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by Hypertrophy
Introduction
All too often athletes are looking for a food or diet that will
increase their performance "during competition". This is a misguided
approach. The key role for nutritional intervention is during the
training period. Nutrition will have the greatest impact on
"performance" if it is used as an adaptive facilitator after
appropriately periodized training sessions rather than as a magic
potion. This must be done on a consistent basis. When implemented
properly, strategic post-exercise nutrition can greatly effect the
extent to which the athlete adapts to training. From this perspective,
training and diet can not be considered as separate factors. The food
and supplements that you take and the work that you faithfully perform
is training. On the day of competition it will not be the athlete
who trained harder who wins, it will be the athlete who trained smarter.
Exercise causes acute changes in the metabolic environment of muscle
tissue. These changes favor catabolism during exercise, and anabolism
immediately after exercise. Because these changes are acute, some
lasting only a few hours, the post exercise meal is critical to
optimizing the anabolic effect of exercise. This article will discuss
post exercise nutritional strategies based on current research in this
area.
During exercise muscles use metabolic fuels at an accelerated rate.
In order for physical work to be continuous, the body mobilizes stored
fuels to make available fatty acids, glucose, and amino acids for
oxidation. This is a catabolic process and cannot occur simultaneous to
anabolic process’ such as glycogen formation and protein synthesis.
In order for the body to recover from exercise, the catabolic
environment must be quickly changed to an anabolic environment. The food
that you eat after training effects the hormonal milieu in your body in
order for this to take place. With the rapid introduction of
carbohydrate, protein, and fat into the system post exercise, the body
is able to begin reparations on damaged tissue and replenish fuel
reserves.
Carbohydrates
Carbohydrates are important for performance and perhaps more
importantly for recovery. Studies have shown an increased ability of
muscle tissue to take up serum glucose immediately following strenuous
exercise (Goodyear 1998). This is due to what is called, "non-insulin
dependant glucose uptake". After a meal, muscle cells transport glucose
across the cell membrane in response to the hormone insulin. Insulin
binds with its receptors at the cell surface causing a cascade of events
that ends with proteins, called glucose transporters, being translocated
to the cell surface. Once at the cell surface, these glucose
transporters allow glucose to pass through the membrane where they can
be phosphorilated and eventually stored as glycogen.
Membrane transport of glucose will exhibit saturation kinetics
similar to the effect of increasing substrate concentration on the
activity of enzymes. The rate of glucose entry into your muscle cells is
limited by the number of glucose transporters. Once all available
glucose transporters are associated with a glucose molecule, the rate of
glucose entry will go no higher.
There are at least 5 different classes of glucose transporter
proteins. They are designated GLUT1, GLUT2, GLUT3, GLUT4, and GLUT5.
Each class of GLUT protein differs in its kinetic parameters and are
found in specific tissues. GLUT-4 is the primary isoform regulated by
insulin, and sensitive to muscle contraction.
Muscle contractions, much like insulin, cause a separate set
of GLUT-4 proteins to be temporarily translocated to the surface of the
muscle cell (Sherman 1996). This greatly increases the rate at which
muscle tissue can take in glucose from the blood after a bout of
exercise. The effects of exercise on glucose uptake lasts for a few
hours into the post exercise period. If the post exercise meal is
lacking in carbohydrates, the replenishment of glycogen is delayed. If
carbohydrates are lacking in the diet, exercise will cause a glucose
deficit and glycogen stores will continue to fall without being
replenished to pre exercise levels.
There has been some controversy about which type of carbohydrate is
best for post exercise glycogen replenishment. Some argue that simple
sugars such as dextrose are best after exercise. Others say that drinks
with glucose polymers are best. Still others say that there is no need
to buy fancy sports drinks and that simply eating a meal high in
carbohydrates such as pasta or rice is sufficient. Studies have shown no
difference between different types of carbohydrates eaten post exercise
and the rate of glycogen replenishment as long as sufficient quantities
of carbohydrate are consumed (Burke 1997). Even when the post exercise
meal contains other macronutrients such as proteins and fats, the rate
of glycogen replenishment is not hindered, given there is sufficient
carbohydrate in the meal as well. These studies tell us that the rate
limiting step in glycogen replenishment after exercise is not in
digestion or the glycemic index of a given source of carbohydrate. Over
a 24 hour period it is the total amount of carbohydrate consumed that is
important.
