However, this approach belies the established anti-catabolic effect of insulin on skeletal muscle. More importantly, muscle protein synthesis, which is the primary regulated turnover variable in healthy humans, is stimulated by the consumption of dietary amino acids, a process that is saturated at a moderate protein intake.

While limited research has explored the effect of intermittent fasting on muscle-related outcomes, we propose that infrequent meal feeding and periods of prolonged fasting characteristic of models of intermittent fasting may be counter-productive to optimizing muscle protein turnover and net muscle protein balance.

The present commentary will discuss the regulation of muscle protein turnover across fasted and fed cycles and contrast it with studies exploring how dietary manipulation alters the partitioning of fat and lean body mass.

It is our position that intermittent fasting likely represents a suboptimal dietary approach to remodel skeletal muscle, which could impact the ability to maintain or enhance muscle mass and quality, especially during periods of reduced energy availability.

Skeletal muscle's central role is the production of contractile force. However, this tissue also serves as the primary site of postprandial glucose disposal 1 and is the largest contributor to resting energy expenditure 2 , which collectively positions it as a vital tissue for the maintenance of health and function.

Muscle is a dynamic tissue in a constant state of turnover as characterized by rates of muscle protein synthesis MPS and muscle protein breakdown MPB.

These liberated AA enter the muscle's free intracellular pool whereby they may serve as a fuel source e. Intramuscular free AA can also be released into circulation to be used by other tissues for synthesis, oxidation or as substrates for gluconeogenesis or ketogenesis e.

The prevailing view is that MPB plays a relatively minor role in the regulation of muscle mass in healthy humans 7 , although whole body protein breakdown that is influenced by higher turning over non-muscle protein pools may play a greater role in whole body net protein balance 8.

MPS is the sequencing of individual AA, made available through protein breakdown or exogenous sources e. When MPS exceeds MPB, a positive muscle net protein balance and, by extension anabolic environment, occurs.

In healthy adults, MPS is generally the more responsive variable and is the primary mediator of muscle net protein balance 7 and long-term changes in muscle mass 9.

However, MPS is also important for replacing old, damaged, and mutated tissue proteins to maintain muscle quality The dietary strategy of intermittent fasting IF has become a topic of interest as an avenue to improve health 13 , 14 and is often divided into three subclasses: alternate-day fasting, whole-day fasting, and time-restricted eating TRE Alternate-day fasting involves alternating between ad libitum feeding days and very low energy intake e.

Whole-day fasting typically consists of 1—2 days of either complete abstinence from calories or severe restriction on fasting days plus ad libitum eating on the other days.

Thus, these IF strategies ultimately have a marked influence on the availability of postprandial dietary AA to support MPS and insulin to attenuate MPB. Many of the health promoting effects of IF are mediated by its effectiveness to induce weight loss For example, when IF is compared to controls with no intervention it generally results in weight loss 16 , 17 , although when compared to continuous energy restriction it is not superior in this outcome By first principles, this suggests that IF may be an elementary means of inducing energy deficiency with no further diet modifications, which may in the short term enhance dietary adherence This proposition is supported by the observation that skipping meals for up to 12 weeks is not compensated for by an increase in energy intake at subsequent meals consumed ad libitum Additionally, 18 h compared to 12 h fasting has demonstrated significantly lower ghrelin levels, which could contribute to the reported reduced desire to eat and increased fullness over a 24 h period Thus, as reduced energy availability can influence MPS rates 22 , 23 , IF strategies would need to consider the impact of total energy intake as a potential confounder contributing to the postprandial regulation of muscle protein turnover.

The following discussion outlines the current understanding of muscle protein metabolism in relation to the anticipated effect of IF as a dietary strategy on muscle mass and remodeling. The breakdown and removal of muscle proteins is regulated by the ubiquitin-proteosome, calpain, and autophagy systems.

While some benefits of IF are suggested to be mediated by increased autophagy 24 , induction of this system with short term fasting i. In contrast, the ubiquitin-proteosomal and calpain systems are the primary systems regulating nutrient and contraction-induced changes in MPB in humans 7 and therefore will be the primary focus of the present review.

MPB is sensitive to feeding indirectly via the nutrient i. Maximal reductions in MPB require only modest elevations in plasma insulin concentrations i.

This enhancement in MPB is demonstrated both with an overnight ~10 h fast 31 , 35 and prolonged 60—72 h fasting 36 — Given that IF typically involves a relatively prolonged fasting period i.

