FISIOFIRMAN INDONESIA

The Case for Carbohydrate: An Overview

You’ve seen the images on TV: a struggling athlete sweating and in pain, trying to cross the finish line of a race, or another, in agony, being helped off the racecourse. These are highly trained athletes who are competing at the highest level. Others, famously called “weekend warriors,” also are looking to improve performance so they are fit enough to participate in individual or team sports. How does carbohydrate fit in with these images?

Athletes continually seek new strategies to improve performance, whether these strategies are beneficial or potentially dangerous. Nourishing the body with adequate nutrients, especially carbohydrates, before, during and after an athletic event can improve performance in a number of sports or activities.

Carbohydrate ingestion is important before, during and after exercise. Adequate endogenous carbohydrate stores (muscle and liver glycogen and blood glucose) are critical for optimum athletic performance during intermittent high-intensity work and prolonged endurance exercise. Consuming carbohydrate-rich foods and fluids before exercise restores liver glycogen, especially for morning exercise when liver glycogen is depleted following an overnight fast. Timing is important, however, so athletes should adjust the amount of carbohydrates ingested before exercise to allow sufficient time for digestion and absorption and to avoid gastrointestinal upset.

Consuming carbohydrates during exercise can improve performance by maintaining blood glucose levels

and carbohydrate oxidation. Also, consuming adequate carbohydrates after glycogen-depleting exercise facilitates rapid glycogen restoration, especially among athletes engaged in daily intense training or tournament activity.¹

In addition to fueling with carbohydrates according to intensity and endurance levels required by the activity, using multiple carbohydrate sources compared to a single source allows for greater performance in events lasting more than three hours. Multiple transportable carbohydrate consumption also allows for rapid resynthesis of muscle glycogen after exercise, which is especially important for athletes who train intensely every day or for those who compete in multiple events over a short period of time.²

Nutritional strategies that enhance and improve carbohydrate availability before, during and after exercise are recommended to enhance endurance performance.¹

Substrate Utilization

Carbohydrate and fat. Carbohydrates and fats are the primary fuel sources used during endurance exercise (protein provides a minimal contribution). The relative amount of fat and carbohydrate oxidized depends on the intensity of exercise. At low intensities, fat provides the majority of energy to the system; but as intensity increases, a greater percentage of carbohydrate is oxidized to provide energy. As a result, exercise performance in endurance events is dependent upon carbohydrate ingestion and use, and it may even be directly correlated to carbohydrate intake.^2-4

As a high-energy substrate (more than twice that of protein and carbohydrate), fat has the potential to provide hours of fuel to the exercising body. Research on the application of fat ingestion during exercise, with limited carbohydrate intake, may have its application; however, research is still emerging. Likewise, metabolic efficiency, or other fat-adaptation practices may be appropriate for some endurance athletes; however, the current position stances of the American College of Sports Medicine and the Academy of Nutrition and Dietetics (formerly the ADA) support the included guidelines and recommendations.⁵

Protein and fiber. Both protein and fiber are essential nutrients for overall health and play an important role in the overall diets of athletes. Protein with meals typically slows gastric emptying and therefore may be beneficial only in small amounts before exercise, or farther from the beginning of exercise (>2 hours). Likewise, fiber (albeit having numerous general health benefits) also slows gastric emptying, which may contribute to gastric upset, or increased transit time, during exercise.

Energy Stores in Humans⁶
Tissue Fuel	Reserve (g)	Provides Fuel For
Tissue Fuel	Reserve (g)	Starvation	Walking	Marathon
Blood Glucose*	20	40 minutes	15 minutes	4 minutes
Liver Glycogen*	80	3.5 hours	70 minutes	18 minutes
Muscle Glycogen*	350	14 hours	5 hours	70 minutes
Fat	9,000 to 15,000	34 days	11 days	3 days
Body Protein	6,000	15 days	5 days	1.3 days
*Endogenous carbohydrate stores

Effectiveness of a Pre-Exercise Meal

Consuming carbohydrate-rich foods and fluids two to four hours before exercise contributes to a number of positive effects in the body. This practice may:⁷

Restore liver glycogen, especially for morning exercise when liver glycogen is depleted
Increase muscle glycogen stores, if they are not fully restored from the previous exercise session
Ensure hydration
Diminish hunger, which may impair performance
Provide a psychological boost

Research suggests that the pre-exercise meal contain 1 g to 4 g of carbohydrates per kilogram of body weight (1g/kg to 4 g/kg) and be consumed one to four hours before exercising.¹ To avoid potential gastrointestinal distress, when blood is diverted from the gut to the exercising muscles, the carbohydrate and calorie content of the meal should be reduced the closer to exercise it is consumed. For example, a carbohydrate feeding of 1 g/kg is appropriate one hour before exercise, 2 g/kg of carbohydrates two hours prior, 3 g/kg of carbohydrates three hours prior, and 4 g/kg of carbohydrates four hours before exercise. To further decrease the chances of gastrointestinal distress, all pre-competition rituals, including food and fluid consumption, should be practiced regularly to account for individual reactions.

