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Fasted Versus Nonfasted Aerobic Exercise on Body Composition: Considerations for Physique Athletes

May 2020
Strength & Conditioning Journal Publish Ahead of Print(5)

DOI:10.1519/SSC.0000000000000565

Authors:

Guillermo Escalante

California State University, San Bernardino

Christopher Barakat

The University of Tampa

Physique athletes often incorporate aerobic exercise as part of their exercise program to increase caloric expenditure for the purposes of improving their body composition. One method used by some physique competitors is to perform aerobic exercise in the fasted state under the assumption that low glycogen levels after an overnight fast allow for greater mobilization of stored fat to be used for fuel because carbohydrates are not readily available to produce energy. The purpose of this article is to examine the existing literature on the effect of fasted versus fed cardio on improving body composition for physique athletes.

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Fasted Versus Nonfasted

Aerobic Exercise on Body

Composition:

Considerations for

Physique Athletes

Guillermo Escalante, DSc, ATC, CSCS, CISSN

and Christopher Barakat, MS, ATC, CSCS, CISSN

California State University San Bernardino, San Bernardino, California; and

Competitive Breed, LLC and The Human

Performance Laboratory, University of Tampa, Tampa, Florida

ABSTRACT

Physique athletes often incorporate

aerobic exercise as part of their exer-

cise program to increase caloric

expenditure for the purposes of

improving their body composition. One

method used by some physique com-

petitors is to perform aerobic exercise

in the fasted state under the assump-

tion that low glycogen levels after an

overnight fast allow for greater mobili-

zation of stored fat to be used for fuel

because carbohydrates are not readily

available to produce energy. The pur-

pose of this article is to examine the

existing literature on the effect of

fasted versus fed cardio on improving

body composition for physique ath-

letes.

INTRODUCTION

Physique athletes compete in vari-

ous divisions within the physique

sport inclusive of bodybuilding,

physique,classicphysique,ﬁgure,well-

ness, ﬁtness, and bikini. Although the

levels of muscularity and leanness vary

depending on the division in which an

individual competes in, physique ath-

letes typically aim to lose body fat while

maintaining (or gaining) muscle mass

during their contest preparation period.

To achieve low levels of body fat while

maintaining muscle mass, evidence indi-

cates that competitors typically follow

an 8–16+ week diet in which energy

expenditure increases and caloric intake

decreases (4,8,17,24,31,33,42,49,51).

Because physique competitors resis-

tance train year round with the aim

to maximize muscularity, the increased

caloric expenditure during the contest

preparation phase as a means to

enhance an energy deﬁcit primarily

comes from adding aerobic exercise

into their training regimen. Although

there are many ways in which phy-

sique athletes may perform aerobic

exercise (i.e., type, intensity, duration,

frequency, etc.), performing aerobic

exercise, or “cardio,” as the ﬁrst thing

in the morning after an overnight fast is

a common strategy used by some com-

petitors (17,25,49). The theory behind

performing fasted cardio is that low

glycogen levels after an overnight fast

allow for greater mobilization of stored

fat to be used for fuel because carbohy-

drates are not readily available to pro-

duce energy. Although in theory this

may seem promising, the purpose of

this article is to examine the existing

literature on the effect of fasted versus

fed cardio on improving body compo-

sition for physique athletes.

ACUTE EFFECTS OF FASTED AND

NONFASTED AEROBIC EXERCISE

Many researchers have examined the

acute effects of fasted and fed aerobic

exercise on carbohydrate and fat

metabolism. In a systematic review

and meta-analysis by Vieira et al. (62),

the authors analyzed 27 studies with

a total of 273 participants and con-

cluded that performing low-intensity

(;40–70% heart rate max) aerobic

exercise in a fasted state induces higher

fat oxidation than exercise performed in

the fed state (62). Many factors have

been demonstrated to impact fuel uti-

lization during exercise (2,62). Some of

these factors include, but are not limited

to, training status, nutritional status (i.e.,

fed versus fasted, macronutrient con-

sumption, etc.), body fat percentage,

exercise type, duration, and intensity

Address correspondence to Guillermo Esca-

lante, gescalan@csusb.edu.

KEY WORDS:

fasted aerobic exercise; nonfasted aer-

obic exercise; body composition; fat

loss; physique athletes

(5,19,47,54,57,58). Comprehending

how exogenous substrate supply, or the

lack thereof (i.e., fasting), impacts the

acute metabolic responses to exercise

may alter what might be optimal for

physique athletes to implement to

improve body composition.

It is well understood that carbohydrate

consumption before exercise leads to

an increase in blood glucose levels,

and this fuel source (glucose) is efﬁ-

ciently used for muscle contraction,

but also inhibits fat oxidation

(3,13,14,26,30). Conversely, training in

a fasted state has been shown to stim-

ulate the rate of lipolysis and fat oxida-

tion (26,48), partly due to the low levels

of insulin and high levels of epineph-

rine (6). At the cellular level, distinct

differences in metabolism are observed

when comparing fed and fasted condi-

tions due to factors such as gene

expression, acute hormonal changes,

skeletal muscle glycogen content, and

hepatic glycogen content.

