Reproduced, with permission, from Muscular Development
"Performance enhancement is not against the
spirit of sport; it is the spirit of sport. To choose to be better is
to be human. Athletes should be given this choice."
Bodybuilding Supplements, Insulin, Amino Acids & Protein Anabolism
--J Savulescu et al. British Journal of Sports Medicine, 2004;38:666-670.
Appropriate resistance exercise leads to significant increase in
skeletal muscle mass (hypertrophy), which can occur through an increase
in muscle protein synthesis, a decrease in muscle protein degradation,
or both. While stimulus (i.e., resistance exercise) is important for
muscle hypertrophy, nutrient availability plays a critical factor in
regulating the degree of hypertrophy. Obviously, the muscle's hormonal
milieu also has a major impact on muscle protein synthesis.
It's now clear that both increased insulin and increased availability of
are important to maximize muscle protein anabolism. The importance of
availability of amino acids for the stimulatory effects of insulin to
be evident was highlighted by Bennet and colleagues, who reported that
insulin, given with sufficient amino acids, can significantly stimulate
protein anabolism via stimulation of protein synthesis and inhibition
of protein breakdown.
This is in line
with the recent data by Borsheim and co-workers, who showed that
protein balance over the muscle remains negative after resistance
exercise, when only carbs are ingested.
In sharp contrast, amino acid ingestion alone significantly increases muscle protein anabolism after resistance exercise.
However, consumption of both amino acids and carbs result in much greater effects on muscle protein anabolism,
suggesting an interactive effect between insulin, amino acid
availability and resistance exercise. Also, it's well-established that
the stimulatory effect of amino acids after exercise is greater than
the effect of amino acids on muscle protein synthesis, when given at
Thus, nutrient timing is also an important consideration.
Given the fact that raising the blood insulin level is key to
stimulating muscle protein synthesis and limiting protein degradation
it's not surprising that some hardcore gym rats abuse insulin to
increase muscle mass and strength. According to MD's own drug guru
William Llewellyn, insulin injections can produce "rapid and noticeable
[muscle] growth ... almost immediately after starting insulin therapy."
Most athletes choose to administer insulin immediately after a workout.
They apparently realize that it's the most anabolic time of the day to
use this hormone. However, insulin abuse is extremely risky business--
one mistake in dosage and/or diet can be fatal or leave one as a
vegetable. Fortunately, recent studies have focused on safe nutritional
mixtures containing protein hydrolysates, certain added
(especially leucine) and high-glycemic (fast-acting) carbs.
Based on the best available evidence including thorough examination of
cutting edge bodybuilding supplements
I would suggest that dietary supplementation-induced post-exercise
hyperinsulinemia (a high level of insulin in the blood) supported by
protein hydrolysate and leucine ingestion-induced hyperaminoacidemia
(high levels of amino acids in blood) increases net protein deposition
in muscle, leading to increased skeletal muscle hypertrophy and
strength in conjunction with appropriate resistance training. Let's
examine some science behind my hypothesis.
Amino Acid & Insulin Secretion
Insulin is a peptide hormone produced by the beta cells of the
pancreas. It was once believed that insulin secretion was controlled
almost entirely by blood glucose concentration, i.e., by eating
carb-containing foods. However, scientists later realized that amino
acids also play a very important role in controlling insulin secretion.
Certain amino acids cause insulin release in humans, even under
conditions where the blood sugar changes little from its basal level.
However, changes in blood sugar levels markedly influence the
responsiveness of beta cells to individual amino acids. Studies on
isolated perfused rat pancreas and islets have demonstrated that
physiological amino acid mixtures and even pharmacological
concentrations of individual amino acids require the presence of
permissive levels of glucose to be effective beta cell stimulants.
However, leucine is an exception.
Contrary to popular belief, oral arginine isn't an effective insulin booster.
Leucine & Muscle Protein Synthesis
The key branched-chain amino acid leucine acts as a nutrient signal to stimulate muscle protein anabolism.
affects muscle protein metabolism by decreasing the rate of protein degradation,
most likely via increases in circulating insulin. In addition, leucine
activates key molecules involved in the regulation of protein
synthesis, which has been shown to occur even in the absence of an
increase in circulating insulin concentrations.
