Food Timing, Circadian Rhythm and Chrononutrition: A Systematic Review of Time-Restricted Eating's Effects on Human Health - MDPI
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nutrients
Review
Food Timing, Circadian Rhythm and Chrononutrition:
A Systematic Review of Time-Restricted Eating’s
Effects on Human Health
Réda Adafer * , Wassil Messaadi, Mériem Meddahi, Alexia Patey, Abdelmalik Haderbache ,
Sabine Bayen * and Nassir Messaadi *
Department of General Medicine, Henri Warembourg Faculty of Medicine, University of Lille, 59000 Lille,
France; wassilme@gmail.com (W.M.); meddahi_meriem@hotmail.fr (M.M.); alexia.patey@gmail.com (A.P.);
abdelmalik.hader@gmail.com (A.H.)
* Correspondence: reda.adafer@gmail.com (R.A.); sabine.bayen@univ-lille.fr (A.B.);
nassir.messaadi@univ-lille.fr (N.M.)
Received: 4 November 2020; Accepted: 6 December 2020; Published: 8 December 2020
Abstract: Introduction: Recent observations have shown that lengthening the daily eating period may
contribute to the onset of chronic diseases. Time-restricted eating (TRE) is a diet that especially limits
this daily food window. It could represent a dietary approach that is likely to improve health markers.
The aim of this study was to review how time-restricted eating affects human health. Method:
Five general databases and six nutrition journals were screened to identify all studies published
between January 2014 and September 2020 evaluating the effects of TRE on human populations.
Results: Among 494 articles collected, 23 were finally included for analysis. The overall adherence
rate to TRE was 80%, with a 20% unintentional reduction in caloric intake. TRE induced an average
weight loss of 3% and a loss of fat mass. This fat loss was also observed without any caloric restriction.
Interestingly, TRE produced beneficial metabolic effects independently of weight loss, suggesting an
intrinsic effect based on the realignment of feeding and the circadian clock. Conclusions: TRE is a
simple and well-tolerated diet that generates many beneficial health effects based on chrononutrition
principles. More rigorous studies are needed, however, to confirm those effects, to understand their
mechanisms and to assess their applicability to human health.
Keywords: time-restricted feeding; time-restricted eating; intermittent fasting; circadian rhythm;
systematic review
1. Introduction
Eating behaviors are the most influential factor in the development of chronic pathologies [1,2].
The main food risk factors identified are the excessive consumption of salt, sugars, processed meats,
soda drinks and an insufficient intake of fruits, vegetables, cereals and polyunsaturated fats [3,4].
Data on eating behaviors generally evaluate the qualitative and quantitative aspects of nutrition.
However, little information exists on the temporal characteristics of food and their impact on the
occurrence of diseases.
The daily feeding time is the period from the start of the first meal to the end of the last meal of the
day. An American cohort of 15,000 adults estimated this feeding time to be 12 h for most individuals,
and it even reached 15 h for more than half of them [5]. An Indian study found the same results
and suggested that the lengthening of the daily feeding time may be a factor in the development of
metabolic disorders [6].
Thus, recent observations have indicated that reducing the daily feeding time may limit the
development of noncommunicable diseases. For example, Marinac et al. suggest that prolonging the
Nutrients 2020, 12, 3770; doi:10.3390/nu12123770 www.mdpi.com/journal/nutrientsNutrients 2020, 12, 3770 2 of 15
length of the nightly fasting interval may be a strategy for reducing the risk of breast cancer recurrence [7].
A cohort of 420 individuals showed that eating late may negatively influence weight loss [8] and the
authors of a study on a cohort of 2650 adult women suggested that reducing evening energy intake
and fasting for longer nightly intervals may lower systemic inflammation and subsequently reduce the
risk of breast cancer and other inflammatory and metabolic diseases [9].
Intermittent fasting (IF) is a dietary intervention that alternates between a period of fasting and a
period of normal eating (1–3 days per week) [10,11]. Among various forms of IF, alternate day fasting
(ADF) is defined as a continuous sequence of a fast day (i.e., 100% energy restriction) followed by and
a feed day (ad libitum food consumption), resulting in 36-h fasting [12,13]. IF represents a dietary
approach of growing interest as a weight loss and health improvement strategy [14–16].
Time-restricted feeding (TRF) is a form of IF that limits the daily food consumption to a period
of 4–12 h, which induces a fasting window of 12–20 h per day [17]. However, TRF differs from IF in
two aspects: (1) TRF does not require caloric restriction and (2) it requires a consistent daily eating
window [18].
This dietary approach has shown beneficial effects in animals. In rodent models, it has
been demonstrated that TRF protects mice fed a high fat diet against obesity, hyperinsulinemia,
hepatic steatosis and inflammation [19]. Another study showed that TRF attenuates the onset of
metabolic diseases and reverses the progression of metabolic diseases in mice with pre-existing obesity
and type II diabetes, hepatic steatosis and hypercholesterolemia [20]. A study on Drosophila showed
that TRF attenuates age-related cardiac decline [21].
The time-restricted eating (TRE) is used to refer to human models. Human trials and systematic
reviews on TRE have supported the findings of animal studies and have demonstrated beneficial
effects on cardiovascular metabolism [22]. A recent systematic review and meta-analysis of 19 studies
showed that TRE leads to weight loss and a reduction in fat mass with a preservation of fat-free mass
and also has beneficials effects on cardiometabolic parameters such as blood pressure, fasting glucose
concentration and cholesterol profiles [18].
The purpose of this study is to systematically review the international literature, exploring the
effects of TRE on human health.
2. Method
This work is a systematic descriptive review of the literature, following the international PRISMA
recommendations [23].
2.1. Collection and Selection of Items
The collection and selection of articles was carried out by three independent researchers from
September 2019 to September 2020 using the keys words time-restricted feeding, time-restricted eating
and time-restricted nutrition.
The screened databases were MEDLINE, Web of Science, Scopus, Science Direct and the Cochrane
Library. In addition, the following specialized journals were analyzed: Nutrition Reviews from the
Oxford Academy, Nutrition Reviews from the Wiley Online Library, Obesity from the Wiley Online Library,
the American Journal of Clinical Nutrition, Nutrition—Annual Review of Nutrition and Clinical Nutrition.
The research equations used for each database are listed in Supplemental Method S1.
The included articles were all clinical trials, published between January 2014 and September 2020,
in English, evaluating TRE on adult human populations.
Literature reviews, meta-analyses and any other type of publication were excluded, as were
studies on Muslim fasting.
Once the articles were collected, they were selected through a process including three steps.