Studies have demonstrated that carbo-

hydrate intake signiﬁcantly inhibits the

exercise-induced changes in mRNA

content that are crucial for fat metabo-

lism, such as fatty acid translocase/

CD36 and carnitine palmitoyltransfer-

ase (11,12). On the contrary, exercising

with low initial glycogen levels (due to

dietary carbohydrate restriction and/or

being in a fasted state) has been shown

to increase basal muscle glycogen con-

tent (23,45,65), mitochondrial oxidative

capacity (28,43), and overall fat-

oxidation rates during low-moderate-

intensity exercise (28,65). Furthermore,

it is well established that during an over-

night fast, glucagon/growth hormone

levels increase, blood glucose/insulin

levels decrease, and energy substrates

are pulled from liver glycogen stores,

which heavily depletes this energy

reserve (44,55). The combination of

the aforementioned acute responses to

fasted aerobic exercise are some of the

reasons that physique athletes rational-

ize using fasted cardio over fed cardio.

Vieira et al. (62) reported that relative

glucose concentrations did not seem to

differ when exercise was performed

fasted versus fed (p50.91). Interest-

ingly, fasted exercise has demonstrated

the ability to increase basal glycogen

content compared to fed exercise. For

example, Van Proeyen et al. (61)

observed a 22% increase in skeletal

muscle basal glycogen content in their

fasted group (p,0.05), whereas no

change occurred in their carbohydrate

fed group (p50.99). Moreover, net

glycogen breakdown during exercise

was similar between the pretest and

posttest for both conditions. Hypothet-

ically, the acute increases in fat oxida-

tion and the effects fasted exercise has

demonstrated regarding the increase in

muscle glycogen are beneﬁcial for

a physique athlete. Because a physique

athlete’s primary concern is body com-

position and aesthetics, these adapta-

tions may translate to a leaner physique

with more muscle fullness over time. In

addition, this increase in basal glycogen

content may improve the physique

athlete’s performance during their

resistance training exercise regimen,

which is crucial for their ability to build

and/or preserve muscle during a caloric

deﬁcit.

Viera et al. (62) also concluded that the

acute enhancements in fat oxidation

during fasted exercise are derived from

intramyocellular triglycerides (IMCT)

(53,61). Fasted exercise has demon-

strated a reduction in IMCT by

;60% (6,40), whereas fed exercise

was unable to demonstrate any change

in IMCT levels (6). The acute effects on

IMCT that fasted training has demon-

strated seem to be a superior means to

improve insulin sensitivity compared

to exercise in a fed state (60). These

differences may improve carbohydrate

tolerance and may impact how phy-

sique athletes can optimize their nutri-

tional strategies (i.e., carbohydrate

intake) and nutrient timing strategies.

In addition, to the best of the authors’

knowledge, no data exist on how

IMCT levels may impact the visual aes-

thetics of a physique competitor at low

levels of body fat. Perhaps, oxidizing

fatty acids from IMCT and reducing

that storage impacts the muscle’s

appearance (i.e., muscle striations or

separation between muscles (i.e., rectus

femoris, vastus lateralis, medialis, sarto-

rius, etc.). However, it is important to

note that this is purely speculative and

has not been investigated. One impor-

tant confounding variable is the demo-

graphic typically studied (i.e.,

untrained, obese or overweight, or

endurance athletes). Physique athletes

are lean and muscular athletes who are

not generally concerned with their aer-

obic performance capabilities. As pre-

viously mentioned, aerobic exercise is

generally used as one method to

increase their calorie deﬁcit, maximize

fat oxidation, and improve body

composition.

In another systematic review and

meta-analysis by Aird et al. (2), the au-

thors analyzed 46 studies to investigate

the effects of fasted versus fed state

exercise on performance and exercise

metabolism. Out of the 46 studies, 45 of

them analyzed postexercise alterations

in various metabolic biomarkers

between the fasted and fed conditions

that are potentially relevant to the ef-

fects of fasted versus fed cardio on

body composition. In regards to the

responses of fasted versus fed cardio

on glucose, free fatty acids, metabolic

hormone signaling, skeletal muscle

metabolism, and adipose tissue metab-

olism, the data are sometimes contra-

dictory. Some variables that seem to

signiﬁcantly impact these markers are

exercise intensity, duration, subject

demographic (i.e., sedentary, obese/

overweight, aerobic athletic popula-

tion, etc.), meal composition, and tim-

ing in the fed group (2). Aird et al. (2)

noted that metabolic ﬂexibility is a key

variable inﬂuencing the body’s ability

to shift from glucose to fat oxidation

during different physiological condi-

tions such as exercising in a fasted or

fed state. Furthermore, it is well under-

stood that the body composition and

lifestyle factors of the subjects signiﬁ-

cantly impact their ability to efﬁciently

use glucose or oxidize fat (50). Thus,

the ﬁndings Aird et al. (2) reported

regarding lack of changes observed in

postexercise blood glucose, insulin, and

free fatty acids in 6 of the 8 studies

Fasted Versus Nonfasted Cardio for Fat Loss

VOLUME 00 | NUMBER 00 | MAY 2020

using sedentary and/or overweight/

obese participants may not carry over

to physique athletes.

