Journal of the International Society of Sports Nutrition volume 5 , Article number: 17 Cite this article. Metrics details. An Erratum to this article was published on 14 October Position Statement: The position of the Society regarding nutrient timing and the intake of carbohydrates, proteins, and fats in reference to healthy, exercising individuals is summarized by the following eight points: 1.

Adding PRO to create a CHO:PRO ratio of 3 — may increase endurance performance and maximally promotes glycogen re-synthesis during acute and subsequent bouts of endurance exercise. Ingesting CHO alone or in combination with PRO during resistance exercise increases muscle glycogen, offsets muscle damage, and facilitates greater training adaptations after either acute or prolonged periods of supplementation with resistance training.

Post-exercise ingestion immediately to 3 h post of amino acids, primarily essential amino acids, has been shown to stimulate robust increases in muscle protein synthesis, while the addition of CHO may stimulate even greater levels of protein synthesis. The addition of creatine Cr 0. Nutrient timing incorporates the use of methodical planning and eating of whole foods, nutrients extracted from food, and other sources.

The timing of the energy intake and the ratio of certain ingested macronutrients are likely the attributes which allow for enhanced recovery and tissue repair following high-volume exercise, augmented muscle protein synthesis, and improved mood states when compared with unplanned or traditional strategies of nutrient intake.

Previous research has demonstrated that the timed ingestion of carbohydrate, protein, and fat may significantly affect the adaptive response to exercise.

The overall concept of macronutrient ratio planning for the diets of athletes is not addressed directly within this position stand, as there is no one recommendation which would apply to all individuals.

However, the ISSN refers the reader to the latest Institute of Medicine Guidelines for Macronutrient intake as a source of more general information [ 1 ]. The purpose of this collective position statement is to highlight, summarize, and assess the current scientific literature, and to make scientific recommendations surrounding the timed ingestion of carbohydrates CHO , protein PRO , and fat.

The enclosed recommendations are suitable for researchers, practitioners, coaches and athletes who may use nutrient timing as a means to achieve optimum health and performance goals. This position stand is divided into three primary sections: pre-exercise, during exercise and post-exercise.

Each section concludes with several bullet points that highlight the key findings from each of the areas. Nutritional considerations prior to exercise have traditionally examined the administration of CHO to maximize endogenous glycogen stores [ 2 — 6 ] and maintain serum glucose levels during endurance exercise [ 4 , 7 ].

More recently, studies have begun to provide data supporting the contention that pre-exercise ingestion of CHO, amino acids, PRO, and creatine Cr prior to resistance training are effective modalities for enhancing exercise training adaptations [ 8 — 12 ] and decreasing exercise associated muscle damage [ 12 , 13 ].

As glycogen levels diminish, exercise intensity, and work output decrease [ 14 ], and frequently muscle tissue breakdown and immunosuppression ensues [ 16 , 17 ]. Due to the well-established connection between negative body changes and the depletion of glycogen stores, the concept of CHO loading is likely the oldest form of all the nutrient timing practices.

Traditional CHO loading studies utilized a glycogen depletion phase typically lasting 3 — 6 days prior to increasing CHO intake [ 2 — 5 , 18 ].

Maximal levels of glycogen storage, however, may be achieved after just 1 — 3 days of consuming a high-CHO diet while minimizing physical activity [ 2 , 4 ]. Serum glucose levels increased during exercise in the high-CHO condition with no changes evident in the low-CHO condition.

Finally, post-exercise glucose levels were also significantly greater for the high-CHO condition when compared to the low-CHO condition, suggesting that individuals subjected to the high-CHO condition were better able to sustain blood glucose levels. Another study by Bussau et al.

Research involving the ingestion of single high CHO feedings has also demonstrated the promotion of higher levels of muscle glycogen and an improvement of blood glucose maintenance euglycemia , though changes in performance have been equivocal [ 14 , 19 — 22 ].

In a study completed by Coyle et al. In contrast, Febbraio et al. Earnest et al. compared the effects of the pre-exercise ingestion of honey low-glycemic , dextrose high-glycemic and a placebo over a kilometer time trial in a crossover fashion. In general, research involving CHO ingestion within an hour prior to exercise demonstrates equivocal results regarding changes in performance, but studies have routinely shown the ability of CHO ingestion to maximize glycogen utilization and promote CHO oxidation.

Hawley and Burke [ 22 ] summarized several studies that administered some form of CHO within one hour prior to exercise: one study reported a decrease in performance [ 23 ], three studies reported an increase in performance [ 24 — 26 ] and five studies reported no effect [ 21 , 27 — 30 ] Additional File 1.

The authors concluded that the effect on the net PRO status breakdown vs. synthesis was greater when the supplement was ingested before exercise. They speculated that the increased serum amino acid levels present when tissue blood flow levels were significantly increased, likely led to an increase in PRO synthesis [ 9 ].

In this case the authors concluded that a pro-anabolic response was found when the whey PRO was ingested both before and after resistance exercise, but no differences were found between the two administration times [ 31 ].

Findings from these studies suggest that ingestion of amino acids and CHO, or whey PRO, before resistance exercise can maximally stimulate PRO synthesis after completion of the exercise bout [ 9 , 31 ]. Many studies have explored the use of pre-exercise PRO and CHO ingestion in preventing acute exercise-induced muscle damage [ 13 ], as well as the damage that may occur during prolonged periods of regular resistance training [ 8 , 10 — 12 , 32 ].

Although the authors reported that the level of the muscle damage marker creatine kinase had increased and maximal force production of the muscle was reduced, the administration or timing of the nutrients did not appear to alter these markers of muscle damage [ 13 ].

On both exercise days, the supplement was ingested 30 min prior to beginning the exercise bout. Additionally, multi-nutrient supplementation significantly increased serum levels of both growth hormone and free and total testosterone during and after the exercise bouts [ 12 ].

These latter findings suggest that pre-exercise ingestion may also create a favorable anabolic hormone environment.

In another study involving unilateral resistance training, pre-exercise supplementation of whey PRO and leucine resulted in greater increases in maximal strength [ 11 ]. One study compared the pre-exercise and post-exercise ingestion of 1.

