International Journal of Sport Nutrition and Exercise Metabolism, 2006, 16, 494-509
© 2006 Human Kinetics, Inc.
The Effect of Whey Isolate and Resistance
Training on Strength, Body Composition,
and Plasma Glutamine
Paul J. Cribb, Andrew D. Williams, Michael F. Carey,
and Alan Hayes
Different dietary proteins affect whole body protein anabolism and accretion
and therefore, have the potential to influence results obtained from resistance
training. This study examined the effects of supplementation with two proteins,
hydrolyzed whey isolate (WI) and casein (C), on strength, body composition, and
plasma glutamine levels during a 10 wk, supervised resistance training program.
In a double-blind protocol, 13 male, recreational bodybuilders supplemented their
normal diet with either WI or C (1.5 gm/kg body wt/d) for the duration of the
program. Strength was assessed by 1-RM in three exercises (barbell bench press,
squat, and cable pull-down). Body composition was assessed by dual energy X-ray
absorptiometry. Plasma glutamine levels were determined by the enzymatic method
with spectrophotometric detection. All assessments occurred in the week before
and the week following 10 wk of training. Plasma glutamine levels did not change
in either supplement group following the intervention. The WI group achieved a
significantly greater gain (P < 0.01) in lean mass than the C group (5.0 ± 0.3 vs.
0.8 ± 0.4 kg for WI and C, respectively) and a significant (P < 0.05) change in
fat mass (–1.5 ± 0.5 kg) compared to the C group (+0.2 ± 0.3 kg). The WI group
also achieved significantly greater (P < 0.05) improvements in strength compared
to the C group in each assessment of strength. When the strength changes were
expressed relative to body weight, the WI group still achieved significantly greater
(P < 0.05) improvements in strength compared to the C group.
Key Words: protein supplement, lean mass, body fat loss
Some (8, 37) but not all (33) studies indicate that a higher protein intake (approxi-
mately 1.5 to 2 times the current Recommended Daily Allowance) is advantageous
for muscle and strength development during resistance training. Bodybuilders and
other strength athletes widely use protein supplements to achieve high protein
intakes (up to 3 times the RDA) (23, 27). Aside from quantity, certain types of protein
The authors are with the Exercise Metabolism Unit, Center for Ageing, Rehabilitation, Exercise and
Sport (CARES) and the School of Biomedical Sciences, Victoria University, Melbourne Victoria 8001,
Whey Isolate and Resistance Training 495
affect whole body protein anabolism and accretion (4, 11, 12) and therefore, have
the potential to affect muscle and strength development during resistance training
(22). The type of protein consumed may influence results from resistance training
due to variable speeds of absorption, differences in amino acid profiles, unique
hormonal response, or positive effects on antioxidant defense (22).
Whey is a protein that generally contains a higher concentration of essential
amino acids than other protein sources (7), and has rapid absorption kinetics (4, 11,
12). Supplementation results in a higher blood amino acid peak and stimulation of
protein synthesis compared to casein (the other major bovine milk protein) (4, 11,
12). The consumption of a whey protein meal provides a higher postprandial leucine
balance and net protein gain in young and older men compared to an isonitrogenous
casein meal (11). Due to its favorable effect on protein metabolism and lean body
mass (LBM) accretion, whey protein may enhance adaptations from resistance
training. During 6 wk of resistance training, whey protein supplementation (1.2
g/kg body weight/d) resulted in an almost two-fold higher gain (2.1 vs 1.2 kg) in
LBM compared to a carbohydrate control (8). However, no studies have examined
the effects of whey protein supplementation in comparison to other proteins (such
as casein) during resistance training, particularly in resistance-trained individuals
consuming a high protein intake.
