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Fasted Versus Nonfasted Aerobic Exercise on Body Composition: Considerations for Physique Athletes Article  in  Strength and conditioning journal · May 2020 DOI: 10.1519/SSC.0000000000000565

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California State University, San Bernardino

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Fasted Versus Nonfasted Aerobic Exercise on Body Composition: Considerations for Physique Athletes Guillermo Escalante, DSc, ATC, CSCS, CISSN1 and Christopher Barakat, MS, ATC, CSCS, CISSN2 California State University San Bernardino, San Bernardino, California; and 2Competitive Breed, LLC and The Human Performance Laboratory, University of Tampa, Tampa, Florida

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ABSTRACT 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.

INTRODUCTION

hysique athletes compete in various divisions within the physique sport inclusive of bodybuilding, physique, classic physique, figure, wellness, fitness, and bikini. Although the levels of muscularity and leanness vary depending on the division in which an

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Address correspondence to Guillermo Escalante, [email protected].

individual competes in, physique athletes 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 indicates 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 resistance 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 physique 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 competitors (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 carbohydrates are not readily available to produce 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 composition 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 concluded 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 utilization during exercise (2,62). Some of these factors include, but are not limited to, training status, nutritional status (i.e., fed versus fasted, macronutrient consumption, etc.), body fat percentage, exercise type, duration, and intensity KEY WORDS:

fasted aerobic exercise; nonfasted aerobic exercise; body composition; fat loss; physique athletes

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Fasted Versus Nonfasted Cardio for Fat Loss

(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 efficiently used for muscle contraction, but also inhibits fat oxidation (3,13,14,26,30). Conversely, training in a fasted state has been shown to stimulate the rate of lipolysis and fat oxidation (26,48), partly due to the low levels of insulin and high levels of epinephrine (6). At the cellular level, distinct differences in metabolism are observed when comparing fed and fasted conditions due to factors such as gene expression, acute hormonal changes, skeletal muscle glycogen content, and hepatic glycogen content. Studies have demonstrated that carbohydrate intake significantly inhibits the exercise-induced changes in mRNA content that are crucial for fat metabolism, such as fatty acid translocase/ CD36 and carnitine palmitoyltransferase (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 content (23,45,65), mitochondrial oxidative capacity (28,43), and overall fatoxidation rates during low-moderateintensity exercise (28,65). Furthermore, it is well established that during an overnight 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 rationalize 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 (p 5 0.91). Interestingly, 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 (p 5 0.99). Moreover, net glycogen breakdown during exercise was similar between the pretest and posttest for both conditions. Hypothetically, the acute increases in fat oxidation 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 composition and aesthetics, these adaptations 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 demonstrated 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 demonstrated 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 physique athletes can optimize their nutritional 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 aesthetics 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, sartorius, etc.). However, it is important to note that this is purely speculative and has not been investigated. One important confounding variable is the demographic 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 aerobic performance capabilities. As previously 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 authors 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 effects 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 metabolism, the data are sometimes contradictory. Some variables that seem to significantly impact these markers are exercise intensity, duration, subject demographic (i.e., sedentary, obese/ overweight, aerobic athletic population, etc.), meal composition, and timing 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 conditions such as exercising in a fasted or fed state. Furthermore, it is well understood that the body composition and lifestyle factors of the subjects significantly 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

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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 exercise. These findings suggest that triglyceride 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 mechanisms that upregulate lipid mobilization 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 upregulated 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 hormone have been shown to increase catecholamines (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 differences 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 composition of fed versus fasted state aerobic exercise 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: n 5 10, Fed: n 5 9) 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 5 79.2 6 3.0 kg versus Fast Post 77.7 6 3.0, p , 0.01; Fed Pre 5 80.5 kg 6 4.6 versus Fed Post 5 78.4 6 4.6, p , 0.05), but only the fasted group lost a significant amount of body fat percentage (Fast Pre 5 19.4 6 1.3% versus Fast Post 18.6% 6 1.5%, p , 0.05; Fed Pre 5 19.3% 6 1.2 versus Fed Post 5 18.8 6 1.0, 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 6 183) versus the fasted group (2,466 kcal 6 143) during the initial 15 days of the study (57). Furthermore, the exercise sessions were loosely controlled because one participant was reported to participate in swimming as part of his exercise session, 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 6 10.6–46.7 minutes 6 10.7 for the fasted group versus 51.3 minutes 6 10.7–49.3 minutes 6 12.07 for the fed group (57). Finally, body composition was measured using skinfold calipers (57), which may lead to more variability in the assessments as opposed to using Dual X-Ray Absorptiometry or a bioelectrical spectroscopy 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 metaanalysis on the effect of overnight fasted exercise on weight loss and body composition, Hackett and Hagstrom (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 nonrandomized 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 authors 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 aerobic exercise on body mass, % body fat, and lean mass (21). Several limitations, some of which were discussed in the article, should be considered 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 results 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 Schoenfeld et al., provided the participants with a customized hypocaloric meal plan that was tracked using a daily online 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 similar and parallel how physique competitors approach their diet when attempting to lose body fat.