The first was the selection of articles based on a reading of their titles. The remaining articles were then
selected based on their abstract. Finally, the full article was read completely before being included or
excluded according to the abovementioned criteria.Nutrients 2020, 12, 3770 3 of 15
All the selection steps were carried out blindly by three operators. In the case of disagreement,
a discussion between the three operators and the supervisor was carried out until consensus was reached.
For the constitution of the database, the authors used the Rayyan QCRI web application, specialized
in systematic literature reviews [24].
2.2. Data Analysis and Extraction
The data were extracted from the original articles and classified in a table (Supplemental Table S1)
according to the following themes: reference of the article, type of study, characteristics of the
participants, main outcomes, main results and level of evidence. These data were then synthesized in
a table for analysis. Data extraction and analysis was carried out by a single operator, the author of
the review.
All the included articles will be referred to in this paper as RXX, with XX being a number.
2.3. Level of Evidence Classification
Levels of evidence were classified according to the Downs and Black checklist [25], which is a
27-item validity score assessing all the methodological aspects of clinical trials. Two questions
about the double-blind method (14 and 15) were uncounted, which brought the score to 25
(Supplemental Table S2).
The second indicator was the classification provided by the High French Health Authority
(HAS) [26] (Supplemental Table S3—HAS gradation).
The combination of these two indicators allowed for the determination of three levels of
evidence—high, medium and low.
3. Results and Discussion
3.1. Selected Articles and Characteristics
Preliminary research identified four hundred and ninety-four articles, including clinical trials,
literature reviews and other relevant work. After the exclusion of one hundred and six duplicates,
three hundred and eighty-eight articles remained, from which 22 have been finally selected [27–49].
An article was added during the full article reading stage (R15—[41]), making a total of 23 articles
included for analysis (see flow chart in Figure 1).
The literature on TRE is limited, with only 23 articles having been published, reporting the results
of 22 trials. The studies took place over periods ranging from four days to four months and involved
groups of 8 participants for the smallest sample and 105 participants for the largest one. The overall
level of evidence was low to medium, with 10 controlled randomized trials with short intervention
periods (average of 33.5 days) and small samples (average n = 21) for the medium-quality evidence
studies. The other 11 studies were of low quality, with three non-randomized controlled studies and
eight single-arm non-controlled trials. One study had a high level of evidence, with a controlled and
randomized protocol and the largest sample of the review trials (105 participants) (R23).
However, it is important to note that 28 experiments evaluating TRE were still in progress at
the closure of the collection period (March 2020). Among these 28 trials, 26 are randomized and
involve larger samples (mean n = 81), which will provide better quality evidence on the subject.
These observations indicate that TRE is a research subject of growing interest and knowledge.Nutrients 2020, 12, 3770 4 of 15
Nutrients 2020, 12, x FOR PEER REVIEW 4 of 16
Figure 1. Flow chart of article selection strategy.
Figure 1. Flow chart of article selection strategy.
3.2. Types of Time-Restricted Eating: Clarification of Terms
The literature on TRE is limited, with only 23 articles having been published, reporting the
Time-restricted
results of feedingtook
22 trials. The studies is an intermittent
place fastranging
over periods which consists
from four indays
limiting
to fourthemonths
daily feeding
and
period [17]. However, the definition of the restriction is still imprecise in studies
involved groups of 8 participants for the smallest sample and 105 participants for the largest one. on humans andThevaries
fromlevel
overall 8 to 12
ofh,evidence
depending onlow
was the sources.
to medium, with 10 controlled randomized trials with short
First, the nomenclature
intervention periods (average of 33.5 days)used to and
describe the type(average
small samples of time-restricted
n = 21) for the feeding practiced is
medium-quality
evidence studies. The other 11 studies were of low quality, with three non-randomized controlled by
standardized: TRE followed by the number of hours of feeding and fasting in a 24-h period, separated
a slash.
studies andFor example,
eight TRE 8/16
single-arm indicates a restriction
non-controlled trials. Oneof the daily
study had afeeding period
high level of to 8 h for awith
evidence, 16 h afast.
Among the 22 studies in the review, only one practiced a restriction
controlled and randomized protocol and the largest sample of the review trials (105 participants) equal to 12 h or less (R13),
all the others having limited daily nutrition to a window of 10 h or less. These data clarify the definition
(R23).
ofHowever,
TRE in humans and indicate
it is important to notethat it starts
that from a period
28 experiments of 10 h,TRE
evaluating a daily
werefast of in
still 14 progress
h and more.at the
closure of the collection period (March 2020). Among these 28 trials, 26 are randomized review
The 8/16 variant is the most common form of TRE, with 50% of the trials in the (n = 12).
and involve
Onesamples
larger TRE protocol
(mean(R1) n =did notwhich
81), impose anyprovide
will hours ofbetter
fastingquality
but required
evidence participants to shift their
on the subject. Thesefirst
meal and advance the time of their last daily meal by an hour and
observations indicate that TRE is a research subject of growing interest and knowledge. a half.[17]. However, the definition of the restriction is still imprecise in studies on humans and varies from
8 to 12 h, depending on the sources.
First, the nomenclature used to describe the type of time-restricted feeding practiced is
standardized: TRE followed by the number of hours of feeding and fasting in a 24-h period, separated
by a slash. For example, TRE 8/16 indicates a restriction of the daily feeding period to 8 h for a 16 h
fast.
Nutrients 2020, 12, 3770 Among the 22 studies in the review, only one practiced a restriction equal to 12 h or less (R13), 5 of 15
all the others having limited daily nutrition to a window of 10 h or less. These data clarify the
Nutrients 2020, 12, x FOR PEER REVIEW 5 of 16
definition of TRE in humans and indicate that it starts from a period of 10 h, a daily fast of 14 h and
3.2. Types of Time-Restricted Eating: Clarification of Terms
The food window more. can also vary during the day. For example, Sutton et al. (R4) introduced the
The 8/16 variant is theTime-restricted
most common feeding form of isTRE, with 50% offast
an intermittent thewhich
trials in the review (n = 12).
concept of early One TRE (eTRE), in
TRE protocol (R1)
which the feeding
didHowever,
not impose
period started earlier inconsists
the day in limiting
(R2, the
R4daily
andfeeding
R5). period
[17]. the any hours of
definition of the
fasting but required
restriction participants
is still imprecise to shifton
in studies their
humans and varies from
By extension, delayed first meal orandlate TRE
advance 8 the (dTRE)
to 12time of their
h, dependingdelays
laston the
daily
the intake
meal
sources. of the
by an hour and first
a half. meal (R3, R7, R8, R9, R12,
R14 and R23). Hutchinson The food window canFirst,
et al. (R11) alsohave
vary during
evaluated
the nomenclature the day.used For example,
both toearly
describeSutton
and ettype
thelate al. TRE.