A high protein intake that is commonly consumed by strength athletes may
have a negative impact on plasma glutamine (19). A decrease in resting plasma
glutamine caused by intense or prolonged exercise may cause immunosuppression
that results in a higher incidence of infection (illness) and slower wound healing
(19). In athletes, dietary protein intake expressed relative to body mass (g · kg · d)
is shown to be significantly inversely related to plasma glutamine concentrations
(19). Compared to other athletes (such as runners, swimmers, and cyclists) weight
lifters exhibit the lowest plasma glutamine concentrations despite the consumption
of a high protein intake (19). A decline in plasma glutamine concentrations has
been shown to occur during intense (anaerobic) training programs (15). Therefore,
bodybuilders and other strength athletes that characteristically follow high protein
diets maybe predisposed to a decline in plasma glutamine concentrations during
Hydrolyzed whey isolate is a protein supplement that contains the highest con-
centration of the essential amino acids, including the branched-chain amino acids
(BCAA) than other protein sources (9). The BCAA are the major precursors for
glutamine synthesis and supplementation is shown to prevent a decline in plasma
glutamine that is seen after endurance exercise (2). Supplementation with a rich
source of BCAA such as whey isolate may attenuate a decline in plasma glutamine
levels that may occur during intense anaerobic exercise training. However, no
studies have assessed the effects of protein supplementation on plasma glutamine
concentrations during resistance training.
Therefore, the aim of this study was to examine the effects of a hydrolyzed
whey isolate (WI) in comparison to casein (C) supplementation on strength, body
composition, and plasma glutamine during a 10 wk intense resistance training
program. We hypothesized that, compared to C, supplementation with WI would
provide greater gains in LBM and strength and/or enhance plasma glutamine values
during the resistance training program.
496 Cribb et al.
Materials and Methods
Nineteen male recreational (not highly trained) bodybuilders commenced this 12-
wk study but only thirteen completed all required components (C; n = 7, WI; n =
6) (six subjects did not finish the program for reasons unrelated to this study). To
qualify as subjects the men a) had no current or past history of anabolic steroid
use; b) had at least 2 y of resistance-training experience (and submitted a detailed
description of their current training program); c) had not ingested any ergogenic
supplement for an 8-wk period prior to the start of supplementation; and d) agreed
not to ingest any other nutritional supplements, or nonprescription drugs that may
affect muscle growth or the ability to train intensely during the study.
All subjects were informed of the potential risks of the investigation before
signing an informed consent document approved by the Human Research Ethics
Committee of Victoria University and the Department of Human Services, Victoria,
Australia. All procedures conformed to National Health and Medical Research
Council guidelines for the involvement of human subjects for research. After
baseline testing the subjects were matched for maximal strength in three weight
training exercises (see strength assessments) and then randomly assigned to either
Immediately after all baseline testing, the subjects were given their designated
protein supplement, C or WI, in a double-blind procedure. The protein supple-
ment was provided to the subjects in identical, unmarked, sealed containers. The
macronutrient content of the supplements were as follows; approximately 90 g
protein, 3 g carbohydrate, 1.5 g fat/100 g for WI (VP2 Hydrolyzed Whey Isolate);
approximately 90 g protein, 3 g carbohydrate, 1.5 g fat/100 g for C. Supple-
ments were supplied by AST Sports Science, Golden, CO and contained no other
performance-enhancing substances. The WI was independently assessed on two
separate occasions (Naturalac Nutrition Ltd., Mt. Eden, New Zealand) and met
label ingredients on both occasions.
The subjects were instructed to consume 1.5 g of the supplement per kilogram
of body weight per day while maintaining their habitual daily diet. The chosen
supplement dose was based on previously reported intakes of this population (23,
27). The 1.5 g · kg · d supplement dose was divided into smaller equal servings
and consumed throughout the day. For example, an 80 kg subject consumed four
30 g servings per day; one with breakfast, lunch, directly after training, and one
final serving was consumed with the evening meal. Subjects were given a container
of the supplement at the start of each week and asked to return it empty to verify
compliance with the dosing procedure. In addition to having to return the container,
the subjects were asked to document the time of day they took the supplement in
training diaries provided to them.