With the contraction-induced anabolic stimulus of resistance exercise there is an increase in MPB, although this primarily serves to provide AA precursors to support MPS in the fasted state 39 , Thus, resistance exercise may help retain muscle mass with IF by attenuating the negative muscle protein balance of fasted, rested muscle.

However, the exercise-induced increase in MPB is completely ablated with exogenous AA 41 , highlighting an important role for dietary AA to support muscle anabolism via attenuated catabolism as well.

Dietary AA are the primary stimulators of and precursors for the synthesis of new muscle proteins The equivalent of ~0. Importantly, after attainment of peak MPS i. Resistance exercise can prolong this postprandial muscle protein synthetic response i.

There is some evidence that energy deficiency may increase the acute meal protein intake required to maximize MPS 22 , 59 with estimates of ~0.

While protein and AA may have an insulinogenic effect 29 , insulin only has a permissive effect for supporting maximal rates of MPS at rest and after exercise 29 , 30 , Thus, manipulating the amount and timing of dietary AA ingestion represents the most important nutritional variable to optimize MPS.

AA oxidation is generally low after an overnight fast but can increase with the duration of the fast i. While meal protein ingestion initiates a normal postprandial increase in AA oxidation 62 , dietary AA consumed in excess of their ability to be incorporated into new body especially muscle proteins are further irreversibly oxidized and their nitrogen excreted 43 — It has been suggested that the protein dose required to enhance whole body anabolism may be substantially greater than that required at the level of the muscle 63 , Accordingly, it is theorized that AA may be sequestered in splanchnic tissue primarily the gut to be later broken down and made available for synthesis of other tissues including muscle 63 , although this has yet to be demonstrated.

Thus, it is arguably more beneficial to consume acute meal protein intakes that maximize MPS yet minimize AA oxidation in order to optimize the daily dietary protein efficiency. In support of this notion, a recent study 21 comparing a 6 h feeding window with 3 meals to a 12 h feeding window with three meals protein intake of ~0.

A current limitation to the field of IF research is that no study, to the best of our knowledge, has measured muscle protein kinetics with alternate-day fasting or TRE.

However, information may be gleaned from studies investigating the impact of daily feeding pattern on protein metabolism. For example, consuming a balanced pattern of moderate protein-containing meals i.

These longer acute trials i. Collectively these acute studies support the concept that meal feeding pattern, irrespective of total protein intake, can influence whole body and muscle protein remodeling with large protein-containing meals stimulating postprandial AA oxidization rather than muscle tissue synthesis Figure 1.

Thus, based on the acute research to date, we argue that the lost opportunity for AA-induced MPS with more feedings may not be compensated for with fewer feedings at higher doses, as what is likely to occur with IF.

Figure 1. Schematic representation of the effect of different types of IF on acute muscle protein kinetics. Changes in muscle protein synthesis MPS and breakdown, amino acid oxidation OX , and circulating insulin concentration over 24 h at rest with whole day fasting A , TRE with one meal B , TRE with two meals over 6—8 h C , and an unrestricted eating window ~16 h with balanced meal pattern D.

Size of arrows reflects the relative protein and energy content of each meal. Shaded dark gray areas indicate time in net positive protein balance and light gray areas indicate time in net negative protein balance, which are summarized as net 24 h response in MPS, MPB, and net muscle protein balance NB; MPS—MPB E.

To our knowledge, no studies have examined whether adaptations in MPB, MPS, and AA oxidation take place over time to an IF protocol. Available literature suggests that following an overnight fast, the first meal demonstrates a similar MPS response to other meals 65 , including those preceded by a large protein containing mixed-meal 4 h prior Randomized control trials analyzing the effect of IF on fat free mass FFM demonstrate similar 19 , 69 — 81 outcomes compared to controls.

As IF often results in negative energy balance and weight loss 16 , 17 , when IF is compared to continuous energy restriction some systematic reviews suggest similar 82 or enhanced 83 preservation of FFM. The divergence in some of these results may be due to the differences in the types of IF or the self-selected meal frequency by research participants.

As discussed above, there is a broad range of IF protocols and those which result in fewer meals e. It is also important to note that the length of the studies to date may not have been sufficient to elucidate differences in FFM given the sensitivity of body composition measurement modalities used and their ability to detect changes over short i.

When IF is coupled with the potent anabolic stimulus of resistance exercise, a systematic review 93 observed no significant differences in FFM outcomes when compared to those resistance training with a normal diet. However, given the normal diet group also did not experience gains in FFM, as would be expected, the length i.