(R4) introduced
Three studies
of time-restricted the feeding(R16,
practiced is
concept of early TRE (eTRE), in which
standardized: TREthe feedingby
followed period startedofearlier
theperiod
number hours in the day (R2,
ofparticipants.
feeding R4 andin
and fasting R5).
a 24-h period, separated
R17 and R18) allowed the self-selection
By extension, delayedby or alate
of
TREFor
the
(dTRE)
food
delays
intake
the8/16
intake
by
of the first
the
meal (R3,
slash. example, TRE indicates a restriction ofR7,theR8, R9,feeding
daily R12, R14 period to 8 h for a 16 h
TRE is generallyand R23).anHutchinson
every-day (except
et al.
fast. (R11) haveforevaluated
R12 andboth R13), earlywater
and late (except
TRE. Three forstudies
R13) (R16,
and 17 adandlibitum fast,
which means thatR18) allowed the self-selection
participants can eatAmong of the
until the food
satiety intake period
without
22 studies in by
any
the review,therestriction
participants.
only one practiced on the quality equal
a restriction of quantity
to 12 h orof
less (R13),
TRE is generally all
an the
every-day
others (except
having for R12 and
limited dailyR13), water to
nutrition (except
a windowfor R13) of and
10 had orlibitum
less. These data clarify the
food intake, except for four studiesparticipants
fast, which means that
which used iso-caloric
canineat until satiety
protocols
without
(R2, R4, R19, R21). of
definition of TRE humans and indicate thatany restriction
it starts from aon the quality
period of 10 h, a daily fast of 14 h and
These characteristics
quantity of foodshow that
intake, TRE
except
more. for could
four be
studies adaptable
which used to the
iso-caloric participants’
protocols (R2, eating
R4, R19, R21).habits, which
may positively influence These characteristics show
dietary adherence. thatvariant
The 8/16 TRE could is thebemost
adaptable
common to the participants’
form of TRE, with eating
50%habits,
of the which
trials in the review (n = 12).
may positively influence Onedietary adherence.
TRE protocol (R1) did not impose any hours of fasting but required participants to shift their
3.3. Adherence to 3.3.
TRE and Effect
Adherence onfirst
to TRE and
meal and advance the time of their last daily meal by an hour and a half.
Calorie Consumption
Effect on Calorie Consumption
The food window can also vary during the day. For example, Sutton et al. (R4) introduced the
TRE concept of early
was overall well-tolerated, TREan(eTRE), in which the feeding period started earlier inR10,
the day (R2, R4 and R5).
TRE was overall well-tolerated, with anwith adherence
adherence ratesuperior
rate superior to to
80% in eight
80% in studies
eight (R6,
studies (R6, R10,
By R21)
R12, R16, R17, R18, R20, extension,
on thedelayed
10 that or lateevaluated
have TRE (dTRE) delays the
adherence intake
(Table 1). of the first meal
However, Gabel(R3,
et R7, R8, R9, R12, R14
R12, R16, R17, R18, R20, R21) on the
al. (R7) have reportedand 10 that have
R23). Hutchinson
a dropout evaluated
rate of 24% et
andal.in
(R11) adherence
havefeasibility
another (Table
evaluatedstudy
both early 1).
(R22),and However,
the late Gabel
TRE. Three
compliance et(R16,
to studies al. 17 and
(R7) have reported a dropout
the 9/15 TRE was rate
72 ±R18)of allowed
24% 24%~5and
(i.e., in anotheroffeasibility
the self-selection
days/week). study
the food intake period(R22),
by the the compliance to the
participants.
TRE is generally an every-day (except for R12 and R13), water (except for R13) and ad libitum
9/15 TRE was 72 ± 24% (i.e., ~5 days/week).
fast, which means that
Table participants
1. Synthesis can eat until satiety without any restriction on the quality of
of results.
Level of quantity of food intake, except for four Energy studies which used iso-caloric protocols (R2, R4, R19, R21).
Study [Ref] Population Protocol
Evidence Table
These 1. Synthesis
characteristics show ofthat TRE could Metabolic
results.
Balance be adaptable Effect
to theOther Results
participants’ eating habits, which
may positively ↓ Food window
influence dietary adherence.
R1 n = 13 ↓ body 1.9% fat Only 19%
Level of of 3 h
Study [Ref] Antoni et al. Population HealthyProtocol ↓ dailyBalance
Energy energy mass index
Metabolic EffectwithdrawalOther Results
Evidence Low 10-week non-
2018 3.3. Adherence
adults, to TRE and Effect onintake Calorie Consumption
↓ fasting blood including one
randomized
R1 [27] ↓ Food
29–57 years.window of 3 h ↓ body 1.9% fat
glucose lost to follow-up
n = 13 TRE was controlled
overall trial.
well-tolerated, with an adherence rate superior to 80% inOnly 19%
eight studies (R6, R10,
Antoni et al. 10-week mass index
Low Healthy adults, ↓ daily energy intake ↑ BDNFwithdrawal including
2018 R12, R16, R17, R18, R20, R21) on the 10 that have evaluated
non-randomized ↓ fastingadherence
blood (Table 1). However, Gabel et
29–57 years. Early TRE 6/18 ↓ IGF1one lost to follow-up
[27] al. (R7) havecontrolled trial.a dropout rate of 24% and
reported ↓ 24-h
in another glucose
glucose and
feasibility studyof(R22), the compliance to
4-day Modification
hyperglycemic
R2 the 9/15n =TRE
11 was
Early TRE72 ± 24% (i.e., ~5
6/18
randomized Nodays/week).
difference ↓ 24-h glucose and genes ↑ BDNF
excursion
R2 Jamshed et 4-day randomized
Healthy controlled iso- in calorie hyperglycemic expressions ↓ IGF1
= 11
nMedium No difference in ↓ insulin
Jamshed et al. al. 2019 controlled iso-caloric
adults, caloric crossover intake (iso- 1. Synthesis ofexcursion involvedModification
in of genes
Medium Healthy adults, calorieTable
intake resistanceresults.
2019 [28] 32 ± crossover
7 years. trial with3.5 to 5
trial with caloric) ↓ insulin resistancecircadian expressions involved
32 ± 7 years. (iso-caloric) ↑ total cholesterol,
[28] Study [Ref] 3.5 to 5Level
weeks
weeks of of wash-
Population Protocol LDLc, ↑ totalEnergy
cholesterol,rhythm, in circadian
Metabolic Effect rhythm,
Other Results
HDLc
Evidenceout
of wash-out LDLc,Balance
HDLc longevity, longevity, autophagy
↓ Food window autophagy
R1 n = 13 ↓ body 1.9% fat Only 19%
of 3 h ↓ body mass
↓ body mass of
of 0.6
Antoninet al.
