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Moro et al. J Transl Med (2016) 14:290
DOI 10.1186/s12967-016-1044-0
RESEARCH
Eects ofeight weeks oftime-restricted
feeding (16/8) onbasal metabolism,
maximal strength, body composition,
inammation, andcardiovascular risk factors
inresistance-trained males
Tatiana Moro1 , Grant Tinsley2 , Antonino Bianco3 , Giuseppe Marcolin1 , Quirico Francesco Pacelli1,
Giuseppe Battaglia3 , Antonio Palma3 , Paulo Gentil5 , Marco Neri4 and Antonio Paoli1*
Abstract
Background: Intermittent fasting (IF) is an increasingly popular dietary approach used for weight loss and overall
health. While there is an increasing body of evidence demonstrating beneficial effects of IF on blood lipids and other
health outcomes in the overweight and obese, limited data are available about the effect of IF in athletes. Thus, the
present study sought to investigate the effects of a modified IF protocol (i.e. time-restricted feeding) during resistance
training in healthy resistance-trained males.
Methods: Thirty-four resistance-trained males were randomly assigned to time-restricted feeding (TRF) or normal
diet group (ND). TRF subjects consumed 100 % of their energy needs in an 8-h period of time each day, with their
caloric intake divided into three meals consumed at 1 p.m., 4 p.m., and 8 p.m. The remaining 16 h per 24-h period
made up the fasting period. Subjects in the ND group consumed 100 % of their energy needs divided into three
meals consumed at 8 a.m., 1 p.m., and 8 p.m. Groups were matched for kilocalories consumed and macronutri-
ent distribution (TRF 2826 ± 412.3 kcal/day, carbohydrates 53.2 ± 1.4 %, fat 24.7 ± 3.1 %, protein 22.1 ± 2.6 %, ND
3007 ± 444.7 kcal/day, carbohydrates 54.7 ± 2.2 %, fat 23.9 ± 3.5 %, protein 21.4 ± 1.8). Subjects were tested before
and after 8 weeks of the assigned diet and standardized resistance training program. Fat mass and fat-free mass were
assessed by dual-energy x-ray absorptiometry and muscle area of the thigh and arm were measured using an anthro-
pometric system. Total and free testosterone, insulin-like growth factor 1, blood glucose, insulin, adiponectin, leptin,
triiodothyronine, thyroid stimulating hormone, interleukin-6, interleukin-1β, tumor necrosis factor α, total cholesterol,
high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides were measured. Bench
press and leg press maximal strength, resting energy expenditure, and respiratory ratio were also tested.
Results: After 8 weeks, the 2 Way ANOVA (Time * Diet interaction) showed a decrease in fat mass in TRF compared
to ND (p = 0.0448), while fat-free mass, muscle area of the arm and thigh, and maximal strength were maintained
in both groups. Testosterone and insulin-like growth factor 1 decreased significantly in TRF, with no changes in
ND (p = 0.0476; p = 0.0397). Adiponectin increased (p = 0.0000) in TRF while total leptin decreased (p = 0.0001),
although not when adjusted for fat mass. Triiodothyronine decreased in TRF, but no significant changes were detected
in thyroid-stimulating hormone, total cholesterol, high-density lipoprotein, low-density lipoprotein, or triglycerides.
© 2016 The Author(s). This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
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and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/
publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Open Access
Journal of
Translational Medicine
*Correspondence: antonio.paoli@unipd.it
1 Department of Biomedical Sciences, University of Padova, Padua, Italy
Full list of author information is available at the end of the article
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Moro et al. J Transl Med (2016) 14:290
Background
Fasting, the voluntary abstinence from food intake for a
specified period of time, is a well-known practice asso-
ciated with many religious and spiritual traditions. In
fact, this ascetic practice is referenced in the Old Tes-
tament, as well as other ancient texts such the Koran
and the Mahabharata. In humans, fasting is achieved
by ingesting little to no food or caloric beverages for
periods that typically range from 12h to 3weeks. Mus-
lims, for example, fast from dawn until dusk during the
month of Ramadan, while Christians, Jews, Buddhists,
and Hindus traditionally fast on designated days or peri-
ods [1]. Fasting is distinct from caloric restriction (CR),
in which daily caloric intake is chronically reduced by
up to 40%, but meal frequency is maintained [2]. In
contrast to fasting, starvation is a chronic nutritional
deficiency that is commonly incorrectly used as a sub-
stitute for the term “fasting”. Starvation could also refer
to some extreme forms of fasting, which can result in
an impaired metabolic state and death. However, starva-
tion typically implies chronic involuntary abstinence of
food, which can lead to nutrient deficiencies and health
impairment. While a prolonged period of fasting is dif-
ficult to perform for the normal population, an inter-
mittent fasting (IF) protocol has been shown to produce
higher compliance [3]. Typically, IF is defined by a com-
plete or partial restriction in energy intake (between 50
and 100% restriction of total daily energy intake) on
1–3days per week or a complete restriction in energy
intake for a defined period during the day that extends
the overnight fast. e most studied of the above form
of IF is Ramadan fasting: during the holy month of
Ramadan, which varies according to the lunar calendar,
Muslims abstain from eating or drinking from sunrise
to sunset. e effects of Ramadan have been extensively
investigated, not only on health outcomes [1, 4–8],
but also on exercise performance [9–16]. Moreover, in
recent years a focus on other forms of IF, unrelated to
religious practice, has emerged. One such form, alter-
nate day fasting (ADF; fasting every other day) is organ-
ized with alternating “feast days,” on which there is an
“ad libitum” energy intake, and “fast days” with reduced
or null energy intake.