Outside of the laboratory, carbohydrate intake is strongly associated with race day performance among marathon runners and triathletes.^2,3 A study of the 2009 London Marathon determined that competitors who consumed greater than 7 g/kg body weight of carbohydrate the day prior to the race had significantly faster race speed and maintained that pace longer than those who consumed less than 7 g/kg.³ Similarly, analysis of an Ironman triathlon revealed that carbohydrate intake during the event inversely correlated to finishing time, resulting in a better performance.²

Studies That Defined Carbohydrate Use for Athletes

Based on the results of a study from the late 1970s, athletes were cautioned to abstain from eating carbohydrates in the hour before exercise. This study concluded that consuming glucose 30 minutes prior to high-intensity cycling caused an initial, rapid drop in blood glucose, which reduced exercise time.⁷ The authors attributed the impaired endurance to accelerated muscle glycogen depletion, although muscle glycogen was not measured. High blood insulin levels induced by the pre-exercise carbohydrate feeding were determined to be the cause for this chain of events.⁷

Subsequent studies have contradicted these results.⁷ Pre-exercise carbohydrates either improve performance by 7% to 20% or have no detrimental effect. In most cases, the decline in blood glucose (likely resulting from post-prandial insulin rebound) observed during the first 20 minutes of exercise is self-correcting with no apparent effects on the athlete.⁷ The exercise-induced rise in epinephrine, norepinephrine and growth hormone inhibits the release of insulin and counters insulin’s effect in lowering blood glucose.

Glycemic index. A 1991 study that manipulated the glycemic response to pre-exercise meals first sparked interest in the use of the glycemic index

(GI) in the sports setting. The GI is a measure of the effect of carbohydrates on blood sugar levels

. Carbohydrates that break down quickly during digestion and release glucose rapidly into the bloodstream have a high GI; carbohydrates that break down more slowly, releasing glucose more gradually into the bloodstream, have a low GI.⁷

In theory, low-GI food choices may provide a more sustained source of fuel when consumed before exercise. Low-GI foods (beans, milk and pasta) provide a slow and sustained release of glucose to the blood, without an accompanying insulin surge. Lentils (low GI) were consumed one hour prior to moderate-intensity cycling and increased endurance compared with the same amount of carbohydrates from potatoes (high GI). The lentils promoted lower postprandial blood glucose and insulin responses, as well as more stable blood glucose levels

during exercise than the potatoes.⁷

Some athletes react negatively to carbohydrate feedings in the hour before exercise and experience symptoms of hypoglycemia and a rapid onset of fatigue. The precise reason for this extreme reaction is not known, further emphasizing the importance of practicing fueling strategies. Preventive strategies for these individuals include consuming low-GI carbohydrates before exercise, eating carbohydrates only a few minutes before exercise, and waiting until exercising to consume carbohydrates.⁷ It is important to consider the overall importance of the pre-exercise meal for maintaining carbohydrate availability, since endurance athletes also consume carbohydrate-rich foods and fluids during prolonged exercise. Research has evaluated the effects of the GI of pre-exercise meals on metabolism and performance when carbohydrates were also consumed during prolonged cycling. There were no differences in carbohydrate oxidation or time to fatigue among the low-GI meal (pasta), high-GI meal (potatoes) and controls.⁸ Thus, the beneficial effects of the pre-exercise meal are diminished when adequate carbohydrates are consumed during exercise.

In recent years, though, the practice of basing carbohydrate intake recommendations on GI has faded. The measurement of GI is highly variable, and most athletes (and non-athletes) consume meals with multiple food items rather than a single serving of carbohydrate. Moreover, most studies have failed to show performance benefits from consuming low-GI meals before exercise.^7-10

Endurance Exercise

Consuming carbohydrates during exercise that lasts one hour or longer can delay the onset of fatigue and improve endurance capacity by maintaining blood glucose levels

and carbohydrate oxidation in the latter stages of exercise.¹¹ Carbohydrates eaten while exercising supplement the body’s limited endogenous stores of carbohydrates. It has been found that consuming carbohydrates during cycling at 70% of VO₂max can delay fatigue by 30 to 60 minutes.^4,11 Carbohydrates have also been shown to improve performance during running. The simple truth is that athletes can exercise longer and/or sprint harder at the end of exercise when carbohydrates are available.

