Download Nutrient Timing Considerations for Athletes

Running Head: NUTIRENT TIMING COSIDERATIONS FOR ATHLETES
Patrick Harris
Nutrient Timing Considerations for Athletes
Sport Management concentration in Wellness and Fitness
Department of Exercise Science and Sport Studies
FIT 430 Dr. Hess
California University of PA
Fall 2015
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Nutrient timing can significantly impact the adaptive response of exercise capacity for
peak athletic performance. Research has clearly shown that not ingesting a sufficient amount of
calories and/or enough of the right type of macronutrients may impede an athlete’s training
adaptations while athletes who consume a balanced diet that meets energy needs can augment
physiological training adaptations (Kreider et al., 2010). Additionally, 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 (Kerksick et al., 2008). While current studies have determined calculated nutrient
intake strategies and recommendations for enhancing athletic performance, it is important to note
there is no one recommendation, which would apply to all individuals. Athletes should
experiment with the timing of meals to determine an ideal nutrient intake routine that
compliments their performances outcomes the best. The optimal macronutrient content of a meal
is dependent upon a number of factors including exercise duration and fitness level
(Tarnopolsky, Gibala, Jeukendrup, & Phillips, 2005a). The purpose of this paper is to identify
dietary guidelines for athletes, the physiological influence of nutrient timing, and which type of
methodical planning and consumption of nutrients yields the best results specific to exercise
type.
General Dietary Guidelines for Athletes
The timing and intake of carbohydrates, proteins, and fats can significantly impact the
adaptive response of exercise capacity (Kerksick et al, 2008). A well-designed diet that meets
energy intake needs and incorporates proper timing of nutrients is the foundation upon which a
good training program can be developed (Kreider et al., 2010). For example, Hottenrott and
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colleagues (2012) instructed eighteen athletes to perform a 150 min bicycle ride at 70% of VO2
MAX after following either a self-chosen or a predetermined scientifically developed diet. The
results of the study concluded that a scientifically planned nutrition strategy is more useful for
endurance performance output then self-chosen nutrition strategy. This was mainly due to the
accurate timing and optimal supply of energy, fluid, and electrolytes that the predetermined
strategy provided. In order to maximize training adaptations and competitive performances
athletes must consume enough calories to offset the amount of calories utilized for energy
expenditure. Athletes involved in moderate levels of intense training (e.g., 2  3 hours per day of
intense exercise performed 5  6 times per week) or high volume intense training (e.g., 3  6
hours per day of intense training in 1  2 workouts for 5  6 days per week) may expend 600 
1,200 kcals or more per hour during exercise (Kreider et al., 2010). Thus, the caloric
recommendation for athletes who exercise the amount (volume, frequency, and intensity)
specified in the categories above is around 50  80 kcals/kg/day (2,500  8,000 kcals/day for a
50  100 kg athlete). To ensure athletes can meet caloric recommendations relative to total
energy intake meal frequency according to their type of sport (volume and intensity of training
loads), hours spent training, metabolic type, gender, and body mass index. Irrespective of timing,
regular ingestion of snacks or meals providing both CHO and PRO (3:1 CHO: PRO ratio) helps
to promote recovery and replenishment of muscle glycogen when lesser amounts of carbohydrate
are consumed (Kreider et al., 2010). Nutritionists advise that athletes should consume 4  6
meals per day and snacks in between meals to reach daily caloric intake goals. Nutrient intake
should derive from whole foods when possible, but if dietary recommendations cannot be
achieved through the ingestions of whole foods, high quality supplementation has proven to be
an effective alternative for meeting dietary needs in some cases.