Collectively, Aird et al. (2) reported

that circulating free fatty acids was

greater during fasted versus fed exer-

cise. These ﬁndings suggest that tri-

glyceride mobilization from adipose

tissue is increased during prolonged

fasted aerobic exercise and that these

elevated free fatty acid levels have

potential to be used for fuel (41). Some

evidence has been demonstrated by

Chen et al. (10) regarding the mecha-

nisms that upregulate lipid mobiliza-

tion from adipose tissue in response

to fasted exercise. For example, mRNA

expression of key lipolytic enzymes

such as adipose triglyceride lipase

and hormone-sensitive lipase was up-

regulated only during fasted exercise

(34). Additional evidence regarding

acute hormonal changes have also

favored fasted exercise. For example,

increases in adrenaline, noradrenaline,

and growth hormone were greater in

fasted conditions compared to fed.

Moreover, higher levels of growth hor-

mone have been shown to increase cat-

echolamines (9) which may further

increase fasting-induced lipolysis (16).

When taking all the aforementioned

acute effects of fasted aerobic exercise

into consideration, it is possible that

physique athletes may beneﬁt from this

mode of exercise to improve their body

composition; however, longer training

studies in this population are necessary

to investigate whether signiﬁcant dif-

ferences are observed between the 2

modes of exercise.

CHRONIC EFFECTS OF FASTED

AND NONFASTED AEROBIC

EXERCISE

Comprehending the acute effects of

fasted versus fed cardio are important to

help formulate a theoretical construct

that the 2 modes of cardio may have

on body composition; however, acute

changes in exercise metabolism are not

always indicative of improvements in

reducing fat mass. Trabelsi et al. (57)

investigated the effects of body composi-

tion of fed versus fasted state aerobic exer-

cise during Ramadan in physically active

men and concluded that aerobic training

in the fasted state lowered body weight

and body fat percentage; however, fed

aerobic training decreased only body

weight (57). Nineteen males (Fast: n5

10, Fed: n59) performed aerobic training

3 days per week for 40–60 minutes per

session at a heart rate of 60–80% of their

maximum heart rate for 30 days and both

groups lost a signiﬁcant amount of body

weight (Fast Pre 579.2 63.0kgversus

Fast Po st 77.7 63.0, p,0.01; Fed Pre 5

80.5 kg 64.6 versus Fed Post 578.4 6

4.6, p,0.05), but only the fasted group

lost a signiﬁcant amount of body fat

percentage (Fast Pre 519.4 61.3%

versus Fast Post 18.6% 61.5%, p,0.05;

Fed P re 519.3% 61.2 versus Fed Post 5

18.8 61.0, p.0.05) (57).

Although these results seem to provide

support for fasted cardio, the results

must be interpreted with caution. First

and foremost, the participant’s diets

were tracked but not controlled; hence,

the absolute daily calorie intake was

signiﬁcantly higher in the fed group

(3,056 kcal 6183) versus the fasted

group (2,466 kcal 6143) during the

initial 15 days of the study (57). Fur-

thermore, the exercise sessions were

loosely controlled because one partici-

pant was reported to participate in

swimming as part of his exercise ses-

sion, whereas other participants did

one session of rowing, stationary

cycling, and running every week (57).

Moreover, the average length of each

exercise session for the ﬁrst 15 days of

the intervention to the second 15 days

of the intervention ranged from

46.3 minutes 610.6–46.7 minutes 6

10.7 for the fasted group versus 51.3 mi-

nutes 610.7–49.3 minutes 612.07 for

the fed group (57). Finally, body com-

position was measured using skinfold

calipers (57), which may lead to more

variability in the assessments as

opposed to using Dual X-Ray Absorp-

tiometry or a bioelectrical spectros-

copy device. Collectively, this study

does not provide conclusive evidence

that there is a difference between

fasted and fed cardio with physically

active men when food intake is not

controlled.

In a systematic review and meta-

analysis on the effect of overnight

fasted exercise on weight loss and

body composition, Hackett and Hag-

strom (21) analyzed 5 studies that

included 96 participants (60 males

and 36 females) aged 21–27 years.

The articles analyzed for this review

included randomized and nonrandom-

ized comparative studies that were

published in English, included healthy

adults, compared exercise after an

overnight fast to exercise in a fed state

using a standardized pre-exercise meal,

and measured body mass and/or body

composition (21). Although the au-

thors stated caution is warranted when

interpreting their ﬁndings due to the

limited number of studies available on

the topic, they reported trivial to small

intragroup and intergroup effect sizes

for the effect of fasted versus fed aero-

bic exercise on body mass, % body fat,

and lean mass (21).