A growing body of evidence suggests that, in general,
IF could represent an useful tool for improving health
in general population due to reports of improving blood
lipids [17–20] and glycaemic control [3], reducing circu-
lating insulin [21], decreasing blood pressure [1, 21–23],
decreasing inflammatory markers [7] and reducing fat
mass even during relatively short durations (8–12weeks)
[23]. ese reported effects are probably mediated
through changes in metabolic pathways and cellular
processes such as stress resistance [24], lipolysis [3, 17,
25–27], and autophagy [28, 29]. One particular form of IF
which has gained great popularity through mainstream
media is the so-called time-restricted feeding (TRF).
TRF allows subjects to consume adlibitum energy intake
within a defined window of time (from 3–4h to 10–12h),
which means a fasting window of 12–21 h per day is
employed. A key point concerning the IF approach is that
generally calorie intake is not controlled, but the feeding
times are.
In sports, IF is studied mainly in relationship with
Ramadan period [9–16], whilst TRF has become very
popular among fitness practitioners claiming supposed
effects on maintenance of muscle mass and fat loss. Very
limited scientific information is available about TRF
and athletes, and mixed results have been reported [22,
30, 31]. We demonstrated very recently [30] that TRF
did not affect total body composition nor had negative
effects on muscle cross-sectional area after 8weeks in
young previously-untrained men performing resistance
training, despite a reported reduction in energy intake
of~650kcal per fasting day in the TRF group. us the
aim of the present study was to investigate the effects of
an isoenergetic TRF protocol on body composition, ath-
letic performance, and metabolic factors during resist-
ance training in healthy resistance trained males. We
hypothesized that the TRF protocol would lead to greater
fat loss and improvements in health-related biomarkers
as compared to a typical eating schedule.
Methods
Subjects
irty-four resistance-trained males were enrolled
through advertisements placed in Veneto region’s gyms.
Resting energy expenditure was unchanged, but a significant decrease in respiratory ratio was observed in the TRF
group.
Conclusions: Our results suggest that an intermittent fasting program in which all calories are consumed in an 8-h
window each day, in conjunction with resistance training, could improve some health-related biomarkers, decrease
fat mass, and maintain muscle mass in resistance-trained males.
Keywords: Intermittent fasting, Time-restricted feeding, Resistance training, Body composition, Body builders,
Fasting
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Page 3 of 10
Moro et al. J Transl Med (2016) 14:290
e criteria for entering the study were that subjects
must have performed resistance training continuously
for at least 5years (training 3–5days/week with at least
3 years experience in split training routines), be pres-
ently engaged in regular resistance training at the time
of recruitment, be life-long steroid free, and have no
clinical problems that could be aggravated by the study
procedures.
Fifty-three subjects responded to the advertisement,
but 7 were excluded for previous use of anabolic ster-
oids, and 12 declined participation after explanation of
study’s protocol. erefore, 34 subjects (age 29.21±3.8;
weight 84.6±6.2kg) were randomly assigned to a time-
restricted feeding group (TRF; n=17) or standard diet
group (ND; n = 17) through computer-generated soft-
ware. e research staff conducting outcome assessments
was unaware of the assignment of the subjects (i.e. a sin-
gle blind design). Anthropometric baseline character-
istics of subjects are shown in Table1. All participants
read and signed an informed consent document with the
description of the testing procedures approved by the
ethical committee of the Department of Biomedical Sci-
ences, University of Padova, and conformed to standards
for the use of human subjects in research as outlined in
the current Declaration of Helsinki.
Diet
Dietary intake was measured by a validated 7-day food
diary [32–34], which has been used in previous stud-
ies with athletes [35], and analysed by nutritional soft-
ware (Dietnext®, Caldogno, Vicenza, Italy). Subjects
were instructed to maintain their habitual caloric intake,
as measured during the preliminary week of the study
(Table2). During the 8-week experimental period, TRF
subjects consumed 100% of their energy needs divided
into three meals consumed at 1p.m., 4p.m. and 8p.m.,
and fasted for the remaining 16h per 24-h period. ND
group ingested their caloric intake as three meals con-
sumed at 8a.m., 1p.m. and 8p.m. is meal timing was
chosen to create a balanced distribution of the three
meals during the feeding period in the TRF protocol,
while the schedule for the ND group maintained a nor-
mal meal distribution (breakfast in the morning, lunch at
1p.m. and dinner at 8p.m.). e distribution of calories
was 40, 25, and 35% at 1p.m., 4p.m. and 8p.m. respec-
tively for TRF, while ND subjects consumed 25, 40 and
35% of daily calories at 8a.m., 1p.m. and 8p.m. respec-
tively. e specific calorie distribution was assigned by a
nutritionist and was based on the reported daily intake of
each subject.