Nutritional intake was monitored via written dietary recalls. The subjects were
shown how to record nutrient intake and dietary recordings were obtained for 3
d prior to the program. Subsequently, 3 d were also recorded in the first and final
week of the supplementation/training program. The recordings obtained during
Whey Isolate and Resistance Training 497
the supplementation/training program were compared to the recordings taken prior
to supplementation. All recordings were assessed using Nutritionist Pro (Axxya
Systems, Stafford, TX) software. The following assessments occurred in the week
before and immediately after a 10-wk resistance exercise program.
Strength assessments consisted of the maximal weight that could be lifted once
(1RM) in three weight training exercises: barbell bench press, cable pull-down, and
barbell squat. The 1RM testing protocols followed that prescribed by the National
Strength and Conditioning Association (NSCA) (1). Briefly, the subject’s maximal
lift was determined within no more than five single repetition attempts following
three progressively heavier warm-up sets. Subjects were required to successfully lift
each weight before attempting a heavier weight. Each exercise was completed in the
same order during pre and post testing. Exercise execution guidelines were defined
and adhered to for the successful completion of each lift (1). An NSCA-certified
strength and conditioning specialist who was blinded to the groups, supervised
all lifts and showed the subjects how to record training data (i.e., lifts performed,
repetitions, amount of weight lifted, etc.) in training journals.
Whole-body composition measurements were determined using a Hologic model
QDR-4500 dual energy X-ray absorptiometry (DEXA) with the Hologic version
V 7, REV F software (Waltham, MA). Quality control calibration procedures were
performed on a spine and step phantom prior to each testing session according to
procedures previously described (14), and the same licensed operator performed
all scans. Body fat percent percent was calculated by the software by dividing the
amount of measured fat mass by total scanned mass (sum of bone mass, fat mass
and lean mass). For longitudinal studies in which small changes in body composi-
tion are to be detected, whole body scanning with this instrument has been shown
to be accurate and reliable (precision errors: 0.8 to 2.8%) (14, 32).
Blood samples for plasma glutamine analysis were taken by venepuncture without
stasis from a vein in the antecubital space following a 6-h fast. After sampling,
blood was placed in a lithium heparin tube, mixed, and spun in a centrifuge at 4500
rpm and at 4 °C for 5 min. A 1 mL aliquot of plasma was deproteinized in an equal
volume of cold 3M perchloric acid (HCLO4,) vortexed, and centrifuged again for 2
min. The supernatant was then neutralized with 20% potassium hydroxide (KOH).
This was vortexed, centrifuged again, and the neutralized, deproteinized supernatant
stored at –70 oC for subsequent analysis. Plasma glutamine levels were determined
by the enzymatic method with spectrophotometric detection (24).
Resistance Training Protocol
Resistance training began the week after all baseline assessments and continued
for 10 wk. The resistance training program (Max-OT, AST Sport Science, Golden,
498 Cribb et al.
CO) consisted of high-intensity workouts using mostly compound exercises with
free weights (Table 1). The primary goal of the program was to increase maximal
strength and muscle size. The program closely followed the principles documented
by the American College of Sports Medicine for producing effective gains in strength
and muscle hypertrophy (20). Training intensity for the program was determined
using repetition maximums (RM) from strength tests. Once a designated RM was
reached, the subjects were encouraged by the trainer to increase the weight used.
This linearly progressive overload program was divided into three phases; prepa-
ratory (70 to 75% of 1RM), overload phase-1 (80 to 85% of 1RM), and overload
phase-2 (90 to 95% of 1RM). An NSCA-certified strength and conditioning spe-
cialist supervised all subjects perform each weight lifting session in a one-to-one
or two-to-one fashion. The subjects were given training diaries to record exercises,
sets, repetitions performed, and the weight used throughout the program.