The authors found that PRO supplementation significantly increased strength and lean mass when compared to placebo, but no differences were found between the two forms of PRO [ 32 ]. Individuals consuming the protein supplement experienced greater increases in body mass, fat-free mass, strength, serum levels of IGF-1, and intramuscular levels of IGF-1 mRNA, myosin heavy chain I and IIa expression, and myofibrillar protein content [ 10 ].

Collectively, the last two studies mentioned provide additional support for the concept that ingesting PRO before and after exercise can promote a greater training adaptation than consuming only an isoenergetic CHO placebo [ 10 , 32 ].

A study by Cribb and Hayes [ 8 ] used two different feeding strategies to determine the impact of nutrient timing, in regards to an exercise bout, for changes in strength, muscle hypertrophy and body composition.

Significantly greater increases in lean body mass, 1 RM strength, type II muscle fiber cross-sectional area, and higher muscle Cr and glycogen levels were found when the supplements were consumed immediately before and after workouts [ 8 ].

In summary, ingestion of amino acids or PRO, either alone or in combination with CHO, in close temporal proximity to a bout of resistance exercise, appears to significantly increase muscle PRO synthesis [ 9 , 31 ]. Furthermore, adopting this strategy during a resistance training program results in greater increases in 1 RM strength and a leaner body composition [ 8 , 10 — 12 , 32 ].

Depletion of glycogen is associated with increased levels of muscle tissue breakdown and suppression of the immune system [ 16 , 17 ]. Much like the consideration of pre-exercise nutrient supplementation, a majority of the literature which has examined the impact of nutrient administration during exercise has focused on aerobic exercise [ 33 — 36 ], with a lesser emphasis on nutrient administration during resistance exercise [ 37 — 41 ].

The initial research which dealt with nutrient administration during exercise scrutinized the optimal delivery of CHO in an effort to sustain blood glucose. Widrick and colleagues [ 35 ] had participants complete 70 km of self-paced time trials under four different conditions: 1.

high glycogen low glycogen CHO administration maintained blood glucose, while blood glucose declined significantly under the non-CHO conditions. Results from this study suggest exogenous CHO delivery during training is not as important if baseline glycogen levels are high, and if glycogen levels are low, CHO ingestion during endurance exercise will likely improve performance.

In a similar investigation, nine trained athletes consumed both a CHO and a non-CHO control solution while completing a 90 min bout of high-intensity intermittent running [ 34 ].

The CHO solution was 6. When CHO was ingested the participants were able to run significantly longer when compared to the control condition, providing additional evidence that CHO availability may be important for continued exercise performance [ 34 ].

An additional study highlighting the importance of CHO delivery during endurance exercise was completed by Febrraio et al.

in [ 33 ]. This study, like several in this investigative field, utilized trained cyclists as participants. Blood glucose appearance and disappearance, and time trial performance was greater in the CC and PC trials when compared to the PP condition.

The authors concluded that pre-exercise ingestion of CHO improves performance only when CHO ingestion is maintained throughout exercise, and ingestion of CHO during min of cycling improves subsequent time trial performance [ 33 ].

Similarly, a study by Fielding et al. reported that more frequent intake of CHO These findings conflicted with those of Burke et al. Lastly, a study investigated the ability of a consumed CHO-gel preparation to maintain blood glucose levels and enhance performance during a high-intensity intermittent run in soccer players [ 45 ].

As with previous studies that have used CHO solutions, the CHO-gel promoted higher levels of blood glucose and facilitated improved performance in the intermittent bout of running when compared to the placebo [ 45 ].

In summary, the weight of evidence suggests that the ingestion of CHO during endurance type exercise is a well-established strategy to sustain blood glucose levels, spare glycogen [ 6 ], and potentially promote greater levels of performance. The interested reader is encouraged to consult the following reviews [ 15 , 46 — 49 ].

A fairly novel area of research has examined the impact of mixing various forms of CHO in an effort to promote greater levels of CHO oxidation during prolonged exercise. It is well accepted that peak rates of CHO oxidation are commonly around 1 gram of CHO per minute or 60 grams per hour [ 15 , 48 ].

An increase in exogenous CHO availability, and subsequent oxidation, will result in improved maintenance of blood glucose and less reliance on liver and muscle glycogen stores.

Indeed, findings from this research team have regularly reported enhanced CHO oxidation rates, from 1. It should be noted that fructose is not as often used as a CHO supplement due to the potential for gastrointestinal upset. The addition of PRO to CHO during exercise has also been investigated as a means to improve performance and facilitate recovery.

During each session, participants consumed either a placebo, a 7. While the CHO only group increased time to exhaustion A study by Saunders et al. Cyclists exercised to exhaustion on two different occasions separated by 12 — 15 h. During exercise, all participants ingested a 7.

CHO intake levels were the same for each group, although the total caloric intake was different due to the energy supplied by the added PRO. PRO balance was negative during the CHO condition, but these findings were partially reversed protein balance was still negative, but to a lesser degree when PRO was added to the supplement.

The authors concluded that combined ingestion of PRO and CHO improves net PRO balance at rest, as well as during exercise and post-exercise recovery [ 36 ]. Delivering nutrients during single bouts of resistance exercise has been used to determine their impact on changes in muscle glycogen [ 40 ], mitigation of muscle damage [ 13 , 37 ], and promotion of an anabolic response [ 38 , 39 , 41 ].

Over the course of an estimated 40 min resistance training workout using the lower body, 1. The authors concluded that CHO supplementation before and during resistance exercise can maintain muscle glycogen stores and enhance the benefits of training [ 40 ].

Nutrient feedings during exercise have also been researched for their ability to offset muscle damage after intense resistance training [ 37 ].

The authors concluded that the suppression of PRO breakdown and cortisol levels may help to promote accretion of muscle PRO with prolonged periods of resistance training and supplementation.

Their final study examined the influence of a 12 week resistance training program in combination with CHO and EAA supplementation.

Serum insulin and cortisol, urinary markers of PRO breakdown, and muscle cross-sectional area were measured [ 41 ]. Similarly, a study by Beelen et al.

CHO administration becomes even more important when muscle glycogen levels are low at the onset of exercise [ 35 , 42 ]. Many nutritional interventions have been considered to enhance recovery from exercise.

