The Effects of Soy and Whey Protein Supplementation on Acute Hormonal Reponses to Resistance Exercise in Men

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DOI: 10.1080/07315724.2013.770648 · Source: PubMed
Abstract
Objective: For many resistance-trained men concerns exist regarding the production of estrogen with the consumption of soy protein when training for muscle strength and size. Thus, the purpose of this investigation was to examine the effects of soy and whey protein supplementation on sex hormones following an acute bout of heavy resistance exercise in resistance trained men. Methods: Ten resistance-trained men (age 21.7 ± 2.8 [SD] years; height 175.0 ± 5.4 cm; weight 84.2 ± 9.1 kg) volunteered to participate in an investigation. Utilizing a within subject randomized crossover balanced placebo design, all subjects completed 3 experimental treatment conditions supplementing with whey protein isolate (WPI), soy protein isolate (SPI), and maltodextrin placebo control for 14 days with participants ingesting 20 g of their assigned supplement each morning at approximately the same time each day. Following supplementation, subjects performed an acute heavy resistance exercise test consisting of 6 sets of 10 repetitions in the squat exercise at 80% of the subject's one repetition maximum. Results: This investigation observed lower testosterone responses following supplementation with soy protein in addition to a positive blunted cortisol response with the use of whey protein at some recovery time points. Although sex hormone binding globulin (SHBG) was proposed as a possible mechanism for understanding changes in androgen content, SHBG did not differ between experimental treatments. Importantly, there were no significant differences between groups in changes in estradiol concentrations. Conclusion: Our main findings demonstrate that 14 days of supplementation with soy protein does appear to partially blunt serum testosterone. In addition, whey influences the response of cortisol following an acute bout of resistance exercise by blunting its increase during recovery. Protein supplementation alters the physiological responses to a commonly used exercise modality with some differences due to the type of protein utilized.
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The Effects of Soy and Whey Protein Supplementation
on Acute Hormonal Reponses to Resistance Exercise in
Men
William J. Kraemer
a
, Glenn Solomon-Hill
a
, Brittanie M. Volk
a
, Brian R. Kupchak
a
, David
P. Looney
a
, Courtenay Dunn-Lewis
a
, Brett A. Comstock
a
, Tunde K. Szivak
a
, David R.
Hooper
a
, Shawn D. Flanagan
a
, Carl M. Maresh
a
& Jeff S. Volek
a
a
Human Performance Laboratory, Department of Kinesiology, University of Connecticut,
Storrs, Connecticut
Published online: 05 Apr 2013.
To cite this article: William J. Kraemer , Glenn Solomon-Hill , Brittanie M. Volk , Brian R. Kupchak , David P. Looney ,
Courtenay Dunn-Lewis , Brett A. Comstock , Tunde K. Szivak , David R. Hooper , Shawn D. Flanagan , Carl M. Maresh & Jeff
S. Volek (2013) The Effects of Soy and Whey Protein Supplementation on Acute Hormonal Reponses to Resistance Exercise in
Men, Journal of the American College of Nutrition, 32:1, 66-74, DOI: 10.1080/07315724.2013.770648
To link to this article: http://dx.doi.org/10.1080/07315724.2013.770648
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Original Research
The Effects of Soy and Whey Protein Supplementation on
Acute Hormonal Reponses to Resistance Exercise in Men
William J. Kraemer, PhD, FACN, Glenn Solomon-Hill, MA, Brittanie M. Volk, MA, RD, Brian R. Kupchak, PhD,
David P. Looney, MS, Courtenay Dunn-Lewis, MA, Brett A. Comstock, MA, Tunde K. Szivak, MA, David R. Hooper, MA,
Shawn D. Flanagan, MA, MHA, Carl M. Maresh, PhD, Jeff S. Volek, PhD, RD
Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, Connecticut
Key words: sports nutrition, strength training, estradiol, testosterone, cortisol, sex hormone binding globulin
Objective: For many resistance-trained men concerns exist regarding the production of estrogen with the
consumption of soy protein when training for muscle strength and size. Thus, the purpose of this investigation
was to examine the effects of soy and whey protein supplementation on sex hormones following an acute bout of
heavy resistance exercise in resistance trained men.