Table 1 Max-OT Resistance Training Program
General preparatory phase (weeks 1-2) 2 working sets, 10 to 8-RM (70-75% of 1RM)
Barbell dead lift
45° Leg press
Pull up (body weight)
One arm row
Cable row machine
Barbell arm curl
Flat barbell bench press
30° Incline barbell press
Standing shoulder press
Dips (body weight)
Overload Phase-1 (weeks 2-4) 2 working sets, 6-RM (80-85% of 1RM)
45°Leg press machine
Stiff-leg dead lift
Barbell bench press
30° Incline dumbbell press
Standing shoulder press
Dips (with added wt)
Barbell dead lift
Wide grip pull up (added wt)
Cable machine row
Barbell arm curl
Overload Phase-2 (weeks 5-10) 2-3 sets, 4-RM (90-95% of 1RM)
Stiff-leg dead lift
Barbell bench press
45° Incline dumbbell press
Standing shoulder press
Close grip bench press
Barbell dead lift
Close grip pull up (added wt)
Alternate dumbbell curl
Whey Isolate and Resistance Training 499
Subject characteristics are reported as means ± standard deviation. All other
values are reported as means ± standard error. Statistical evaluation of the data
was accomplished by using a two-way analysis of variance (ANOVA) with one
between groups factor (supplement) and one repeated factor (training). Where an
interaction was found, post hoc analysis was performed via t-tests. Changes from
baseline within each group were assessed by a paired t-test while comparisons
between the groups were performed by unpaired t-tests. In addition, comparisons
of the changes made by each group were made using an unpaired t-test. A P value
of less then 0.05 was required for significance.
At baseline there were no differences in the age, training consistency, height, body
weight, strength levels, lean mass or fat mass between the two groups (Table 2).
Table 2 Baseline Characteristics
CharacteristicsCasein Whey Isolate
Total strength 1RM (kgs)
Lean body mass (kg)
Fat mass (kg)
26 ± 5
177 ± 4
79.7 ± 11.2
460 ± 95
62.5 ± 6.4
14.4 ± 4.7
27 ± 7
180 ± 8
84.0 ± 5.0
470 ± 107
67.1 ± 6.5
13.9 ± 3.7
Values are means ± standard deviation of the 13 males who completed all assessments. There were no
significant differences between the groups prior to the training/supplementation program.
No differences in energy or protein intake were detected between the groups or
within the groups throughout the study (Table 3).
Lean mass and fat mass for WI and C are shown in Table 4 and the changes from
pre- to post- shown in Figure 1. There was a significant increase in lean body
mass (P < 0.01) and a significant decrease in body fat (P < 0.05) in the WI group
over the 10 wk resistance training period. There was no significant change in lean
body mass or body fat over the training period in the C group. The increase in lean
body mass was significantly greater (P < 0.01) in the WI than in the C group. A
significant decrease in body fat was seen (P < 0.05) in the WI group compared to
the C group following the training period (Figure 1).
500 Cribb et al.
Table 3 Dietary Analyses
program Week 1*Week 10*
(Kcal/kg/d)C 42.4 ± 4.942.3 ± 5.3 41.6 ± 4.3
WI 41.7 ± 6.843.2 ± 6.8 42.3 ± 7.5
(g/kg/d)C 1.86 ± 0.142.06 ± 0.15 2.10 ± 0.10
WI 1.78 ± 0.18 2.12 ± 0.09 2.11 ± 0.11
Results are means ± standard deviations of 3-d written dietary recalls all participants submitted before
the training/supplementation program and during the first and last week of the training program.
*Includes energy and protein intake from supplementation. No differences in energy or protein intake
were detected between the groups or within the groups throughout the study.