The body of published research supports the practice of ingesting nutrients to enhance performance for both endurance and resistance training athletes. There is also sound evidence which supports the value of post-exercise nutritional supplementation as a means of improving the recovery of intramuscular glycogen, providing a positive stimulation for acute changes in amino acid kinetics and improvement of the net PRO balance, as well as enhancing the overall adaptation to resistance training.

Athletes who ingest 1. within 30 minutes after exercise have been shown to experience a greater rate of muscle glycogen re-synthesis than when supplementation is delayed by two hours, largely due to a greater sensitivity of muscle to insulin [ 61 ].

Additionally, both solid and liquid forms of CHO promote similar levels of glycogen re-synthesis [ 15 , 62 , 63 ]. Moreover, different forms of CHO have different effects on insulin levels, with fructose ingestion being associated with lower levels of glycogen re-synthesis than other forms of simple carbohydrates [ 64 ].

If an athlete is glycogen-depleted after exercise, a CHO intake of 0. Similarly, maximal glycogen re-synthesis rates have been achieved when 1. Consequently, frequent feedings of CHO in high amounts over the 4 — 6 hours following exercise is recommended to ensure recovery of muscle and liver glycogen [ 15 , 49 ].

Several studies have suggested that adding PRO to CHO supplementation after exercise may help to promote greater recovery of muscle glycogen and attenuate muscle damage. Ivy and colleagues [ 69 ] instructed cyclists to complete a 2. While glycogen replenishment did not differ between the two CHO conditions low CHO [ Both authors concluded that ingestion of either CHO preparation resulted in greater restoration of muscle glycogen when compared to a placebo.

Furthermore, the availability of essential amino acids EAA following exercise, especially the branched-chain amino acids, have been reported to influence recovery by optimizing PRO re-synthesis as well as glycogen re-synthesis rates after exercise [ 61 , 69 , 70 , 72 — 74 ].

As these studies suggest, the ingestion of CHO 1 — 1. A single bout of resistance training modestly stimulates PRO synthesis, but also further stimulates PRO breakdown resulting in an overall negative PRO balance after exercise [ 75 , 76 ]; an effect which shifts PRO balance more towards neutral as training status progresses [ 76 ].

Infusion or ingestion of amino acids increases amino acid concentrations at rest or after resistance exercise [ 77 ]. In addition, providing CHO in combination with amino acids immediately before or after exercise may further increase amino acid availability and post-exercise PRO synthesis [ 73 , 78 ].

Consequently, increasing the concentration and availability of amino acids in the blood is an important consideration when attempting to promote increases in lean tissue and improve body composition with resistance training [ 77 , 79 ].

Ingestion of a large dose of CHO g alone and within 1 h after resistance exercise causes marginal improvements in overall PRO synthesis while maintaining a negative net PRO balance [ 78 ]. While no studies have found CHO to be detrimental, it is not the ideal nutrient in isolation to consume after resistance exercise.

Its inclusion, however, is an important consideration regarding stimulation of glycogen re-synthesis and enhanced palatability [ 69 , 72 ].

The EAAs, however, in dosages ranging from 6 — 40 grams have routinely been shown to play a primary role in promoting muscle PRO synthesis [ 74 , 80 ], though adding CHO to them may enhance this effect [ 9 , 81 ]. Regarding post-exercise timing, ingestion of amino acids after resistance exercise has been shown at many different time points to stimulate increases in muscle PRO synthesis, cause minimal changes in PRO breakdown and increase overall PRO balance [ 74 , 75 , 80 ].

Unfortunately, the optimal time point for supplementation has not yet been demonstrated. Similar changes have been found in studies that have administered amino acids alone, or with CHO, immediately, 1 h, 2 h and 3 h after exercise [ 9 , 74 , 79 , 81 ].

Levenhagen et al. They reported significantly greater levels of PRO synthesis when the nutrients were ingested immediately before the exercise bout.

In summary, the optimal dosage and ratio of EAAs and CHO necessary to optimize protein balance is not currently known. A summary of relevant findings is provided in Table 2 Additional File 2. In an attempt to stimulate greater adaptations associated with resistance training researchers have investigated the impact of administering varying combinations of CHO and PRO after 1 — 3 h post-exercise each exercise bout over the course of training [ 8 , 10 , 32 , 84 — 91 ].

The collective findings of these studies support the rationale for post-exercise administration of CHO and PRO to facilitate greater improvements in strength and body composition. Additionally, PRO source may be an important consideration as studies have suggested that whey PRO may exhibit a faster kinetic digestive pattern when compared to casein PRO [ 92 , 93 ].

Furthermore, this faster kinetic pattern for whey PRO is responsible for greater increases in PRO synthesis upon ingestion, with little to no impact over PRO breakdown. Casein PRO, on the other hand, releases its amino acids at a slower rate from the gut. This kinetic pattern results in little control over PRO synthesis, but a powerful attenuation of PRO breakdown.

When both of these milk PRO sources are compared using area under the curve analysis, results suggest that casein may be responsible for a greater overall improvement in PRO balance when compared to whey [ 92 , 93 ].

Cr is a popular dietary supplement that has been heavily researched for its ability to increase performance and facilitate positive training adaptations [ 94 , 95 ].

For example, Tarnopolsky et al. Changes in fat-free mass, muscle fiber area, 1 RM, and isokinetic strength improved in both groups, but were not different among groups. Another study had participants resistance train for 11 weeks while consuming daily one of the following: 1 0. Supplementation in the first three groups resulted in greater increases in 1 RM strength and muscle hypertrophy when compared to CHO only, but no differences were found among the groups ingesting Cr in conjunction with either CHO or PRO [ 85 ].

In contrast, two published studies have suggested that the addition of Cr may be responsible for greater increases in muscle hypertrophy.

The first study had participants complete heavy resistance training for 10 weeks while ingesting one of the following isoenergetic groups: 1 1. Similarly, Kerksick and colleagues [ 88 ] had participants complete 12 weeks of resistance training while ingesting a blend of whey and casein PRO, with or without Cr.

While all groups saw increases in strength and muscle mass, those groups ingesting Cr with the PRO blend experienced greater gains in body mass and fat-free mass. Though these findings are somewhat mixed, the available data does provide support that adding Cr to a post-exercise regimen of CHO and PRO may help to facilitate greater improvements in body composition during resistance training [ 84 , 85 , 88 , 90 ].