Several limitations, some of which were

discussed in the article, should be con-

sidered before generalizing the results

of the review by Hackett and Hagstrom

(21) to physique competitors. First, only

2 (involving females exclusively) of the 5

studies investigated changes in % body

fat and lean mass; thus, it is difﬁcult to

determine the precise effects of fasted

versus fed exercise on fat mass and

fat-free mass, which are critical for

a physique competitor to consider as

opposed to weight loss alone. Second,

because the effect of fasted versus fed

cardio on fat mass and fat-free mass

was only reported in females, their re-

sults cannot be generalized to males.

Furthermore, the dietary interventions

used in the meta-analysis lacked

homogeneity. Only one study in the

meta-analysis, performed by Schoen-

feld et al., provided the participants

with a customized hypocaloric meal

plan that was tracked using a daily on-

line diary and was geared toward

weight loss (52). Hence, out of the 5

studies included in the review article,

only one study’s design would be sim-

ilar and parallel how physique com-

petitors approach their diet when

attempting to lose body fat.

Strength and Conditioning Journal | www.nsca-scj.com 3

Despite the similarities of using a hypo-

caloric diet with aerobic exercise to

lose body fat between physique com-

petitors and the participants in the

Schoenfeld et al. (52) study, many var-

iables remain different. All the partici-

pants in the Schoenfeld et al. study

were females and were prescribed

a daily protein intake of 1.8 g/kg of

body mass along with 60 minutes of

low-moderate steady-state intensity

walking 3 days per week. Moreover,

all aerobic exercise sessions were

supervised and the participants were

instructed not to perform any addi-

tional structured exercise for the dura-

tion of the 4-week study (52). In

addition, the participants in the fasted

and fed exercise groups had baseline

body fat percentages of 26.3 67.9%

and 24.8 68.4%, respectively. In con-

trast to the participants in the Schoen-

feld et al. study (52), physique

competitors are recommended and

have reported to consume more pro-

tein per day (8,17,24,27,42,49), perform

aerobic exercise at various frequencies/

durations/intensities (17,25,42,49), par-

ticipate in a structured resistance train-

ing program (17,25,42,49), and perform

an 8–16+ week intervention to get to

extremely low levels of body fat

(4,8,17,24,31,33,42,49,51). Because

preparation for a competition requires

time, the longer the prep, the more

important “small” changes can com-

pound to yield greater ﬁnal results.

Furthermore, physique competitors

starting contest preparation generally

begin their fat-loss intervention at rel-

atively low body fat levels; for example,

baseline body fat levels of 10.5–14% for

men and 20.3–22.7% for women have

been reported (27,42,49,56).

Although there are clearly many differ-

ences between physique competitors

and the participants in the study by

Schoenfeld et al. (52), the study was

executed well and is a good compari-

son for the chronic effects of fasted

versus fed cardio that partly represents

a program physique competitors may

follow. Speciﬁcally, the results of this

investigation revealed that both the

fasted and fed cardio groups lost

a signiﬁcant amount of weight and fat

mass over the course of the 4-week

intervention with no statistically signif-

icant between-group differences noted

in body mass, fat mass, or fat-free mass

(52). However, a closer look at the data

because they relate to physique com-

petitors is worth investigating.

The fasted group went from 26.3 6

7.9% body fat to 25.0 67.7% body fat

and from 16.5 65.5 kg to 15.4 65.5 kg

of fat mass, whereas the fed group went

from 24.8 68.4% body fat to 24.1 6

8.5% body fat and from 15.7 66.3kgto

15.0 66.1 kg of fat mass (52). Although

the differences between the 2 groups

did not reach statistical signiﬁcance, fail-

ing to reach statistical signiﬁcance does

not always mean it is not practically

relevant. Speciﬁcally in the world of

physique competition, the difference

between winning and losing might be

found in small effect sizes that do not

reach statistical signiﬁcance in research.

In addition, because the individual re-

sults of the participants were not re-

ported in this study, it is not possible

to determine the individual variability

of fat mass and fat-free mass over the

course of the intervention. Furthermore,

this is compounded by limitations of

longitudinal training studies that require

signiﬁcant time and effort commitments

from the participants. Thus, smaller

sample sizes and shorter intervention

periods are common limitations in

many training studies. Finally, the hor-

monal and metabolic changes that a lean

physique competitor will encounter to

get to extremely low levels of body fat

will be more drastic as they get closer to

competition compared to an individual

who starts a fat loss program at higher

levels of body fat and is only looking to

get to “healthy” levels of body fat (59).

Hence, any minor beneﬁt that may be

derived from fasted cardio should be

considered and further investigated

with physique competitors undergoing

conditions that more closely represent

how they may perform fasted and fed

cardio before deﬁnitive conclusions can

be drawn about the effectiveness of the

2 modes of cardio to improve body

composition.