Methods: Ten resistance-trained men (age 21.7 ± 2.8 [SD] years; height 175.0 ± 5.4 cm; weight 84.2 ±
9.1 kg) volunteered to participate in an investigation. Utilizing a within subject randomized crossover balanced
placebo design, all subjects completed 3 experimental treatment conditions supplementing with whey protein
isolate (WPI), soy protein isolate (SPI), and maltodextrin placebo control for 14 days with participants ingesting
20 g of their assigned supplement each morning at approximately the same time each day. Following supplemen-
tation, subjects performed an acute heavy resistance exercise test consisting of 6 sets of 10 repetitions in the squat
exercise at 80% of the subject’s one repetition maximum.
Results: This investigation observed lower testosterone responses following supplementation with soy protein
in addition to a positive blunted cortisol response with the use of whey protein at some recovery time points.
Although sex hormone binding globulin (SHBG) was proposed as a possible mechanism for understanding
changes in androgen content, SHBG did not differ between experimental treatments. Importantly, there were no
significant differences between groups in changes in estradiol concentrations.
Conclusion: Our main findings demonstrate that 14 days of supplementation with soy protein does appear to
partially blunt serum testosterone. In addition, whey influences the response of cortisol following an acute bout
of resistance exercise by blunting its increase during recovery. Protein supplementation alters the physiological
responses to a commonly used exercise modality with some differences due to the type of protein utilized.
INTRODUCTION
Athletes and fitness enthusiasts engaging in resistance train-
ing often use protein supplementation in concert with nutritional
behaviors to enhance appropriate anabolic and physiological re-
sponses. Increases in health-conscious lifestyles as well as veg-
etarian and vegan diets have encouraged the utilization of soy
protein as an alternative to meat, poultry, and other animal-based
proteins. Nevertheless, a disparity persists in America between
soy supplementation and animal-based proteins due to lack of
familiarity, disapproval of taste or texture, and concern over the
potentially pro-estrogenic or anti-anabolic effects of soy protein
[1, 2]. Although such fears may largely stem from bodybuilding
mythologies, there is limited research on soy protein supple-
Address correspondence to: William J. Kraemer, PhD, FACN, Human Performance Laboratory, Department of Kinesiology, Gampel Pavilion Unit 1110, University of
Connecticut, Storrs, CT 06269. E-mail: William.Kraemer@uconn.edu
mentation and its acute effects on hormonal responses to heavy
resistance exercise.
Hormones play an important role in the anabolic signaling
that promotes adaptations to intense resistance exercise. These
signals facilitate changes in tissue size, density, and function
that ultimately result in desirable phenotypic outcomes, includ-
ing hypertrophy and gains in strength and power [3–6]. Among
other hormones that increase in response to acute intense resis-
tance exercise, testosterone works through direct and indirect
pathways to interact with receptors on and within target tissue
cells to produce potent anabolic signals that promote muscle
protein synthesis [6, 7]. The emergence of soy protein has raised
concerns about its possible effects on the normal anabolic re-
sponse to resistance training. Much of the debate is centered
Journal of the American College of Nutrition, Vol. 32, No. 1, 66–74 (2013)
C
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Whey and Soy Proteins and Hormone Concentrations
around isoflavones, naturally occurring componds found in soy
that possess estrogenic properties [8], which may affect the func-
tions of androgenic hormones such as testosterone and estradiol.
Soy isoflavones contain naturally occuring nonsteroidal sub-
stances that possess estrogen-like activities (referred to as phy-
toestrogens). Like many substances (e.g., tamoxifen, an antie-
strogen used to treat breast cancer), phytoestrogenic compounds
have the ability to bind to estrogen receptors. In humans, soy
food products are the primary source of isoflavones. The pop-
ularity of the soy-based diet was promoted by positive findings
between soy isoflavone comsumption and lower incidences of
diseases such as coronary heart disease [9] and prostate, colon,
and breast cancers [10, 11]. It has also been shown to help in
the prevention of osteoporois [11]; reduce serum concentrations
of total cholesterol, low-density lipoproteins, and triglycerides
[12, 13]; aid in weight management programs; and act as a part
of hormone replacement therapy for women during menopause
[14]. Despite the possible benefits of soy in the human diet,
evidence from numerous studies has demonstrated the ability
of soy to alter testosterone [15], sex hormone binding globu-
lin (SHBG) [16], estradiol [17], and the testosterone : estra-
diol ratio [16]. Possible mechanisms include isoflavone-induced
increases in hepatic sex hormone binding globulin synthesis,
which would reduce the availability of testosterone to enter tar-
get cells and elicit a biological response [18]. Isoflavones may
also inhibit enzymes involved in androgen synthesis such as 17ß-
hydroxysteroid dehydrogenase [19] and 5 alpha-reductase [20].