Table 4 Lean Mass and Fat Mass Data (PRE and POST training)
Whey Isolate Casein
Lean mass (kg)
67.1 ± 2.7
72.1 ± 2.8a
62.5 ± 2.4
63.3 ± 2.3b
Fat mass (kg)
13.9 ± 1.5
12.5 ± 1.3 a
14.4 ± 1.8
14.5 ± 1.8
Values are mean ± standard error of 13 males. asignificant difference between pre- and post- values;
bsignificant difference between WI and C groups
Maximal 1-RM in the barbell squat, bench press, and cable pull-down (both absolute
and relative to body weight) are shown in Table 5 and the changes from pre- to
post- shown in Figure 2. The resistance training program resulted in significant
(P < 0.05) increases in muscle strength in the three lifting exercises in both the
C and WI groups. However, strength improvements were significantly greater (P
< 0.05) in the WI group for all three exercises assessed compared to the casein
group (Figure 2) such that the WI group were significantly stronger (P < 0.05)
in all exercises than the C group following the training period. When expressed
relative to body weight, the strength improvements were still significantly greater
(P < 0.05) in the WI group for all three exercises assessed compared to the casein
group (Figure 3)
Whey Isolate and Resistance Training 501
Figure 1 — Body composition changes before and after 10 wk of resistance training and
supplementation. Values are means ± standard error of 13 males (casein = 7; whey isolate
= 6). Lean body mass and fat mass was assessed by DEXA in the week immediately before
and after the 10 wk resistance training program. *Indicates significant (P < 0.05) difference
between the two groups.
lean massfat mass
Change in body composition (kgs)
Table 5 Strength Data (PRE and POST training)
80.2 ± 7.3
155.5 ± 6.0
71.0 ± 4.5
123.2 ± 8.6
0.94 ± 0.09
1.79 ± 0.11
0.91 ± 0.08
1.54 ± 0.09*
84.0 ± 9.1
132.0 ± 5.0
87.0 ± 10.0
105.5 ± 9.5*
1.01 ± 0.11
1.51 ± 0.07
1.10 ± 0.1
1.31 ± 0.1*
71.7 ± 6.8
106.8 ± 3.6
72.0 ± 5.0
92.7 ± 5.4*
0.85 ± 0.09
1.22 ± 0.04
0.90 ± 0.06
1.16 ± 0.04*
Values are means ± standard error of 13 males. Strength is expressed in absolute terms and also expressed
relative to body mass. There was a significant increase in strength in all exercises pre- to post- in both
groups. *significant difference between WI and C groups.
502 Cribb et al.
There were no significant effects of either training or supplementation on plasma
glutamine levels for the C and WI groups (Table 6).
squat bench presspulldown
change in strength/ kg body weight
Figure 3 — Strength improvements relative to body weight before and after 10 wk of
resistance training and supplementation. Values are means ± standard error of 13 males
(casein = 7; whey isolate = 6). Strength changes are expressed relative to kilograms of
body weight in the three exercises. *Indicates significant (P < 0.05) difference in strength
improvements between the two groups.
change in strength (kgs)
Figure 2 — Strength improvements before and after 10 wk of resistance training and
supplementation. Values are means ± standard error of 13 males (casein = 7; whey isolate
= 6). Strength (1RM) was assessed in three exercises (barbell squat, barbell bench press,
cable pull-down) the week immediately before and after a 10 wk resistance training pro-
gram. *Indicates significant (P < 0.05) difference in strength improvements between the
Whey Isolate and Resistance Training 503
Using two groups of matched, resistance-trained males, this study demonstrated
that whey isolate (WI) provided significantly greater gains in strength, LBM, and
a decrease in fat mass compared to supplementation with casein (C) during an
intense 10 wk resistance training program. Neither supplement had an effect on
plasma glutamine levels. However, when interpreting the results, the following
aspects should be considered.
