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Nutrition
101 Home Fundamentals
of Nutrition
What
is a
Food Portion?
Your
Nutrition Style
Your
Activity Style
Physiology
of Nutrition
Lecture Series
Lecture
1
Lecture
2
Lecture
3
Lecture
4
Lecture
5
Lecture
6
Lecture
7
Lecture
8
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Lecture
6 continued
Components
of Fitness
Flexibility
- ability to bend without injury.
Flexibility is dependent on the elasticity
of muscles, tendons, ligaments, and joints. Stretching
for at least 10 seconds with gradual tension will
improve flexibility.
Strength -
the ability to work against resistance.
Strength of particular
muscle groups can be increased by careful heavy
resistance training at 60 to 80 % of single repetition
maximum with three sets of 8 to 12 reps.
Endurance
- the ability to sustain effort over a period of time.
High repetition
exercises such as push-ups, pull-ups, and
sit-ups increase endurance.
Cardiovascular
Endurance - the ability of the cardiovascular system to
sustain effort over a period of time.
This effort should involve larger
muscle groups and be at 60 to 90 % of MHR.
How Many Calories
are Burned ?
Exercise output can
be quantified as METs which are a ratio of the energy being burned to
that burned at rest. An individual at rest burns about 1 Cal/per kg/per
hour (depending on lean body mass content) and this rate is one MET. Therefore
a 50 kg woman would be expending about 10 mets if she was in a heavy aerobics
exercise class expending 500 Cal/hour.
|
500
Calories/hour
|
=
10 METs |
|
1
Cal/kg X 50 kg
|
Typical
MET levels (for comparison only, since they differ by individual):
For a 150 pound male:
|
Activity
|
MET
level
|
Calories/Hr
|
| Writing |
1.7
|
118
|
| Walking |
4
|
299
|
| Basketball |
10
|
544
|
| Bicycling |
3
|
204
|
| Eating |
1.4
|
93
|
| Jogging |
7
|
476
|
| Weightlifting |
9
|
612
|
III. Control of Muscle
Protein Metabolism/Anabolism
The
area of sports nutrition and anabolic strategies draws its rationale from
the physiology of starvation reviewed earlier and on the interrelationships
of fuels during aerobic and anaerobic exercise already discussed. There
are two broad areas which will be discussed:1) Ergogenics which are substances
touted to enhance performance; and 2) Anabolics which are substances touted
to build muscle. The rationales for the various approaches will be reviewed,
but it should be emphasized that there is much room for future research
and contributions in this field.
1.
Ergogenics
The background
to increasing energy and performance is eating a balanced diet meeting
the same dietary recommendations given for the general public. Because
of the importance of loading carbohydrate as emphasized below and because
there are adequate fat stores for exercise, many athletes prefer to shift
from eating a general diet of 30% fat, 50% protein and 20% protein to
one with 70% carbohydrate, 15% fat, and 15% protein on training and performance
days. This diet recommendation provides adequate protein at the level
of 1 gm/kg body weight. A number of studies have demonstrated that this
is an adequate amount of protein which can be kept constant with increased
energy demands as long as adequate carbohydrate is provided. This makes
sense, since protein is rarely used as a fuel in exercise. Furthermore,
most amino acid tablets provide too little protein to be a significant
source of high quality protein which is more easily derived from egg white
or milk protein.
As
already reviewed, in moderate intensity exercise lasting 4 to 6 hours,
60 to 70% of the fuel burned is fat. Exercising for 10 to 15 minutes does
not burn significant amounts of fat. Short bursts of high intensity exercise
burn primarily carbohydrates and require large stores of glycogen in the
muscle. Training causes an increase in the mitochondrial capacity for
fat oxidation which spares glycogen utilization. Therefore, the trained
athlete will burn fat with long term moderate intensity exercise, but
will also want to be sure that the glycogen stores are repleted.
Everything
that follows in regard to ergogenics does not apply to the weekend athlete,
but to the trained high performance athlete where differences in mood,
energy, and minor differences in metabolism can be the 0.3 seconds difference
between a gold and silver medal in the Olympics. Since many of these effects
are minor, they are difficult to demonstrate in standard scientific experiments
using normal subjects who are not highly trained athletes.
A. Water
and Bicarbonate
It
is recommended that 0.4 to 0.6 liters (14 to 20 oz.) of cool water be
ingested 15 to 20 minutes before exercising (1). Typical insensible
losses of water in an athlete total about 2.4 liters per day. It is
also recommended that 0.5 to 2.0 liters/hour be ingested in most forms
of exercise activity. In heavy endurance performance, it is recommended
that 3.0 liters/hour be ingested. Dehydration leads to decreased aerobic
capacity (2). Bicarbonate is an important buffer which can neutralize
organic acids accumulated from protein breakdown, and also help to neutralize
lactic acid released from muscle during anaerobic glycolysis. When lactic
acid combines with bicarbonate, carbon dioxide gas and water are formed.