Reductions in these enzymes could lead to lower concentrations
of plasma testosterone and dihydrotestosterone in androgen tar-
get cells such as skeletal muscle. However, evidence involving
soy isoflavone usage in humans has not been consistent.
The primary purpose of this investigation was to study the
effects of short-term protein supplementation with whey protein,
soy protein, or a carbohydrate control on the known hormonal
response patterns to an acute bout of heavy resistance exercise.
It was our hypothesis that the distinguishing nutritional compo-
sition of whey protein would result in a more favorable acute ex-
ercise hormonal response in comparison to soy protein. Whey, a
complex protein source, has a high prevalence of essential amino
acids, which are indispensable for stimulating skeletal muscle
protein synthesis [21, 22]. Compared to soy protein, whey con-
tains a higher proportion of essential amino acids, especially
branched-chain amino acids (leucine, isoleucine, and valine),
which are potent nutrient modulators of signaling molecules
and protein synthesis [23]. Ingestion of whey protein alone has
been shown to stimulate muscle protein synthesis [24, 25] and
when provided before or after exercise augments the anabolic
response to resistance training [24, 26]. The high degree of
branched-chain amino acids in whey (10 g per 100 g of pro-
tein) is especially critical for stimulating protein anabolism. In
particular, leucine has been shown to stimulate protein synthe-
sis by activating the mammalian target of rapamycin signaling
pathway [27]. Our study would thus serve as a novel examina-
tion of the hormonal response patterns to an acute bout of heavy
resistance exercise following short-term supplementation with
either soy protein or whey protein.
MATERIALS AND METHODS
Subjects
All participants provided written informed consent to par-
ticipate after being briefed on the risks and benefits of the
investigation. The study was approved by the institutional re-
view board for the use of human subjects at the University of
Connecticut. Ten healthy resistance-trained men were recruited
and volunteered to participate in this investigation. The physical
characteristics of the subjects were the following: age, 21.7 ±
2.8 years; height, 175.0 ± 5.4 cm; and weight, 84.2 ± 9.1 kg.
None of the subjects had any orthopedic, endocrine, or other
medical problems that might confound the results of this inves-
tigation. Subjects filled out a medical questionnaire and were
screened by a physician for any medications, pathologies, or
orthopedic problems that would confound the study findings.
Registered dieticians also screened the potential subjects for
dietary habits and use of supplements. No other supplements
were allowed. Vegetarians, vegans, or subjects who consumed
high-protein diets were excluded from the study.
Experimental Design
Utilizing a within subject randomized crossover balanced
placebo design, all subjects completed each of the 3 treatment
conditions (referred to as cycles). The experimental design can
be seen in Fig. 1. During each of the 3 cycles, subjects sup-
plemented with whey protein isolate (WPI), soy protein isolate
Fig. 1. Study protocol. Treatments 1–3, randomized crossover trials of whey, soy, or carbohydrate supplementation.
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Whey and Soy Proteins and Hormone Concentrations
(SPI), or an isoenergetic maltodextrin placebo control (CHO)
each day for 14 days. At the end of the supplementation period,
subjects reported to the Human Performance Laboratory at the
University of Connecticut for an acute heavy resistance exercise
test (AHRET) consisting of 6 sets of 10 repetitions of the squat
exercise [28]. Blood samples were obtained to determine the se-
lected biochemical and hormonal concentrations. Following the
acute exercise protocol, subjects used a washout period consist-
ing of no supplementation for 14 days before reporting for the
next cycle of supplementation. Subjects performed their regular
resistance training regimen during the experimental period un-
til 72 hours prior to AHRET. Activity logs were used to allow
subjects to replicate their behaviors during each experimental
cycle.