Blood glucose becomes an increasingly important source of carbohydrates as muscle glycogen stores decline. Consuming carbohydrates during endurance exercise maintains blood glucose levels

at a time when muscle glycogen stores are diminished. During prolonged exercise, ingested carbohydrates can account for up to 30% of the total carbohydrates oxidized. Carbohydrate use — and therefore ATP production — can continue at a high rate, enhancing endurance.¹¹ The performance benefits of consuming carbohydrates during exercise may be additive to those of a pre-exercise meal. Cyclists who received carbohydrates both three hours before and during exercise were able to exercise longer than when receiving carbohydrates either before exercise or during exercise. Combining carbohydrate feedings improved performance more than either fueling alone; however, the improvement in performance with pre-exercise carbohydrates was less than when smaller quantities of carbohydrates were consumed during exercise.¹¹ Thus, to obtain a continuous supply of glucose, the endurance athlete should consume carbohydrates during exercise.

Central Nervous System Benefits of Carbohydrate Consumption

Beyond physiological benefits, recent evidence suggests that carbohydrates may improve performance during high-intensity exercise lasting 45 to 75 minutes (i.e. 15-kilometer run or 25-mile bicycle time-trial) by exerting a positive influence on the central nervous system. Further, studies have demonstrated that a carbohydrate mouth rinse improves performance, possibly by activating areas of the brain associated with motivation and reward. Beneficial effects are typically seen when an athlete has not eaten for a while, such as after an overnight fast or several hours after a meal.^4,12

Stop-and-Go Sports

Carbohydrates may also improve performance in stop-and-go sports such as basketball, soccer, football and tennis, which require repeated bouts of high-intensity, short-duration effort lasting an hour or longer.¹³ At the least, carbohydrate ingestion does not seem to impede performance.⁴ Carbohydrates may improve performance in stop-and-go sports by:^2,4,13

Selectively sparing glycogen in type II (fast-twitch) muscle fibers
Increasing glycogen resynthesis in type II muscle fibers during rest or low-intensity periods
A combination of both
Increasing blood glucose
Stimulating the central nervous system

Appropriate Food Choices for Optimum Fueling

High-carbohydrate foods for pre-exercise meals include fruit, cereal, bread products, low-fat or nonfat dairy products, dairy substitutes, vegetables and legumes. One-hundred percent fruit juices and nonfat milk are quality high-carbohydrate beverages. Athletes may also use liquid meals or high-carbohydrate liquid supplements.

Foods that are low in fat, low to moderate in protein, and low in fiber are less likely to cause gastrointestinal upset.¹ The high fat content of popular breakfast foods (bacon, sausage, cheese and biscuits) slows gastric emptying and can contribute to feeling sluggish. Carbohydrates are the most efficient source of energy and are rapidly digested. Liquid meal supplements or smoothies may be easier for some athletes to digest and can therefore be consumed if an athlete is unable to tolerate solid foods before competition.⁷

Athletes should choose palatable, familiar and well-tolerated foods. The timing, amount and type of carbohydrate foods and drinks should be chosen to suit the needs of the event and individual preferences/experiences. Choices high in fat, protein and fiber may need to be avoided to reduce risk of gastrointestinal discomfort during the event (as these foods have a slower gastric emptying rate than carbohydrates).

Limiting fiber intake, for example, in the pre-exercise meal close to the beginning of exercise may prevent a bathroom stop during exercise (while merely inconvenient during training, it can be disastrous during competition). Gas-forming foods such as beans, broccoli, cauliflower and onions should also be avoided. However, eating higher amounts of fiber four hours before exercise or a competition should not cause any distress.

Liquid meals. Liquid-meal products, such as homemade smoothies or shakes, can easily fulfill the requirements for pre-exercise fueling, as many are high in carbohydrates, palatable and provide energy and fluid. Liquid meals can often be consumed closer to competition than solid foods because of their shorter gastric emptying time; this may help to avoid pre-competition nausea for athletes, as tension may cause an associated delay in gastric emptying resulting in discomfort.

Liquid meals also produce a low stool residue, thereby minimizing immediate weight gain following the meal. This may be especially advantageous for athletes who need to “make weight.” Liquid meals are also convenient fuel for athletes competing in daylong competitions, tournaments or meets, and they can be used for nutritional supplementation during heavy training when calorie requirements are extremely elevated. Benefits of liquid meals include:

Shorter gastric emptying time (minimizes nausea)
Low stool residue (minimizes weight gain)
Convenience
Nutritional supplementation without feeling “full”
Potential for high energy-dense meal or meal replacement

Many athletes and nutritionists choose to make custom smoothies, which may include milk, protein powder and fruit in a blender (athletes with lactose intolerance can use soy, almond, coconut or lactose-free milk). For variety, yogurt and natural flavoring (vanilla or cinnamon) can be added, and fruit juice or honey can provide sweetness and more carbohydrates. Currently, other popular “boosts” to smoothies include chia gel, flax seeds, coconut oil, unsweetened cocoa powder and raw greens.