In fact, a recent study suggests that resistance training-induced gains in FFM over 12 weeks are enhanced with a balanced as compared to a skewed daily protein distribution in healthy young men despite consuming a moderate i. Collectively, research to date evaluating the impact of IF on changes in body composition in young adults with and without prescribed exercise is equivocal.

Therefore, it is important to acknowledge that the hypothesis of IF having consequences for muscle mass in particular may be complex. Based on our current understanding of acute muscle protein metabolism, the potential effect of IF may be small relative to other lifestyle related variables e.

A limitation in evaluating the impact of IF on muscle mass and function is the overreliance on whole body estimates of FFM, which have been questioned as to their ability to specifically delineate skeletal muscle mass given they include substantial organ and non-muscle lean tissue 98 , Therefore, future research should include muscle specific outcomes e.

If the hypothesis of more protein feedings per day being optimal for mass and remodeling based on the acute literature is true, IF may represent a dietary conundrum for some populations. While IF is often employed to reduce feeding intakes, restrict total energy intake, and maintain a low insulin profile to help mobilize and metabolize endogenous fat 13 , 14 , based on our current understanding of the acute, nutritional regulation of muscle protein turnover it seems antithetical to what would presumably optimize muscle protein synthesis and net muscle protein balance as summarized in Figure 1.

There is also evidence that reduced energy availability, which often occurs in tandem with IF 16 , 17 , 20 , increases the per meal protein intake required to maximize muscle protein synthesis 22 , Thus, while this would ostensibly favor larger protein meals that may be characteristic of TRE in particular, it does not preclude the need to consume protein more frequently, which would ultimately also help meet the higher recommended daily protein intakes that enhance muscle and FFM retention with weight loss 59 , If the acute effects of IF lead to detrimental long-term outcomes for muscle, whole-day, and alternate-day fasting would have the greatest consequential effect on muscle mass and remodeling.

This is due to the prolonged period with greater MPB and lower MPS compounded by the greater energy deficient state likely to occur relative to TRE In consideration of TRE, fewer meals would likely have a greater negative impact on muscle protein turnover Figure 1.

If TRE were to be employed, the hypothesis to improve muscle mass and remodeling suggests that protein intake should be consumed at a daily intake of at least 1. In conclusion, while IF may represent an option for a variety of populations to promote fat loss and improve aspects of metabolic health, additional research needs to focus on the impact of meal frequency on the quantity and quality of muscle mass.

Inasmuch as IF may be purported as the enemy of body fat, future research must ensure this is not also the case for muscle. Thus, studies that concurrently measure muscle protein metabolism and muscle mass and function will be instrumental in resolving these issues.

EW and DM wrote and revised the manuscript. Both authors read and approved the final version. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Thiebaud D, Jaccot E, Defronzo RA, Maeder E, Jequier E, Felber JP. The Effect of Graded Doses of Insulin on Total Glucose Uptake, Glucose Oxidation, and Glucose Storage in Man. doi: PubMed Abstract CrossRef Full Text Google Scholar.

Wang ZM, Ying Z, Bosy-Westphal A, Zhang J, Schautz B, Later W, et al. Specific metabolic rates of major organs and tissues across adulthood: Evaluation by mechanistic model of resting energy expenditure.

Am J Clin Nutr. Johnson MJ, Friedl KE, Frykman PN, Moore RJ. Loss of muscle mass is poorly reflected in grip strength performance in healthy young men. Med Sci Sport Exerc. Fleck SJ, Falkel JE.

Value of Resistance Training for the Reduction of Sports Injuries. Sport Med. Bell KE, von Allmen MT, Devries MC, Phillips SM. Muscle disuse as a pivotal problem in sarcopenia-related muscle loss and dysfunction.

J Frailty Aging. Greenhaff PL, Karagounis LG, Peirce N, Simpson EJ, Hazell M, Layfield R, et al. Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle.

Am J Physiol Endocrinol Metab. Tipton KD, Hamilton DL, Gallagher IJ. Assessing the role of muscle protein breakdown in response to nutrition and exercise in humans. Kim I-Y, Schutzler S, Schrader A, Spencer HJ, Azhar G, Ferrando AA, et al. The anabolic response to a meal containing different amounts of protein is not limited by the maximal stimulation of protein synthesis in healthy young adults.