Nutritional Supplementation
Supplementation consisted of 3 treatment cycles: whey
protein isolate, soy protein isolate, or the maltodextrin placebo
control. All supplement powders were obtained from True
Protein, Inc. (Oceanside, CA). Table 1 outlines the nutritional
composition of each supplement. Throughout the course of each
treatment cycle, subjects were given written and verbal instruc-
tions concerning supplementation. For each cycle, subjects were
Table 1. Nutrient Composition of Each Supplement
Constituent (based on
20 g serving) SPI WPI CHO
Total calories 80 80 80
Protein (g) 17 18 0
Carbohydrates (g) 0 0 20
Fat (g) 1 0 0
Amino acid profile (mg, based on 20 g serving)
Alanine 4740 900
Arginine 1320 400
Aspartic acid 2020 1900
Cystine 220 600
Glutamic acid 3320 3000
Glycine 720 300
Histidine 460 300
Isoleucine 820 900
Leucine 1420 2300
Lysine 1080 1800
Methionine 220 400
Phenylalanine 900 600
Proline 900 900
Serine 900 700
Threonine 660 900
Tryptophan 220 500
Tyrosine 660 700
Valine 880 900
Total isoflavone 26.3
Daidzein 8.0
Genistein 14.7
Glycitein 3.6
SPI = soy protein isolate, WPI = whey protein isolate, CHO = carbohydrate
control.
provided with 14 identical packages containing 20 g of their
assigned supplement for each day of the 2-week period. Each
person was instructed to take one bag per day at approximately
the same time each morning. Subjects were instructed to thor-
oughly mix the entire supplement package with 475–600 ml of
Crystal Light (Kraft Foods, Northfield, IL), which was provided
by the investigators, in order to increase the palpability of the
supplement and to ensure compliance with the specified instruc-
tions. Subjects ingested the supplement within 30 minutes in
order to avoid drinking the supplement continually throughout
the day. The importance of refraining from taking additional
supplements, vitamins, ergogenic aids, or foods high in soy
content was reinforced throughout the course of the study by
investigators and registered dieticians. Throughout the 14 days,
subjects were asked to verify usage of their supplement through
a supplement log in which the date and time of supplementation
was recorded in order to ensure consistency among subjects.
On the mornings of AHRET, subjects were instructed to
report to the laboratory in a fasted state. Subjects did not ingest
food for 12 hours prior to testing; however, they were allowed
to consume water in order to maintain adequate hydration. After
an initial blood draw was obtained, subjects were provided with
the final 20-g dose of the supplement from their assigned cycle
20 minutes before starting the AHRET protocol.
Strength Testing
One-repetition maximum (1RM) squat testing and 3 AHRET
sessions were conducted during this investigation. Subjects were
familiarized with testing protocols. Subjects reported to the lab-
oratory for a familiarization session in which their correct tech-
nique for performing the squat exercise was validated using a
modified Smith machine (Life Fitness, Franklin Park, IL) with
a computer interface [28]. Each subject’s squat 1RM was mea-
sured following the technique previously described [28]. Briefly,
a dynamic warm-up was performed followed by 8–10 repetitions
at 50% of their estimated 1RM and another set of 2–5 repeti-
tions at 85% of their 1RM. Subsequently, 3–5 maximal trials
were used to determine the 1RM of the individual.
The AHRET squat protocol performed consisted of 6 sets
of 10 repetitions at 80% of the 1 RM with 2 minutes’ rest be-
tween sets on a Smith machine (instrumented with computer and
Plyometric Power System [PPS] software; Norsearch, Lismore,
Australia). This protocol and system have been used for years
in our laboratory to assess physiological responses to heavy
resistance exercise [28]. The starting weight, which was 80%
of 1RM, was determined from the subject’s preliminary 1RM
strength testing. If subjects were not able to perform 10 repeti-
tions during a particular set, the weight was reduced to allow for
completion of a 10-repetition maximum set on the subsequent
set. AHRET exercise test resistance loads were recorded and
then matched to remove the influence of total work from cycle
to cycle.
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Whey and Soy Proteins and Hormone Concentrations
Fig. 2. Experimental protocol.
Blood collection time point.
Blood Sampling and Biochemical Analyses
The experimental protocol for the study can be seen in Fig. 2.
Subjects reported to the laboratory in the morning after 12 hours
of fasting and rested quietly for 10 minutes before an indwelling
Teflon cannula was inserted into an antecubital vein. All sub-
jects reported to the laboratory between 6:00 and 10:00
AM and
each subject arrived at the same time for each AHRET visit in
order to minimize any possible diurnal variations in exercise
performance, hormones, and energy metabolism. A total of 7
blood samples were obtained during each of the 3 AHRET visits
at the following times: pre-exercise (prior to taking the supple-
ment, PRE), after the third set of squats (MID), immediately
after the sixth set of squats (IP), and at + 5, + 15, + 30, and
+ 60 minutes postexercise. Upon the completion of the sixth set
of squats, subjects were transferred to phlebotomy chair where
they remained until 60 minutes postexercise. All blood draws
were taken in a standardized seated body position.