PROTEIN-ENHANCED AEROBIC

EXERCISE

Because physique athletes strive for

efﬁcient fat loss and preservation (or

increase) in fat-free mass when prepar-

ing for a competition, the effect of

fasted versus fed cardio exercise on

fat mass and fat-free mass is more

important than weight loss alone. In

one study, investigators reported an

increased nitrogen loss equivalent to

approximately 14 grams of amino

acids per hour during 60 minutes of

fasted cardio (39). Moreover, studies

have shown that consuming food

before exercise increases the thermic

effect of the exercise session, which

leads to greater postexercise energy

expenditure compared to fasted exer-

cise (15,20,35). Evidence suggests that

dietary protein consumed before or

during exercise provides an anticata-

bolic stimulus, which provides a sensi-

ble rationale for exercising individuals

concerned with minimizing protein

breakdown during endurance exercise

(29). Moreover, preliminary research

suggests that consuming a high-

protein meal immediately before exer-

cise may have positive effects on post-

exercise energy expenditure compared

to preexercise carbohydrate intake

(22,64) or fasted conditions (47).

Finally, consuming a high-protein meal

in the morning has demonstrated to

improve feelings of satiety during the

day, decrease continuous snacking,

enhance body composition, and

improve weight loss in conjunction

with a hypocaloric diet (36–38,63).

In a study by Gieke et al. (18), inves-

tigators looked at the effects of various

types of protein feeding before

moderate-intensity exercise in

a fasted-state in 11 college-aged males.

In this randomized, counterbalanced,

crossover investigation, each partici-

pant underwent 4 testing sessions and

was assigned to ingest 1 of the 4 sup-

plementation conditions: 25 g of whey

protein isolate, 25 g casein protein, 25 g

maltodextrin, or a noncaloric control

(18). Using indirect calorimetry, sub-

strate oxidation and resting energy

expenditure were measured at baseline,

Fasted Versus Nonfasted Cardio for Fat Loss

VOLUME 00 | NUMBER 00 | MAY 2020

30 minutes later during aerobic exer-

cise performed for 30 minutes at 55–

60% heart rate reserve, and 15 minutes

after exercise (18). The authors re-

ported that postexercise energy expen-

diture was higher with the

consumption of protein compared to

the ingestion of maltodextrin and

tended to be greater than the noncalo-

ric control (18). Furthermore, the

ingestion of protein improved postex-

ercise fat oxidation, whereas no change

was noted in the other groups (18).

Finally, fat oxidation during exercise

increased for all groups but the inges-

tion of casein oxidized signiﬁcantly

more fat than whey protein

during minutes 10–15 and 25–30 of

the exercise session (18). In closing,

the authors concluded that rates of

energy expenditure and fat oxidation

can be altered after casein consump-

tion before moderate-intensity aerobic

exercise and that fasting did not lead to

increased fat oxidation during or after

exercise (18). Thus, it seems that per-

forming “protein-enhanced cardio”

may offer some beneﬁts to physique

athletes as opposed to performing

fasted cardio or fed cardio that includes

the intake of other nutrients.

CONCLUSION

The effectiveness of any fat loss inter-

vention is ultimately dictated by creat-

ing a consistent caloric deﬁcit over

time; however, it is important to com-

prehend the complexity of the calories

in versus calories out equation that

seems to be simple at the surface. Dur-

ing periods of prolonged energy

restriction that accompany fat loss,

the body undergoes several metabolic

adaptations aimed at decreasing

energy expenditure, improving meta-

bolic efﬁciency, and increasing signals

for energy intake that become even

more impactful as a person gets leaner

(60). Simply stated, altering one side of

the energy equation eventually triggers

an inverse response on the other side of

the equation. Hence, despite lowering

energy intake and increasing exercise

time and/or intensity, the body’s abil-

ity to lose more body fat becomes

exponentially more challenging.

Because physique competitors must

reach unusually low levels of body fat

to succeed in their sport, fat loss pla-

teaus are often encountered that are

difﬁcult to overcome. Some of these

plateaus may not be signiﬁcant for

the average person attempting to lose

a few pounds of body fat; however,

physique competitors with a desire to

win must overcome these obstacles if

they are to succeed at maximizing their

improvements in body composition.

Although no conclusive evidence ex-

ists on the superiority of fasted versus

fed cardio to improve body composi-

tion, research on physique competitors

has not been performed, to the best of

the authors’ knowledge. Because criti-

cal differences such as starting body fat

levels, protein intake, resistance train-

ing programming, and cardio exercise

prescription exist between physique

competitors and other populations,

the effects of fasted versus fed cardio

on other populations may not carry

over to physique competitors. Further-

more, subtle changes in body compo-

sition that may be irrelevant to those in

other populations may be the differ-

ence between winning and losing

a physique competition. Moreover,

physique competitors commonly use

thermogenic supplements (i.e., caf-

feine, yohimbine, etc.) before cardio

that have been shown to increase the

acute fat oxidation effects (1,7,32,46),

with some data demonstrating these

acute changes resulted in signiﬁcant

reductions in fat mass and body fat

percentage over a 21-day period (46).

Although further discussion of this

topic is beyond the scope of this article,

it is something that should be consid-

ered because ingesting these supple-

ments may alter how the body

responds to fasted versus fed cardio.