One limitation of this study was the low subject number of the groups. It is
possible the differences in the group’s results could be (at least partly) attributed
to the attrition of subjects. Another important factor that may have confounded our
results was the mean weight of the groups in their initial make-up. Although there
was no statistical difference in energy or protein intake between the two groups,
nor was there a statistically significant difference in starting body weight, the mean
weight of the subjects in the WI group was approximately 4.5 kg greater than the
C group at the start of the study. On a per kilogram per day basis (see Tables 2
and 3) the WI group consumed approximately 250 kcal/d more than the C group
throughout the study. This energy difference could have accounted for at least some
of the difference in lean mass gains between the two groups. Studies by Butterfield
(9), Calloway (10), and Todd (36) have demonstrated that by increasing energy
intake, nitrogen balance is improved. Moreover, Todd et al. (36) demonstrated that
increased energy intake and exercise actually increased utilization of the available
protein. To help clarify the importance of the effect of body weight on the strength
differences observed, the strength changes were expressed as absolute (Figure 2)
and relative to body weight (Figure 3). In both instances, the strength improvements
were still significantly greater (P < 0.05) in the WI group for all three exercises
assessed compared to the C group.
To our knowledge, this is the first study that has directly compared the effects
of WI and C supplementation on body composition and strength changes during
a structured, supervised resistance training program using experienced subjects.
Demling and DeSanti (13) completed an open trial that compared the effects of
whey protein supplementation (60 g/d) to a casein-based meal replacement prod-
uct on body composition and strength changes during a 12-wk resistance training
program. In this study, a group of overweight, sedentary individuals followed a
calorie-restricted diet during the exercise program. While a greater decrease in
fat mass and increase in LBM was seen in the group given the meal replacement,
the product contained added vitamins, minerals, amino acids, carbohydrate, and a
number of proteins, including whey. Therefore, it is difficult to attribute the results
Table 6 Plasma Glutamine Values
Whey Isolate Casein
0.76 ± 0.24
0.66 ± 0.19
0.57 ± 0.24
0.63 ± 0.33
Values are mean ± standard error of 13 males. Glutamine values are expressed as (mmol/L). There were
no significant changes in plasma glutamine from the training/supplementation program.
504 Cribb et al.
obtained from this product to one particular nutrient source. Only one study has
examined the effects of whey protein supplementation in comparison to casein in
healthy adults (n = 20), but this investigation did not involve exercise training (21).
In this study, after the 10 wk supplementation period (20 g/d), the whey group
demonstrated a decrease in body fat percentage (but maintained body weight) and
an improvement in anaerobic performance, without taking part in an exercise pro-
gram (21). A study on rodents has shown that supplementation with whey (alpha
lactalbumin) during 6 wk of exercise training resulted in better improvements in
body composition compared to supplementation with casein or carbohydrate (5).
The rodents fed a whey protein meal before daily exercise showed greater lean
mass and less fat mass post-training compared to rodents fed an equivalent amount
of casein or carbohydrate (5). The consumption of whey protein (but not casein
or carbohydrate) preserved lipid oxidation in the hours during and after exercise,
suggesting a greater utilization of body fat for fuel (5). The results of our study
and the results of others that have directly compared the effects of whey protein to
casein (5, 21) suggest that whey protein has a greater capability to augment body
composition changes during exercise. However, the exact mechanism(s) behind
these improvements is unclear.
A high stimulation of protein synthesis is one essential mechanism to the
development of muscle hypertrophy, along with a decreased rate of protein break-
down (30). A high concentration of essential amino acids in the blood also acts
synergistically to enhance the anabolic response of resistance training by stimulat-
ing a higher increase in protein synthesis (34) and reduce protein breakdown (3).
Generally, whey protein supplements contain a higher dose of the essential amino
acids than casein and other protein sources (44 to 48 g/100 g protein for WI vs.
34 to 35 g/100 g for C) (7). In addition, whey and casein appear to differ in their
capacity to present their amino acids to tissues (4, 11, 12, 35). Studies that have
assessed the digestion-absorption characteristics of these two protein supplements
show that generally, whey is rapidly absorbed and provides a higher (albeit transient)
increase in blood amino acid concentrations and stimulation of protein synthesis (for
up to 2 h) compared to an equivalent or larger dose of casein (4, 11, 12). A single
bout of resistance training can influence protein metabolism for up to 36 h (30).