The addition of CHO may increase PRO synthesis even more, while pre-exercise consumption may result in the best response of all [ 9 ]. The scientific literature associated with nutrient timing is an extremely popular, and thus ever-changing, area of research.

Upon reviewing the available literature, the following conclusions can be drawn at this point in time:. whey and casein exhibit different kinetic digestion patterns and may subsequently differ in their support of training adaptations. However, including small amounts of fat does not appear to be harmful, and may help to control glycemic responses during exercise.

Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. aspx ]. Bussau VA, Fairchild TJ, Rao A, Steele P, Fournier PA: Carbohydrate loading in human muscle: an improved 1 day protocol.

Eur J Appl Physiol. Article CAS PubMed Google Scholar. Goforth HW, Laurent D, Prusaczyk WK, Schneider KE, Petersen KF, Shulman GI: Effects of depletion exercise and light training on muscle glycogen supercompensation in men.

Am J Physiol Endocrinol Metab. Article PubMed Central CAS PubMed Google Scholar. Kavouras SA, Troup JP, Berning JR: The influence of low versus high carbohydrate diet on a min strenuous cycling exercise.

Int J Sport Nutr Exerc Metab. PubMed Google Scholar. Sherman WM, Costill DL, Fink WJ, Miller JM: Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance.

Int J Sports Med. Yaspelkis BB, Patterson JG, Anderla PA, Ding Z, Ivy JL: Carbohydrate supplementation spares muscle glycogen during variable-intensity exercise. J Appl Physiol.

CAS PubMed Google Scholar. Coyle EF, Coggan AR, Hemmert MK, Ivy JL: Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. Cribb PJ, Hayes A: Effects of supplement timing and resistance exercise on skeletal muscle hypertrophy. Med Sci Sports Exerc.

Article PubMed Google Scholar. Tipton KD, Rasmussen BB, Miller SL, Wolf SE, Owens-Stovall SK, Petrini BE, Wolfe RR: Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise. Willoughby DS, Stout JR, Wilborn CD: Effects of resistance training and protein plus amino acid supplementation on muscle anabolic, mass, and strength.

Amino Acids. Coburn JW, Housh DJ, Housh TJ, Malek MH, Beck TW, Cramer JT, Johnson GO, Donlin PE: Effects of leucine and whey protein supplementation during eight weeks of unilateral resistance training. J Strength Cond Res.

Kraemer WJ, Hatfield DL, Spiering BA, Vingren JL, Fragala MS, Ho JY, Volek JS, Anderson JM, Maresh CM: Effects of a multi-nutrient supplement on exercise performance and hormonal responses to resistance exercise.

White JP, Wilson JM, Austin KG, Greer BK, St John N, Panton LB: Effect of carbohydrate-protein supplement timing on acute exercise-induced muscle damage. J Int Soc Sports Nutr. Article PubMed Central PubMed Google Scholar. Coyle EF, Coggan AR, Hemmert MK, Lowe RC, Walters TJ: Substrate usage during prolonged exercise following a preexercise meal.

Tarnopolsky MA, Gibala M, Jeukendrup AE, Phillips SM: Nutritional needs of elite endurance athletes. Part I: Carbohydrate and fluid requirements.

Eur J Sport Sci. Article Google Scholar. Joint Position Statement: nutrition and athletic performance. American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada.

Gleeson M, Nieman DC, Pedersen BK: Exercise, nutrition and immune function. J Sports Sci. Sherman WM, Costill DL, Fink WJ, Hagerman FC, Armstrong LE, Murray TF: Effect of a Earnest CP, Lancaster S, Rasmussen C, Kerksick C, Lucia A, Greenwood M, Almada A, Cowan P, Kreider R: Low vs.

high glycemic index carbohydrate gel ingestion during simulated km cycling time trial performance. Febbraio MA, Keenan J, Angus DJ, Campbell SE, Garnham AP: Preexercise carbohydrate ingestion, glucose kinetics, and muscle glycogen use: effect of the glycemic index.

Febbraio MA, Stewart KL: CHO feeding before prolonged exercise: effect of glycemic index on muscle glycogenolysis and exercise performance. Hawley JA, Burke LM: Effect of meal frequency and timing on physical performance.

Brit J Nutr. Foster C, Costill DL, Fink WJ: Effects of preexercise feedings on endurance performance. Med Sci Sports. Okano G, Takeda H, Morita I, Katoh M, Mu Z, Miyake S: Effect of pre-exercise fructose ingestion on endurance performance in fed men. Sherman WM, Peden MC, Wright DA: Carbohydrate feedings 1 h before exercise improves cycling performance.

Am J Clin Nutr. Thomas DE, Brotherhood JR, Brand JC: Carbohydrate feeding before exercise: effect of glycemic index. Chryssanthopoulos C, Hennessy LC, Williams C: The influence of pre-exercise glucose ingestion of endurance running capacity.

Br J Sports Med. Devlin JT, Calles-Escandon J, Horton ES: Effects of preexercise snack feeding on endurance cycle exercise. Hargreaves M, Costill DL, Fink WJ, King DS, Fielding RA: Effect of pre-exercise carbohydrate feedings on endurance cycling performance. McMurray RG, Wilson JR, Kitchell Bs: The effects of fructose and glucose on high intensity endurance performance.

Res Quart for Exerc and Sport. Tipton KD, Elliott TA, Cree MG, Wolf SE, Sanford AP, Wolfe RR: Ingestion of casein and whey proteins results in muscle anabolism after resistance exercise.

Candow DG, Burke NC, Smith-Palmer T, Burke DG: Effect of whey and soy protein supplementation combined with resistance training in young adults. Febbraio MA, Chiu A, Angus DJ, Arkinstall MJ, Hawley JA: Effects of carbohydrate ingestion before and during exercise on glucose kinetics and performance.

Nicholas CW, Williams C, Lakomy HK, Phillips G, Nowitz A: Influence of ingesting a carbohydrate-electrolyte solution on endurance capacity during intermittent, high-intensity shuttle running.