ND subjects were instructed to consume the entire
breakfast meal between 8 a.m. and 9 a.m., the entire
lunch meal between 1p.m. and 2p.m., and the entire din-
ner meal between 8p.m. and 9p.m. TRF subjects were
instructed to consume the first meal between 1 p.m.
and 2p.m., the second meal between 4p.m. and 5p.m.,
and the third meal between 8p.m. and 9p.m. No snacks
between the meals were allowed except 20g of whey pro-
teins 30min after each training session. Every week, sub-
jects were contacted by a dietician in order to check the
adherence to the diet protocol. e dietician performed a
structured interview about meal timing and composition
to obtain this information.
Table 1 Subject characteristics atbaseline
Results presented as mean±SD. Results are not statistically signicantly
dierent
TRF ND
Age 29.94 ± 4.07 28.47 ± 3.48
Weight (kg) 83.9 ± 12.8 85.3 ± 13
Height (cm) 178 ± 5 177 ± 4
FM (kg) 10.9 ± 3.5 11.3 ± 4.5
FFM (kg) 73.1 ± 5.7 73.9 ± 3.9
Table 2 Diet composition andmacronutrients distribution at basal level and during the experimental period inboth
groups
Results presented as mean±SD. No signicant dierences were detected between groups and within groups
TRF basal TRF exp ND basal ND exp
Total (kcal/day) 2826 ± 412.3 2735 ± 386 3007 ± 444.7 2910 ± 376.4
Carbohydrates (kcal/day) 1503.4 ± 225.95 1400.3 ± 118.8 1654 ± 222.4 1609.2 ± 201.5
Fat (kcal/day) 698 ± 178.5 683.8 ± 61.6 728.7 ± 195 647.7 ± 183.4
Protein (kcal/day) 624.5. ± 59.5 650.3. ± 62.5 637 ± 72.9 643.1 ± 69.3
% Carbohydrates 53.2 ± 1.4 51.2 ± 3.6 54.7 ± 2.2 55.3 ± 4.2
% Fat 24.7 ± 3.1 25 ± 2.8 23.9 ± 3.5 22.6 ± 3.2
% Protein 22.1 ± 2.6 23.8 ± 3.1 21.4 ± 1.8 22.1 ± 3.2
Protein (g/kgbw) 1.86 ± 0.2 1.93 ± 0.3 1.9 ± 0.3 1.89 ± 0.4
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Page 4 of 10
Moro et al. J Transl Med (2016) 14:290
Training
Training was standardized for both groups, and all sub-
jects had at least 5years of continuous resistance train-
ing experience prior to the study. Training consisted of 3
weekly sessions performed on non-consecutive days for
8weeks. All participants started the experimental proce-
dures in the months of January or February 2014.
e resistance training program consisted of 3 differ-
ent weekly sessions (i.e. a split routine): session A (bench
press, incline dumbell fly, biceps curl), session B (mili-
tary press, leg press, leg extension, leg curl), and session
C (wide grip lat pulldown, reverse grip lat pulldown and
tricep pressdown). e training protocol involved 3 sets
of 6–8 repetitions at 85–90 % 1-RM, and repetitions
were performed to failure (i.e. the inability to perform
another repetition with correct execution) with 180s of
rest between sets and exercises [36]. e technique of
training to muscular failure was chosen because it is one
of the most common practices for body builders, and it
was a familiar technique for the subjects. As expected,
the muscle action velocity varied between subjects due to
their different anatomical leverage. Although there was
slight variation of repetition cadence for each subject, the
average duration of each repetition was approximately
1.0s for the concentric phase and 2.0s for the eccentric
phase [37].
e research team directly supervised all routines to
ensure proper performance of the routine. Each week,
loads were adjusted to maintain the target repetition
range with an effective load. Training sessions were per-
formed between 4:00 and 6:00 p.m. Subjects were not
allowed to perform other exercises other than those
included in the experimental protocol.
Measurements
Body weight was measured to the nearest 0.1kg using an
electronic scale (Tanita BWB-800 Medical Scales, USA),
and height to the nearest 1 cm using a wall-mounted
Harpenden portable stadiometer (Holtain Ltd, UK). Body
mass index (BMI) was calculated in kg/m2. Fat mass and
fat-free mass were assessed by dual energy X-ray absorp-
tiometry (DXA) (QDR 4500 W, Hologic Inc., Arling-
ton, MA, USA). Muscle areas were calculated using the
following anthropometric system. We measured limb
circumferences to the nearest 0.001m using an anthro-
pometric tape at the mid-arm and mid-thigh. We also
measured biceps, triceps, and thigh skinfolds to the near-
est 1mm using a Holtain caliper (Holtain Ltd, UK). All
measurements were taken by the same operator (AP)
before and during the study according to standard pro-
cedures [38, 39]. Muscle areas were then calculated using
a previously [40] validated software (Fitnext®, Caldogno,
Vicenza, Italy). Cross-sectional area (CSA) measured
with Fitnext® has an r2=0.88 compared to magnetic res-
onance and an ICC of 0.988 and 0.968 for thigh and arm,
respectively [40–42].
Ventilatory measurements were made by standard
open-circuit calorimetry (max Encore 29 System, Vmax,
Viasys Healthcare, Inc., Yorba Linda, CA, USA) with
breath-by-breath modality. e gas analysis system was
used: Oxygen uptake and carbon dioxide output val-
ues were measured and used to calculate resting energy
expenditure (REE) and respiratory ratio (RR) using the
modified Weir equation [43]. Before each measurement,
the calorimeter was warmed according to the manufac-
turer’s instructions and calibrated with reference gases of
known composition prior to each participant.