Therefore, it is tempting to suggest that repeated doses of whey protein consumed
throughout the day may interact with resistance-exercised muscles to provide a
higher anabolic response and better muscle mass accretion over the longer term.
However, a recent study has shown that casein is capable of stimulating muscle
anabolism after resistance exercise equally as effectively (if not slightly better) than
whey (35). This research (35) directly examined whey and casein’s acute impact on
protein metabolism after resistance training exercise and showed that a 20 g bolus
dose of either protein resulted in similar increases in muscle protein net balance
and net muscle protein synthesis despite different patterns of blood amino acid
responses. Therefore, the data obtained from acute response studies do not appear
to provide a connection to our results. In addition, the effects of repeated doses of
either protein combined with resistance training on whole body protein metabolism
over the course of a day, days, or weeks is not known. The contrast of our results to
the data from acute response studies highlight the need for future investigations to
establish a link between acute metabolic perturbations and long-term adaptations
in muscle and strength development.
Whey Isolate and Resistance Training 505
Aside from differences in essential amino acid concentrations and absorption
kinetics, whey protein and casein differ in their concentration of cysteine. The
amino acid cyst(e)ine (cysteine and its disulfide twin cystine) is thought to play a
key role in the regulation of whole body protein metabolism as well as underlie
improvements in body composition (i.e., an increase in LBM and/or a decrease
in fat mass) (16, 18). WI contains a three- to four-fold higher concentration of
cyst(e)ine compared other protein sources, including casein (7). An abundant
supply of cyst(e)ine in the blood is necessary for hepatic catabolism of cyst(e)ine
into protons and sulfate; a process that inhibits carbamoylphosphate synthesis (the
first and rate limiting step of urea biosynthesis) (16). This process down-regulates
urea production, promotes glutathione synthesis, and shifts whole body nitrogen
disposal in favor of preserving the muscle amino acid pool (16). In humans, whey
protein supplementation is shown to augment this pathway (21, 29) and provide an
improvement in body composition without exercise, whereas casein supplementa-
tion was shown not to provide this effect (21). In rodents, whey protein feeding is
shown to augment this pathway of protein metabolism in a dose-dependant manner
(26). Therefore, WI’s ability to provide better improvements in body composition
during resistance training maybe at least partly due to its greater contribution of
cyst(e)ine to the diet.
Aside from amino acid profiles and absorption characteristics, the process-
ing methods used during the manufacture of a protein supplement (i.e., degree of
isolation and or hydrolyzation) may have an impact on muscle anabolism (22). A
number of studies have shown that the same nitrogen load is absorbed faster when
delivered as hydrolyzed protein peptides rather than as whole protein or free amino
acids (25). Similarly, some studies have reported an increase in nitrogen incorpora-
tion into tissue protein in animals fed hydrolyzed whey peptides compared with
those receiving the same amount of nitrogen as whole protein or free amino acids
(6, 31). In humans a partially hydrolyzed whey protein was shown to be absorbed
faster and induced a high rate of protein synthesis compared to casein (a whole
protein) (4, 11, 12). However, whether hydrolyzation has a practical beneficial
effect such as faster muscle mass accretion or improved recovery from exercise is
not clear as it has not been adequately studied (25). The greater strength and LBM
gains seen in our study by the group that consumed the hydrolyzed (short chain
peptide) WI compared to casein (a whole protein) suggests that the differences in
the manufacture of the proteins may have been a contributing factor, although to
what extent is unclear.