All blood samples were collected in appropriate test tubes
for plasma or serum determinations. Blood samples were
centrifuged at 3500 rpm and 4
C for 10 minutes. Resulting
serum or plasma was aliquoted and stored at 80
C until
analyzed at a later date with only one thaw. Blood samples were
analyzed for total testosterone and sex hormone binding glob-
ulin was analyzed in duplicate via mass spectrometry (Steroid
Hormone Assay Lab, Boston Medical Center, Boston, MA). An
ultrasensitive enzyme-linked immunosorbent assay (ELISA;
ALPCO, Salem, NH) was used to analyze estradiol from serum
in duplicate. The sensitivity of the assay was 3 pg·ml
1
and had
intra- and interassay coefficients of variation (CVs) of 4.2%
and 8.9%, respectively. Cortisol was analyzed in duplicate from
serum sample via ELISA (CALBiotech, Spring Valley, CA).
Intra-assay CV was 3.4% and the inter-assay CVs was 4.5%.
The sensitivity of the assay was 10 ng·ml
1
. Sex hormone bind-
ing globulin was performed in duplicate with ELISA (GenWay
Biotech, Inc., San Diego, CA) with intra- and interassay CVs of
4.9% and 8.5%, respectively. The sensitivity of the assay was
0.77 nmol·L
1
. All blood sample concentrations via ELISAs
were determined using a Versamax tunable microplate reader
(SoftMax
R
Pro 5, Molecular Devices, Sunnyvale, CA) with
the appropriate wavelength used for each particular assay.
Dietary Analyses
Subjects were provided with food diaries during the 72 hours
preceding each AHRET trial. Following the first AHRET, sub-
jects were provided a copy of their food diary and asked to
replicate their diet prior to the remaining AHRET testing days.
During the 72 hours prior to AHRET testing, subjects refrained
from exercise, alcohol, and high doses of caffeine (no more than
one cup of coffee).
Statistical Analyses
The data are presented as means and standard deviations. Us-
ing the nQuery Advisor software (Statistical Solutions, Saugus,
MA), it was determined that an n size of 10 for each variable
was adequate to defend the 0.05 alpha level of significance with
a Cohen probability level of at least 0.80 for each dependent
variable. Data were log10 transformed if assumptions were not
met and reanalyzed. Data were analyzed using a repeated mea-
sures two-way analysis of variance (Treatment × Time points).
In the event of a significant F-score, Fisher’s least significant
difference post hoc test was used to determine pair-wise dif-
ferences. Where appropriate, area under the curve (trapezoidal
rule method) was calculated to gain some insights into molar
exposure time of steroids where differences occurred. The level
of significance in this study was set at p 0.05.
RESULTS
Testosterone
The results for total testosterone can be seen in Fig. 3.
Testosterone concentrations were significantly elevated above
pre-exercise values at MID through + 30 minutes of recovery
for both WPI and CHO control conditions. For the SPI treat-
ment group, testosterone was significantly elevated from PRE
at the IP, + 5-minute, and + 15-minute time points. Addition-
ally, SPI was significantly lower than WPI and control CHO at
+ 5-, + 15-, and + 30-minute time points. A significant inter-
action between groups and time was observed with main effects
obviously demonstrated for time.
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Whey and Soy Proteins and Hormone Concentrations
Fig. 3. Effects of supplement and time point on changes in total testosterone (nmol·L
1
).
Significantly different from corresponding PRE value ( p
0.05),
Significantly ( p 0.05) different from WPI and CHO treatments.
Cortisol
The results of the cortisol response patterns can be seen
in Fig. 4. Significant increases occurred from PRE concentra-
tions for the WPI from MID to 5 minutes postexercise with no
significant increases occurring during the remainder of the re-
covery period. This was different than the SPI and CHO control
treatment conditions, where significant elevations above resting
values occurred from MID through 30 minutes of recovery. The
WPI consumption cortisol level was significantly lower than the
other two treatment conditions at 15 and 30 minutes postex-
ercise. A significant interaction between groups and time was
observed with main effects obviously demonstrated for time.
Estradiol
The results indicate no significant interaction effect between
treatment groups and time point and no main effects for supple-
ment or time point. Mean estradiol concentrations with standard
deviations for each supplement and time point are presented in
Table 2.