The rate limiting step in glucose uptake during exercise is
determined by the rate of phosphorylation once glucose has entered the
muscle cell (Halseth 1998). Glycogen synthase activity is also a
possible rate limiting step (Halseth 1998). These processes are not
readily influenced by the composition of the "post exercise" meal, but
rather by the extent to which glycogen was depleted during exercise as
well as the amount of carbohydrate and fat consistently included in the
diet.
It is recommended that at least 0.7 - 1.0 gram of carbohydrate per
kilogram body weight be consumed immediately after exercise and then
again 1-2 hours later. If you experience gastric upset try increasing
the amount of water you consume with the carbs. Try to shoot for a total
of 7-10 grams of carbohydrate per kilogram of body weight over a 24 hour
period 3 for maximum glycogen storage. This may well be in
excess of caloric needs but it is important to shoot for this intake if
glycogen storage is your primary goal.
Protein
Protein is another critical nutrient to included in the post exercise
meal. Protein is essential to post exercise anabolism. Protein provides
amino acids which are used to rebuild damaged tissues as well as provide
enzymes and carrier proteins necessary for adaptation to exercise.
Without protein, which supplies essential amino acids for endogenous
protein synthesis, the body’s ability to adapt to exercise is greatly
diminished.
Studies have shown a 12 to 14 day period after the onset of an
unaccustomed exercise program, in which nitrogen balance, the ratio of
protein intake to protein loss, is negative (Butterfield 1987). Any
study looking at protein needs and exercise must take this into account.
Nitrogen balance during this period appears to be insensitive to total
caloric intake, but can be improved with a high protein intake if
adequate calories are supplied (Gontzea 1975). Even though additional
protein intake will prevent nitrogen balance from becoming negative, it
will still fall despite high protein intake during the first two weeks
of exercise.
Muscle specific messenger RNA (mRNA) produced subsequent to training
has a half life of only 4-5 hours. It is so short because mRNA has no
"quality control" mechanism built into the coding. By keeping the half
life short, any errors in the sequence won’t be able to produce enough
defective proteins to do irreparable damage to the cell or organism.
This also allows tight control of protein metabolism.
The timing of protein intake is important. If the anabolic stimulus
from exercise is to be maximized, a steady flow of amino acids must
bathe the muscle while mRNA content is high. It should be no surprise
that the optimum time for protein intake after your workout is
relatively brief compared to frequency of training a particular muscle.
Muscle protein synthetic rate (MPS) is elevated in humans by up to 50%
at about 4 hours following a bout of heavy resistance training, and by
109% at 24 hours following training. A study done by Macdougall
(MacDougall et al 1995) further examined the time course for
elevated muscle protein synthesis by examining its rate at 36 hrs
following a bout of heavy resistance training. Six healthy young men
performed 12 sets of 6- to 12-RM elbow flexion exercises with one arm
while the opposite arm served as a control. MPS was calculated from the
in vivo rate of incorporation of L-[1,2-13C2] leucine into biceps
brachii of both arms over 11 hours. At an average time of 36 hours
post-exercise, MPS in the exercised arm had returned to within 14% of
the control arm value, the difference being nonsignificant. The
following conclusions can be drawn from this study, following a bout of
heavy resistance training, muscle protein synthetic rate increases
rapidly, is more than double at 24 hours, and then declines rapidly so
that at 36 hours it has almost returned to baseline.
Current recommendations for total protein intake for athletes
is between 1.6-1.8 grams per kilogram body weight, depending on who you
read, however, it is not uncommon for bodybuilders to consume in excess
of 2 grams per kg of body weight with no ill effects. It should be
remembered that the body does not have the capacity to effectively store
amino acids. Protein should be eaten at least every 3-4 hours. The
evening meal should contain slowly digesting protein that will allow a
steady release of amino acids into your system well into the night.
Dinner is a perfect time for steak or other meat dishes.
Fat
Little is known about the effects of fat in the "post-exercise" meal.
Total fat intake is probably more important for a bodybuilder than just
considering the post-workout meal.