Am J Physiol Metab. Mitchell CJ, Churchward-Venne TA, Cameron-Smith D, Phillips SM. What is the relationship between the acute muscle protein synthesis response and changes in muscle mass?

J Appl Physiol. Layman DK, Anthony TG, Rasmussen BB, Adams SH, Lynch CJ, Brinkworth GD, et al. Defining meal requirements for protein to optimize metabolic roles of amino acids. Zurlo F, Larson K, Bogardus C, Ravussin E.

Skeletal muscle metabolism is a major determinant of resting energy expenditure. J Clin Invest. Li R, Xia J, Zhang X, Gathirua-Mwangi WG, Guo J, Li Y, et al. Associations of muscle mass and strength with all-cause mortality among US older adults.

Paoli A, Tinsley G, Bianco A, Moro T. The influence of meal frequency and timing on health in humans: the role of fasting. Tinsley GM, La Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans.

Nutr Rev. Peterson CM. Intermittent fasting induces weight loss, but the effects on cardiometabolic health are modulated by energy balance. Pellegrini M, Cioffi I, Evangelista A, Ponzo V, Goitre I, Ciccone G, et al. Effects of time-restricted feeding on body weight and metabolism. A systematic review and meta-analysis.

Rev Endocr Metab Disord. Welton S, Minty R, O'Driscoll T, Willms H, Poirier D, Madden S, et al. Intermittent fasting and weight loss Systematic review. Can Fam Physician. PubMed Abstract Google Scholar. Rynders CA, Thomas EA, Zaman A, Pan Z, Catenacci VA, Melanson EL.

Effectiveness of intermittent fasting and time-restricted feeding compared to continuous energy restriction for weight loss. Varady KA, Bhutani S, Church EC, Klempel MC. Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults.

Sievert K, Hussain SM, Page MJ, Wang Y, Hughes HJ, Malek M, et al. Effect of breakfast on weight and energy intake: systematic review and meta-analysis of randomised controlled trials.

Ravussin E, Beyl RA, Poggiogalle E, Hsia DS, Peterson CM. Early time-restricted feeding reduces appetite and increases fat oxidation but does not affect energy expenditure in humans.

Areta JL, Burke LM, Camera DM, West DWD, Crawshay S, Moore DR, et al. Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficit.

Pasiakos SM, Vislocky LM, Carbone JW, Altieri N, Konopelski K, Freake HC, et al. Acute energy deprivation affects skeletal muscle protein synthesis and associated intracellular signaling proteins in physically active adults.

J Nutr. Anton S, Leeuwenburgh C. Fasting or caloric restriction for Healthy Aging. Exp Gerontol. Dethlefsen MM, Bertholdt L, Gudiksen A, Stankiewicz T, Bangsbo J, van Hall G, et al.

Training state and skeletal muscle autophagy in response to 36 h of fasting. Møller AB, Vendelbo MH, Christensen B, Clasen BF, Bak AM, Jørgensen JOL, et al. Physical exercise increases autophagic signaling through ULK1 in human skeletal muscle.

Abdulla H, Smith K, Atherton PJ, Idris I. Role of insulin in the regulation of human skeletal muscle protein synthesis and breakdown: a systematic review and meta-analysis. Wilkes EA, Selby AL, Atherton PJ, Patel R, Rankin D, Smith K, et al.

Blunting of insulin inhibition of proteolysis in legs of older subjects may contribute to age-related sarcopenia. Glynn EL, Fry CS, Drummond MJ, Dreyer HC, Dhanani S, Volpi E, et al. Muscle protein breakdown has a minor role in the protein anabolic response to essential amino acid and carbohydrate intake following resistance exercise.

Am J Physiol Regul Integr Comp Physiol. Staples AW, Burd NA, West DWD, Currie KD, Atherton PJ, Moore DR, et al. Carbohydrate does not augment exercise-induced protein accretion versus protein alone. Med Sci Sports Exerc.

Felig P, Marliss E, Pozefsky T, Cahill GF. Amino acid metabolism in the regulation of gluconeogenesis in man. Cahill GF. Starvation in man. Clin Endocrinol Metab. CrossRef Full Text Google Scholar. Felig P, Owen OE, Wahren J, Cahill GF.

Amino acid metabolism during prolonged starvation. Biolo G, Zhang XJ, Wolfe RR. Role of membrane transport in interorgan amino acid flow between muscle and small intestine. Odessey R, Khairallah EA, Goldbert AL. Origin and possible significance of alanine production by skeletal muscle.