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Carbohydrates
Muscle glycogen, the predominant form of stored glucose in the body, and blood glucose
are the main energy substrates for muscle contraction during exercise. Sustaining adequate
glycogen stores is vital for optimum performance and recovery. Signifying, carbohydrates are
probably the most important energy source of the three macronutrients, and typically make up
the majority of an athlete’s diet. While the percentage of carbohydrate intake should consist of
the larger ratio of an athlete’s dietary intake, the body only stores limited amounts of
carbohydrates. For example, the body of a well-nourished 70 kg elite cyclist would have
approximately 400  600 g of stored carbohydrates available to fuel muscular activity
(Tarnopolsky, Gibala, Jeukendrup, & Phillips, 2005a). Within the span of 1 hour, an elite cyclist
can utilize up to half their available body carbohydrates during intense activity and virtually
deplete these stores during a stage race or prolonged training ride (Tarnopolsky, Gibala,
Jeukendrup, & Phillips, 2005a). Therefore, replenishing glycogen stores throughout the various
stages of exercise is essential for maintaining energy levels for performance and recovery. If an
athlete’s carbohydrate intake is insufficient the body will begin to breakdown muscle protein to
make up for the deficit. Athletes involved in moderate amounts of intense training (e.g., 2  3
hours per day of intense exercise performed 5  6 times per week) typically need to consume a
diet consisting of 55-65% carbohydrate (i.e., 5  8 grams/kg/day or 250  1,200 grams/day for
50  150 kg athletes) in order to sustain liver and muscle glycogen stores (Kreider et al., 2010).
Athletes involved in high volume intense training (e.g., 3  6 hours per day of intense training in
1  2 workouts for 5  6 days per week) may need to consume 8  10 grams/day of carbohydrate
(i.e., 400  1,500 grams/day for 50  150 kg athletes) in order to maintain muscle glycogen
levels (Kreider et al., 2010).
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As there are a variety of carbohydrates (simple and complex) to choose from, selecting
performance efficient carbohydrates can be unclear, but is nevertheless essential for optimizing
the availability of energy. Jamurtas et al. (2011) reported exercise performance has been
positively affected by low glycemic index (LGI) food typically found in the form of complex
carbohydrates (whole grains, fruits, and vegetables). The ingestion of complex carbs typically
takes place before exercise, and provides energy that can be used over an extended period of
time. During and after exercise muscles depend on the quick delivery of carbohydrates for
replacing glycogen stores, and require carbohydrate sources that do not take as long to be
available for the body to use. High glycemic index foods, such as a sports drink with simple
carbohydrates (glucose, ribose, sucrose) or juice can be effective for replenishing glycogen stores
during exercise and restoring them after exercise. Fructose consumption during all stages of
exercise should be minimized as it is absorbed at a slower rate and increases the likelihood of
gastrointestinal problems (Kreider et al., 2010). The exact timing and portion recommendations
will be discussed later in this review.
Protein & Amino Acids
Unlike carbohydrates, protein is not a substrate which provides a vast amount of energy
to power muscular work. In fact, protein contributes very little, generally no more than 1  3%,
to the total amount of energy used during even moderate intensity exercise (Tarnopolsky, Gibala,
Jeukendrup, & Phillips, 2005b). However, protein consumption is necessary for maintaining a
constant synthesis of muscle protein. Proteins are constantly being broken down, transformed,
and or rebuilt, which is why consuming protein rich foods is necessary for maintaining a positive
amount of essential amino acids in the body. For athletes sustaining an appropriate level of
amino acids is fundamental for providing and retaining structure to muscles, and can also be used
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as an energy source when needed. If an insufficient amount of protein is obtained from the diet,
an athlete will maintain a negative nitrogen balance, which can increase protein catabolism, slow
recovery, and over time, may lead to muscle wasting and training intolerance (Kreider et al.,
2010).
Dietary recommendations for protein are a highly debated topic, and for many athletes
ingesting a suitable amount of protein that compliments their individual needs can be confusing.
While it was once suggested that athletes do not need to consume more than the recommended
daily amount (RDA) individual’s involved in a general fitness program, research over the last
decade has indicated that athletes engaged in intense training need to ingest about two times the
RDA of protein in their diet (1.5  2.0 g/kg/d) in order to maintain protein balance (Kreider et
al., 2010).
When choosing a source protein, athletes must consider variations that are specific to
protein type. Namely, the rate of digestion and/ or absorption and metabolic activity of the
protein are important considerations, which directly affect whole body catabolism and
anabolism. Ideal sources of high quality protein include lean animal meats (complete proteins)
such as chicken or turkey, as well as soy based vegetable protein. High quality protein sources
are easily digestible, contain all of the essential amino acids, and have extra amino acids for nonessential amino acid synthesis. In regards to exercise performance gains, protein intake is
particularly important before and after exercise, but can also be beneficial during exercise in
some cases.