= 20 Healthy ↓ daily energy mass index withdrawal
R3 R3 LowDelayed TRE 10-week non- ± 1 kg 0.6 ± 1 kg
n = 20 2018 Delayed TRE 8/16
Healthy adults, intake ↓ fasting blood including one
Smith et al. Smith et al. 8/16 randomized↓ body↓ fat bodyin fat in
Low women, [27]
Healthy Low women, 4-week 29–57 years. glucose lost to follow-up
2017 2017 4-week single- controlled trial. participants
participants that that
21.3 ± 1.2 years. 21.3 ±single-arm
1.2 trial
[29] [29] arm trial strength
strength trainedtrained (>3 ↑ BDNF
years.
Early TRE 6/18 (>3 day/week)
day/week) ↓ IGF1
↓ 24-h glucose and
4-day Modification of
hyperglycemic
R2 Early TRE 6/18 n = 11 randomized ↓ insulin (fasting,
No difference genes
excursion
R4 n=8 Jamshed 5-week
et controlled, Healthy controlled iso- mean in and peak)
calorie expressions
Medium No difference in ↓ insulin
Sutton et al. Pre-diabetic al. 2019 randomized, adults, caloric crossover↑ insulin intake sensitivity
(iso- ↓ desire to eat involved in
Medium calorie intake resistance
2018 overweighted men, [28]isocaloric crossover 32 ± 7 years. trial with 3.5 to 5↓ insulin resistance
caloric) ↓ 8-isoprostane circadian
(iso-caloric) ↑ total cholesterol,
[30] 59 ± 9 years. trial with 7 weeks of weeks of wash- ↑ triglycerides rhythm,
LDLc, HDLc
wash-out out ↓ blood pressure longevity,
autophagy
↓ several aspects
Early TRE 6/18 ↓ body mass of 0.6
No difference in
n = 20 of hunger
R5 R3 4-day controlled, Delayed TRE ± 1 kg
n = 11 Healthy calorie intake ↓ in morning ghrelin,
Ravussin et al. Smith et al.randomized, 8/16 ↓ body fat in
Medium Healthy adults, Low (standardized meals)
women, leptin and GLP-1
2019 iso-caloric crossover
2017 4-week single- participants that
32 years. 21.3Energy
± 1.2 expenditure ↓ average ghrelin
[31] [29] trial with 3.5 to 5 arm trial strength trained
years. unchanged ↑ in evening PYY
weeks of wash-out (>3 day/week)
(satiety)
R6 Physical activity
n = 23 TRE 8/16
Gabel et al. unchanged. ↓ 4% weight
Low Obese, 12-week 80% mean adherence.
2019 No measure of calorie ↓ 5% fat mass
50 ± 2 years. single-arm trial.
[32] intake
Delayed TRE 8/16 ↓ 2.6% of
74% adherence rate.
R7 and 9 12-week, relative weight
n = 23 ↓ of 350 kcal/day No one in the TRE
Gabel et al. non-randomized ↓ of relative BMI
Low Obese, Physical activity group reported
2018, 2014 controlled trial ↓ systolic blood
50 ± 2 years. unchanged. dropping out due to
[33,34] with matched pressure of
issues with the diet.
historical group. 7 ± 2 mmHg3.3. Adherence to TRE and Effect on Calorie Consumption
TRE was overall well-tolerated, with an adherence rate superior to 80% in eight studies (R6, R10,
R12, R16, R17, R18, R20, R21) on the 10 that have evaluated adherence (Table 1). However, Gabel et
al. (R7) have reported a dropout rate of 24% and in another feasibility study (R22), the compliance to
Nutrients 2020, 12, x FOR PEER
Nutrients
REVIEW2020, 12, x FOR PEER REVIEW 5 of 16 5 of 16
the 9/15 TRE was 72 ± 24% (i.e., ~5 days/week).
3.2. Types of Time-Restricted
Nutrients 2020, 12, 3770 3.2. Types
Eating:
of Time-Restricted
Clarification of
Eating:
TermsClarification of Terms 6 of 15
Table 1. Synthesis of results.
Time-restricted feeding Time-restricted
is an intermittent feeding fast which
is an intermittent
consists in limitingfast which theconsists
daily feedingin limiting period the daily feeding period
Level of Energy
[17].
Study [Ref]
However, [17].Population
the definition However,
of the restriction Protocol
the definition is stillofimprecise
theBalance
restriction isMetabolic
in studies stillon Effect in
imprecise
humans and Other
studies
varies Results
onfromhumans and varies from
Evidence
8 to 12 h, depending on 8 tothe12sources.
h, depending ↓ Food
Table onwindow
1.theCont.
sources.
R1 2020, 12, x FOR PEER REVIEW
Nutrients n = 13 ↓ body 1.9% fat Only 19% 5 of 16
First, of 3 h
Antoni et al. the nomenclature First,
Healthy usedthe to nomenclature
describe theused ↓type
daily toenergy
ofdescribe
time-restricted the index
mass typefeedingof time-restricted
practiced
withdrawal is feeding practiced is
Low 10-week non-
standardized:
Level of 2018 TRE followed
standardized:by the number
adults, TRE followed of hours byofthe feeding
number
intake and offasting
hours of
↓ fastingin feeding
ablood
24-h period,
andincluding
fasting
separated
in a 24-h period, separated
one
Study [Ref] 3.2. Types Population
of Time-Restricted Protocol
Eating: randomized of
Clarification Energy
Terms Balance Metabolic Effect Other Results
by a [27]
Evidence slash. For example, 29–57
by aTRE slash. years.
8/16 For indicates
example,
controlled a restriction
TRE
trial. 8/16 indicates
of the daily a restriction
feeding glucose period
of the to lost
8 htofeeding
daily follow-up
for a 16 period
h to 8 h for a 16 h
fast. Time-restricted feeding fast. is an intermittent fast which consists in limiting the daily feeding ↑ BDNF period ↓ TNF-α
[17]. Among
However, thethe22definition
studiesAmong inof thethereview,
the Early
restriction
22 TREisone
studies
only 6/18
still No
in practiced
the difference
imprecise
review, a in in
studies
restriction
only 24-hon
↓one humans
practiced
equal
glucose to
and12 a and ↓less
h orvaries
restriction IGF1 from
(R13),
equal ↓ IL-1
to 12β h or less (R13),
Modification of ↓ IGF 1
R8 8
alltothe
12 h, depending
others = 34 on
n having all the
thesources.
limited others
daily8/16
TRE having
nutrition 4-day
+ RT limited to acalorie
window
daily intake between
nutrition
of 10 htoor a less.
window
hyperglycemic ↓These
fat massofdata
10 hclarify
or less. theThese data clarify the
R2 n = 11 randomized Nogroups
difference genes ↑ adiponectin
Moro et al. definition Adults
First,et of
theTRE who
nomenclature
in humans
definition 8-week
used
and randomized
ofindicate
TRE tocontrolled
describe
in humans
that itiso- the
starts
and type
from
indicate of time-restricted
a period
that itofstarts ↓ blood
excursion
10 h,from glucose
feeding
a daily a periodlevels
fast practiced
ofof 1410 h, is
h↓ respiratory
and a daily fast
MediumJamshed Healthy No indifference
calorie expressions ratioof 14 h and
2016 strengthMediumtrain, controlled trial. ↓↓insulin
insulin resistance
standardized:
more.al. 2019 TRE followed
more.adults, by the number caloric of hours of feeding
crossover in physical
intake and fasting in a 24-h period,
(iso- separated
involved (lipid
in oxidation)
[35] 29.21 ± 3.8 years. TRE + RT vs. RT ↓ triglycerides
resistance
by a [28]
slash.