Essential fatty acids in sufficient quantities have the ability to
alter physiology. Fatty acids such as omega-3s’ and omega-6s’, when
consumed in differing ratios in a consistent and deliberate manner, can
alter the composition of cell membranes which alters the production of
prostaglandins in working muscles and thereby can modify everything from
glucose transport to protein synthesis (Hayashi 1999). These effects are
seen after at least 5 days of consuming of these fats in moderate to
high doses. Eating them immediately after training and at no other time
will most likely not have any dramatic effect.
Some forms of fat may delay gastric emptying which theoretically
could slow the rate at which nutrients become available to tissues. We
can only speculate whether this would have any "long term" effect on
gains. Most research indicates that glycogen replenishment is delayed
but not reduced when gastric emptying is prolonged.
There is some indication that cholesterol may be an important
nutrient immediately after high intensity resistance exercise. Total
cholesterol has been shown to be significantly lowered for at least 90
hours following a single bout of resistance exercise (Smith 1994). Serum
cholesterol may be needed for incorporation into damaged cell membranes
after resistance exercise. I’m not implying that you should eat a high
cholesterol meal right after training. Taken together, research is still
lacking where the optimal levels and composition of post-exercise fats
are concerned.
Fluids
I couldn’t really write an article about post exercise nutrition
without at least mentioning fluid replacement. Hydration is extremely
important on the cellular level. Muscle growth is inhibited by
dehydration. In bodybuilding we tend not to focus on fluid
replacement because unlike runners or cyclists, most bodybuilders do
not become dehydrated after a single workout. The rate at which you
become dehydrated from training depends on how much you sweat (Gisolfi
1990). Some people sweat a lot when lifting and others don’t sweat a
drop. A good rule of thumb is to drink 1 ml for every calorie that you
need. So, if you eat 3,500 calories a day, try to drink 3 ½ liters. If
you exercise in hot or humid climates add 2 cups of water for every
pound you lose while exercising.
It’s about synergy
As mentioned earlier, macronutrient intake modulates post-exercise
protein synthesis in ways that are just beginning to be understood. Yes,
protein is required to supply essential amino acids for protein
synthesis, but what is the mechanism by which protein is controlling
this process? Also, are carbohydrates and fats needed only for fuel
replacement, or do they play an "interactive" role in post exercise
protein synthesis? Recent research has shed light on these questions.
Researchers from the Division of Nutritional Sciences at the
University of Illinois examined the effect of post exercise meal
composition on protein synthesis. To do this, they looked specifically
at the activity of specific proteins known to regulate protein synthesis
at the translational level.
Initiation of translation (the binding of mRNA to the ribosomal
pre-initiation complex) requires group 4 eukaryotic initiation
factors (eIFs). These initiation factors interact with the mRNA in
such a way that makes translation (the construction of new proteins from
the mRNA strand) possible. Two eIFs, called eIF4A and eIF4B, act in
concert to unwind the mRNA strand. Another one called eIF4E binds to
what is called the "cap region" and is important for controlling which
mRNA strands are translated and also for stabilization of the mRNA
strand. Finally, eIF4G is a large polypeptide that acts as a scaffold or
framework around which all of these initiation factors and the mRNA and
ribosome can be kept in place and proper orientation for translation.
The researchers in this study looked at the association of the mRNA
cap binding protein eukaryotic initiation factor-4-E (eIF4E) with the
translational inhibitor 4E-eukaryotic initiation factor binding
protein-1 (4E-BP1) in the acute modulation of skeletal muscle protein
synthesis during recovery from exercise. Fasting male rats were run on a
treadmill for 2 h at 26 m/min and were fed immediately after exercise
with either saline, a carbohydrate-only meal, or a nutritionally
complete meal using Ensure Powder (54.5% carbohydrate, 14% protein, and
31.5% fat). Exercised animals and non-exercised controls were studied 1
h post-exercise.
Muscle protein synthesis decreased 26% after exercise and was
associated with a fourfold increase in the amount of eIF4E present in
the inactive eIF4E.4E-BP1 complex and a concomitant 71% decrease in the
association of eIF4E with eIF4G. Refeeding the complete meal, but not
the carbohydrate meal, increased muscle protein synthesis equal to
controls, despite similar plasma concentrations of insulin.
Additionally, eIF4E.4E-BP1 association was inversely related and
eIF4E.eIF4G association was positively correlated to muscle protein
synthesis. This study demonstrates that recovery of muscle protein
synthesis after exercise is related to the availability of eIF4E for 48S
ribosomal complex formation, and post-exercise meal composition
influences recovery via modulation of translation initiation.