Widrick JJ, Costill DL, Fink WJ, Hickey MS, McConell GK, Tanaka H: Carbohydrate feedings and exercise performance: effect of initial muscle glycogen concentration. Koopman R, Pannemans DL, Jeukendrup AE, Gijsen AP, Senden JM, Halliday D, Saris WH, van Loon LJ, Wagenmakers AJ: Combined ingestion of protein and carbohydrate improves protein balance during ultra-endurance exercise.

Baty JJ, Hwang H, Ding Z, Bernard JR, Wang B, Kwon B, Ivy JL: The effect of a carbohydrate and protein supplement on resistance exercise performance, hormonal response, and muscle damage. Haff GG, Koch AJ, Potteiger JA, Kuphal KE, Magee LM, Green SB, Jakicic JJ: Carbohydrate supplementation attenuates muscle glycogen loss during acute bouts of resistance exercise.

McConell G, Snow RJ, Proietto J, Hargreaves M: Muscle metabolism during prolonged exercise in humans: influence of carbohydrate availability.

Fielding RA, Costill DL, Fink WJ, King DS, Hargreaves M, Kovaleski JE: Effect of carbohydrate feeding frequencies and dosage on muscle glycogen use during exercise. Burke LM, Claassen A, Hawley JA, Noakes TD: Carbohydrate intake during prolonged cycling minimizes effect of glycemic index of preexercise meal.

Patterson SD, Gray SC: Carbohydrate-gel supplementation and endurance performance during intermittent high-intensity shuttle running. Dennis SC, Noakes TD, Hawley JA: Nutritional strategies to minimize fatigue during prolonged exercise: fluid, electrolyte and energy replacement.

J Sports Sciences. Article CAS Google Scholar. Jeukendrup AE: Carbohydrate intake during exercise and performance. Jeukendrup AE, Jentjens R: Efficacy of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research.

Workouts consisted of 3—4 sets of 6—10 repetitions of multiple exercises for the entire body. Training was carried out on 4 day-a-week split routine with intensity progressively increased over the course of the study period. After 10 weeks, no significant differences were noted between groups with respect to body mass and lean body mass.

The study was limited by its use of DXA to assess body composition, which lacks the sensitivity to detect small changes in muscle mass compared to other imaging modalities such as MRI and CT [ 76 ].

Hulmi et al. High-intensity resistance training was carried out over 21 weeks. Supplementation was provided before and after exercise.

At the end of the study period, muscle CSA was significantly greater in the protein-supplemented group compared to placebo or control. A strength of the study was its long-term training period, providing support for the beneficial effects of nutrient timing on chronic hypertrophic gains.

Again, however, it is unclear whether enhanced results associated with protein supplementation were due to timing or increased protein consumption. Most recently, Erskine et al. Subjects were 33 untrained young males, pair-matched for habitual protein intake and strength response to a 3-week pre-study resistance training program.

After a 6-week washout period where no training was performed, subjects were then randomly assigned to receive either a protein supplement or a placebo immediately before and after resistance exercise. Training consisted of 6— 8 sets of elbow flexion carried out 3 days a week for 12 weeks.

No significant differences were found in muscle volume or anatomical cross-sectional area between groups. The hypothesis is based largely on the pre-supposition that training is carried out in a fasted state. During fasted exercise, a concomitant increase in muscle protein breakdown causes the pre-exercise net negative amino acid balance to persist in the post-exercise period despite training-induced increases in muscle protein synthesis [ 36 ].

Thus, in the case of resistance training after an overnight fast, it would make sense to provide immediate nutritional intervention--ideally in the form of a combination of protein and carbohydrate--for the purposes of promoting muscle protein synthesis and reducing proteolysis, thereby switching a net catabolic state into an anabolic one.

Over a chronic period, this tactic could conceivably lead cumulatively to an increased rate of gains in muscle mass. This inevitably begs the question of how pre-exercise nutrition might influence the urgency or effectiveness of post-exercise nutrition, since not everyone engages in fasted training.

Tipton et al. Although this finding was subsequently challenged by Fujita et al. These data indicate that even minimal-to-moderate pre-exercise EAA or high-quality protein taken immediately before resistance training is capable of sustaining amino acid delivery into the post-exercise period.

Given this scenario, immediate post-exercise protein dosing for the aim of mitigating catabolism seems redundant. The next scheduled protein-rich meal whether it occurs immediately or 1—2 hours post-exercise is likely sufficient for maximizing recovery and anabolism.

On the other hand, there are others who might train before lunch or after work, where the previous meal was finished 4—6 hours prior to commencing exercise. This lag in nutrient consumption can be considered significant enough to warrant post-exercise intervention if muscle retention or growth is the primary goal.

Layman [ 77 ] estimated that the anabolic effect of a meal lasts hours based on the rate of postprandial amino acid metabolism. However, infusion-based studies in rats [ 78 , 79 ] and humans [ 80 , 81 ] indicate that the postprandial rise in MPS from ingesting amino acids or a protein-rich meal is more transient, returning to baseline within 3 hours despite sustained elevations in amino acid availability.

In light of these findings, when training is initiated more than ~3—4 hours after the preceding meal, the classical recommendation to consume protein at least 25 g as soon as possible seems warranted in order to reverse the catabolic state, which in turn could expedite muscular recovery and growth.

However, as illustrated previously, minor pre-exercise nutritional interventions can be undertaken if a significant delay in the post-exercise meal is anticipated.

An interesting area of speculation is the generalizability of these recommendations across training statuses and age groups. Burd et al. This suggests a less global response in advanced trainees that potentially warrants closer attention to protein timing and type e.

In addition to training status, age can influence training adaptations. The mechanisms underlying this phenomenon are not clear, but there is evidence that in younger adults, the acute anabolic response to protein feeding appears to plateau at a lower dose than in elderly subjects.

Illustrating this point, Moore et al. In contrast, Yang et al. These findings suggest that older subjects require higher individual protein doses for the purpose of optimizing the anabolic response to training. The body of research in this area has several limitations.

First, while there is an abundance of acute data, controlled, long-term trials that systematically compare the effects of various post-exercise timing schemes are lacking. The majority of chronic studies have examined pre- and post-exercise supplementation simultaneously, as opposed to comparing the two treatments against each other.