Sex Hormone Binding Globulin
The results indicate no significant interaction effect between
treatment groups and time point and no main effects for supple-
ment or time point. Mean SHBG concentrations with standard
Fig. 4. Effects of supplement and time point on changes in cortisol (nmol·L
1
).
Significantly different from corresponding PRE value ( p 0.05),
Significantly ( p 0.05) different from WPI treatment.
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Whey and Soy Proteins and Hormone Concentrations
Table 2. Effects of Supplement and Time Point on Changes in Estradiol (nmol·L
1
)
WPI SPI CHO
Time point (minutes) Mean SD Mean SD Mean SD
PRE 23 ±10.4 24.7 ±13.2 23.2 ±11.0
MID 25.5 ±12.7 25.1 ±15.5 19.5 ±7.7
IP 26.4 ±14.3 26 ±14.8 20.6 ±8.5
+ 5 24.5 ±14.1 26.4 ±15.3 21.6 ±8.2
+ 15 23.6 ±11.0 25.1 ±15.2 19.9 ±8.4
+ 30 24.1 ±10.2 23.8 ±13.5 17.3 ±7.8
+ 60 22.4 ±8.5 20.7 ±12.3 16.6 ±7.7
WPI = whey protein isolate, SPI = soy protein isolate, CHO = carbohydrate control, PRE = pre-exercise and prior to supplement ingestion, MID = middle of exercise
(after set 3), IP = immediately postexercise (after set 6).
deviations for each supplement and time point are presented in
Table 3.
DISCUSSION
The primary findings of this investigation indicate that there
were no significant differences between treatment groups in
estradiol concentrations. From 5 to 30 minutes postexercise
there were lower testosterone values and higher cortisol values
following supplementation with soy protein compared to whey
protein. This may suggest diminished anabolic signaling and
a reduction in testosterone’s contributions to the total anabolic
effects. Because cortisol values in SPI mirrored those observed
in the CHO placebo group, whey protein supplementation ap-
peared to attenuate the cortisol response during the recovery
period. Sex hormone binding globulin has been proposed as
a possible mechanism for understanding changes in androgen
content; however, in our study SHBG did not differ between
experimental treatments.
There were no significant differences in estradiol concentra-
tions between treatment groups or time points. This supports
the majority of previous studies that have shown no signifi-
cant effects on estradiol following soy consumption. Estradiol
has increased in some situations; however, the mechanism(s) of
these changes remains to be fully elucidated. Specifically, stud-
ies by Hamilton-Reeves et al. [29] and Dillingham et al. [17]
reported significant increases in serum estradiol 6 months and
8 weeks after supplementation with low doses of isoflavones
(6 and 2 mg·d
1
, respectively). Our study utilized a relatively
low concentration of isoflavones (26.3 mg per daily serving)
with the aim of replicating isoflavone concentrations similar to
consumption levels in the United States [30]. Therefore, the
effect of soy supplementation in conjunction with resistance ex-
ercise on estradiol concentrations with greater concentrations of
isoflavones remains to be investigated.
Although reductions in testosterone concentrations after re-
sistance exercise have been attributed to increased androgen
receptor content in the active skeletal muscle and thus increased
muscle uptake, prior research has shown that this response oc-
curs only after an initial period of androgen receptor stabiliza-
tion followed by a subsequent period of decrease that extends
beyond 60 minutes postexercise [31]. Because the SPI treatment
produced a testosterone response that was significantly lower
than the WPI and from the IP time point to the + 30-minute
time point, this response cannot be explained by greater skeletal
muscle uptake. This might be due to the fact that the upregulation
of androgen receptors in response to exercise and nutrition may
not be rapid enough (i.e., upregulation may take more than 60
minutes) to help explain the decrease in testosterone concentra-
tions in the SPI treatment condition [6, 28, 31, 32]. Importantly,
similar testosterone values in CHO and WPI demonstrated that
Table 3. Effects of Supplement and Time Point on Changes in Sex Hormone Binding Globulin (nmol·L
1
)
WPI SPI CHO
Time point (minutes) Mean SD Mean SD Mean SD
PRE 32.6 ±9.5 28.1 ±9.5 30.8 ±12.0
MID 35.1 ±11.6 35.1 ±10.4 36.3 ±10.9
IP 35.6 ±10.8 36.8 ±12.1 36.7 ±12.3
+536.6±11.8 35.6 ±11.6 35.4 ±12.6
+15 35.1 ±10.5 33.3 ±9.9 33.9 ±10.6
+30 31.8 ±8.5 32.9 ±10.6 33.5 ±11.8
+60 29.9 ±9.6 29.3 ±10.4 30.8 ±10.0
WPI = whey protein isolate, SPI = soy protein isolate, CHO = carbohydrate control, PRE = pre-exercise and prior to supplement ingestion, MID = middle of exercise
(after set 3), IP = immediately postexercise (after set 6).