After exercise, recovery of muscle protein synthesis requires dietary
branched-chain amino acids
to increase tissue levels of leucine.10 The important bottom line is
that insulin and leucine allow skeletal muscle to coordinate protein
synthesis with physiological state and dietary intake.
If you wish to read a more detailed review, see the recent paper by Norton and Layman in
The Journal of Nutrition
Rapidly Absorbed Protein Hydrolysates
Protein hydrolysates (i.e., pre-digested proteins) are produced from
purified protein sources by heating with acid or preferably, the
addition of enzymes, followed by purification procedures.6 Hydrolysis
process mimics our own digestive actions; thus, many experts feel it's
an ideal way to process dietary protein, especially when rapid
absorption is important (e.g., immediately after exercise). However,
extreme bitterness is a negative attribute associated with most protein
hydrolysates ("Dude, this stuff taste like donkey ball extract").
Fortunately, specific debittering methods have produced relatively neutral-tasting protein hydrolysates.
Extensively hydrolyzed proteins containing mostly di- and tripeptides
(chains of two and three amino acids) are absorbed more rapidly than
free-form amino acids, and much more rapidly than intact
considerably greater absorption rate of amino acids from the di- and
tripeptides (compared to the amino acid mixture) appears to be the
result of uptake by a system that has a greater transport capacity than
the amino acid carrier system, thus minimizing competition among its
Current evidence indicates that only di- and tripeptides are absorbed intact.
Larger peptides appear to require hydrolysis before their breakdown products can be absorbed.
While the starter protein and method of hydrolysis affect absorptive
characteristics, the peptide-chain length is the most important
variable. Protein hydrolysates produced from various sources showed
increased amino acid absorption in humans when the proportion of di-
and tripeptides was increased.
in order to maximize the absorption rate, the ideal protein hydrolysate
should contain mainly di- and tripeptides. Such a protein hydrolysate
seems to produce the most immediate hyperaminoacidemia. In general,
it's the kinetics of the absorption (rather than the net absorption of
amino acids) that determines the greater nutritional value of the
The use of a protein hydrolysate in
is preferred because it results in a faster increase in blood amino
acid concentrations during a two-hour period than does intact protein
. And in turn, the levels of essential amino acids in the blood regulate muscle protein synthesis.
A practical advantage is that one can ingest a protein
hydrolysate-containing supplement immediately after exercise without
getting bloated and not excessively suppressing appetite, so one can
eat another meal sooner, possibly optimizing the post-exercise
"anabolic window." In addition, protein hydrolysates strongly stimulate
is the most popular protein hydrolysate among athletes. Whey protein
has been singled out as the ultimate source of protein based on an
excellent amino acid profile.
Whey may offer other benefits, too.
Casein hydrolysate is also utilized in some protein mixtures, but I
prefer whey hydrolysates. By the way, the biological value of
hydrolyzed collagen (also known as gelatin) is zero; thus, collagen
supplementation as a protein source isn't recommended, so stay away
from those poor-quality protein bars containing collagen. However, it's
been suggested that hydrolyzed collagen may be useful in counteracting
degenerative joint diseases (e.g., osteoarthritis).
Finally, some commercial products are enriched with wheat gluten
hydrolysate (i.e., "glutamine peptides"). Wheat gluten has a unique
amino acid profile: glutamyl residues account for about 40 percent of
the amino acids.
is an important fuel for some cells of the immune system, and may have specific immunostimulatory effects.
Protein Hydrolysate/Carb/Leucine Drinks, Insulin Secretion & Nitrogen Utilization
A study at the Copenhagen Muscle Research Center was implemented to
determine the effects different protein-containing solutions have on
insulin response and amino acid availability in healthy humans.
Four different 600 mL solutions were used. The glucose solution
(control) contained only glucose (25 g/L), and the three additional
solutions contained the same quantity of glucose plus protein (0.25
g/kg body mass), but proteins were derived from different sources: whey
hydrolysate, pea hydrolysate and a complete cow's milk solution. This
study indicated that:
- Ingestion of glucose and protein
hydrolysate results in synergistic and fast increases in blood insulin.
In fact, protein hydrolysates stimulated an increase in blood insulin
that was two and four times greater than that produced by the intact
milk protein solution and glucose solution, respectively.
- Protein hydrolysates are
absorbed at a faster rate from the gut than are intact milk proteins,
as reflected by the rapid increase in the blood concentration of amino
acids in peripheral blood.