J Biol. Bak AM, Møller AB, Vendelbo MH, Nielsen TS, Viggers R, Rungby J, et al. Differential regulation of lipid and protein metabolism in obese vs. Lean subjects before and after a h fast.

Carlson MG, Snead WL, Campbell PJ. Fuel and energy metabolism in fasting humans. Pozefsky T, Tancredi RG, Moxley RT, Dupre J, Tobin JD. How do you think about that? white plate with spoon and fork, Intermittent fasting concept, ketogenic diet, weight loss. Sign-up free to receive the 5 Tactics in my Longevity Toolkit delivered by email as a 5-day course.

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There are some more factors that comes into play beside the timing of your meals, things like a balanced diet, physical activity, managing stress levels and quality sleep. Intermittent fasting can be a great starting point to embark on a journey to a new me, being the initial spark for building new, healthy habits.

I have been fasting with the coach plan for 7 weeks. I have lost I recently started the treadmill just before I break my fast. However, I experience lightheadedness something awful immediately after I complete my 35 minute session.

I immediately down about 16oz of water and wait it out, but it is worrisome because it takes about minutes to get back to a normal state. Another option is keeping the length of the fasting periods but trying a less intense training. A general advice you should always follow is making sure to eat protein-rich and nutrient-rich meals during your fasting periods so that your body is best prepared for the training.

And of course, drinking enough is very important as well. We wish you all the best 🙏. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. This website uses cookies so that we can provide you with the best user experience possible.

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Skip to content. Intermittent fasting: building muscle mass or losing it? Here are the best tips: 1. Prefer working out at the end of your fasting period. Refrain from extremely long periods of fasting. Take good care of your body. Also, make sure not to eat too little and give your body enough time to recover.

Intermittent fasting and muscle building — this is how it works Intermittent fasting does NOT cause your muscles to atrophy. Author: Svenja Taubert. Ευχαριστώ πολλλυ. Γεια σου Χρήστο! Καταναλώστε τους υδατάνθρακες σας σε συνδυασμό με τις πρωτεΐνες κυρίως μετά την προπόνηση με βάρη στην αρχή του διατροφικού σας παραθύρου για να ενισχύσετε τις ορμόνες μυϊκής οικοδόμησης και να επιταχύνετε την αποκατάσταση 3.

Καλή τύχη! Τα καταφέρνεις! Nevertheless here are some recommendations that should take your progress to the next level: 1. Good luck! You got this! How can I turn abdominal section into a a learn section. Thank you, Sara.

Hi Sara! Hi Sean! Happy to hear that! Wishing you best of luck in your journey, Matt! Hi Michelle! You might want to give it a try and see for yourself how your body and mind change 🙂. Leave a Reply Cancel reply Your email address will not be published.

Close GDPR Cookie Settings Privacy Overview Strictly Necessary Cookies 3rd Party Cookies. Privacy Overview. Strictly Necessary Cookies Strictly necessary cookies are mandatory and cannot be deselected. Enable or Disable Cookies. These liberated AA enter the muscle's free intracellular pool whereby they may serve as a fuel source e.

Intramuscular free AA can also be released into circulation to be used by other tissues for synthesis, oxidation or as substrates for gluconeogenesis or ketogenesis e.

The prevailing view is that MPB plays a relatively minor role in the regulation of muscle mass in healthy humans 7 , although whole body protein breakdown that is influenced by higher turning over non-muscle protein pools may play a greater role in whole body net protein balance 8.

MPS is the sequencing of individual AA, made available through protein breakdown or exogenous sources e. When MPS exceeds MPB, a positive muscle net protein balance and, by extension anabolic environment, occurs.

In healthy adults, MPS is generally the more responsive variable and is the primary mediator of muscle net protein balance 7 and long-term changes in muscle mass 9. However, MPS is also important for replacing old, damaged, and mutated tissue proteins to maintain muscle quality The dietary strategy of intermittent fasting IF has become a topic of interest as an avenue to improve health 13 , 14 and is often divided into three subclasses: alternate-day fasting, whole-day fasting, and time-restricted eating TRE Alternate-day fasting involves alternating between ad libitum feeding days and very low energy intake e.

Whole-day fasting typically consists of 1—2 days of either complete abstinence from calories or severe restriction on fasting days plus ad libitum eating on the other days.