The carbon dioxide is excreted through the lungs. By increasing the
concentration of bicarbonate in blood, the buffering capacity is increased
for lactic acid.
B. Carbohydrate
Loading
It
was previously recommended that a 3 day regimen be used to load glycogen
stores (3-5) but during rest days prior to an event it is now recommended
that a 65-70% carbohydrate diet be ingested as discussed above. Many
athletes also load carbohydrates just before an event. This pre-exercise
loading depends on the period remaining until exercise and will vary
from 1 to 4 gm carbohydrate/kg as follows (6):
Example:
for a 64 kg athlete |
1
hr. before exercise: 64 g. of carbohydrate |
| 2
hr. before exercise: 128 g. |
| 3
hr. before exercise: 192 g. |
| 4
hr. before exercise: 256 g. |
During exercise
it is recommended that 15 to 30 gm/ half hour be ingested (7,8). The
most rapid glycogen depletion occurs immediately after exercise. Waiting
2 to 3 hours after exercise to ingest carbohydrates reduces the rate
of glycogen repletion, while taking 50 to 75 grams of carbohydrate within
30 minutes followed by 50 to 75 gm every 2 hr can help speed glycogen
repletion (9).
C. Branched Chain
Amino Acids
The branched
chain amino acids (isoleucine, leucine, and valine) have a special role
in metabolism. Alanine is one of the most important amino acids used
for glucose synthesis between meals or in the fasting state via the
Alanine Cycle (see below).
| Alanine
--> liver to form glucose |
|
NH2
removed to form pyruvate in the process then
pyruvate to glucose by gluconeogenesis |
|
Glucose formed
from Alanine is then utilized, releasing pyruvate
|
| Pyruvate
-->muscle |
|
where
it gains an NH2 to form Alanine again |
The Branched Chain
AA's donate this NH2 through the action of a specific enzyme
branched chain amino acid oxidase which utilizes only these three amino
acids.
During intense exercise
with increased glucose utilization, the levels of the BCAA drop. This
drop can be prevented by feeding or infusing the BCAA, but the effects
on performance are minor. A second effect reported by athletes is in
preventing the depression or drop in mood that occurs when blood glucose
levels fall. The mechanism for this effect has to do with the transport
of tryptophan into the brain by a neutral amino acid transport system
that transports both valine and tryptophan into the cerebrospinal fluid.
With carbohydrate ingestion there is a rise in insulin levels which
leads to increased tryptophan transport and increased serotonin synthesis.
This theory is the basis of the so-called Carbohydrate Craver's Diet
by Judith Wurtman, based on research in animals done by her husband
Richard Wurtman at M.I.T. Tryptophan's effects on sleep, and the effects
of a warm glass of milk in promoting sleep are based on the same concept.
| Tryptophan
-->
|
|
Tryptophan
-->Serotonin |
|
Common
Transport Protein --> CNS
|
| Valine
--> |
|
Valine
--> Other Metabolites |
D. Phosphate
When glucose
is utilized in cells, the first biochemical step is phosphorylation.
In diabetic patients who are out of control and given insulin, low phosphate
levels can result as the high glucose levels in the blood are driven
into cells. Unless phosphate is provided these diabetics will have low
phosphate levels leading to bursting of their red blood cells. Phosphate
salts in the athlete are also meant to enhance glucose utilization for
glycogen synthesis which requires phosphorylation.
E. Carnitine
Carnitine
is synthesized from two amino acids (lysine and methionine) by two hydroxylase
enzymes containing ferrous iron and L-ascorbic acid. It is found in
heart, skeletal muscle, and other tissues where fatty acid oxidation
occurs. Carnitine is needed to transport any fatty acids of greater
than 8-10 carbon chain length into the mitochondria for oxidation to
carbon dioxide and water with the production of energy. Since during
heavy exercise fat is a primary fuel, this is taken to enhance fat utilization
and sparing of glycogen stores.
F. Glutamine
Glutamine
is the most abundant amino acid in the body, and constitutes more than
60% of the free intracellular amino acids in skeletal muscle. Glutamine
plays an essential role in a number of metabolic processes including
interorgan transfer of nitrogen, renal ammonia synthesis, hepatic gluconeogenesis,
and hepatic glycogen synthesis. Circulating levels of glutamine may
also regulate muscle protein synthesis and breakdown. Glutamine is an
important substrate for cells growing in culture, for proliferating
lymphocytes, and for the cells of the gastrointestinal tract.
Combinations of
glutamine, branched chain amino acids and carnitine are ingested by
some athletes
based on the above rationale. Results are poorly documented.
2.
Anabolics
Anabolic agents are designed to cause muscle hypertrophy (increase in
the size but not the number of muscle cells) with an increase in muscle
strength.
A. Insulin - leads
to amino acid uptake and protein synthesis
B. Growth Hormone
- increases muscle protein synthesis by increasing insulin-like growth
factor I (IGF-1) levels. IGF-1 is also called somatomedin. Arginine
and Insulin release growth hormone.