Fats
Amongst many athletes there is a big misconception that fat is not a fundamental part of a
diet. However, including small amounts of fat in an athlete’s diet does not appear to be harmful,
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and may help to control glycemic responses during exercise. Maintenance of energy balance,
replenishment of intramuscular triacylglycerol (fat within the muscle) stores, and adequate
consumption of essential fatty acids are of greater importance among athletes and allow for
somewhat increased intake (Kreider et al., 2010). Fats also act as a primary source of energy at
rest and during periods of recovery between bouts of activity.
Generally, it is recommended that athletes consume a moderate amount of fat
(approximately 30% of their daily caloric intake)(Kreider et al., 2010). However, some high
volume activities and sports require higher percentages of dietary fat to replace energy stores.
The exact proportion of fat needed in one day is dependent on an athlete’s physical condition and
training/competition schedule. Athletes can satisfy their dietary fat requirements by eating wellbalanced meals containing small to moderate amounts of fat. For instance, 6 oz. of yoghurt, 2
tbsp. of mixed nuts, and ¼ cup of oatmeal contains 12 g of fat. Athletes are encouraged to eat
foods with monounsaturated fats (avocados olives, and nuts) and polyunsaturated fats (salmon,
tuna, sardines) as opposed to foods with trans and saturated fats. Fats could be found a nearly all
food groups. Therefore, athletes should strive to make healthy food choices without exceeding an
amount that is detrimental to health and exercise performance. Though, educational plans about
how athletes can successfully make good food choices and implement healthy dietary fat
proportions may be necessary to yield the best results.
Vitamins & Minerals
In contrast to daily-recommended intakes values of macronutrients the body requires
much smaller quantities of micronutrients. Most recommended dietary allowances (RDA) for
vitamins and minerals can be obtained with the right diet. In the case athletes cannot attain
optimum micronutrient levels through dieting, supplementation may be an option to fulfill the
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deficit. Research has shown many vitamins cannot be used as an ergogenic aid for athletes.
However, some vitamins may help athletes tolerate training to a greater degree by reducing
oxidative damage (Vitamin E, C) and/or help to maintain a healthy immune system during heavy
training (Vitamin C)(Kreider et al., 2010). Athletes are encouraged to eat anti-oxidant rich foods
such as grapes, blueberries, and dark green vegetables. Of the minerals reviewed, calcium, iron,
sodium (phosphate and chloride), potassium, and zinc appear to possess health value for athletes
under certain conditions (Kreider et al., 2010). Sodium and potassium are particularly important
for athletes as the electrolytes are lost in sweat and must be replaced to optimize performance.
Although the supplementation of certain vitamins and minerals can serve to fill shortages,
excessive quantities have not been shown to have ergogenic effects on athletic performance,
cannot be used by the body, and in some cases can even be toxic to the body.
Water
Water is arguably the most important nutrient for athletes although it not a direct source
of energy. Athletes typically have greater fluid needs compared to the average individual who
does not exercise regularly. Thus it is imperative for athletes to properly hydrate. Poor hydration
levels can lead to decreases in performance standards and potentially dangerous scenarios
associated with dehydration such as cardiovascular collapse, heat illness, heart stoke, and
possibly even death. Exercise performance can be significantly impaired when 2% or more of
body weight is lost through sweat. For example, when a 70-kg athlete loses more than 1.4 kg of
body weight during exercise (2%), performance capacity is often significantly decreased
(Kreider et al., 2010). The normal sweat rate of athletes range from 0.5 to 2.0 L/h depending on
temperature, humidity, exercise intensity, and their sweat response to exercise (Kreider et al.,
2010). Before exercise Sawka et al. (2007) recommends slowly drinking 400  600 milliliters
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(13  20 oz) or the equivalent of about 5  7 milliliters per kilogram of body weight at least 4
hours prior to exercise. If urine is not produced, or and highly concentrated, slowly drink more
fluid (i.e., 3  5 mL/kg) about two hours before exercise (Sawka et al., 2007). Also, athletes are
encouraged to drink 200  300 milliliters (7  10 oz) 10 to 20 minutes prior to exercise (Sawka
et al., 2007). In order to maintain fluid balance and prevent dehydration, athletes need to ingest
0.5 to 2 L/h of fluid, which is around 6  8 oz. of cold water or a sports drink (preferably
containing 6  8% of carbohydrates) every 5 to 15-min during exercise in order to offset weight
loss (Kreider et al., 2010). Furthermore, athletes should weigh themselves prior to and after
exercise to determine the amount of fluid lost during exercise. For every pound of weight lost an
athlete should drink approximately 2  3 cups or 16  24 ounces of fluid to replace depleted fluid
stores. In all cases a drink should contain sodium (180  540 mg/dl) for optimal absorption and
prevention of hyponatremia (low plasma sodium)(Tarnopolsky, Gibala, Jeukendrup, & Phillips,
2005a).