Oxygen uptake was measured (mL/min) and also nor-
malized to body weight (mL/kg/min), and the respira-
tory ratio was determined. After resting for 15min, the
data were collected for 30min, and only the last 20min
were used to calculate the respiratory gas parameters [37,
44]. All tests were performed in the morning between 6
and 8a.m. while the subjects were supine. e room was
dimly lit, quiet, and approximately 23°C. Subjects were
asked to abstain from caffeine, alcohol consumption
and from vigorous physical activity for 24h prior to the
measurement.
Blood collection andanalysis protocol
Blood samples taken from the antecubital vein at base-
line and after 8weeks were collected in BD Vacutainers
Tubes (SST™ II Advance, REF 367953). Samples were
centrifuged (4000 RPM at 4°C using centrifuge J6-MC
by Beckman), and the resultant serum was aliquoted
and stored at −80°C. All samples were analysed in the
same analytical session for each test using the same rea-
gent lot. Before the analytical session, the serum sam-
ples were thawed overnight at 4 °C and then mixed.
Interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α),
and interleukin-1β (IL-1β) were measured using Quan-
tikine HS Immunoassay Kit (R&D Systems, Minneapo-
lis, MN, USA). e inter-assay coefficient of variations
(CVs) were 3.5–6.2 and 3.2–6.3% for IL-6, TNF-α and
IL-1β respectively. Insulin-like growth factor 1 (IGF-1)
was measured using the analyzer Liaison XL (DiaSorin
S.p.A, Vercelli-Italy). is test is a sandwich immunoas-
say based on a chemiluminescent revelation, and the CV
for IGF-1 was between 5.6 and 9.6%; the reference range
for this test depends on age and gender. Fasting total cho-
lesterol, high-density lipoprotein cholesterol (HDL-C),
low-density lipoprotein cholesterol (LDL-C), and triglyc-
erides (TG) were measured by an enzymatic colorimet-
ric method using a Modular D2400 (Roche Diagnostics,
Basel, Switzerland). LDL-C fraction was calculated from
Friedewald’s formula: LDL-C=TC−HDL-C−(TG/5).
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Moro et al. J Transl Med (2016) 14:290
e inter-assay CVs for total cholesterol, HDL-C, and
triacylglycerol concentrations were 2.9, 1.8, and 2.4 %,
respectively. Glucose was measured in triplicate by the
glucose oxidase method (glucose analyzer, Beckman
Instruments, Palo Alto, CA, USA), with a CV of 1.2%.
Leptin and adiponectin were measured by radioim-
munoassay using commercially available kits (Leptin:
Mediadiagnost; Adiponectin: DRG Diagnostic); insulin
was measured with a chemiluminescent immunoassay
(Siemens Immulite 2000). e assay sensitivity was 1ng/
mL, and inter- and intra-assay CVs were less than 10, 5,
and 6% for leptin, adiponectin, and insulin, respectively.
yroid-stimulating hormone (TSH), free thyroxine (T4),
and free triiodothyronine (T3) were measured by auto-
mated chemiluminescence methods (ACS 180 SE; Bayer,
Milan, Italy). Plasma testosterone was determined using
Testosterone II (Roche Diagnostics, Indianapolis, IN,
USA) performed on Modular Analytics E 170 analyzer
with electrochemiluminescent detection.
Strength tests
One repetition maximum (1-RM) for the leg press and
the bench press exercises was measured on separate days.
Subjects executed a specific warm-up for each 1-RM test
by performing 5 repetitions with a weight they could nor-
mally lift 10 times. Using procedures described elsewhere
[45], the weight was gradually increased until failure
occurred in both of the exercises tested. e greatest load
lifted was considered the 1-RM. Previously published
ICCs for test–retest reliability for leg press and bench
press 1-RM testing was 0.997 and 0.997, respectively, in
men, with a coefficient of variation of 0.235 for LP and
0.290 for BP [46]. 1-RM was also assessed at baseline and
after 4 and 8weeks for all training exercises so that the
necessary adjustments for possible strength increases
could be made, thus ensuring that subjects continued to
train at a relative intensity of 85–90% of their 1-RM.
Statistical analysis
Results are presented as mean±standard deviation. e
sample size was obtained assuming an interaction of a
Root Mean Square Standardized Effect (RMSSE) of 0.25
with a fixed power of 80% and an alpha risk of 5% for
the main variable. rough the Shapiro–Wilk’sW test,
we assessed the normality. An independent samples t
test was used to test baseline differences between groups.
e two-way repeated-measures ordinary ANOVA was
performed (using time as the within-subject factor and
diet as the between-subject factor) in order to assess dif-
ferences between groups over the course of the study.
Moreover we adopted a mixed model ANOVA with the
fixed variable fat mass expressed in kg as covariate vs
Time* Diet as random variables. All differences were
considered significant at P<0.05. Post-hoc analyses were
performed using the Bonferroni test. In order to reduce
the influence of within group variability a univariate test
of significance (ANCOVA) was performed. We fixed as
depended variable the Δ pre-post for each group and the
baseline values of the outcomes were adopted as covari-
ate; IF vs ND were assumed as categorical predictors.
e analysis was performed through STATISTICA
software (Vers. 8.0 for Windows, Tulsa, USA) and Prism
5 GraphPad software (Abacus Concepts GraphPad Soft-
ware, San Diego, USA).