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Fasted Versus Nonfasted Cardio for Fat Loss

Despite the similarities of using a hypocaloric diet with aerobic exercise to lose body fat between physique competitors and the participants in the Schoenfeld et al. (52) study, many variables remain different. All the participants 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 additional structured exercise for the duration 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 6 7.9% and 24.8 6 8.4%, respectively. In contrast to the participants in the Schoenfeld et al. study (52), physique competitors are recommended and have reported to consume more protein per day (8,17,24,27,42,49), perform aerobic exercise at various frequencies/ durations/intensities (17,25,42,49), participate in a structured resistance training 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 compound to yield greater final results. Furthermore, physique competitors starting contest preparation generally begin their fat-loss intervention at relatively 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 differences between physique competitors and the participants in the study by Schoenfeld et al. (52), the study was executed well and is a good comparison 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 significant 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 competitors is worth investigating. The fasted group went from 26.3 6 7.9% body fat to 25.0 6 7.7% body fat and from 16.5 6 5.5 kg to 15.4 6 5.5 kg of fat mass, whereas the fed group went from 24.8 6 8.4% body fat to 24.1 6 8.5% body fat and from 15.7 6 6.3 kg to 15.0 6 6.1 kg of fat mass (52). Although the differences between the 2 groups did not reach statistical significance, failing 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 results of the participants were not reported 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 hormonal 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 preparing 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 exercise (15,20,35). Evidence suggests that dietary protein consumed before or during exercise provides an anticatabolic stimulus, which provides a sensible rationale for exercising individuals concerned with minimizing protein breakdown during endurance exercise (29). Moreover, preliminary research suggests that consuming a highprotein meal immediately before exercise may have positive effects on postexercise 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), investigators 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 participant underwent 4 testing sessions and was assigned to ingest 1 of the 4 supplementation conditions: 25 g of whey protein isolate, 25 g casein protein, 25 g maltodextrin, or a noncaloric control (18). Using indirect calorimetry, substrate oxidation and resting energy expenditure were measured at baseline,

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30 minutes later during aerobic exercise performed for 30 minutes at 55– 60% heart rate reserve, and 15 minutes after exercise (18). The authors reported that postexercise energy expenditure was higher with the consumption of protein compared to the ingestion of maltodextrin and tended to be greater than the noncaloric control (18). Furthermore, the ingestion of protein improved postexercise fat oxidation, whereas no change was noted in the other groups (18). Finally, fat oxidation during exercise increased for all groups but the ingestion 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 consumption before moderate-intensity aerobic exercise and that fasting did not lead to increased fat oxidation during or after exercise (18). Thus, it seems that performing “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 intervention is ultimately dictated by creating a consistent caloric deficit over time; however, it is important to comprehend the complexity of the calories in versus calories out equation that seems to be simple at the surface. During periods of prolonged energy restriction that accompany fat loss, the body undergoes several metabolic adaptations aimed at decreasing energy expenditure, improving metabolic 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 ability 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 plateaus 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 exists on the superiority of fasted versus fed cardio to improve body composition, research on physique competitors has not been performed, to the best of the authors’ knowledge. Because critical differences such as starting body fat levels, protein intake, resistance training 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. Furthermore, subtle changes in body composition that may be irrelevant to those in other populations may be the difference between winning and losing a physique competition. Moreover, physique competitors commonly use thermogenic supplements (i.e., caffeine, 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 considered because ingesting these supplements 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 physique competitors, it is not possible to determine which mode of cardio (if any) is more beneficial than the other for this population. As stated previously, in a meta-analysis on the acute

effects of fasted and fed aerobic exercise on carbohydrate and fat metabolism, 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 training 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). Moreover, performing fasted cardio has been shown to upregulate maximal rates of oxidative enzyme activity, impede intraexercise glycogen breakdown, and increase rates of peripheral and intramyocellular 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 proteinenhanced cardio increases postexercise energy expenditure and improves postexercise fat oxidation. PRACTICAL APPLICATIONS

Based on the current available evidence, the following practical applications 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 minimize losses of fat-free mass by providing 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

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Fasted Versus Nonfasted Cardio for Fat Loss

lack of carbohydrates with prolonged activity. Furthermore, because high-intensity exercise relies primarily on carbohydrates as a source of ATP production, lowerintensity exercise may be more favorable for caloric expenditure so as to prevent the breakdown of proteins to make glucose through gluconeogenesis.  Because improving aerobic performance is not a primary goal for physique athletes, the cardio intensity and modality used should ideally improve recovery from resistance training, minimize systemic fatigue accumulation, and maximize adherence. Thus, it is important that physique athletes perform cardio at an appropriate frequency, intensity, duration, and mode (i.e., cycling, stairmaster, walking, etc.) that best complements the rest of their training 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 Performance at the University of Tampa.

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