Until longer-lasting investigations on

the effects of fasted versus fed versus

protein-enhanced cardio on body

composition are performed on phy-

sique competitors, it is not possible to

determine which mode of cardio (if

any) is more beneﬁcial than the other

for this population. As stated previ-

ously, in a meta-analysis on the acute

effects of fasted and fed aerobic exer-

cise on carbohydrate and fat metabo-

lism, the authors concluded that

performing aerobic exercise in a fasted

state induces more fat oxidation than

exercise performed in the fed state

(11). Chronic fasted-state cardio train-

ing has also been shown to improve

glucose tolerance and insulin sensitivity

during an energy restricted high-fat

diet compared to the same training

conducted after feeding (61). More-

over, performing fasted cardio has been

shown to upregulate maximal rates of

oxidative enzyme activity, impede in-

traexercise glycogen breakdown, and

increase rates of peripheral and intra-

myocellular fat oxidation. However,

because fasted cardio may promote

protein degradation in prolonged

exhaustive sessions, ingesting protein

before cardio may offer a beneﬁt to

physique competitors whose goal is

to lose body fat and maintain (or gain)

fat-free mass in the process even if their

cardio sessions are typically of lower

intensity and duration. Preliminary

data also suggest that protein-

enhanced cardio increases postexercise

energy expenditure and improves post-

exercise fat oxidation.

PRACTICAL APPLICATIONS

Based on the current available evi-

dence, the following practical applica-

tions may be advisable for physique

competitors and coaches:

Physique athletes may use fasted,

fed, or protein-enhanced cardio as

their primary aerobic exercise mode

to increase their caloric expenditure,

increase their overall deﬁcit, and

improve their body composition.

Protein-enhanced cardio may mini-

mize losses of fat-free mass by pro-

viding an anticatabolic stimulus.

Furthermore, protein-enhanced

cardio may increase postexercise

energy expenditure and improve

postexercise fat oxidation as

opposed to fed or fasted cardio.

Fasted exercise can be performed at

various intensities. However, it is not

suggested to perform fasted exercise

for more than 60 minutes due to

potential losses of fat-free mass from

Strength and Conditioning Journal | www.nsca-scj.com 5

lack of carbohydrates with pro-

longed activity. Furthermore,

because high-intensity exercise relies

primarily on carbohydrates as

a source of ATP production, lower-

intensity exercise may be more

favorable for caloric expenditure so

as to prevent the breakdown of pro-

teins to make glucose through

gluconeogenesis.

Because improving aerobic perfor-

mance is not a primary goal for phy-

sique athletes, the cardio intensity

and modality used should ideally

improve recovery from resistance

training, minimize systemic fatigue

accumulation, and maximize adher-

ence. Thus, it is important that phy-

sique athletes perform cardio at an

appropriate frequency, intensity,

duration, and mode (i.e., cycling,

stairmaster, walking, etc.) that best

complements the rest of their train-

ing demands and lifestyle

preferences.

Conﬂicts of Interest and Source of Funding:

The authors report no conﬂicts of interest

and no source of funding.

Guillermo

Escalante is an

associate professor

of Kinesiology at

California State

University San

Bernardino.

Christopher

Barakat is owner

and coach at the

Competitive Breed,

LLC, and Adjunct

Instructor of

Human Perfor-

mance at the Uni-

versity of Tampa.

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Fasted Versus Nonfasted Cardio for Fat Loss

VOLUME 00 | NUMBER 00 | MAY 2020

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Dec 2018
Sports Nutr Rev J

Background Competitive bodybuilders employ a combination of resistance training, cardiovascular exercise, calorie reduction, supplementation regimes and peaking strategies in order to lose fat mass and maintain fat free mass. Although recommendations exist for contest preparation, applied research is limited and data on the contest preparation regimes of bodybuilders are restricted to case studies or small cohorts. Moreover, the influence of different nutritional strategies on competitive outcome is unknown. Methods Fifty-one competitors (35 male and 16 female) volunteered to take part in this project. The British Natural Bodybuilding Federation (BNBF) runs an annual national competition for high level bodybuilders; competitors must qualify by winning at a qualifying events or may be invited at the judge’s discretion. Competitors are subject to stringent drug testing and have to undergo a polygraph test. Study of this cohort provides an opportunity to examine the dietary practices of high level natural bodybuilders. We report the results of a cross-sectional study of bodybuilders competing at the BNBF finals. Volunteers completed a 34-item questionnaire assessing diet at three time points. At each time point participants recorded food intake over a 24-h period in grams and/or portions. Competitors were categorised according to contest placing. A “placed” competitor finished in the top 5, and a “Non-placed” (DNP) competitor finished outside the top 5. Nutrient analysis was performed using Nutritics software. Repeated measures ANOVA and effect sizes (Cohen’s d) were used to test if nutrient intake changed over time and if placing was associated with intake. ResultsMean preparation time for a competitor was 22 ± 9 weeks. Nutrient intake of bodybuilders reflected a high-protein, high-carbohydrate, low-fat diet. Total carbohydrate, protein and fat intakes decreased over time in both male and female cohorts (P < 0.05). Placed male competitors had a greater carbohydrate intake at the start of contest preparation (5.1 vs 3.7 g/kg BW) than DNP competitors (d = 1.02, 95% CI [0.22, 1.80]). Conclusions Greater carbohydrate intake in the placed competitors could theoretically have contributed towards greater maintenance of muscle mass during competition preparation compared to DNP competitors. These findings require corroboration, but will likely be of interest to bodybuilders and coaches.