C. Anabolic Androgens
- synthetic forms of testosterone which are more potent. They are most
effective in adolescents, children or in women. In adult males high
dose testosterone has been shown to build muscle. This may be important
and effective in the elderly.
3.
General Dietary Guidelines for Training
Exercise
requires different diets depending on the goal of the athlete.
A
diet moderate to high in carbohydrates is used by aerobic exercisers and
endurance runners. In this type of diet, carbohydrate should be about
55 to 70% of total calories, with the endurance athlete meeting the higher
figure. Fat intake will then be reduced from typical 36% of total calories
to between 15% and 30 %. Protein will then make up the rest with about
10 to 15% of total calories. Multiple servings of fruits, vegetables,
cereals, and grains rather than simple sugars will help maintain glycogen
stores, avoid hypoglycemia, and maintain overall energy levels. This will
result in a thin look typical of the long distance runner with relatively
low muscle and fat mass. However, this athlete will have a lower energy
expenditure than the muscular athlete and so will have a harder time maintaining
weight if they deviate to a high fat/high calorie diet. Many women seek
this "never too thin, never too rich" look characteristic of
models. It is a luxury of our modern era of nutrition, antibiotics, dietary
supplements and sanitation that such individuals can survive without dying
of an infectious disease. They often eat salad with no chicken on top,
skip breakfast, and eat tiny dinners. This behavior is related to binge-eating
behaviors when they lose control, and it is interesting that those societies
that have a high incidence of obesity also have a high incidence of eating
disorders, including bulimia and anorexia.
For
muscle-building regimens, athletes should consume 1.0 to 1.5 grams of
protein per kg per day (0.5 to 0.7 grams per pound body weight). This
is slightly above to about double the RDA for protein of 0.8 gm/kg/day.
This can easily be achieved by eating normal foods without taking protein
supplements. For example, 80 grams of protein could be obtained from 4
ounces of chicken, 3 ounces of tuna, and 3 glasses of non-fat milk per
day. This does not include the protein found in grains and vegetables.
If you are a vegetarian, it is possible to obtain the protein you need
from soy and other high quality vegetable proteins through combining of
legumes (beans) and rice or corn. The amino acids in these foods are complementary
increasing the biological value of the proteins. Alternatively, you can
eat soybean protein, which is the only complete protein in the plant world.
Soybean protein isolates are available which provide the protein without
the natural soybean fat. Tofu is about 40% fat, and lite Tofu is about
30% fat.
What
about the "Zone" diet ? This plan is based on concepts borrowed
from several sources including a misreading of the diabetes literature.
It is basically a 30% protein, 30% fat, 40% carbohydrate diet. It "works"
to cause weight loss for those individuals with an increased muscle mass,
since it organizes the eating plan. It does not work for individuals with
a low muscle mass, since the 30% fat is associated with too many calories
to permit weight loss. In humans, it is difficult to separate fat and
calories (with the exception of the artificial non-metabolizable fat,
olestra). This diet and Met-Rx plan before it, increased the importance
of increased protein in the diet. Many individuals attempting to lose
weight made the mistake of reducing dietary protein intake which led to
weight and muscle loss and a decrease in metabolism (sarcopenic obesity).
By increasing protein intake and raising consciousness about heavy resistance
(muscle-building) as well as aerobic exercises, these diets influence
the public’s dieting behaviors.
References
1.
American College of Sports Medicine, Position stand on the prevention
of thermal injuries during distance running. Med Sci Sports Exerc 16:ix,
1984.
2. Sherman W, Costill D. The marathon: dietary manipulation to optimize
performance. Am J Sports Med 12:44, 1984.
3. Sherman W, Costill D, Fink W et al Effect of exercise-diet manipulation
on muscle glycogen and its subsequent utilization during performance.
Int J Sports Med. 2:114,1981.
4. Sherman W, Costill D, Fink W et al Carbohydrate loading: a practical
approach. Med Sci Sports Exerc 13:90(abst), 1981.
5. Sherman W, et al. Effect of 4 hr. pre-exercise carbohydrate feeding
on cycle performance. Med Sci Sports Exerc 12:598-604, 1989.
6. Coyle EF, Montain SJ Carbohydrate and fluid ingestion during exercise:
are there trade-offs ? Med Sci Sports Exerc 24:671-678, 1992.
7. Coggan AR, Coyle EF Carbohydrate ingestion during prolonged exercise:
effects on metabolism and performance. Exerc Sports Sci Rev 19: 1-40,1991.
8. Murray R, Paul GL, Siefert JG et al. Responses to varying rates of
carbohydrate ingestion after exercise. Med Sci Sports Exerc 23: 713-718,1991.
9. Ivy J, Katz AL, Cutler CL et al. Muscle glycogen synthesis after exercise:
Effect of time of carbohydrate ingestion. J Appl Physiol 64: 1480-1485,
1988.
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