- Whey protein hydrolysate
elicited the greatest availability of amino acids during the three-hour
postprandial (occurring after meal) period. The authors attributed this
difference to the rapid increase in blood amino acids evoked during the
first 40 minutes of the digestive period, during which the increase was
about 37 percent greater after the ingestion of whey protein
hydrolysate solution than after ingestion of the intact milk protein
It's likely that the high levels of blood amino
acids and increased insulin explains a superiority of protein
hydrolysates over intact proteins in promoting better nitrogen
utilization (i.e., protein anabolism). The co-ingestion of carbs
appears to affect the absorption kinetics, as Calbet and Holst showed
that whey and casein proteins and their respective hydrolysates
administered alone produce similar rates of intestinal absorption of
It should be noted that the degree of hydrolysis (i.e., the
peptide-chain length) also affects absorption kinetics. Unfortunately,
many scientists don't provide any information on protein hydrolysates
used in their studies.
More recently, Kaastra and
colleagues determined the extent to which the combined ingestion of
high-glycemic carbs and a casein protein hydrolysate, with or without
additional leucine, can increase insulin levels during post-exercise
Fourteen male athletes were subjected to three randomized crossover
trials in which they performed two hours of exercise. Thereafter,
subjects were studied for three and a half hours during which they
ingested carbs only (0.8 g/kg/h), carbs + protein hydrolysate (0.8 and
0.4 g/kg/h, respectively), or carbs + protein hydrolysate + free
leucine (0.8, 0.4 and 0.1 g/kg/h, respectively) in a double-blind
The results revealed that blood insulin
responses were 108 percent and 190 percent greater in the carbs +
protein hydrolysate and carbs + protein hydrolysate + leucine trial,
respectively, compared with the carbs-only trial. This study also
indicated that the addition of free phenylalanine, as applied in
isn't necessary to obtain such high post-exercise insulin responses.
Similarly, Manders and co-workers examined blood insulin responses
after co-ingestion of casein protein hydrolysate, with and without
additional free leucine, with a single bolus of high-glycemic carbs.
Again, the subjects participated in three trials in which blood insulin
responses were determined after the ingestion of beverages of different
composition: carbs only (0.7 g/kg), carbs + protein hydrolysate (0.7
and 0.3 g/kg, respectively) or carbs + protein hydrolysate + leucine
(0.7, 0.3 and 0.1 g/kg, respectively). The results indicated that blood
insulin responses were 66 and 221 percent greater in the healthy
subjects in the carbs + protein hydrolysate and carbs + protein
hydrolysate + leucine trials, respectively, compared with those in the
carbs only trial. In other words, this study also demonstrated that
co-ingestion of a protein hydrolysate with additional leucine strongly
augments insulin secretion after the consumption of a single bolus of
The notion that the
protein hydrolysates have strong insulin-boosting properties
is also supported by the studies examining the effects of intact
protein-containing post-exercise drinks. Ivy and co-workers compared
effects of carb + intact protein drink (80 g of carbs, 28 g of protein,
6 g of fat), low-carb drink (80 g of carbs, 6 g of fat), or high-carb
drink (108 g of carbs, 6 g of fat) and concluded that blood insulin
levels didn't differ at any time among treatments.
However, Zawadzki and colleagues observed that blood insulin levels for
the carbs + intact protein treatment (112 and 40.7 g, respectively)
were somewhat higher than those for the carbs-only treatment (112 g of
A post-exercise drink containing a mixture of free amino acids also has a potent effect on insulin secretion.
However, a large dose of amino acids can cause gastrointestinal discomfort.
Protein Hydrolysate/Carb/Leucine Drinks and Post-exercise Muscle Anabolism
A sophisticated study by Koopman and colleagues investigated
post-exercise muscle protein anabolism and whole body protein balance
following the combined ingestion of high-glycemic carbs, with or
without whey protein hydrolysate and/or leucine.
Their nutritional protocol was rather rigorous; the subjects received a
beverage volume of 3 ml/kg every 30 minutes to ensure a given dose of
0.3 g high-glycemic carbs/kg and 0.2 g/kg of a protein hydrolysate
every hour, with or without the addition of 0.1 g/kg/h leucine.