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Lipolytic suppression following carbohydrate ingestion limits fat oxidation during exercise

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Oct 1997

This study determined if the suppression of lipolysis after preexercise carbohydrate ingestion reduces fat oxidation during exercise. Six healthy, active men cycled 60 min at 44 ± 2% peak oxygen consumption, exactly 1 h after ingesting 0.8 g/kg of glucose (Glc) or fructose (Fru) or after an overnight fast (Fast). The mean plasma insulin concentration during the 50 min before exercise was different among Fast, Fru, and Glc (8 ± 1, 17 ± 1, and 38 ± 5 μU/ml, respectively; P< 0.05). After 25 min of exercise, whole body lipolysis was 6.9 ± 0.2, 4.3 ± 0.3, and 3.2 ± 0.5 μmol ⋅ kg-1⋅ min-1and fat oxidation was 6.1 ± 0.2, 4.2 ± 0.5, and 3.1 ± 0.3 μmol ⋅ kg-1⋅ min-1during Fast, Fru, and Glc, respectively (all P < 0.05). During Fast, fat oxidation was less than lipolysis ( P < 0.05), whereas fat oxidation approximately equaled lipolysis during Fru and Glc. In an additional trial, the same subjects ingested glucose (0.8 g/kg) 1 h before exercise and lipolysis was simultaneously increased by infusing Intralipid and heparin throughout the resting and exercise periods (Glc+Lipid). This elevation of lipolysis during Glc+Lipid increased fat oxidation 30% above Glc (4.0 ± 0.4 vs. 3.1 ± 0.3 μmol ⋅ kg-1⋅ min-1; P < 0.05), confirming that lipolysis limited fat oxidation. In summary, small elevations in plasma insulin before exercise suppressed lipolysis during exercise to the point at which it equaled and appeared to limit fat oxidation.

Effect of Overnight Fasted Exercise on Weight Loss and Body Composition: A Systematic Review and Meta-Analysis

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Full-text available

Nov 2017

It remains unclear whether training in fasted compared to fed states leads to greater weight loss and whether this practice results in beneficial or detrimental changes in body composition. We conducted a systematic review to examine the effect of overnight-fasted versus fed exercise on weight loss and body composition. Seven electronic databases were searched using terms related to fasting and exercise. Inclusion criteria were: randomised and non-randomised comparative studies; published in English; included healthy adults; compared exercise following an overnight fast to exercise in a fed state; used a standardized pre-exercise meal for the fed condition; and measured body mass and/or body composition. A total of five studies were included involving 96 participants. Intra-group analysis for the effect of fasted and fed aerobic exercise revealed trivial to small effect sizes on body mass. The inter-group effect for the interventions on body mass was trivial. Intra-group effects were small for % body fat and trivial for lean mass in females, with trivial effects also found for the inter-groups analyses. Whilst this is the first systematic review and meta-analysis to investigate this topic, caution is warranted when interpreting the findings due to the limited number of studies and hence insufficient data.

International Society of Sports Nutrition Position Stand: Protein and exercise

Article

Full-text available

Jun 2017
Sports Nutr Rev J

Position statement The International Society of Sports Nutrition (ISSN) provides an objective and critical review related to the intake of protein for healthy, exercising individuals. Based on the current available literature, the position of the Society is as follows: 1) An acute exercise stimulus, particularly resistance exercise, and protein ingestion both stimulate muscle protein synthesis (MPS) and are synergistic when protein consumption occurs before or after resistance exercise. 2) For building muscle mass and for maintaining muscle mass through a positive muscle protein balance, an overall daily protein intake in the range of 1.4–2.0 g protein/kg body weight/day (g/kg/d) is sufficient for most exercising individuals, a value that falls in line within the Acceptable Macronutrient Distribution Range published by the Institute of Medicine for protein. 3) There is novel evidence that suggests higher protein intakes (>3.0 g/kg/d) may have positive effects on body composition in resistance-trained individuals (i.e., promote loss of fat mass). 4) Recommendations regarding the optimal protein intake per serving for athletes to maximize MPS are mixed and are dependent upon age and recent resistance exercise stimuli. General recommendations are 0.25 g of a high-quality protein per kg of body weight, or an absolute dose of 20–40 g. 5) Acute protein doses should strive to contain 700–3000 mg of leucine and/or a higher relative leucine content, in addition to a balanced array of the essential amino acids (EAAs). 6) These protein doses should ideally be evenly distributed, every 3–4 h, across the day. 7) The optimal time period during which to ingest protein is likely a matter of individual tolerance, since benefits are derived from pre- or post-workout ingestion; however, the anabolic effect of exercise is long-lasting (at least 24 h), but likely diminishes with increasing time post-exercise. 8) While it is possible for physically active individuals to obtain their daily protein requirements through the consumption of whole foods, supplementation is a practical way of ensuring intake of adequate protein quality and quantity, while minimizing caloric intake, particularly for athletes who typically complete high volumes of training. 9) Rapidly digested proteins that contain high proportions of essential amino acids (EAAs) and adequate leucine, are most effective in stimulating MPS. 10) Different types and quality of protein can affect amino acid bioavailability following protein supplementation. 11) Athletes should consider focusing on whole food sources of protein that contain all of the EAAs (i.e., it is the EAAs that are required to stimulate MPS). 12) Endurance athletes should focus on achieving adequate carbohydrate intake to promote optimal performance; the addition of protein may help to offset muscle damage and promote recovery. 13) Pre-sleep casein protein intake (30–40 g) provides increases in overnight MPS and metabolic rate without influencing lipolysis.