This prevents the possibility of isolating the effects of either treatment. That is, we cannot know whether pre- or post-exercise supplementation was the critical contributor to the outcomes or lack thereof.

Another important limitation is that the majority of chronic studies neglect to match total protein intake between the conditions compared. Further, dosing strategies employed in the preponderance of chronic nutrient timing studies have been overly conservative, providing only 10—20 g protein near the exercise bout.

More research is needed using protein doses known to maximize acute anabolic response, which has been shown to be approximately 20—40 g, depending on age [ 84 , 85 ]. There is also a lack of chronic studies examining the co-ingestion of protein and carbohydrate near training.

Thus far, chronic studies have yielded equivocal results. On the whole, they have not corroborated the consistency of positive outcomes seen in acute studies examining post-exercise nutrition.

Another limitation is that the majority of studies on the topic have been carried out in untrained individuals. Muscular adaptations in those without resistance training experience tend to be robust, and do not necessarily reflect gains experienced in trained subjects.

It therefore remains to be determined whether training status influences the hypertrophic response to post-exercise nutritional supplementation. A final limitation of the available research is that current methods used to assess muscle hypertrophy are widely disparate, and the accuracy of the measures obtained are inexact [ 68 ].

As such, it is questionable whether these tools are sensitive enough to detect small differences in muscular hypertrophy. Although minor variances in muscle mass would be of little relevance to the general population, they could be very meaningful for elite athletes and bodybuilders.

Thus, despite conflicting evidence, the potential benefits of post-exercise supplementation cannot be readily dismissed for those seeking to optimize a hypertrophic response. Practical nutrient timing applications for the goal of muscle hypertrophy inevitably must be tempered with field observations and experience in order to bridge gaps in the scientific literature.

With that said, high-quality protein dosed at 0. For example, someone with 70 kg of LBM would consume roughly 28—35 g protein in both the pre- and post exercise meal. Exceeding this would be have minimal detriment if any, whereas significantly under-shooting or neglecting it altogether would not maximize the anabolic response.

Due to the transient anabolic impact of a protein-rich meal and its potential synergy with the trained state, pre- and post-exercise meals should not be separated by more than approximately 3—4 hours, given a typical resistance training bout lasting 45—90 minutes.

If protein is delivered within particularly large mixed-meals which are inherently more anticatabolic , a case can be made for lengthening the interval to 5—6 hours. This strategy covers the hypothetical timing benefits while allowing significant flexibility in the length of the feeding windows before and after training.

Specific timing within this general framework would vary depending on individual preference and tolerance, as well as exercise duration. One of many possible examples involving a minute resistance training bout could have up to minute feeding windows on both sides of the bout, given central placement between the meals.

In contrast, bouts exceeding typical duration would default to shorter feeding windows if the 3—4 hour pre- to post-exercise meal interval is maintained. Even more so than with protein, carbohydrate dosage and timing relative to resistance training is a gray area lacking cohesive data to form concrete recommendations.

It is tempting to recommend pre- and post-exercise carbohydrate doses that at least match or exceed the amounts of protein consumed in these meals.

However, carbohydrate availability during and after exercise is of greater concern for endurance as opposed to strength or hypertrophy goals. Furthermore, the importance of co-ingesting post-exercise protein and carbohydrate has recently been challenged by studies examining the early recovery period, particularly when sufficient protein is provided.

Koopman et al [ 52 ] found that after full-body resistance training, adding carbohydrate 0. Subsequently, Staples et al [ 53 ] reported that after lower-body resistance exercise leg extensions , the increase in post-exercise muscle protein balance from ingesting 25 g whey isolate was not improved by an additional 50 g maltodextrin during a 3-hour recovery period.

For the goal of maximizing rates of muscle gain, these findings support the broader objective of meeting total daily carbohydrate need instead of specifically timing its constituent doses.

Collectively, these data indicate an increased potential for dietary flexibility while maintaining the pursuit of optimal timing.

Kerksick C, Harvey T, Stout J, Campbell B, Wilborn C, Kreider R, Kalman D, Ziegenfuss T, Lopez H, Landis J, Ivy JL, Antonio J: International Society of Sports Nutrition position stand: nutrient timing. J Int Soc Sports Nutr.

Article PubMed Central PubMed Google Scholar. Ivy J, Portman R: Nutrient Timing: The Future of Sports Nutrition. Google Scholar. Candow DG, Chilibeck PD: Timing of creatine or protein supplementation and resistance training in the elderly.

Appl Physiol Nutr Metab. Article CAS PubMed Google Scholar. Nutr Metab Lond. Article Google Scholar. Kukuljan S, Nowson CA, Sanders K, Daly RM: Effects of resistance exercise and fortified milk on skeletal muscle mass, muscle size, and functional performance in middle-aged and older men: an mo randomized controlled trial.

J Appl Physiol. Lambert CP, Flynn MG: Fatigue during high-intensity intermittent exercise: application to bodybuilding. Sports Med. Article PubMed Google Scholar. MacDougall JD, Ray S, Sale DG, McCartney N, Lee P, Garner S: Muscle substrate utilization and lactate production.

Can J Appl Physiol. Robergs RA, Pearson DR, Costill DL, Fink WJ, Pascoe DD, Benedict MA, Lambert CP, Zachweija JJ: Muscle glycogenolysis during differing intensities of weight-resistance exercise.

CAS PubMed Google Scholar. Goodman CA, Mayhew DL, Hornberger TA: Recent progress toward understanding the molecular mechanisms that regulate skeletal muscle mass.

Cell Signal. Article PubMed Central CAS PubMed Google Scholar. Nat Cell Biol. Jacinto E, Hall MN: Tor signalling in bugs, brain and brawn. Nat Rev Mol Cell Biol. Cell Metab. McBride A, Ghilagaber S, Nikolaev A, Hardie DG: The glycogen-binding domain on the AMPK beta subunit allows the kinase to act as a glycogen sensor.

Am J Physiol Endocrinol Metab. Churchley EG, Coffey VG, Pedersen DJ, Shield A, Carey KA, Cameron-Smith D, Hawley JA: Influence of preexercise muscle glycogen content on transcriptional activity of metabolic and myogenic genes in well-trained humans.

