
d) Is essential for normal muscle function.
2. Phosphorus
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a) Provides strength and rigidity to bones.
b) Is essential in metabolism, cell membrane structure, and the buffering system.
3. Iron-crucial for oxygen transportation
4. Sodium, potassium, and chloride
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a) Enable neural impulses to control muscle activity.
b) Maintain water balance and distribution.
c) Maintain normal cardiac rhythm.
F. Water
1. Functions
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a) Regulates body temperature.
b) Maintains blood pressure.
2. Water constitutes 60% of total body weight in males and 50% in females.
Key Point: A water loss ranging from 9% to 12% of total body weight can lead to death.
II. Water and electrolyte balance
A. Water balance at rest
1. Relatively constant under normal, resting conditions
2. Water loss
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a) Evaporates from the skin.
b) Evaporates from the respiratory tract.
c) Excreted from the kidneys.
d) Excreted from the large intestine.
B. Water balance during exercise
1. Acceleration of water loss during exercise
2. Sweat production during exercise
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a) Environmental temperature affects the amount.
b) Body size affects the amount.
c) Metabolic rate affects the amount.
Key Point: During a marathon, sweating and body water loss from respiration can reduce body water content by 6% to 10% even though the runner drinks plenty of fluids during the race.
C. Dehydration and exercise performance (Visit the Gatorade Sports Science Institute.)
1. Negative effects of minimal changes in body water content on endurance performance
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a) Exercise tolerance decreases.
b) Both heart rate and body temperature increase.
2. Effects of dehydration on performance is less severe in shorter events.
D. Electrolyte balance during exercise
1. Electrolyte loss in sweat
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a) Sweat rate influences loss.
b) State of training influences loss.
c) Level of heat acclimatization influences loss.
2. Electrolyte loss in urine
E. Replacement of body fluid losses
1. Thirst
2. Benefits of fluid intake during exercise
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a) Minimizes dehydration.
b) Minimizes body temperature increases.
c) Minimizes cardiovascular stress.
3. Hyponatremia
III. The athlete’s diet (Visit CompEat it is an interesting site)
A. The vegetarian diet (Visit Adirondack Sports & Fitness.)
B. The precompetition meal
1. Glycogen stores and glucose level
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a) Contributes little to muscle glycogen stores.
b) Can ensure a normal blood glucose level.
2. Advantages of a liquid meal for reduction of indigestion and other digestion problems
C. Muscle glycogen replacement and loading
1. Theory regarding the greater the amount of glycogen stored, the better the endurance performance
2. Åstrand’s regimen
3. Alternative regimen
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a) Maintain a normal diet.
b) Reduce training intensity.
IV. Gastrointestinal function during exercise
A. Gastric emptying at rest
1. Neural and hormonal regulation
2. Potential influences
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a) Caffeine
b) Emotional distress
c) Diurnal variations
d) Environmental conditions
e) Menstrual cycle phase
B. Exercise intensity
1. Significantly slower rate of gastric emptying during intense exercise
2. Increased rate of gastric emptying during less intense exercise (e.g., walking)
C. No change in gastric emptying rates with varying exercise duration
D. Different rate of gastric emptying with different modes of exercise
E. Intestinal absorption of nutrients
1. Delay of intestinal absorption during endurance exercise
2. Association between endurance-exercise diarrhea and emotional origin
V. Designing sports drinks
A. Carbohydrate-type drinks
B. Carbohydrate concentration
1. Slower gastric emptying of carbohydrate solutions than of water or a weak salt solution
2. Relationship between improved performance and ingestion of at least 50 g of sugar per hour
C. Re-hydration with sports drinks
D. Solutions that work best
Key Point: Various ideas have been proposed as to which solution is the best, but to date no ideal solution has been identified.