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Whey and Soy Proteins and Hormone Concentrations
it is really the SPI treatment that caused changes in the testos-
terone response pattern. The majority of evidence from previous
research on isoflavones alone has shown no effect on testos-
terone [13, 16, 29, 33–36]. Most studies have tended to focus on
varied concentrations of isoflavones in soy food and no consen-
sus has been determined, although there is some evidence that
testosterone declines following supplementation [15]. Dilling-
ham et al. [17] did demonstrate significant differences in a low-
concentration isoflavone content, which was a factor taken into
account when selecting our soy protein. However, it was surpris-
ing that the low concentration of isoflavones used in this study
were sufficient to cause a blunted testosterone response. Further
research on the dose–response patterns of different concentra-
tions of isoflavones with acute response of resistance exercise
with would help to further explain this phenomenon.
Testosterone has been shown to peak early after exercise
and return to baseline by 60 minutes postexercise [37]. All 3
treatment groups followed prior replicated research on the re-
sponse of testosterone to pre-exercise and postexercise feeding
with protein and carbohydrate [37, 38]. A theory by Chandler
et al. [39] proposed that the acute response of testosterone fol-
lowing pre-exercise supplementation might be derived from a
decrease in testosterone synthesis/secretion and/or an increase
in metabolic clearance; however, that study also showed that
postexercise decreases in testosterone were not associated with
decreased luteinizing hormone. Although luteinizing hormone
was not decreased in the study by Chandler et al. [39], there
could still be a decrease in the testicular response to luteinizing
hormone. Thus, an increase in androgen receptor uptake remains
the primary hypothesis for the decreases observed into recovery
[31, 32]. Additionally, a signal from the exercise-induced in-
creases of testosterone to the receptors may also be vital for such
a response. Data also indicate that macronutrient balance may
be an important determining factor of postexercise testosterone
values. A low percentage of dietary fat and a high protein-to-
carbohydrate ratio have been associated with lower concentra-
tions of testosterone in healthy men [40]. Although the trend
is highly repeatable even during 3 days of consecutive exercise
[37], the exact mechanism remains to be fully understood. Dif-
ferences in the effects of whey and soy protein supplementation
on sex hormone responses to acute resistance exercise are fur-
ther highlighted by our observations on cortisol. The SPI and
CHO groups demonstrated similar and characteristic responses
to resistance exercise at each time point [41]. This indicates that
the observed differences between whey and soy groups can be
attributed to features of whey protein that provided a positive
blunting effect on the cortisol response. Our finding diverges
from a previous investigation where a whey protein supplement
elicited no differences in postexercise cortisol values compared
to a placebo [42]. The considerably lower total volume of work
in the present investigation may explain this discrepancy.
Sex hormone binding globulin has been proposed as a possi-
ble mechanism for understanding changes in androgen content;
however, in our study SHBG did not differ between experimen-
tal treatments. Sex hormone binding globulin was thought to be
a major influence on this testosterone response pattern and our
results did show an interaction effect between supplement and
time in SHBG concentrations. There were significant increases
in SHBG concentrations in all 3 treatment conditions during ex-
ercise and up to + 30 minutes postexercise. SHBG is believed
to play an important role in balancing both bound and unbound
androgens and estrogens in the blood [43]. A shift in SHBG
could suggest a possible shift in either testosterone or estrogen
because both bind to SHBG. Previous studies have also shown
no significant changes in SHBG following ingestion of soy-
containing protein [13, 33, 36]. Like testosterone, factors such
as diet, physical activity, and body weight cannot be ruled out as
possible confounding factors to SHBG [44]. SHBG concentra-
tions, like testosterone, were lower following supplementation
in which the protein-to-carbohydrate ratio was higher compared
to placebo [45]. Diets logs (diaries) were continually recorded
for 72 hours prior to AHRET days and subjects were instructed
to replicate meals; however, complete diet control could be a
limiting factor in this study as the study was conducted in a
“free living” environment. However, diet records and adherence
were monitored (e.g., meetings and phone calls) by the research
team to ensure replication validity.