Dennis PB, Jaeschke A, Saitoh M, Fowler B, Kozma SC, Thomas G: Mammalian TOR: a homeostatic ATP sensor. Camera DM, West DW, Burd NA, Phillips SM, Garnham AP, Hawley JA, Coffey VG: Low muscle glycogen concentration does not suppress the anabolic response to resistance exercise.

Lemon PW, Mullin JP: Effect of initial muscle glycogen levels on protein catabolism during exercise. Blomstrand E, Saltin B, Blomstrand E, Saltin B: Effect of muscle glycogen on glucose, lactate and amino acid metabolism during exercise and recovery in human subjects.

J Physiol. Ivy JL: Glycogen resynthesis after exercise: effect of carbohydrate intake. Int J Sports Med. Richter EA, Derave W, Wojtaszewski JF: Glucose, exercise and insulin: emerging concepts. Derave W, Lund S, Holman GD, Wojtaszewski J, Pedersen O, Richter EA: Contraction-stimulated muscle glucose transport and GLUT-4 surface content are dependent on glycogen content.

Am J Physiol. Kawanaka K, Nolte LA, Han DH, Hansen PA, Holloszy JO: Mechanisms underlying impaired GLUT-4 translocation in glycogen-supercompensated muscles of exercised rats. PubMed Google Scholar. Berardi JM, Price TB, Noreen EE, Lemon PW: Postexercise muscle glycogen recovery enhanced with a carbohydrate-protein supplement.

Med Sci Sports Exerc. Ivy JL, Goforth HW, Damon BM, McCauley TR, Parsons EC, Price TB: Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement.

Zawadzki KM, Yaspelkis BB, Ivy JL: Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise. Tarnopolsky MA, Bosman M, Macdonald JR, Vandeputte D, Martin J, Roy BD: Postexercise protein-carbohydrate and carbohydrate supplements increase muscle glycogen in men and women.

Jentjens RL, van Loon LJ, Mann CH, Wagenmakers AJ, Jeukendrup AE: Addition of protein and amino acids to carbohydrates does not enhance postexercise muscle glycogen synthesis. Jentjens R, Jeukendrup A: Determinants of post-exercise glycogen synthesis during short-term recovery.

Roy BD, Tarnopolsky MA: Influence of differing macronutrient intakes on muscle glycogen resynthesis after resistance exercise. Parkin JA, Carey MF, Martin IK, Stojanovska L, Febbraio MA: Muscle glycogen storage following prolonged exercise: effect of timing of ingestion of high glycemic index food.

Fox AK, Kaufman AE, Horowitz JF: Adding fat calories to meals after exercise does not alter glucose tolerance. Biolo G, Tipton KD, Klein S, Wolfe RR: An abundant supply of amino acids enhances the metabolic effect of exercise on muscle protein. Kumar V, Atherton P, Smith K, Rennie MJ: Human muscle protein synthesis and breakdown during and after exercise.

Pitkanen HT, Nykanen T, Knuutinen J, Lahti K, Keinanen O, Alen M, Komi PV, Mero AA: Free amino acid pool and muscle protein balance after resistance exercise.

Biolo G, Williams BD, Fleming RY, Wolfe RR: Insulin action on muscle protein kinetics and amino acid transport during recovery after resistance exercise. Fluckey JD, Vary TC, Jefferson LS, Farrell PA: Augmented insulin action on rates of protein synthesis after resistance exercise in rats. Denne SC, Liechty EA, Liu YM, Brechtel G, Baron AD: Proteolysis in skeletal muscle and whole body in response to euglycemic hyperinsulinemia in normal adults.

Gelfand RA, Barrett EJ: Effect of physiologic hyperinsulinemia on skeletal muscle protein synthesis and breakdown in man. J Clin Invest. Heslin MJ, Newman E, Wolf RF, Pisters PW, Brennan MF: Effect of hyperinsulinemia on whole body and skeletal muscle leucine carbon kinetics in humans.

Kettelhut IC, Wing SS, Goldberg AL: Endocrine regulation of protein breakdown in skeletal muscle. Diabetes Metab Rev. Kim DH, Kim JY, Yu BP, Chung HY: The activation of NF-kappaB through Akt-induced FOXO1 phosphorylation during aging and its modulation by calorie restriction.

Greenhaff PL, Karagounis LG, Peirce N, Simpson EJ, Hazell M, Layfield R, Wackerhage H, Smith K, Atherton P, Selby A, Rennie MJ: Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle.

Rennie MJ, Bohe J, Smith K, Wackerhage H, Greenhaff P: Branched-chain amino acids as fuels and anabolic signals in human muscle. J Nutr. Capaldo B, Gastaldelli A, Antoniello S, Auletta M, Pardo F, Ciociaro D, Guida R, Ferrannini E, Sacca L: Splanchnic and leg substrate exchange after ingestion of a natural mixed meal in humans.

Power O, Hallihan A, Jakeman P: Human insulinotropic response to oral ingestion of native and hydrolysed whey protein. Amino Acids. Glynn EL, Fry CS, Drummond MJ, Dreyer HC, Dhanani S, Volpi E, Rasmussen BB: 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. Tipton KD, Ferrando AA, Phillips SM, Doyle D, Wolfe RR: Postexercise net protein synthesis in human muscle from orally administered amino acids. Miller SL, Tipton KD, Chinkes DL, Wolf SE, Wolfe RR: Independent and combined effects of amino acids and glucose after resistance exercise.

Koopman R, Beelen M, Stellingwerff T, Pennings B, Saris WH, Kies AK, Kuipers H, van Loon LJ: Coingestion of carbohydrate with protein does not further augment postexercise muscle protein synthesis. Staples AW, Burd NA, West DW, Currie KD, Atherton PJ, Moore DR, Rennie MJ, Macdonald MJ, Baker SK, Phillips SM: Carbohydrate does not augment exercise-induced protein accretion versus protein alone.

Borsheim E, Cree MG, Tipton KD, Elliott TA, Aarsland A, Wolfe RR: Effect of carbohydrate intake on net muscle protein synthesis during recovery from resistance exercise. Koopman R, Wagenmakers AJ, Manders RJ, Zorenc AH, Senden JM, Gorselink M, Keizer HA, van Loon LJ: Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects.