Results
After 8 weeks, a significant decrease in fat mass was
observed in the TRF group (−16.4 vs −2.8 % in ND
group), while fat-free mass was maintained in both
groups (+0.86 vs +0.64%). e same trend was observed
for arm and thigh muscle cross-sectional area. Leg press
maximal strength increased significantly, but no differ-
ence was present between treatments. Total testosterone
and IGF-1 decreased significantly in TRF after 8weeks
while no significant differences were detected in ND.
Blood glucose and insulin levels decreased significantly
only in TRF subjects and conformingly a significant
improvement of HOMA-IR was detected. In the TRF
group, adiponectin increased, leptin decreased (but this
was not significant when normalized for fat mass), and
T3 decreased significantly compared to ND, without any
significant changes in TSH. No significant changes were
detectable for lipids (total cholesterol, HDL-c and LDL-
c), except for a decrease of TG in TRF group. TNF-α and
IL-1β were lower in TRF at the conclusion of the study
as compared to ND. A significant decrease of respiratory
ratio in TRF group was recorded (Tables3, 4).
Discussion
Fasting is a relatively well-studied metabolic state in
sports and physical exercise due to studies of the “Rama-
dan” period observed by Muslim athletes [12, 14]. How-
ever, only a single study has reported its effect during a
resistance training program aimed at achieving skeletal
muscle growth [30]. Our data demonstrate that during
a RT program, TRF was capable of maintaining mus-
cle mass, reducing body fat, and reducing inflammation
markers. However, it also reduced anabolic hormones
such testosterone and IGF-1.
A key point of the TRF approach utilized in the pre-
sent study is that total daily calorie intake remained the
same while the frequency of meals (i.e. time between
meals) was altered. is is dissimilar to many other IF
regimens. ere are a number of different IF protocols,
most of which have the goal of reducing total energy
intake. Additionally, unlike ADF and some other forms of
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Page 6 of 10
Moro et al. J Transl Med (2016) 14:290
IF, the regimen utilized in the present study employed the
same schedule each day, consisting of 16h fasting and 8h
feeding.
Although IF has received a great amount of attention
in recent years, the majority of studies have investigated
the effects of IF in overweight, obese or dyslipidemic
subjects [19–21, 47–50]. However, little is known about
the effects of such nutritional regimens in athletes, and
more specifically, in body builders or resistance-trained
individuals. e present study provides the first in-depth
investigation of IF in this population of athletes. With
the exception of reduced triglycerides, our results do not
confirm previous research suggesting a positive effect of
IF on blood lipid profiles [17–19, 47, 49, 51, 52], how-
ever, it has to be taken into account that our subjects
were normolipemic athletes. e magnitude of reduction
in triglycerides was also smaller than is typically seen in
individuals who have elevated concentrations prior to IF.
As reported, a decrease of fat mass in individuals per-
forming IF was observed. Considering that the total
amount of kilocalories and the nutrient distribution
were not significantly different between the two groups
(Table2), the mechanism of greater fat loss in IF group
cannot simply be explained by changes in the quantity or
quality of diet, but rather by the different temporal meal
distribution. Many biological mechanisms have been
Table 3 Major results ofexperiment withstatistics adopted highlighted initalics text
Results are presented as mean±SD
n.s. not statistically signicantly dierent (p>0.05)
IF pre IF post ΔIF t test ND pre ND post ΔND t test 2 Way ANOVA
Time*Diet
FFM (kg) 73.08 ± 3.88 73.72 ± 4.27 n.s. 73.93 ± 3.9 74.41 ± 3.59 n.s. n.s.
FM (kg) 10.90 ± 3.51 9.28 ± 2.47 0.0005 11.36 ± 4.5 11.05 ± 4.274 n.s. 0.0448
Arm muscle CSA (cm2) 48.52 ± 3.80 49.37 ± 3.66 n.s. 48.93 ± 4.05 50.17 ± 6.27 n.s. n.s.
Thigh CSA (cm2) 148 ± 34.87 153.77 ± 36.83 n.s. 150.26 ± 22.21 157.35 ± 32.56 n.s. n.s.
Bench press 1-RM (kg) 107.08 ± 18.01 110.36 ± 16.53 n.s. 109.82 ± 14.72 110.57 ± 15.11 n.s. n.s.
Leg press 1-RM (kg) 282.8 ± 30.11 290.00 ± 27.77 n.s. 298.56 ± 25.76 309 ± 68.94 n.s. n.s.
Adiponectin (μg/mL) 11.8 ± 4.3 13.9 ± 3.7 0.0001 10.8 ± 5.5 10.9 ± 4.3 n.s. 0.0000
Leptin (ng/mL) 2.1 ± 0.6 1.8 ± 0.4 0.0002 2.4 ± 0.5 2.3 ± 0.4 n.s. 0.0001
Leptin (ng/mL/kg bw) 0.21 ± 0.07 0.2 ± 0.06 n.s. 0.24 ± 0.11 0.24 ± 0.11 n.s. n.s.