Physiological Advantages of Nutrient Timing
Any supplement, food product, or dietary manipulation that enhances work capacity or
athletic performance can be defined as a nutritional ergogenic aid. Ergogenic aids may allow an
individual to tolerate heavy training to a greater degree by helping them recover faster or help
them stay injury-free and/or healthy during intense training (Kreider et al., 2010). There is a
growing debate concerning the value of certain nutritional supplements and their potential to
enhance performance and recovery. Some sports nutrition specialists only consider a supplement
ergogenic if studies show that the supplement significantly enhances exercise performance (e.g.,
helps you run faster, lift more weight, and/or perform more work during a given exercise
task)(Kreider et al., 2010). As there are a wide variety of supplements available, choosing
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supplements can be confusing and difficult. When in doubt athletes should consult a qualified
nutritionist before experimenting with a supplement that could have potentially ergolytic
(supplement that impairs performance) effects and be detrimental to one’s health. Ergogenic aids
should be carefully researched and identified as safe, legal, and effective before consumption. If
the right approach to selecting and utilizing ergogenic aids is taken athletes can increase their
chances of enhancing athletic performance and promoting a swift, efficient recovery.
Performance Related Training Adaptations
Nutrition related performance gains vary between sports, and are usually specifically
tailored to needs and goals of the athlete. For example, a weightlifter uses energy differently to a
long distance runner, and therefore requires a diet that will facilitate short, powerful bursts of
energy rather than a diet that sustains energy over a longer period of time. The work volumes and
intensities of each discipline vary, which is why dietary recommendations must be particular to
the individual and energy demands of the sport or exercise. In this review, the performance
related outcomes of two types of athletes were investigated: strength/power athletes and
endurance athletes.
Examining strength/power athletes, the success of their sport consists of activities of
short duration. Weight lifting, track and field events (discus, high jump, hammer throw, sprints,
etc.), and gymnastics are a few sports that rely on short bursts of energy to perform high intensity
muscle contractions. Most research regarding physiological adaptations is not sport specific, and
instead examines the relationship between resistance training and muscle growth, strength, and
power. The principal concept influencing the various aspects of resistance training seems to be
the balance of muscle protein synthesis. When positive, the net protein balance favors increases
in muscle mass (i.e., muscle hypertrophy)(Babault, Deley, Le Ruyet, Morgan, & Allaert, (2014).
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For example, pre-exercise ingestion of essential amino acids or protein alone increases muscle
protein synthesis. In addition, ingesting protein and carbohydrates pre and post exercise has been
shown to produce significantly greater levels of muscle protein synthesis (Kerksick et al., 2008).
Furthermore, Tang, Moor, Kujbida, Tarnopolsky, and Phillips (2009) concluded muscle protein
synthesis has been shown to be greater with soluble proteins such as whey when compared with
casein. Also, ingestion of essential amino acids (histidine, isoleucine, leucine, lysine, methionine,
phenylalanine, threonine, tryptophan, and valine) following resistance exercise has been shown
to increase protein synthesis and enhance gains in strength and muscle mass during training
(Kreider et al., 2010). Meaning maximum strength, power, and muscle growth (hypertrophy) are
limited by protein synthesis rates.