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example, is the32The
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2019 2017 elderly adults, 4-week single- participants ofthat
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Hutchinson isetthe 21.3
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± 1.2 common trial.
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12). studies
[36] [29] 77.1 years. and al.R23).
(R11) Hutchinson
have evaluated arm et
trial (R11) early
have evaluated
late both
strength Three
early
trained late
(R16, TRE. Three
and (R16, 17 and
years. 84% mean adherence.
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R18) protocol
allowed (R1)
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(>3 participants
day/week) to shift
by the participants. their
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and
R21). R5). (R2, hunger,
R4, R19, R21).
Medium Pre-diabetic men, in eTRE
2019 By extension, randomized trialdelays
with the intake No measure offirst meal (R3, R7, R8, R9, R12,fullness, or desire
These55 ±delayed
3 years. or late
characteristics show
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characteristics
TRE could be
show adaptable
that TRE oftothecould
the participants’
be adaptable eating
↓ triglycerides to the habits,
inparticipants’ R14 eating
which habits, which
[37] 2 weeks of wash-out calorie intake to eat.
and
mayR23). Hutchinson
positively influence et al.
may (R11)adherence.
dietary
positively have evaluated
influence both early
dietary adherence. two groups
and late TRE. Three studies (R16, 17 and
R18) allowed the self-selection of the food intake period by the participants. Conservation of
R12 n = 18 TRE 4/20 + RT vs. ↓ of 650 kcal/day
3.3. Adherence
TRE isAdults to TRE3.3.
generally andAdherence
Effect on (except Calorie
to TRE and Consumption
Effect andonR13), Calorie Consumption No significant lean mass,
Tinsley et al. who an every-day RT alone. for R12 between fasting water
days(except for R13) and ad libitum
Medium
fast, TRE
which means that participants can eat until satiety without any change in weight
restriction on the muscular
quality of volume and
2016 strength-train,
was overall well-tolerated, 8-week
TRE was overall randomized
with anwell-tolerated, and
adherence ratewith non-fasting superior days
an adherence
to 80% and inrate
eight
fatsuperior
studiesto(R6,
mass 80% R10,
in eight
muscular studies (R6, R10,
strength.
[38] quantity 22 ± 2.4 years. controlled trial. ↓ weekly calorie intake
R12, R16,ofR17, food intake,
R18, R20,
R12, except
R21)
R16,on for
R17,
thefour10 studies
R18, thatR20, have which
R21) onused
evaluated the 10 iso-caloric
that haveprotocols
adherence (Table
evaluated 1).(R2, R4, R19,Gabel
However,
adherence R21).mean
(Table
95% et1). adherence.
However, Gabel et
al. (R7)These
have characteristics
reportedal. show
a dropout
(R7) havethat
rate TRE
reported
of 24% couldaand beinadaptable
dropout anotherrate of to theand
feasibility
24% participants’
study
in another (R22), eating habits,
feasibility
the compliance which
study (R22),
to the compliance to
TRE 12/12:
may
the 9/15positively
TRE was influence
72 ±the24% dietary
9/15
(i.e.,TRE~5adherence.
TRE days/week).
was 72 ± 24% (i.e., ~5 days/week).
50 years
R13
n = 40 + 20 years No change in body
Gasmi et al. No difference in
3.3. Adherence
Medium = TRE
20 y (nto 40) vs.and Effect on Calorie
Control 50 years
Table 1.Consumption
Synthesiscalorie
of results.
Table composition
1. Synthesis of results. and ↓ immuno-senescence
2017 intake.
50 years (n = 20) + 20 years muscular function
[39] TRE was overall
Level of well-tolerated, with of
Level an adherence rate
12-week randomized, superior to 80% in eight
Energy Energystudies (R6, R10,
Study [Ref] Study [Ref]
Population ProtocolPopulation ProtocolMetabolic Effect Other
Metabolic
Results Effect Other Results
R12, R16, R17,Evidence
R18, R20, R21) on theEvidence
10 trial.
controlled that have evaluated adherence (Table Balance
Balance 1). However, Gabel et
al. (R7) ↓ Food ↓ Food window
window another feasibility
R1 have reported a dropout = 13 rate of
n Delayed
R1 TRE24%
8/16and in
n = 13 ↓study
body 1.9%(R22),
fat the compliance
↓ body
Only to fat
19% 1.9% Only 19%
of 3 h ↑ calorie intakeof
from
3h
R14 the 9/15etTRE
Antoni n = 40
al. was 72 ± 24% (i.e.,
Antoni et al.~5 days/week).
8-week
Healthy randomized Healthy↓ daily energy ↓ fat↓index
mass mass of 4%–7%
daily energy mass index
withdrawal withdrawal
Low 10-week non- 20 to 200 kcal/day
Low 10-week non- No side effects in 90%
Tinsley et al. 2018 Women who 2018 controlled trial.
adults, adults, intake ↓ fasting
in per
bloodprotocolincluding
intake ↓ fasting
one blood including one
Medium randomized No difference in
randomized of participants at the
2019 [27] strength-train 29–57 -RT + placebo
[27] years. Table 29–57 years.