IL-6 (ng/L) 1.33 ± 0.23 1.08 ± 0.22 0.0035 1.24 ± 0.38 1.19 ± 0.33 n.s. n.s.
TNF-α (ng/L) 5.58 ± 0.92 5.13 ± 0.8 0.0001 5.69 ± 0.77 5.86 ± 0.72 n.s. n.s.
IL-1β (ng/L) 0.93 ± 0.19 0.81 ± 0.07 0.0042 0.92 ± 0.12 0.94 ± 0.12 n.s. 0.0235
Testosterone total
(nmol/L) 21.26 ± 6.51 16.86 ± 4.25 0.0001 18.60 ± 5.68 18.85 ± 4.57 n.s. 0.0476
IGF-1 (ng/mL) 216.94 ± 49.55 188.90 ± 31.48 0.0109 215.59 ± 56.25 218.41 ± 42,24 n.s. 0.0397
Insulin (mU/mL) 2.78 ± 0.6 1.77 ± 0.9 0.0303 2.56 ± 0.5 2.22 ± 0.4 n.s. n.s.
TSH (mUI/L) 1.28 ± 0.6 1.27 ± 0.7 n.s. 1.30 ± 0.8 1.31 ± 0.6 n.s. n.s.
T3 (ng/dL) 83.21 ± 17.23 74.32 ± 26.66 0.0001 81.12 ± 20.00 82.35 ± 25.55 n.s. n.s.
Glucose (mg/dL) 96.64 ± 5.1 85.92 ± 7.13 0.0011 95.21 ± 47.77 96.02 ± 65.32 n.s. n.s.
Total cholesterol (mg/
dL) 193.45 ± 6.6 191.37 ± 11.2 n.s. 196.33 ± 9.93 197.12 ± 15.66 n.s. n.s.
Cortisol (ng/mL) 174.25 ± 56.78 186.05 ± 68.5 n.s. 191.24 ± 70.34 185.78 ± 65.89 n.s. n.s.
HDL-c (mg/dL) 54.11 ± 5.89 58.06 ± 6.11 0.0142 53.33 ± 9.67 54.12 ± 9.9 n.s. n.s.
LDL-c (mg/dL) 114.58 ± 11.33 110.26 ± 12.27 n.s. 115.58 ± 9.9 116.08 ± 11.56 n.s. n.s.
TG (mg/dL) 123.78 ± 15.12 115.23 ± 11.77 0.0052 137.10 ± 16.98 134.58 ± 15.66 n.s 0.0201
REE (kcal/day) 1880 ± 94.15 1891 ± 100.56 n.s. 1901 ± 88.76 1895 ± 93.56 n.s. n.s.
RR 0.83 ± 0.02 0.81 ± 0.01 0.0421 0.83 ± 0.03 0.83 ± 0.02 n.s. n.s.
Mixed model ANOVA
with FM as covariate
Adiponectin (μg/mL) 11.8 ± 4.3 13.9 ± 3.7 10.8 ± 5.5 10.9 ± 4.3 0.0000
Leptin (ng/mL) 2.1 ± 0.6 1.8 ± 0.4 2.4 ± 0.5 2.3 ± 0.4 0.0002
Leptin (ng/mL/kg bw) 0.21 ± 0.07 0.2 ± 0.06 0.24 ± 0.11 0.24 ± 0.11 0.0135
IL-1β (ng/L) 0.93 ± 0.19 0.81 ± 0.07 0.92 ± 0.12 0.94 ± 0.12 0.0224
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Page 7 of 10
Moro et al. J Transl Med (2016) 14:290
advocated to explain these effects. One is the increase of
adiponectin that interacts with adenosine 5′-monophos-
phate-activated protein kinase (AMPK) and stimulates
Peroxisome proliferator-activated receptor gamma coac-
tivator 1-alpha (PGC-1α) protein expression and mito-
chondrial biogenesis. Moreover, adiponectin acts in the
brain to increase energy expenditure and cause weight
loss [53]. It is notable that in the present study, the dif-
ferences in adiponectin between groups remained even
when normalized relative to body fat mass, whereas the
significant decrease of leptin (that might be considered a
unfavorable factor for fat loss) was no longer significant
when normalized for fat mass. Other hypothesis is an
enhanced thermogenic response to epinephrine [54] or
an increase in REE [55] after brief periods of fasting, but
our preliminary data didn’t support this point.
Interestingly, although reductions in the anabolic hor-
mones testosterone and IGF-1 were observed, this did
not correspond to any deleterious body composition
changes or compromises of muscular strength over the
duration of the study. It has been previously reported that
men performing caloric restriction have lower testoster-
one than those consuming non-restricted Western diets
[56], however, the present experiment did not restrict
calories in the IF group. In animal models, IF influences
the hypothalamo-hypophysial-gonadal axis and testos-
terone concentration probably through a decrease in
leptin-mediated effects [57], but it must be considered
that mice on a an every-other-day feeding regimen con-
sume about 30–40% less calories over time compared to
free feeding animals and that in our study, no differences
in leptin concentration were seen when normalized for
fat mass. Also, the reduction of IGF-1 in the TRF group
deserves some discussion. A previous study by Bohulel
etal. [11] reported no changes in the GH/IGF-1 during
Ramadan intermittent fasting. Even though it is plausible
that IF mimics caloric restriction through common path-
ways (e.g. AMPK/ACC) (adenosine 5′-monophosphate-
activated protein kinase/acetyl-CoA-carboxylase) [58],
recent data on humans showed no influences of caloric
restriction on IGF-1 [59, 60]. It is possible that the
increase of adiponectin and the decrease of leptin could
influence the IGF-1 concentration, even though it is
unclear to what extent changes in adipokines impact cir-
culating IGF-1 levels following weight loss [59].