The results of this study tell us a few things:
1. Insulin (via carbohydrate intake) alone is not enough to prevent
4E-BP1 from sequestering eIF4E. EIF4E must be free to bind to eIF4G in
order for protein synthesis (i.e. recovery from training and net muscle
growth) to begin. Insulin as well as amino acids must be present at
the same time as indicated by the results from the group that were
fed a mixed nutrient meal. So although feeding of the carbohydrate meal
resulted in elevated blood glucose and elevated insulin levels,
carbohydrates alone are not sufficient to allow protein synthesis to
begin.
2. The only group that experienced a significant drop in
cortisol levels was the mixed meal group. The carbohydrate-only group
showed that neither blood glucose nor insulin had any effect on reducing
cortisol levels. In contrast, the mixed meal group showed cortisol
levels even below those in the control group who did no exercise and
were also fed the same meal.
It would have been nice for the authors of this experiment to have
explored the effect of the fat content in the "mixed meal". From the
results we saw that cortisol was lower in the mixed meal group. We can
only speculate wether this was due to the protein, the fat, or some
combination of protein, fat and carbs. Further research in this area
should take into consideration all components of the post exercise meal.
One other issue that might be addressed in humans is the time frame
during which re-alimentation is critical to "long term" adaptation to
exercise.
In closing...
Post-exercise nutrition is critical if one wants to maximize the
anabolic effects of exercise. The post exercise meal should consist of
carbohydrate, protein and fat in a form that is easily and quickly
digestible. There are many meal replacement products that fit the bill.
Just pick the one you like the most. Don’t worry about sugar content
because right after a workout, fat storage is not a big issue. A liquid
meal is the most practical method of post-exercise feeding although it
is probably not essential. The ratio of macronutrients depends somewhat
on the nature of the training session. An emphasis on high glycemic
carbs, complete readily digestible proteins such as whey or high quality
soy, and essential fats such as flax oil will meet the criteria for an
effective post exercise meal.
References:
Burke LM. Nutrition for post-exercise recovery.
Aust J Sci Med Sport Mar;29(1):3-10, 1997
Butterfield GE, Whole-body protein utilization in
humans. Med. Sci. Sports Exrc., Vol. 19, No. 5 (Supplement), pp.
S157-S165, 1987.
Gisolfi CV., Lamb DRR. (Eds.) Perspectives In Exercise
Science and Sports Medicine Volume 3: Fluid Homeostasis During Exercise.
Cooper Publishing Group, LLC 1990.
Gontzea I, Sutzescu P, Dumitrache S. The influence of
adaptation to physical effort on nitrogen balance in man. Nutr. Rept.
Inturn. 11:231-236, 1975
Goodyear LJ, Kahn BB, Exercise, glucose transport, and
insulin sensitivity. Annu. Rev. Med. 49:235-261, 1998
Halseth AE, Bracy DP, Wasserman DH. Limitations to
exercise- and maximal insulin-stimulated muscle glucose uptake. J.
Appl. Physiol. 85(6):2305-2313, 1998
Hayashi N, Tashiro T, Yamamori H, Takagi K, Morishima
Y, Otsubo Y, Sugiura T,
Furukawa K, Nitta H, Nakajima N, Suzuki N, Ito I
Effect of intravenous omega-6 and omega-3 fat emulsions on nitrogen
retention and protein kinetics in burned rats. Nutrition 1999
Feb;15(2):135-9
MacDougall JD, Gibala MJ, Tarnopolsky MA, MacDonald
JR, Interisano SA,
Yarasheski KE The time course for elevated muscle
protein synthesis following heavy resistance exercise. Can J Appl
Physiol 1995 Dec;20(4):480-6
Sherman LA, Hirshman MF, Cormont M, Le
Marchand-Brustel Y, Goodyear LJ. Different effects of insulin and
exercise on Rab4 distribution in rat skeletal muscle. Endocrinology
137:266-73, 1996
Smith L.L, Fulmer M.G, Holbert D, McCammon M.R,
Houmard J.A, Frazer D.D, Nsien E, and Isreal R.G. The impact of a
repeated bout of eccentric exercise on muscular strength, muscle
soreness and creatine kinase. Br. J. Sports Med.1994; 28 (4)
267-271.
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