Endurance athletes engage in continuous activity lasting between 30 minutes and four
hours. The extreme caloric demand of long-duration exercise stresses the body’s glycogen stores.
Hence the main adaptations concerning endurance athletes have to do with maintaining blood
glucose levels and high levels of carbohydrate oxidation, and the promotion of glycogen
synthesis. Research involving the ingestion of single pre-exercise high carbohydrate feedings has
demonstrated the promotion of higher levels of muscle glycogen and an improvement of blood
glucose maintenance (Kerksick et al., 2008). Moreover, it has been established that carbohydrate
ingestion at frequent intervals, or late into submaximal aerobic exercise can maintain plasma
glucose concentrations, and support performance through a number of mechanisms including
glycogen preservation and increased total carbohydrate oxidation rates (Roberts, Tarpey, Kass,
Tarpey, & Roberts, M., 2014). For example, Too et al. (2012) evaluated 11 adult male runners
who consumed either a placebo (water), raisins, or sport chews before and every 20-minutes
during 80-minuntes (75%VO2max) of treadmill running followed by a 5-km time trial. This
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study suggests that raisins and chews promote higher level carbohydrate oxidation and improved
running performance compared to water only (Too et al., 2012). On the contrary, the recovery of
muscle glycogen stores together with subsequent rate of utilization during exercise is not related
to the potential ergogenic effect of protein (McLellan, Pasiakos, & Lieberman, 2014). The
maintenance of blood glucose levels, high levels of carbohydrate oxidation, and the promotion of
glycogen synthesis are largely dependent on carbohydrates consumption before and during
extensive exercise.
Recovery Related Adaptations
Many nutritional interventions have been considered to enhance recovery from exercise
(Kerksick et al., 2008). Typically recovery related adaptations that result from the timed
ingestion of nutrients commence after exercise. There is 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 protein balance, as well as enhancing the overall adaptation to
resistance training (Kerksick et al., 2008). In a study conducted by Babault, Deley, Le Ruyet,
Morgan, and Allaert (2014), 68 actively trained men took part in a 10-week lower limb
resistance training program during which they were required to ingest either a placebo, soluble
milk protein, and micellar casein) three times a day on training days, and twice a day on nontraining days. The results of the of the research revealed enhanced muscle endurance (i.e.,
number of repetitions), reduced fatigue (i.e., muscle power loss) and slightly enhanced recovery
(i.e., vertical jump height) with a supplement composed of fast-digesting protein (soluble milk
protein) as compared with a slow-digesting protein (micellar casein) or with a placebo (Babault
et al., 2014). In another study, 40 resistance-trained subjects performed a standardized resistance
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training workout and then ingested 40 g of whey protein with 120 g of sucrose (S), honey
powder (H), or maltodextrin (M)(Kreider et al, 2007). Evidence from this study implies that
carbohydrate and protein ingestion following exercise significantly influences glucose and
insulin concentrations thus lessening the immunosuppressive effects of intense exercise, and
promoting post-exercise anabolic responses during the first two hours of recovery. Additionally,
Thibault and colleagues supplemented eight male regionally ranked tennis players with either a
preselected sports drink (carbohydrate and protein mix) or a placebo during and after the
completion of three tennis matches of 2-hours in duration to assess fatigability induced by
repeated matches. This study demonstrated that compared to water, a sports drink composed of
supplemental macronutrients can limit the onset of fatigue and facilitate recovery. It is well
established that feeding during the post exercise period is required to bring about a positive net
protein balance (Burd, Tang, Moore, & Phillips, 2009), increase the rate of protein synthesis,
decrease the rate of protein degradation, and possibly aid recovery (Kreider et al., 2010). Many
studies have agreed with these findings in that post workout supplementation is vital to recovery
and training adaptations (Willoughby, Stout, & Wilborn, 2007). The findings demonstrate post
exercise ingestion of protein and carbohydrates can augment recovery adaptations.