1. Synthesis of results. analysis for the
glucose glucose
lost to follow-up lost to follow-up
controlled trial. physical activity trial.
controlled end of the protocol
[40] 18–30 years. -TRE + RT + placebo 2 TRE groups
and REE ↑ BDNF ↑ BDNF
Study [Ref]
Level of -TRE + RT + HMB Energy
Population EarlyProtocol
TRE 6/18 Metabolic Effect
Early TRE 6/18 Other ↓ IGF1
Results ↓ IGF1
Evidence Balance ↓ 24-h glucose and ↓ 24-h glucose and
TRE 10/14 every4-day day, 4-day Modification of Modification of
↓ Food window hyperglycemic hyperglycemic
R1
R2 R2n = 13
11 3-weekrandomizedn = 11 No difference randomized ↓ body 1.9% fat
No difference Onlygenes19% genes
of 3 h excursion excursion
R15 Antoni
Jamshed et et
al. n= 8 Healthy
Jamshed single-arm
et trial. iso-
controlled Healthy↓ daily energy
controlled iso-mass index
in calorie in calorie withdrawal
expressions expressions
Low
Medium 10-week non-
Medium ↓ insulin
↓ weight by 4% ↓ insulin
↑ sleep quality
Gill et al. 2015 Low al.2018
2019 Obese adults, al. 2019 adults,
Smartphone-based
caloric crossover
randomized
↓ calorie
adults, intake
intake
intake 20% ↓ fasting intake
(iso-ofcrossover
caloric blood (iso- including
involved
2 one
in involved in
[27]
↓ BMI by 1.15 kg/mto
resistance ↓ hunger
resistance
[41] [28] 18 years. 32[28]
29–57
±assessment
7 years. of
trial caloric
with 3.5 trial with 3.5 to 5glucosecaloric) lost circadian
32to± 57 years. caloric) follow-up circadian
controlled trial. ↑ total cholesterol, ↑ total cholesterol,
quantityweeks
and of wash- weeks of wash- rhythm, rhythm,
LDLc, HDLc ↑ BDNF
LDLc, HDLc
timing intake out out longevity, longevity,
Early TRE 6/18 ↓ IGF1
↓ 24-h glucose and autophagy autophagy
4-day Modification of
↓ body
hyperglycemic
mass of 0.6 ↓ body mass of 0.6
R2 n = 10 nTRE20 8/16 every
= 11 day
randomized n = 20 No difference genes
R3 R3 Delayed TRE Delayed TRE excursion
± 1 kg ± 1 kg
R16 Jamshed et Overweight with self-selection
Healthy of iso-
controlled Healthy in calorie expressions
Smith et al. Medium Smith et al. 8/16 8/16 ↓ insulin
↓ body fat in ↓ body
Mean adherence
fat in
Lee et al. 2020 Low al. 2019 sedentary Low women,eating window.
adults, caloric
Low crossover women, intake (iso- involved in
2017 2017 4-week single- 4-week single- resistancethat
participants participantsofthat
84%.
[42] [28] elderly adults, 3221.3 1.2 4-week
± 7 ±years. trial with 3.5 21.3
to 5 ± 1.2 caloric) circadian
[29] [29] arm trial ↑strength
arm trial total cholesterol,
trained strength trained
77.1 years. single-arm
years. weeks
trial.of wash-years. rhythm,
LDLc,
(>3 HDLc
day/week) (>3 day/week)
out longevity,
autophagy
↓ weight of
↓ body mass of 0.6
nTRE
= 20 8/16 every day 1.7 ± 2.5 kg
R17 R3 n = 40 Delayed TRE ± 1 kg
with self-selection of
Healthy ↓ BMI of
Kesztyüs et al. Smith et al.Abdominally 8/16 ↓ body fat in Mean adherence of
Low Low the food intake period
women, 0.6 ± 0.9 kg/m2
2019 2017 obese, 4-week single- participants that 86 ± 15%
21.3 ± 1.212-week ↓ WC −5.3 ± 3.2 cm
[43] [29] 49.1 ± 12.4 years. arm trial strength trained
single-arm trial.
years. ↓ HbAc1 by
(>3 day/week)
1.4 ± 3.5 mmol/mol
↓ body weight (−3%) Mean adherence of
↓ BMI (−3%) 85 ± 12%.
↓ body fat (−3%) 63.2% participants
TRE 10/14 every day ↓ visceral fat were somehow
R18
n = 19 with self-selection of ↓ by 8.62% ± 14.47%. rating (−3%) engaged in TRE at
Wilkinson et al.
Low Adults with MetS the food intake period. No difference in ↓ WC-4.46 ± 6.72 cm 16 ± 4 months.
2020
59 ± 11 years. 12-week physical activity. ↓ total cholesterol ↑ in sleep duration by
[44]
single-arm trial. ↓ LDLc, 12.45 min.
↓ non-HDLc ↑ in sleep duration
↓ systolic and and efficiency in 84%
diastolic BP of participants.Nutrients 2020, 12, 3770 7 of 15
Table 1. Cont.
Level of
Study [Ref] Population Protocol Energy Balance Metabolic Effect Other Results
Evidence
↓ body mass in
↑ adiponectin in
TRE 8/16 every day ad both groups
both groups.
R19 n = 22 libitum vs. Isocaloric ↓ body fat mass in
Improvement in
McAllister et al. Physically (↓ 300 kcal No difference in both groups
Medium subjective outcomes
2019 active men, from baseline). calorie intake ↓ systolic BP in
(alertness, energy,
[45] 22 ± 2.5 years. 4-week randomized both groups
focus, mood)
controlled trial. ↑ HDLc in
in ad libitum.
both groups
(1) vs. non-TRE group
↓ of eating window in
↓ body weight
TRE group (9.9 ± 2 h)
↓ lean mass
n = 20 TRE 8/16 ad libitum compared with
↓ visceral fat
R20 Overweight adults every day. No difference in non-TRE group.
(2) vs.
Chow et al. with prolonged 12-week controlled physical activity. Adherence in TRE:
Low preintervention
2020 eating window non-randomized trial. No measure of 83.1%
measures
[46] (15.4 ± 0.9 h/day). TRE 8/16 group vs. calorie intake. Correlation between
↓ body weight
45.5 ± 12 years. non-TRE group. restriction of eating
↓ fat mass
window with fat and
↓ lean mass
visceral masses loss
↓ visceral fat
↓ nocturnal glucose
AUC TRE group
100% adherence.
TRE 8/16 every day vs. ↓ peak insulin
n = 11 No difference in Improvement of
non-TRE (15 h/day). concentrations at
R21 Overweight/obese calorie intake subjective feelings
5-day randomized breakfast in
Parr et al. 2020 Medium and (iso-caloric). (well-being and
crossover trial with a TRE group
[47] sedentary men. No difference in satisfaction)
10-day wash ↓ peak glucose
38 ± 5 years. physical activity. ↓ evening hunger in
out period. concentration at
TRE group
breakfast in
TRE group
n = 19 No difference in
R22 TRE 9/15 every day. Mean compliance of
Obese adults calorie intake.
Parr et al. 2020 Low 4-week singe-arm NS. 72 ± 24%
with T2D. Adherence to TRE
[48] non-randomized trial (5 days/week).
50 ± 9 years. reduces calorie intake.