Thus, these IF strategies ultimately have a marked influence on the availability of postprandial dietary AA to support MPS and insulin to attenuate MPB. Many of the health promoting effects of IF are mediated by its effectiveness to induce weight loss For example, when IF is compared to controls with no intervention it generally results in weight loss 16 , 17 , although when compared to continuous energy restriction it is not superior in this outcome By first principles, this suggests that IF may be an elementary means of inducing energy deficiency with no further diet modifications, which may in the short term enhance dietary adherence This proposition is supported by the observation that skipping meals for up to 12 weeks is not compensated for by an increase in energy intake at subsequent meals consumed ad libitum Additionally, 18 h compared to 12 h fasting has demonstrated significantly lower ghrelin levels, which could contribute to the reported reduced desire to eat and increased fullness over a 24 h period Thus, as reduced energy availability can influence MPS rates 22 , 23 , IF strategies would need to consider the impact of total energy intake as a potential confounder contributing to the postprandial regulation of muscle protein turnover.

The following discussion outlines the current understanding of muscle protein metabolism in relation to the anticipated effect of IF as a dietary strategy on muscle mass and remodeling.

The breakdown and removal of muscle proteins is regulated by the ubiquitin-proteosome, calpain, and autophagy systems. While some benefits of IF are suggested to be mediated by increased autophagy 24 , induction of this system with short term fasting i.

In contrast, the ubiquitin-proteosomal and calpain systems are the primary systems regulating nutrient and contraction-induced changes in MPB in humans 7 and therefore will be the primary focus of the present review.

MPB is sensitive to feeding indirectly via the nutrient i. Maximal reductions in MPB require only modest elevations in plasma insulin concentrations i. This enhancement in MPB is demonstrated both with an overnight ~10 h fast 31 , 35 and prolonged 60—72 h fasting 36 — Given that IF typically involves a relatively prolonged fasting period i.

With the contraction-induced anabolic stimulus of resistance exercise there is an increase in MPB, although this primarily serves to provide AA precursors to support MPS in the fasted state 39 , Thus, resistance exercise may help retain muscle mass with IF by attenuating the negative muscle protein balance of fasted, rested muscle.

However, the exercise-induced increase in MPB is completely ablated with exogenous AA 41 , highlighting an important role for dietary AA to support muscle anabolism via attenuated catabolism as well.

Dietary AA are the primary stimulators of and precursors for the synthesis of new muscle proteins The equivalent of ~0. Importantly, after attainment of peak MPS i. Resistance exercise can prolong this postprandial muscle protein synthetic response i.

There is some evidence that energy deficiency may increase the acute meal protein intake required to maximize MPS 22 , 59 with estimates of ~0. While protein and AA may have an insulinogenic effect 29 , insulin only has a permissive effect for supporting maximal rates of MPS at rest and after exercise 29 , 30 , Thus, manipulating the amount and timing of dietary AA ingestion represents the most important nutritional variable to optimize MPS.

AA oxidation is generally low after an overnight fast but can increase with the duration of the fast i. While meal protein ingestion initiates a normal postprandial increase in AA oxidation 62 , dietary AA consumed in excess of their ability to be incorporated into new body especially muscle proteins are further irreversibly oxidized and their nitrogen excreted 43 — It has been suggested that the protein dose required to enhance whole body anabolism may be substantially greater than that required at the level of the muscle 63 , Accordingly, it is theorized that AA may be sequestered in splanchnic tissue primarily the gut to be later broken down and made available for synthesis of other tissues including muscle 63 , although this has yet to be demonstrated.

Thus, it is arguably more beneficial to consume acute meal protein intakes that maximize MPS yet minimize AA oxidation in order to optimize the daily dietary protein efficiency. In support of this notion, a recent study 21 comparing a 6 h feeding window with 3 meals to a 12 h feeding window with three meals protein intake of ~0.

A current limitation to the field of IF research is that no study, to the best of our knowledge, has measured muscle protein kinetics with alternate-day fasting or TRE.

However, information may be gleaned from studies investigating the impact of daily feeding pattern on protein metabolism. For example, consuming a balanced pattern of moderate protein-containing meals i.

These longer acute trials i. Collectively these acute studies support the concept that meal feeding pattern, irrespective of total protein intake, can influence whole body and muscle protein remodeling with large protein-containing meals stimulating postprandial AA oxidization rather than muscle tissue synthesis Figure 1.

Thus, based on the acute research to date, we argue that the lost opportunity for AA-induced MPS with more feedings may not be compensated for with fewer feedings at higher doses, as what is likely to occur with IF.