Repeated boluses were taken every 30 minutes until t = 330 minutes
after exercise. The results revealed that the whole body protein
synthesis rates were highest in the carbs + protein hydrolysate +
leucine trial. Similarly, muscle anabolism in the vastus lateralis
muscle was significantly greater in the carbs + protein hydrolysate +
leucine trial compared with the carbs-only trial, with intermediate
values observed in the carbs + protein hydrolysate trial. Thus, the
authors concluded that, "The additional ingestion of free leucine in
combination with protein and carbohydrate likely represents an
effective strategy to increase muscle anabolism following resistance
exercise." This study used rather large doses of added leucine;
however, other recent studies have shown that relatively small doses
can improve exercise performance
and enhance the acquisition of strength.
Although the Koopman study indicates that dietary
supplementation-induced, post-exercise hyperinsulinemia plus
hyperaminoacidemia can have favorable effects on the acute phase
response to resistance training, the effects of repeated
supplementation on long-term adaptations to resistance training are
currently unclear. To shed some light on this issue, Bird and
co-workers examined the effects of chronic, high-glycemic carb and/or
essential amino acid supplementation on hormonal and muscular
adaptations in untrained young men.
All subjects followed the same supervised, resistance-training protocol
two times per week for 12 weeks. Following resistance exercise, the
subjects consumed either a high-glycemic carb, an essential amino acid
(6 g), a combined high-glycemic carb + essential amino acid supplement,
or a placebo containing only aspartame and citrus flavoring. The
results revealed that carb + essential amino acid supplementation
enhances muscular and hormonal adaptations to a greater extent than
either carbs or essential amino acids consumed independently.
Specifically, carb + essential amino acid ingestion demonstrated the
greatest relative increase in type I muscle fiber cross-sectional area.
Changes in type II muscle fibers exhibited a similar trend.
While beyond the scope of this article, it's very likely that chronic
reductions in the exercise-induced cortisol response associated with
post-exercise carb-amino acid ingestion also positively impact the
skeletal muscle hypertrophic adaptation to resistance training via
reductions in hormone-mediated protein degradation.
You Can Have Your Protein Shake & Drink It, Too!
Contrary to some beliefs, higher protein intake has no adverse effects on healthy kidneys,
appears to have positive effects on bone health, as they increase
circulating insulin-like growth factor I (IGF-1), which plays an
important role in bone formation.
For example, Ballard and co-workers reported that a protein supplement
during a strength and conditioning program led to an increase in blood
concentrations of IGF-I in those subjects compared with the
concentrations in a group of persons who also trained, but consumed an
isocaloric carb supplement.
serum bone alkaline phosphatase concentrations increased over time and
tended to be higher in the protein group than in the carb group,
indicating increased bone formation. In addition, IGF-I plays a
critical role in development, growth, repair and maintenance of
Thus, IGF-I may
partially explain why many strength-power athletes (especially
bodybuilders) feel that a very high protein intake is beneficial for
skeletal muscle hypertrophy. Indeed, studies indicate increased
positive nitrogen balance when protein intake is increased;
however, more research is clearly needed before the mystery of protein
requirements in those attempting to increase muscle mass is settled.
Traditionally, the term "protein requirement" has meant the amount of
dietary protein that must be consumed to provide the amino acids needed
for the synthesis of those proteins irreversibly catabolized in the
course of the body's metabolism. It should be noted, however, that
strength-power athletes don't care about the minimum amount of protein
necessary to sustain normal body functions. Rather, they are interested
maximal gains in muscle mass and/or strength
. Other potential benefits of higher protein intake should be considered, too.
The studies reviewed in this article clearly indicate that
with nutritional mixtures containing protein hydrolysates, added
leucine and high-glycemic carbs strongly augment insulin secretion,
compared with the high-glycemic carbs-only trial. When post-exercise
hyperinsulinemia is supported by protein hydrolysate and leucine
ingestion-induced hyperaminoacidemia, net protein deposition in muscle
should occur. Thus, I would suggest that
post-exercise recovery drinks
containing these nutrients
(e.g., BioQuest MyoZene)
can lead to increased skeletal muscle hypertrophy and strength in conjunction with appropriate resistance training.
PS. Obviously, there are other potentially useful ingredients for
post-exercise supplements, but they are discussed in my future MD
Read Post-Exercise Supplementation Update
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