↓ body weight in
TRE group (1.17%)
dTRE 8/16 every day.
R23 n = 105 No difference in compared to
12-week controlled
Miguet et al. Overweight and calorie intake. baseline that was
High randomized trial.
2020 obese adults. No measure of not significantly
TRE 8/16 vs.
[49] 46.5 ± 10.5 years. physical activity. different from
control group.
control group
(0.75%).
X: No measurement. NS: non-significant modification (p > 0.05). Abbreviations: AUC: area under the curve; BDNF:
brain-derived neurotrophic factor; BP: blood pressure; HDLc: HDL cholesterol; HMB: hydroxy-methyl-butyrate
supplementation; IL: interleukin; insulin R: insulin resistance; insulin-S: insulin sensitivity; LDLc: LDL cholesterol;
MetS: metabolic syndrome; REE: resting energy expenditure; RT: resistance training; T2D: type 2 diabetes; WC:
waist circumference.
Otherwise, adherence to meal timing was self-declared by the participants in diet diaries or
interviews for most of the studies (R1, R3, R6, R7, R10, R11, R12, R13, R14, R16, R17, R19, R22, R23).
Food intake measurement was also based on participants’ self-declarations (R1, R7, R8, R9, R12, R13,
R14, R19, R22, R23). The food intake was not even tracked in seven of the studies (R3, R6, R10, R11,
R16, R17, R20). These limitations could lead to declaration and confusion bias.
This limitation is an inherent difficulty in measuring health behaviors like food intake
in free-living conditions. Gill and Panda (R15) developed a smartphone application which
combines a photograph and an optional notification added by the participant (myCircadianClock,
mCC—www.mycircadianclock.org). This method, also used in Wilkinson et al. (R18) and Chow et al.
(R20), can represent an interesting way to reduce the methodological bias involved in food tracking.
Studies have thereby shown that using a mobile application is more accurate for monitoring compliance
to a dietary protocol than a traditional diet diary, and that it can also improve adherence to
this protocol [50].
A recent literature review indicated that the main determinants of adherence to a diet are
the ability to reduce the desire to eat and to conform to the patient’s eating habits [51]. In the
present review, hunger remained stable in four studies (R4, R5, R11, R21), and in Ravussin et al.
(R5) participants reported an improvement in several components of appetite by reducing hungerNutrients 2020, 12, 3770 8 of 15
discomfort and the desire to eat. In addition, time-restricted eating appears less restrictive than classic
diets, with no limitation in the quality or quantity of the food, and thus more adaptability to the
participants’ eating behaviors.
Not only the adherence, but the long-term adherence is the most important factor of the success
of a diet on overall health benefits [52]. The studies in this review were four days to 4 months long,
which is a relatively short time to conclude. In the trial conducted by Wilkinson et al. (R18), 63% of
the participants were somehow engaged in TRE 16 months after the end of the 12-week intervention.
This result suggests that TRE could be a sustainable dietary intervention and it would be interesting to
evaluate adherence over a longer period (12 to 24 months).
One may have expected that the restriction of feeding time would increase the calorie intake.
Inversely, TRE reduced caloric consumption by 20% on average, without an alteration of macronutrient
distribution (Table 1). Interestingly, this calorie restriction has been described as not intentional by
the participants, which is likely to protect them against cognitive restriction. A study revealed that
cognitively-restrained eaters increase their energy intake compared to baseline and lose less body
weight than unrestrained eaters after a 10-month dietary intervention [53].
Moreover, TRE provides a similar level of calorie restriction to other voluntary restrictive dietary
measures, such as continuous caloric restriction. Indeed, the CALERIE is the largest ever study to
evaluate continuous caloric restriction in a non-obese population [54] and its results indicated that
even the most motivated subjects were unable to maintain a 25% calorie restriction over two years.
Put together, these findings suggest that (1) TRE could represent a more sustainable strategy for
patients who want to reduce their caloric intake and (2) TRE could produce a more sustainable body
weight loss than voluntarily restrictive diets.
3.4. Metabolic Effects of TRE
It has been established in the literature that intermittent fasting produces beneficial metabolic
effects via caloric restriction [55,56]. This principle is confirmed by the results of the review, with an
average weight loss of 3% and fat mass perdition (Table 1), body fat loss and a decrease in the level
of fasting glucose concentration (R1), weight loss and BMI reduction in (R7, R9, R15, R18), a drop in
systolic blood pressure (R7, R9, R18), a reduction in waist circumference and a decrease in cholesterol
concentration (R18).
Interestingly, six studies on TRE have shown beneficial metabolic effects, regardless of the calorie
restriction (Table 1). For example, a randomized iso-caloric study evaluating eTRE showed a decrease
in the average blood sugar level and reduced insulin resistance (R2). Likewise, a crossover randomized
trial (R21) demonstrated that short-term TRE improved nocturnal glycemic control. An iso-caloric
trial on eTRE 8/16 (R4) showed an improvement in glucose tolerance and a major decrease in systolic
blood pressure, comparable to the results obtained with pharmacological treatment with an ACE
inhibitor [57]. Moro et al. reported that a combination of TRE 8/16 with regular physical activity
reduced fat mass, decreased blood glucose levels, improved insulin resistance and lowered triglyceride
levels (R8). Grant et al. (R14) showed a reduction of 4%–7% of fat mass, despite an increase in
caloric intake between groups, but only on a per protocol analysis. McAllister et al. showed body
weight and fat mass loss, a reduction in systolic blood pressure and an increase in HDL cholesterol in
two groups applying 8/16 TRE in ad libitum and isocaloric conditions, with no difference between
groups (R19). The authors suggested that this effect was due to the increase in adiponectin levels.
Adiponectin is an adipokine of which the secretion increases during fasting [58] and which could
produce a loss of fat mass by increasing energy expenditure [59,60] and by activating AMPK, a kinase
which stimulates lipolysis and insulin-sensitivity [61–63]. An adiponectin level increase was also
observed in the randomized study by Moro et al. (R8). These findings are interesting and suggest that
the TRE could produce positive metabolic effects independently of energy balance.
Although metabolic changes are the result of an imbalance between the energy content of food
eaten and energy expended partly via physical activity [64,65], only three of the six mentioned studiesNutrients 2020, 12, 3770 9 of 15
measured physical activity (R8, R14, R21). In the Moro et al. trial, for example (R8), 8-week TRE
associated with resistance training (RT) produce the abovementioned metabolic effects in comparison
with a group of adults who performed only strength training, with no difference in food intake and
physical activity. In this study, the physical activity was only measured during the training session,
thus the stated effects could be due to an unmeasured energy expenditure increase outside of training
sessions. Tinsley et al. also evaluated the effects of TRE associated with resistance training (R4).