Previous studies have reported mixed results concern-
ing the ability to maintain lean body mass during IF, but
the vast majority of these studies imposed calorie restric-
tion and did not utilize exercise interventions [22]. In our
study, the nutrient timing related to training session was
different between the two groups, and this could affect
the anabolic response of the subjects [61] even though
these effects are still unclear [62]. However, we did not
find any significant differences between groups in fat-
free mass, indicating that the influence of nutrient timing
may be negligible when the overall content of the diet is
similar.
ere is an increasing amount of data suggesting that
IF could potentially be a feasible nutritional scheme to
combat certain diseases. In the present study, both blood
glucose and insulin concentrations decreased in the IF
group. e potential of IF to modulate blood glucose and
insulin concentrations has previously been discussed, but
primarily in the context of overweight and obese indi-
viduals [3]. e concurrent increase in adiponectin and
decrease in insulin may be related to modulation of insu-
lin sensitivity, as adiponectin concentrations have been
positively correlated with insulin sensitivity [21, 50, 63,
64]. Moreover, related to the well-known anti-inflamma-
tory effect of adiponectin, it is possible that the reduction
of inflammatory markers is related to the improvement
of insulin sensitivity. Inflammation plays an pivotal role
Table 4 Univariate tests ofsignicance (ANCOVA)
The Δ pre–post for each depended variable group were considered and the baseline values of the outcomes were adopted as covariate; TRF vs ND were assumed as
categorical predictors
Univariate tests ofsignicance (ANCOVA)
Observations Dependent variables
(pre–post Δ) Categorical predictors
(ΔIF vs ΔND) Covariates (baseline
values) P values
Body weight −0.40 ± 1.76 −0.97 ± 1.58 vs 0.16 ± 1.78 84.63 ± 6.17 0.0354
FM (kg) −0.96 ± 1.72 −1.61 ± 1.53 vs −0.30 ± 1.70 11.12 ± 3.98 0.0070
Adiponectin (μg/mL) −0.45 ± 3.07 2.04 ± 1.52 vs −2.94 ± 1.97 12.83 ± 1.98 0.0000
Leptin (ng/mL) 0.09 ± 0.67 −0.36 ± 0.31 vs 0.54 ± 0.64 1.97 ± 0.52 0.0000
IL-6 (ng/L) −0.15 ± 0.27 −0.25 ± 0.30 vs −0.04 ± 0.20 1.28 ± 0.31 0.0378
TNF-α (ng/L) −0.14 ± 0.47 −0.45 ± 0.37 vs 0.17 ± 0.34 5.63 ± 0.83 0.0000
IL-1β (ng/L) −0.05 ± 0.14 −0.12 ± 0.15 vs 0.02 ± 0.09 0.92 ± 0.15 0.0000
Testosterone total (nmol/L) −2.07 ± 3.60 −4.40 ± 3.02 vs 0.25 ± 2.43 19.93 ± 6.00 0.0000
IGF-1 (ng/mL) −12.38 ± 33.04 −28.00 ± 40.11 vs 3.23 ± 11.13 216.32 ± 38.84 0.0003
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Page 8 of 10
Moro et al. J Transl Med (2016) 14:290
in insulin resistance development through different
cytokines that influence numerous molecular pathways.
For example, insulin resistance could be triggered by
TNF-α via JNK and IKKβ/NF-κB (jun amino-terminal
kinase/inhibitor of NF-κβ kinase) pathways, which may
increase serine/threonine phosphorylation of insu-
lin receptor substrate 1. Moreover IL-6 could decrease
insulin sensitivity in skeletal muscle by inducing toll-
like receptor-4 (TLR-4) gene expression through STAT3
(activator of transcription 3) activation. is relation-
ship is potentially bidirectional as the activation of IKKβ/
NF-κB signalling could, in turn, stimulate the production
of TNF-α [65]. Modulation of some of these inflamma-
tory markers by IF was seen in the present study: TNF-α
and IL-1β were lower in the TRF group than ND at the
conclusion of the study, while IL-6 appeared to decrease
in the TRF group, but was not significantly different from
ND. Previous information on the impact of IF on inflam-
matory markers is limited, but a previous investigation
by Halberg etal. [66] reported no changes in TNF-α or
IL-6 after two weeks of modified IF in a small sample of
healthy young men.
Although a reduction in T3 was observed in the IF
group, no changes in TSH or resting energy expenditure
were observed. e observed reduction in RR in the TRF
group indicates a very small shift towards reliance on
fatty acids for fuel at rest, although a significant statistical
interaction for RR was not present. Fasting RR has been
previously reported to be a predictor of substantial future
weight gain in non-obese men, with individuals who have
higher fasting RR being more likely to gain weight [67].