Strategic Nutrient Timing Recommendations
Maintaining an energy balance by means of a nutrient dense diet, prudent training, and
proper timing of nutrient intake are the cornerstones to enhancing performance and/or training
adaptations (Kerksick et al., 2008). Prolonged exercise will deplete the internal stores of energy,
and careful timing of nutrient delivery can help offset these changes (Kreider et al., 2010).
Essentially, the practice of planned nutrient timing can optimize training and competition efforts.
Researchers have conducted various studies in order to test and validate potential nutrient intake
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recommendations for practical application throughout the different stages of exercise. The
following timed nutrient suggestions are based upon current research findings.
Before Exercise
Nutritional considerations prior to exercise have traditionally examined the
administration of carbohydrates to maximize endogenous glycogen stores (Kerksick et al, 2008).
Most research explicitly focused on the relationship between increasing glycogen stores and
endurance performance. Nonetheless, protein and amino acids also contribute to the composition
of an ideal pre-exercise meal plan. The following research has defined some general
recommendations for nutrient consumption prior to exercise.
Carbohydrate loading, or carb loading, is likely the oldest form of all the nutrient timing
practices. The process involves the larger carbohydrate feelings days prior to competition in
order to maximize the storage of glycogen (or energy) in the muscles and liver. Daily ingestion
of high carbohydrate meals (~65% CHO) is recommended to maintain muscle glycogen, while
increased ingestion rates are employed (~70% CHO) in the 5  7 days leading up to competition
as a means of maximizing muscle and liver glycogen stores and in order to sustain blood glucose
during exercise (Kerksick et al, 2008). Traditional carb loading studies utilized a glycogen
depletion phase typically lasting 3  6 days prior to increasing carbohydrate intakes, however,
maximal levels of glycogen storage may be achieved after just 1  3 days of consuming a highcarb diet while minimizing physical activity (Kerksick et al, 2008). Tarnopolsky, Gibala,
Jeukendrup, and Phillips (2005a) found maximal endogenous glycogen stores are best promoted
by following a high-glycemic, high-carbohydrate diet (600  1000 grams or 8  10 g/kg/d) in a
study comparing the timing of pre exercise carbohydrate intake. In another study, Galloway,
Lott, and Toulouse (2014) confirmed high-intensity exercise capacity was significantly improved
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by ingestion of 32 g of carbohydrate taken 30 min before exercise (14  17% increase),
compared with ingestion of 32 g of carbohydrate 2 hours before exercise, or placebo solutions
ingested 30 min or 2 hours before exercise. In that same study, a similar magnitude of change
(12  15% increase) in exercise capacity, albeit not reaching statistical significance, was
observed over 0% and 12% pre exercise carbohydrate ingestion trials when a 2% carbohydrate
solution was ingested 30 min before exercise (Galloway, Lott, and Toulouse, 2014).
Additionally, ingesting protein and/or amino acids, either alone or in combination with
carbohydrates, has been shown to enhance training adaptations. The optimal carbohydrate and
protein content of a pre-exercise meal dependent upon a number of factors and varies according
to exercise conditions, but general guidelines recommend ingestion of 1  2 g CHO/kg and 0.15
 0.25 g PRO/kg 3  4 hours before competition (Kerksick et al, 2008). In addtion, ingestion of 6
 20 g of essential amino acids (EAA) and 30  40 g of high-glycemic carbohydrate immediately
before exercise can significantly stimulate muscle protein synthesis (Kreider et al., 2010).
During Exercise
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
primarily focused on aerobic exercise (Kerksick et al., 2008), and more specifically the method
of restoring glycogen stores in order to facilitate the continuation of optimum performance.