They measured physical activity during and outside training sessions, which limits the potential bias.
It is necessary for further studies on TRE to systematically control the impact of physical activity to
confirm these interesting effects.
3.5. TRE and the Circadian Clock
It has also been established that the beneficial metabolic effects of a diet are induced by the weight
and/or fat loss it produces [56]. This assertion has been confirmed in seven studies of this review
(R1, R3, R7–9, R8, R17, R18, R19—Table 1). Wilkinson et al., for example, performed a 12-week 10/14
TRE on 19 adults with metabolic syndrome, and recorded LDL and non-HDL cholesterol reduction,
a decrease in systolic blood pressure associated with a body weight loss of 3%, body fat perdition and
the reduction in BMI and waist circumference. In contrast to other diets, TRE generates metabolic
benefits regardless of any loss of weight or fat. For example, Hutchinson et al. showed an improvement
in the glucose tolerance and a decrease in triglycerides in participants practicing eTRE for two weeks
(R11). Furthermore, Sutton et al. recorded an improvement in glucose-tolerance and a decrease in
insulin levels and blood pressure (R4). These promising results suggest that TRE generates an intrinsic
metabolic effect, independently of weight loss or fat mass.
The main mechanism hypothesized to explain this intrinsic effect is its action on the body’s
circadian rhythm [66]. The circadian system represents all the physiological processes involved in a 24-h
cycle, such as the sleep/wake cycle, blood pressure, heart rate, hormone secretion, cognitive performance
and mood regulation [66]. The system is regulated by a number of environmental stimuli such as food
intake, light exposure and physical activity [67]. Growing evidence shows that the disruption of the
circadian system is the cause of many metabolic pathologies like obesity [68,69]. Thus, limiting the
time of food consumption seems to readjust the food intake with the circadian clock [70–73]; this is a
fundamental principle of chrononutrition, which is the study of relationships between circadian clocks
and food intake [74] and which suggests that meal timing affects metabolism [75].
Several results support this hypothesis. First, adiponectin has been established to play a key role
in all the metabolic effects described above, such as the loss of fat mass [62], promotion of glycemic
and lipid metabolism [60,63] and reduction in blood pressure [76]. This molecule is known to actively
regulate the action of the circadian system [77,78]. In addition, a randomized controlled iso-caloric
study involving large-scale gene expression analysis showed that eTRE affected the expression of six
genes involved in circadian rhythm (R2). Finally, a study indicated that TRE produced a significant
and durable improvement of sleep quality (R15) and a 12-week single-arm trial evaluating 10/14 TRE
on 19 adults recorded an increase in sleep duration and efficiency in 84% of the participants. Moreover,
the improvement of sleep quality is known to be directly linked to the enhancement of the circadian
system [79,80]. However, the exact action of TRE on circadian systems remains unclear in humans,
and studies are needed to better understand the mechanisms involved.
A growing number of observations on animal models hypothesize that the positive effects
of physical activity on cardiovascular markers are also due to the ability to restore the circadian
rhythm [81,82]. Moro et al. (R8) compared a group combining a TRE diet and an RT program
(three sessions/week) with a group practicing RT alone for eight weeks. Only the TRE + RT group
recorded a decrease in total body mass and fat mass as well as an improvement in metabolic markers
(glycemic tolerance, decrease in triglycerides). However, as mentioned above, energy expenditure
through physical activity was only recorded during training sessions, which could lead to a classification
bias. Future studies should systematically control this factor and could test TRE alone vs. TRE + RT.Nutrients 2020, 12, 3770 10 of 15
Again, smartphone-based methods represent an interesting strategy to measure physical activity and
energy expenditure in normal living conditions [83].
3.6. Other Effects of TRE
Other beneficial effects were explored in our review. Intermittent fasting has been shown to
prevent cancer by lowering the IGF-1 level in animals [84] and humans [84]. This effect has been stated
in two review studies (R2 and R8) and suggests a protective effect of TRE in carcinogenesis. In addition,
researchers have shown that an intermittent one-month fast leads to a decrease in pro-inflammatory
cytokines [85]. This result was also confirmed by a review study which reported a drop in TNF-α
and IL-1-β levels after 8 weeks of TRE associated with physical training (R8). The decrease in these
mediators of inflammation is otherwise hypothesized to play a role in circadian rhythm improvement
through the action of adiponectin [86]. Gene expression analysis has shown that TRE increases the
expression of four genes involved in autophagy and longevity (R2). This study was also the first
to show that TRE increases the secretion of BDNF, a protective factor against the development of
neurodegenerative diseases [87]. In addition, two studies exploring the effects of TRE in the elderly
showed an improvement in walking speed, a predictor of geriatric robustness [88], as well as an
attenuation of immuno-senescence process (R10 and R13). Furthermore, Sutton et al. (R4) showed that
TRE causes a significant decrease in 8-isoprostane, a biomarker of oxidative stress [89]. Although they
are promising, these observations are based on biological criteria whose clinical implications are limited.
Longitudinal studies are needed to assess the impact of TRE on the morbidity and mortality linked
to these.
4. Conclusions
Our review revealed that reducing the daily feeding period is a well-tolerated dietary approach
for calorie restriction, which would be interesting to evaluate on longer term. Interestingly, TRE differs
from other dietary interventions by producing beneficial effects on many health markers regardless of
the energy balance. These effects suggest that nutrition affects health not only through quantity or
quality of the intakes, but also via the timing of food consumption according to the circadian clock.
More widely, it would be interesting to evaluate whether other health behaviors like sleep quality
or physical activity can influence health markers by their timing according to the circadian clock.
For this purpose, further studies could use smartphone-based methods to measure health behaviors in
free-living conditions. Indeed, smartphones are ubiquitous and present worldwide, available at any
time of the day and can be used as portable monitoring devices to provide detailed information on
lifestyle behaviors according to the circadian clock. This information should help to better understand
the relationship between health behaviors, timing and the occurrence of diseases.
Supplementary Materials: The following are available online at http://www.mdpi.com/2072-6643/12/12/3770/s1,
Table S1: Data extraction, Table S2: Validity score provided by the Downs and Black checklist, Table S3:
HAS gradation, Method S1: Research equations.
Author Contributions: R.A. conducted the review, analyzed the data and wrote the manuscript. A.H. and A.P.
were involved in data collection. M.M., S.B. and W.M. assisted the author in data collection and manuscript
writing. N.M. assisted in manuscript writing and supervised the whole project. All authors have read and agreed
to the published version of the manuscript.
Funding: This research received no external funding.
Acknowledgments: The database constitution was conducted using Rayyan QCRI, a systematic review
web application.
Conflicts of Interest: The authors declare no conflict of interest.You can also read