Figure 1. Schematic representation of the effect of different types of IF on acute muscle protein kinetics. Changes in muscle protein synthesis MPS and breakdown, amino acid oxidation OX , and circulating insulin concentration over 24 h at rest with whole day fasting A , TRE with one meal B , TRE with two meals over 6—8 h C , and an unrestricted eating window ~16 h with balanced meal pattern D.

Size of arrows reflects the relative protein and energy content of each meal. Shaded dark gray areas indicate time in net positive protein balance and light gray areas indicate time in net negative protein balance, which are summarized as net 24 h response in MPS, MPB, and net muscle protein balance NB; MPS—MPB E.

To our knowledge, no studies have examined whether adaptations in MPB, MPS, and AA oxidation take place over time to an IF protocol. Available literature suggests that following an overnight fast, the first meal demonstrates a similar MPS response to other meals 65 , including those preceded by a large protein containing mixed-meal 4 h prior Randomized control trials analyzing the effect of IF on fat free mass FFM demonstrate similar 19 , 69 — 81 outcomes compared to controls.

As IF often results in negative energy balance and weight loss 16 , 17 , when IF is compared to continuous energy restriction some systematic reviews suggest similar 82 or enhanced 83 preservation of FFM.

The divergence in some of these results may be due to the differences in the types of IF or the self-selected meal frequency by research participants. As discussed above, there is a broad range of IF protocols and those which result in fewer meals e.

It is also important to note that the length of the studies to date may not have been sufficient to elucidate differences in FFM given the sensitivity of body composition measurement modalities used and their ability to detect changes over short i. When IF is coupled with the potent anabolic stimulus of resistance exercise, a systematic review 93 observed no significant differences in FFM outcomes when compared to those resistance training with a normal diet.

However, given the normal diet group also did not experience gains in FFM, as would be expected, the length i. In fact, a recent study suggests that resistance training-induced gains in FFM over 12 weeks are enhanced with a balanced as compared to a skewed daily protein distribution in healthy young men despite consuming a moderate i.

Collectively, research to date evaluating the impact of IF on changes in body composition in young adults with and without prescribed exercise is equivocal. Therefore, it is important to acknowledge that the hypothesis of IF having consequences for muscle mass in particular may be complex.

Based on our current understanding of acute muscle protein metabolism, the potential effect of IF may be small relative to other lifestyle related variables e. A limitation in evaluating the impact of IF on muscle mass and function is the overreliance on whole body estimates of FFM, which have been questioned as to their ability to specifically delineate skeletal muscle mass given they include substantial organ and non-muscle lean tissue 98 , Therefore, future research should include muscle specific outcomes e.

If the hypothesis of more protein feedings per day being optimal for mass and remodeling based on the acute literature is true, IF may represent a dietary conundrum for some populations. While IF is often employed to reduce feeding intakes, restrict total energy intake, and maintain a low insulin profile to help mobilize and metabolize endogenous fat 13 , 14 , based on our current understanding of the acute, nutritional regulation of muscle protein turnover it seems antithetical to what would presumably optimize muscle protein synthesis and net muscle protein balance as summarized in Figure 1.

There is also evidence that reduced energy availability, which often occurs in tandem with IF 16 , 17 , 20 , increases the per meal protein intake required to maximize muscle protein synthesis 22 , Thus, while this would ostensibly favor larger protein meals that may be characteristic of TRE in particular, it does not preclude the need to consume protein more frequently, which would ultimately also help meet the higher recommended daily protein intakes that enhance muscle and FFM retention with weight loss 59 , If the acute effects of IF lead to detrimental long-term outcomes for muscle, whole-day, and alternate-day fasting would have the greatest consequential effect on muscle mass and remodeling.

This is due to the prolonged period with greater MPB and lower MPS compounded by the greater energy deficient state likely to occur relative to TRE In consideration of TRE, fewer meals would likely have a greater negative impact on muscle protein turnover Figure 1.

If TRE were to be employed, the hypothesis to improve muscle mass and remodeling suggests that protein intake should be consumed at a daily intake of at least 1. In conclusion, while IF may represent an option for a variety of populations to promote fat loss and improve aspects of metabolic health, additional research needs to focus on the impact of meal frequency on the quantity and quality of muscle mass.

Inasmuch as IF may be purported as the enemy of body fat, future research must ensure this is not also the case for muscle.