Changes in Body Composition and Neuromuscular Performance Through Preparation, 2 Competitions, and a Recovery Period in an Experienced Female Physique Athlete

Article

Jul 2018

Tinsley, GM, Trexler, ET, Smith-Ryan, AE, Paoli, A, Graybeal, AJ, Campbell, BI, and Schoenfeld, BJ. Changes in body composition and neuromuscular performance through preparation, two competitions, and a recovery period in an experienced female physique athlete. J Strength Cond Res XX(X): 000-000, 2018-This prospective case study evaluated an experienced female figure competitor during contest preparation, 2 competitions, and a recovery period. Twelve laboratory sessions were conducted over 8 months. At each visit, body composition was assessed by 4-compartment model, resting metabolic rate (RMR) by indirect calorimetry, and neuromuscular performance by peak force and rate of force development (RFD) on a mechanized squat device. Caloric intake ranged from 965 to 1,610 kcal·d (16.1-24.8 kcal·kg·BM; 18.2-31.1 kcal·kg·FFM), with varying macronutrient intakes (CHO: 0.3-4.8 g·kg; PRO: 1.7-3.0 g·kg; and FAT: 0.2-0.5 g·kg). Body fat was reduced from 20.3 to 12.2% before the first competition and declined to 11.6% before the second competition. Fat-free mass increased by 2.1% before the first competition and peaked at 4.6% above baseline in the recovery period. Resting metabolic rate decreased from 1,345 kcal·d at baseline to a low value of 1,119 kcal·d between competitions. By the end of recovery, RMR increased to 1,435 kcal·d. Concentric and eccentric peak forces declined by up to 19% before the first competition, experienced perturbations in the inter-competition and recovery periods, and remained 5-8% below baseline at study termination. Similarly, RFD decreased by up to 57% before the first competition, was partially recovered, but remained 39% lower than baseline at study termination. Despite favorable body composition changes, neuromuscular performance was impaired during and after the competitive season in an experienced female physique competitor.

Sedentary behaviour is a key determinant of metabolic inflexibility

Article

May 2017
J PHYSIOL-LONDON

Physiological implications of preparing for a natural male bodybuilding competition

Article

Mar 2018
EUR J SPORT SCI

This study aimed to describe the body composition and physiological changes which take place during the in-season and recovery periods of a group of natural bodybuilders. Natural male bodybuilders (n = 9) were assessed 16 (PRE16), 8 (PRE8), and 1 (PRE1) week(s) before, and 4 (POST4) weeks after a bodybuilding competition. Assessments included body composition, resting metabolic rate (RMR), serum hormones, and 7-day weighed food and training diaries. Change in parameters was assessed using repeated-measures analysis of variance. Dietary protein intake remained high throughout the study period (2.8–3.1 g kg⁻¹ d⁻¹). Fat mass (FM) was significantly reduced from PRE16 to PRE1 (8.8 ± 3.1 vs. 5.3 ± 2.4 kg, P < .01). There was a small decrease in lean mass (LM) from PRE8 to PRE1 (71.8 ± 9.1 vs. 70.9 ± 9.1 kg, P < .05). No changes in RMR were observed (P > .05). Large reductions in total and free testosterone (16.4 ± 4.4 vs. 10.1 ± 3.6 nmol L⁻¹, P < .05; 229.3 ± 72.4 vs. 116.8 ± 76.9 pmol L⁻¹, P < .05), and insulin-like growth factor-1 (IGF-1) (27.0 ± 7.7 vs. 19.9 ± 7.6 nmol L⁻¹, P < .05) occurred between PRE16 and PRE1. LM and IGF-1 increased from PRE1 to POST4 (70.9 ± 9.1 vs. 72.5 ± 8.5 kg, P < .05; 19.9 ± 7.6 vs. 25.4 ± 9.3 nmol L⁻¹, P < .05). Despite substantial reductions in FM, participants maintained almost all of their LM. The reduction in anabolic hormone concentration is likely attributable to the prolonged negative energy balance, despite a high dietary protein intake.

Effects of fasted vs fed-state exercise on performance and post-exercise metabolism: A systematic review and meta-analysis

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