CONCLUSION
Only one study has examined soy and whey protein sup-
plementation together in conjunction with resistance training.
Kalman et al. [46] reported that after 12 weeks of supplemen-
tation with soy there were no significant differences between
groups for total testosterone, free testosterone, and SHBG. This
study expanded upon the limited prior research examining the ef-
fects of soy and whey protein supplementation on testosterone,
SHBG, and cortisol responses to an acute bout of resistance
exercise. Contrary to popular misconceptions, soy protein sup-
plementation does not appear to hinder anabolic signaling pos-
texercise by means of eliciting increases in estradiol concentra-
tions. However, our main findings demonstrate that 14 days of
supplementation with soy protein does appear to blunt serum
testosterone. In addition, whey might influence the response of
cortisol during an acute bout of resistance exercise by also blunt-
ing its normal increase. Further research will need to explore a
possible interaction effect on sex hormone binding globulin.
ACKNOWLEDGMENTS
We thank Dr Shalender Bhasin at the Boston University
School of Medicine for his input on the hormonal analyses for
testosterone. We also thank a dedicated group of subjects and
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Whey and Soy Proteins and Hormone Concentrations
the rest of the medical and research staffs at the University of
Connecticut.
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  • ... Vol. 22, Iss. 2, Spr 2016 .. .. [10][11][12] . .... [13] . ...
    ... (GLUT4) [10][11][12] . .... ...
    ... [28] [29] . [10] . . ...
    Article
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  • ... Vol. 22, Iss. 2, Spr 2016 .. .. [10][11][12] . .... [13] . ...
    ... (GLUT4) [10][11][12] . .... ...
    ... [28] [29] . [10] . . ...
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  • ... Vol. 22, Iss. 2, Spr 2016 .. .. [10][11][12] . .... [13] . ...
    ... (GLUT4) [10][11][12] . .... ...
    ... [28] [29] . [10] . . ...
  • ... Q Horizon Med Sci Vol. 22, Iss. 2, Spr 2016 .. ..[10][11][12]. ....[13]. .... . . ...
    ... 22, Iss. 2, Spr 2016 .... .... ....[13].[19]..[20].[24]....[5,25].[7,26,27]. .. ....[28][29].[10]. . .. .... ( ) . . ...
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    Abstract Aims: During recent years, consumption of nutritional supplements has become popular in the athletes to enhance muscle power, function, and hypertrophy. Since the chemical supplements cause side-effects, many experts focus on the traditional medications. The aim of this study was to investigate the effects of short-term circular resistance exercises with Crocus sativus Supplementation on the insulin and estradiol levels. Materials & Methods: In the semi-experimental study, 44 untrained healthy men were selected from the students of Mazandaran University using census method in 2013. The samples were divided into four groups including “water- exercise”, “petal sweat-exercise”, “style-exercise”, and “stigma-exercise”. 2- week resistance exercises consisted of 12 stations (30 seconds with 40% of a maximum repetition per station; 5 sessions a week). 500mg Crocus sativus were daily consumed two times in the morning immediately after the exercises. Blood sampling was done before and 48 hours after the last session. Data was analyzed by SPSS 20 software using one-way ANOVA, Bonferroni post-hoc, and dependent T tests. Findings: There was a significant increase in the estradiol level in stigma- exercise group than water-exercise group (p=0.007). There were significant increases in the plasma estradiol concentration in each stigma-exercise and style-exercise groups after the exercises (p<0.05). However, there was no significant difference between the mean of insulin concentrations in each group (p>0.05). Conclusion: Circular resistance exercises with Crocus sativus supplementation lead to no change in insulin concentration. Nevertheless, consumption of the stigma of Crocus sativus flower can empower the effects of the resistance exercises and enhance estradiol. Keywords Resistance Training Estradiol Insulin Crocus
  • ... A common, if unfounded concern, with soy protein supplementation is the potential for pseudo-estrogen effects of isoflavones, such as genistein, present in soy-derived products, on muscle function. Indeed, one study in resistance trained young adults has shown that soy protein does appear to partially blunt the rise in serum testosterone and attenuates the decrease in elevated cortisol acutely following exercise [18]. However, this study did not demonstrate any differences in exercise capacity between the different supplementation groups. ...
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