Research has demonstrated the appropriate intake of nutrient during exercise is insufficient for
some athletes. Baker, Heaton, Nuccio, and Stein (2014) recorded the dietary intake of 29
skill/team-sport athletes (14  19 y; 22 male, 7 female) for one 24-hr period to test the efficiency
of the athletes’ diets. Dietitians accompanied subjects to the cafeteria and field/court to record
their food and fluid intake during meals and practices/competitions. Other dietary intakes within
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the 24-hr period (e.g., snacks during class) were accounted for by having the subjects take
pictures of food/fluid consumed. The results of the study revealed that the most common
shortfall was carbohydrate intake during exercise. Replacing lost nutrients during exercise is
vital to performance and should not be overlooked. As exercise duration increases beyond 60
min, exogenous sources of carbs become important to maintain blood glucose and muscle
glycogen stores. This carbohydrate source should supply 30  60 grams of carbohydrate per hour
and can typically be delivered by drinking 1  2 cups of a 6  8% carbohydrate solution (8  16
fluid ounces) every 10  15 minutes (Jeukendrup, Jentjens, & Moseley, 2005). Jentjens, Achten,
and Jeukendrup, (2004) suggest mixing different forms of carbohydrates has been shown to
increase muscle carbohydrate oxidation from 1.0 g CHO/min to levels ranging from 1.2 g  1.75
g CHO/min an effect, which is associated with an improvement in time trial performance. The
addition of protein to carbohydrate at a ratio of 3  4:1 (CHO: PRO) has also been shown to
increase endurance performance during both acute exercise and subsequent bouts of endurance
exercise (Kerksick et al., 2008). Lastly, ingesting carbs alone, or in combination with protein,
during resistance exercise increases muscle glycogen stores, offsets muscle damage (Baty et al.,
2007), and facilitates greater training adaptations after acute (Bird, Tarpenning, & Marino, 2006)
and prolonged periods of resistance training (Bird, Tarpenning, & Marino, 2006).
After Exercise
Most post exercise nutritional interventions have been developed for the purpose of
enhancing recovery. The two main adaptations concerned with post exercise nutrient timing are
glycogen and protein re-synthesis. It has been demonstrated that delaying carbohydrate ingestion
by as little as two hours can reduce the rate of muscle glycogen re-synthesis by 50% (Kerksick et
al., 2008). According to Kreider et al. (2010) ingesting carbohydrates and protein immediately
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following exercise doubled training adaptations in comparison to waiting until 2-hours to ingest
carbohydrate and protein. If an athlete is glycogen-depleted after exercise, a carbohydrate intake
of 0.6  1.0 g CHO/kg/h during the first 30 minutes, and again every two hours for 4  6 hours,
can adequately replace glycogen stores (Tarnopolsky, Gibala, Jeukendrup, & Phillips, 2005a).
Similarly, maximal glycogen re-synthesis rates have been achieved when 1.2 g CHO/kg/h is
consumed every 15  30 minutes Tarnopolsky, Gibala, Jeukendrup, & Phillips, 2005a). Frequent
feedings of carbohydrate in high amounts over the 4  6 hours following exercise is
recommended to ensure recovery of muscle and liver glycogen (Tarnopolsky, Gibala,
Jeukendrup, & Phillips, 2005a). Kerksick et al. (2008) discovered different forms of
carbohydrates have different effects on insulin levels, with fructose ingestion being associated
with lower levels of glycogen re-synthesis than other forms of simple carbohydrates (i.e. sucrose,
galactose, ribose). Under these circumstances athletes should lean towards simple carbohydrates
rather than fructose post exercise.
The effect of resistance training on net protein balance can persist up to 24 hours (Burd,
Tang, Moore, & Phillips, 2009). Kreider et al. (2010) reported ingesting carbohydrate and
protein immediately following exercise can enhance carbohydrate storage and protein synthesis.
Daily post-exercise ingestion of a carbohydrates (50  75 g) + protein (20  75 g) promotes
greater increases in strength and improvements in lean tissue and body fat % during while
completing some form of resistance training (Kerksick et al., 2008) In addition, post exercise
(immediately after through 3 hours post) ingestion of 3  6 grams of EAA following resistance
exercise has been shown to increase protein synthesis (Kreider er al., 2010). These findings
underscore the importance of post-exercise carbohydrate and protein ingestion to support protein
synthesis, muscle anabolism, and strength (Kerksick et al., 2008).
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Summary
As with many aspects of science, the literature associated with nutrient timing is an everchanging area of research. New theories and experiments are constantly being developed and
tested in an effort to authenticate information that has not yet been verified. Based on the present
material retrieved in this review, the following conclusions can be made. The manipulation of a
supplement, food source, or diet in order to enhance work capacity or athletic performance can
be considered an ergogenic aid. Hence, nutrient timing can also be expressed as an ergogenic aid.