Thus, studies that concurrently measure muscle protein metabolism and muscle mass and function will be instrumental in resolving these issues. EW and DM wrote and revised the manuscript. Both authors read and approved the final version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Thiebaud D, Jaccot E, Defronzo RA, Maeder E, Jequier E, Felber JP. The Effect of Graded Doses of Insulin on Total Glucose Uptake, Glucose Oxidation, and Glucose Storage in Man.

doi: PubMed Abstract CrossRef Full Text Google Scholar. Wang ZM, Ying Z, Bosy-Westphal A, Zhang J, Schautz B, Later W, et al. Specific metabolic rates of major organs and tissues across adulthood: Evaluation by mechanistic model of resting energy expenditure.

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Associations of muscle mass and strength with all-cause mortality among US older adults. Paoli A, Tinsley G, Bianco A, Moro T. The influence of meal frequency and timing on health in humans: the role of fasting. Tinsley GM, La Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans.

Nutr Rev. Peterson CM. Intermittent fasting induces weight loss, but the effects on cardiometabolic health are modulated by energy balance.

Pellegrini M, Cioffi I, Evangelista A, Ponzo V, Goitre I, Ciccone G, et al. Effects of time-restricted feeding on body weight and metabolism. A systematic review and meta-analysis. You may wonder if you should take protein, creatine or other supplements such as BCAAs during your fasting periods.

This is primarily due to a concern that these periods will negatively affect your muscles. However, as discussed in this article, short periods of fasting are probably not a concern for muscle loss 7 , This mild stress on your body may strengthen it to fight off larger threats, such as disease, in the future If you take supplements containing amino acids including protein and BCAA supplements during your fasting periods, you are signaling your body that you are not fasting Additionally, if you get enough protein in your feeding period, fasting for 16 hours does not appear to be detrimental to your muscles, compared to a normal diet Overall, it is unlikely that you need to take dietary supplements during your fasting periods.

Some supplements, like creatine, may even be more beneficial when taken with food Intermittent fasting is a popular dietary strategy that uses fasting periods longer than a typical overnight fast.

There are several different types of intermittent fasting, including time-restricted eating, alternate-day fasting, periodic fasting, the diet and religious fasting. Nevertheless, adding exercise — especially weight training — to your intermittent fasting program can help you maintain muscle.

However, whether or not you exercise during fasting periods is up to you. Fasting probably does not add benefits, and it could compromise your optimal exercise performance.

Aiming for a slow rate of weight loss and consuming enough protein can help you maintain muscle during intermittent fasting. There are many misconceptions about intermittent fasting and meal frequency. This article debunks the 11 most common myths.

Learn about various intermittent fasting benefits. Intermittent fasting may help reduce cancer side effects and inflammation, extend life span, and…. This is a detailed guide to intermittent fasting IF.

Studies show that it can help you lose weight, improve health and perhaps even live longer. Time-restricted eating is a form of fasting that limits eating to a certain number of hours each day. This guide explains the benefits and how to do…. Intermittent fasting is a very popular health and fitness trend.

It involves eating patterns that cycle between periods of eating and fasting. Discover which diet is best for managing your diabetes. Getting enough fiber is crucial to overall gut health.

Let's look at some easy ways to get more into your diet:. A Quiz for Teens Are You a Workaholic? How Well Do You Sleep? Health Conditions Discover Plan Connect. Nutrition Evidence Based Does Intermittent Fasting Make You Gain or Lose Muscle? By Grant Tinsley, Ph. Types of Intermittent Fasting.

Share on Pinterest. Do You Lose Muscle When Fasting? This is true of weight loss caused by both intermittent fasting and other diets.

Summary When you lose weight, you typically lose both fat mass and lean mass, especially if you do not perform regular exercise. Intermittent fasting does not appear to cause more muscle loss than other weight loss diets.

This is likely because weight loss is the topic of interest in most studies on these diets. Summary Intermittent fasting requires you to eat fewer calories and eat less frequently than a normal diet.

Because of this, you may have trouble getting enough calories and protein to build muscle. Overall, this may not be the best diet for muscle gain. Weight Training Can Help You Maintain Muscle During Intermittent Fasting.

Summary Weight training during intermittent fasting may help you maintain muscle, even when losing fat. Other forms of exercise, such as using a stationary bike or elliptical, may also be beneficial.

Should You Exercise While Fasted? Overall, it seems that exercising while fasted may be a matter of personal preference.

Summary Exercising while fasted is probably not more beneficial than exercising at other times. In fact, it is possible that it could decrease your performance.