Rasmussen BB, Tipton KD, Miller SL, Wolf SE, Wolfe RR: An oral essential amino acid-carbohydrate supplement enhances muscle protein anabolism after resistance exercise.

Tang JE, Manolakos JJ, Kujbida GW, Lysecki PJ, Moore DR, Phillips SM: Minimal whey protein with carbohydrate stimulates muscle protein synthesis following resistance exercise in trained young men. Tipton KD, Elliott TA, Cree MG, Wolf SE, Sanford AP, Wolfe RR: Ingestion of casein and whey proteins result in muscle anabolism after resistance exercise.

Tipton KD, Elliott TA, Ferrando AA, Aarsland AA, Wolfe RR: Stimulation of muscle anabolism by resistance exercise and ingestion of leucine plus protein. Phillips SM, Van Loon LJ: Dietary protein for athletes: from requirements to optimum adaptation.

J Sports Sci. Phillips SM: The science of muscle hypertrophy: making dietary protein count. Proc Nutr Soc. Levenhagen DK, Gresham JD, Carlson MG, Maron DJ, Borel MJ, Flakoll PJ: Postexercise nutrient intake timing in humans is critical to recovery of leg glucose and protein homeostasis.

Tipton KD, Rasmussen BB, Miller SL, Wolf SE, Owens-Stovall SK, Petrini BE, Wolfe RR: Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise.

Fujita S, Dreyer HC, Drummond MJ, Glynn EL, Volpi E, Rasmussen BB: Essential amino acid and carbohydrate ingestion before resistance exercise does not enhance postexercise muscle protein synthesis.

Tipton KD, Elliott TA, Cree MG, Aarsland AA, Sanford AP, Wolfe RR: Stimulation of net muscle protein synthesis by whey protein ingestion before and after exercise.

Coffey VG, Shield A, Canny BJ, Carey KA, Cameron-Smith D, Hawley JA: Interaction of contractile activity and training history on mRNA abundance in skeletal muscle from trained athletes. Timmons JA: Variability in training-induced skeletal muscle adaptation.

Adams G, Bamman MM: Characterization and regulation of mechanical loading-induced compensatory muscle hypertrophy. Comprehensive Physiology.

Esmarck B, Andersen JL, Olsen S, Richter EA, Mizuno M, Kjaer M: Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans.

Cribb PJ, Hayes A: Effects of supplement timing and resistance exercise on skeletal muscle hypertrophy. Willoughby DS, Stout JR, Wilborn CD: Effects of resistance training and protein plus amino acid supplementation on muscle anabolism, mass, and strength.

Hulmi JJ, Kovanen V, Selanne H, Kraemer WJ, Hakkinen K, Mero AA: Acute and long-term effects of resistance exercise with or without protein ingestion on muscle hypertrophy and gene expression. Verdijk LB, Jonkers RA, Gleeson BG, Beelen M, Meijer K, Savelberg HH, Wodzig WK, Dendale P, van Loon LJ: Protein supplementation before and after exercise does not further augment skeletal muscle hypertrophy after resistance training in elderly men.

Am J Clin Nutr. Hoffman JR, Ratamess NA, Tranchina CP, Rashti SL, Kang J, Faigenbaum AD: Effect of protein-supplement timing on strength, power, and body-composition changes in resistance-trained men. Int J Sport Nutr Exerc Metab.

Erskine RM, Fletcher G, Hanson B, Folland JP: Whey protein does not enhance the adaptations to elbow flexor resistance training. Levine JA, Abboud L, Barry M, Reed JE, Sheedy PF, Jensen MD: Measuring leg muscle and fat mass in humans: comparison of CT and dual-energy X-ray absorptiometry.

Layman DK: Protein quantity and quality at levels above the RDA improves adult weight loss. J Am Coll Nutr. Norton LE, Layman DK, Bunpo P, Anthony TG, Brana DV, Garlick PJ: The leucine content of a complete meal directs peak activation but not duration of skeletal muscle protein synthesis and mammalian target of rapamycin signaling in rats.

Wilson GJ, Layman DK, Moulton CJ, Norton LE, Anthony TG, Proud CG, Rupassara SI, Garlick PJ: Leucine or carbohydrate supplementation reduces AMPK and eEF2 phosphorylation and extends postprandial muscle protein synthesis in rats.

Atherton PJ, Etheridge T, Watt PW, Wilkinson D, Selby A, Rankin D, Smith K, Rennie MJ: Muscle full effect after oral protein: time-dependent concordance and discordance between human muscle protein synthesis and mTORC1 signaling.

Bohe J, Low JF, Wolfe RR, Rennie MJ: Latency and duration of stimulation of human muscle protein synthesis during continuous infusion of amino acids. Burd NA, Tang JE, Moore DR, Phillips SM: Exercise training and protein metabolism: influences of contraction, protein intake, and sex-based differences.

Breen L, Phillips SM: Interactions between exercise and nutrition to prevent muscle waste during aging. Br J Clin Pharmacol. Moore DR, Robinson MJ, Fry JL, Tang JE, Glover EI, Wilkinson SB, Prior T, Tarnopolsky MA, Phillips SM: Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men.

Yang Y, Breen L, Burd NA, Hector AJ, Churchward-Venne TA, Josse AR, Tarnopolsky MA, Phillips SM: Resistance exercise enhances myofibrillar protein synthesis with graded intakes of whey protein in older men. Br J Nutr. Download references.

Department of Health Science, Lehman College, Bronx, NY, USA. You can also search for this author in PubMed Google Scholar. Correspondence to Brad Jon Schoenfeld.

AAA and BJS each contributed equally to the formulation and writing of the manuscript. Both authors read and approved the final manuscript. This article is published under license to BioMed Central Ltd. Reprints and permissions.

Aragon, A. Nutrient timing revisited: is there a post-exercise anabolic window?. J Int Soc Sports Nutr 10 , 5 Download citation. Received : 20 December Accepted : 25 January Published : 29 January Anyone you share the following link with will be able to read this content:.

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Abstract Nutrient timing is a popular nutritional strategy that involves the consumption of combinations of nutrients--primarily protein and carbohydrate--in and around an exercise session.