Interestingly, it was reported by Seidell et al. [67] that
although RR was related to future weight gain, RMR was
not. It should be noted that individuals with the highest
risk of future weight gain had fasting RR>0.85 (as com-
pared to individuals who had RR<0.76). In the present
study, the RR at the end of the study in both the TRF
group and ND group do not directly fall into either of
these categories (RR=0.81 and 0.83, respectively).
Based on the present study, a modified IF protocol
(i.e. TRF) could be feasible for strength athletes without
negatively affecting strength and muscle mass. Interest-
ingly, even though androgen concentrations were low-
ered by TRF, there was no difference in muscle mass
changes between groups (+0.64kg in TRF vs +0.48kg
in ND). Caloric restriction in rodents has been reported
to decrease testosterone and IGF-1 even though human
data on long-term severe caloric restriction does not
demonstrate a decrease in IGF-1 levels, but instead an
increased serum insulin-like growth factor binding pro-
tein 1 (IGFBP-1) concentration [60, 68]. However, no data
are available for most forms of IF. Decrease the activity
of the IGF-1 axis could be a desirable target for reducing
cancer risk [69], but it is also well known that the activa-
tion of the IGF-1/AKT/mTOR (insulin-like growth fac-
tor-1/protein kinase B/mammalian target of rapamycin)
pathway is one of the keys for muscular growth. In addi-
tion to altering IGF-1, fasting can promote autophagy
[28], which is important for optimal muscle health [70].
Additionally, there is a possibility that the different eating
patterns of the groups in the present study impacted the
relative contributions of different hypertrophic pathways
in each group.
Some limitations of the present study should be taken
into account. One is the different timing of meals in rela-
tionship to the training sessions that could have affected
the subjects’ responses. On this point, there is not a
consensus among researchers. e beneficial effects of
pre-exercise essential amino acid-carbohydrate sup-
plement have been suggested [61], but the same group
found that ingesting 20g of whey protein either before
or 1 h after 10 sets of leg extension resulted in simi-
lar rates of AA uptake [62]. Additionally, other studies
have reported no benefit with pre-exercise AA feeding
[71, 72]. Another limitation of the present study is that
the energy and macronutrient composition of the diet
was based on interview, and this approach has known
weaknesses. Because of the limitations of this method,
it is possible that differences in energy or nutrient intake
between groups could have existed and played a role in
the observed outcomes.
Conclusions
In conclusion, our results suggest that the modified IF
employed in this study: TRF with 16h of fasting and
8h of feeding, could be beneficial in resistance trained
individuals to improve health-related biomarkers,
decrease fat mass, and at least maintain muscle mass.
is kind of regimen could be adopted by athletes dur-
ing maintenance phases of training in which the goal
is to maintain muscle mass while reducing fat mass.
Additional studies are needed to confirm our results
and to investigate the long-term effects of IF and peri-
ods after IF cessation.
Abbreviations
IF: intermittent fasting; TRF: time-restricted feeding; ND: normal diet; ADF:
alternate day fasting; IL-6: interleukin-6; TNF-α: tumor necrosis factor-α; IL-1β:
interleukin-1β; IGF-1: insulin-like growth factor-1; HDL-C: high-density lipopro-
tein cholesterol; LDL-C: low-density lipoprotein cholesterol; TG: triglycerides;
TSH: thyroid-stimulating hormone; T4: free thyroxine; T3: free triiodothyronine;
1-RM: one repetition maximum; REE: resting energy expenditure; RR: respira-
tory ratio; ACC: acetyl-CoA-carboxylase; AMPK: adenosine 5′-monophosphate-
activated protein kinase; PGC-1α: Peroxisome proliferator-activated receptor
gamma coactivator 1-alpha; HOMA-IR: homeostasis model assessment–insu-
lin-resistance; mTOR: mammalian target of rapamycin; AKT: protein kinase B;
IGFBP-1: insulin-like growth factor binding protein 1; JNK: jun amino-terminal
kinase; IKKβ/NF-κB: inhibitor of NF-κβ kinase; STAT3: activator of transcription 3;
TLR-4: toll-like receptor-4.
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Page 9 of 10
Moro et al. J Transl Med (2016) 14:290
Authors’ contributions
TM and AP designed the study. TM, GM, QFP performed the experiment. TM
and AP analysed the data and wrote the manuscript. MN performed nutri-
tional assessment. GB, AB participated in the design of the study and helped
to draft the manuscript. GT and PG helped to draft the manuscript and partici-
pated in the data analysis. All authors read and approved the final manuscript.
Author details
1 Department of Biomedical Sciences, University of Padova, Padua, Italy.
2 Department of Kinesiology & Sport Management, Texas Tech University,
Lubbock, TX, USA. 3 Sport and Exercise Sciences Research Unit, University
of Palermo, Palermo, Italy. 4 Italian Fitness Federation, Ravenna, Italy. 5 College
of Physical Education and Dance, Federal University of Goias, Goiania, Brazil.
Acknowledgements
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Availability of data and materials
The data of the current study are available at request for scientists wishing to
use them with kind full permission.
Ethics approval and consent to participate
All participants read and signed an informed consent document with the
description of the testing procedures approved by the ethical committee of
the Department of Biomedical Sciences, University of Padova (HEC DSB 02/14),
and conformed to standards for the use of human subjects.
Funding
This research was conducted with authors’ institutional founds.
Received: 20 March 2016 Accepted: 3 October 2016
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