The precise timing and intake of carbohydrates, proteins, and fats can notably affect an athlete’s
adaptive response of exercise capacity. Carbohydrates have the greatest impact on glycogen
stores, and while ingestion does influence adaptations after exercise, an emphasis should be
placed on the importance of pre and during exercise carb intake. Carb intake before and during
training or competition is especially critical for endurance athletes, as prolonged exercise
attenuates the integrity of glycogen stores. Nevertheless, post exercise carbohydrate intake is
necessary for replenishing lost glycogen stores. Although not as common, protein can also be
used as a source of energy. However, protein, and more notably, amino acids are mainly utilized
for stimulating protein synthesis. This process helps muscles maintain structures, decreases the
rate of muscle degeneration, and aids recovery. Including small amounts of fat does not appear to
be harmful, and may help to control glycemic responses during exercise. However, dietary focus
should center on adequate availability and delivery of carbohydrates and protein. Although some
supplements have been proven to be an effective alternative, athletes should strive to reach their
recommended caloric intakes through the consumption of whole foods. Foods rich in vitamin E
and C can reduce oxidative damage to muscle and boost the immune system. Calcium, iron,
sodium (phosphate and chloride), potassium, and zinc appear to positively effect athletes’ health.
NUTIRENT TIMING COSIDERATIONS FOR ATHLETES
18
Sodium and potassium are especially significant for athletes as the electrolytes are lost in sweat
during exercise, and should be replenished during and after exercise. Water is an essential
nutrient for athletes, and proper hydration is imperative for sustaining homeostasis, and can
considerably influence exercise performance.
Most research regarding the physiological adaptations connected to nutrient timing was
not sport specific. Performance related physiological adaptations resulting from timed nutritional
intake mainly pertained to resistance training and the capacity to harness protein synthesis, and
endurance performance and ability to continually sustain glycogen stores. Recovery related
adaptations addressed the significance of a diet that emphasizes improving the recovery of
glycogen and stimulating amino acid kinetics (protein synthesis) in order to lessen the
immunosuppressive effects of intense exercise, promote post-exercise anabolic responses, and in
turn reduce fatigability. In comparison to the consumption of carbohydrate or protein alone, the
combination of carbohydrate and protein intake during and post exercise can lead to greater
training adaptations. Current studies have determined calculated nutrient intake strategies for
enhancing athletic performance. There seems to be exact timing windows and portion sizes that
are favorable for each stage of exercise (pre-exercise, during exercise, and post-exercise).
Findings within this review validate the use of a number of nutritional foods and supplements
that can help improve energy availability, in turn promoting adaptations that are associated with
optimal athletic performance and enhanced recovery. The intake of nutrients should align with
specific athletic ambitions, as food prescription varies according to factors such as exercise type
and intensity. Further research should investigate exact nutrient timing techniques that are sport
discipline specific. Comparing digestions rates, supplemental nutrients, particularly liquid forms,
could be a more efficient method of nutrient administration as opposed to the consumption of
NUTIRENT TIMING COSIDERATIONS FOR ATHLETES
19
raw food, especially during and after exercise. Supplements do not take as long to digest, and
therefore can be absorbed by the body faster. When contemplating supplement use, athletes
should determine if the supplement is legal and safe, if there is scientific evidence to proving the
supplement has ergogenic value, and whether or not it makes sense to add a supplement to their
diet before incorporating supplements into their diets.
Due to the competitiveness that exists within sports, sports nutrition and nutrient timing
will continue to change and advance. Although nutrient timing has been researched extensively
in the past decade, the complex subject is constantly evolving and further research is needed to
determine recommendations that may be useful in the future. In order to understand and apply
nutrient timing methods athletes should proactively strive to stay informed about current planned
nutrient intake recommendations and methods. Monitoring and documenting food intakes, and
communicating with qualified nutritional professionals about sports nutrition are means by
which athletes can analyze and confirm whether or not their dietary practices are current.
NUTIRENT TIMING COSIDERATIONS FOR ATHLETES
20
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