Compared with unsupervised training, the supervision of resistance training
programs by qualified personnel is shown to provide a greater rate and magnitude
of training load increases, which in turn promotes greater strength gains (28). One
of the strengths of our investigation was the supervision of all the subject’s training
sessions by qualified instructors. In our study, the subjects were supervised as in
a personal training scenario (a one-to-one, or two-to-one fashion). This not only
ensured there were no differences in training variables (such as volume, frequency,
duration, and intensity or load), it resulted in substantial improvements in 1RM
strength in each assessment. The large changes in 1RM strength seen in these resis-
tance-trained individuals can be explained by the fact that although the subjects had
been training consistently prior to the study for at least 2 y, none had ever received
professional coaching or personal training by a qualified instructor. Therefore, the
506 Cribb et al.
large changes in 1RM strength in both groups primarily reflect an improvement in
lifting skill and ability to perform each lift in compliance with the strict exercise
execution guidelines. However, this certainly does not alter the fact that the instruc-
tors were blinded to the subjects supplement and the strength increases in all three
exercises were significantly greater with WI supplementation than casein. Dietary
strategies that may promote improvements in functional strength have important
implications for an aging population and others that are prone to muscle wasting
such as cancer, HIV, and cardiac rehabilitation patients.
One important consideration of our study that perhaps makes it unique com-
pared to most other supplementation studies was the implementation of a supplement
dose that is characteristic of many strength athletes, and the impact this had on
the subject’s daily protein intake. Prior to supplementation, the eating patterns of
the subjects were characteristic of most athletes who undertake resistance training
programs, i.e., they consumed a high energy/protein intake and frequent, mixed
macronutrient meals over the 24 h period (23). However, the addition of a large
supplement dose (1.5 g · kg · d) resulted in only a small increase in daily protein
intake, i.e., from 1.86 g · kg · d before the study to 2.10 g · kg · d in week 10 for C
and 1.76 to 2.11 g · kg · d for WI (Table 3). Therefore, it is apparent that the subjects
substituted a large portion of their habitual daily protein (and calorie) intake with
the protein supplement. Why the subject’s daily protein intakes did not change
substantially when the supplement was added to the diet is not clear. Perhaps as
the subjects believed that the supplement would be of benefit to their bodybuilding
results, they may have subconsciously reduced their nutritional intake from other
sources to ensure compliance (i.e., consume all their supplement servings each
day). Another explanation may be a satiety effect that has been observed from
protein supplementation, particularly whey (17). To our knowledge, the effects
of replacing a large portion of protein in the daily diet with one particular source,
such as WI, particularly in athletic individuals undertaking an intense resistance
training program has not been investigated. Even when taking into consideration
the limitations of this study, the differences between the groups in body composi-
tion and strength after the training program were quite dramatic. One possible
explanation for these changes could be that one group replaced a large portion
of their daily protein intake with a protein source that contained a rich source of
essential amino acids and added a high concentration of cysteine to the diet. Over a
period of weeks this may have resulted in a better increase in LBM during intense
resistance training. Although we did not assess absorption characteristics or amino
acid kinetics in this study, our results are consistent with those theories. Based on
our results, further studies involving cellular and/or molecular investigations are
currently being completed by our laboratory.
In conclusion, two matched groups of males were used to examine the effects
of whey isolate and casein supplementation (1.5 g · kg · d) during a 10 wk resistance
training program. Results showed that while neither supplement had an effect on
plasma glutamine values, the group that consumed whey isolate demonstrated a sig-
nificantly greater gain in lean body mass and strength. This group also experienced
a significant decrease in fat mass compared to the casein group, which showed no
change in fat mass after the 10 wk training period. To our knowledge, this is the
first study that has examined the effects of whey isolate and casein supplementa-
tion during a structured, progressive overload program that was supervised on a
Whey Isolate and Resistance Training 507
one-to-one basis by qualified personnel. While it is possible that whey isolate is
a superior protein to casein for enhancing the chronic adaptations of resistance
training, our study does not allow for a definitive conclusion and thus emphasizes
a need for further research in this area.
We would like to acknowledge John Birchall for his kind assistance in the supervision
of all DEXA assessments. AST Sports Science kindly supplied the protein supplements for
this research. Disclosure: Paul Cribb is a consultant to AST Sports Science.
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