Liquid vs. solid carbohydrates. Liquid and solid carbohydrates are equally effective in increasing blood glucose and improving performance, although each has certain advantages.^5,14

Sports drinks and other fluids containing carbohydrates encourage the consumption of water needed to maintain normal hydration during exercise. Carbohydrate ingestion and fluid replacement independently improve performance and their beneficial effects are additive.¹¹ The electrolytes, especially sodium, in sports drinks help replace sweat sodium losses and stimulates thirst.⁵ Sports drinks are a practical way to obtain water, carbohydrates and sodium during most sports and offer the benefit of simplifying the athlete’s nutrition plan for competition.

Carbohydrate-rich foods, energy bars and gels are compact, can be easily carried, provide variety (different flavors and textures) to prevent a boredom-related decline in food intake and help relieve hunger.^14,15

Athletes should drink plenty of water when they eat solid food, especially a sports bar or energy gel; otherwise, the athlete may feel “a rock in the gut.” In addition to aiding digestion, drinking water while eating solid foods encourages the athlete to hydrate adequately. Essentially, water with gels or solid food is equal to a sports drink, if comparable calories are consumed.

When the athlete’s gut blood flow is low (e.g., during intense cycling or running), the athlete should emphasize carbohydrate-rich fluids (sports drinks, liquid meals, high-carbohydrate liquid supplements, fruit juices and carbohydrate gels) to promote rapid gastric emptying and intestinal absorption. When the athlete’s gut blood flow is moderate (e.g., during moderate-paced cycling or slow running), the athlete may be able to consume easily digested carbohydrate-rich foods, such as sports bars, fruit and grain products (fig bars, bagels or graham crackers) in addition to liquid foods and fluids.¹⁶

Athletes can, therefore, generally consume more calories per hour cycling than running and may consume as much as three times the energy on the bike than the run during a race.^2,16 Ironman triathlon competitors often decrease their calorie intake toward the end of the bike segment to start the run with a fairly empty gut to lower the risk of developing gastrointestinal distress. During the run segment of a triathlon, athletes usually consume only sports drinks, gels and water to further reduce the risk of distress.

An athlete’s foods and fluids should be familiar (tested in training), easily digested and enjoyable (to encourage eating and drinking). New food and fluids should never be tested during competition, as the result may be severe indigestion and/or impaired performance. It may also be advantageous to eat or drink before feeling hungry or tired, usually within 30 to 60 minutes after beginning exercise. Adopting a strategy of consuming small amounts of foods and fluids at frequent intervals helps to keep the athlete hydrated while minimizing gastrointestinal discomfort.¹⁶

Carbohydrate Content of Selected Foods*
Food	Portion	Carbohydrate
Gatorade	1 quart (~1 liter)	60 g
PowerBar	1 bar	45 g
GU Energy Gels	2 gels	50 g
Sport Beans	28 beans	50 g
Clif Shot Blok	6	50 g
Graham crackers	3 large	66 g
Fig bars	4 bars	42 g
Banana	1	30 g
^* Information sourced from product labels.

Multiple transportable carbohydrates. The maximum amount of carbohydrates that can be oxidized during exercise from a single carbohydrate source such as glucose is approximately 1 g/min (60 g/hr) because the transporter responsible for carbohydrate absorption in the intestine becomes saturated.⁷ Consuming more than 1 g/min from one source does not raise the rate of carbohydrate oxidation and increases the risk of gastrointestinal distress.¹⁷

By consuming multiple forms of carbohydrates (e.g., glucose and fructose) that use different intestinal transporters (SGLT1 for glucose and GLUT5 for fructose), the total amount of carbohydrates that can be absorbed and oxidized is increased. Research has shown that when glucose and fructose are ingested together in a 2:1 ratio during exercise at a rate of 2.4 g/min (144 g/hr), the rate of exogenous carbohydrate oxidation can reach 1.7 g/min or about 105 g/hr.¹⁷

Drinks containing multiple transportable carbohydrates are also less likely to cause gastrointestinal distress.¹⁷ In theory, consuming multiple transportable carbohydrates should enhance endurance performance by increasing exogenous carbohydrate oxidation and reducing the reliance on endogenous carbohydrate stores. Compared with an isocaloric amount of glucose, the ingestion of glucose and fructose (1.5 g/min) increased peak exogenous carbohydrate oxidation, reduced ratings of perceived exertion and increased self-selected pedaling rate in the latter stages of five hours of cycling at 50% of maximal work rate. While these findings suggested a reduction in fatigue with the ingestion of glucose and fructose compared with glucose alone, direct measures of performance were not obtained.¹⁷

In another study, ingesting glucose and fructose (1.8 g/min) improved cycling time trial performance by 8% compared with an isocaloric amount of glucose following two hours of cycling at 55% of maximal work rate. The glucose and fructose may have promoted better ATP resynthesis compared with glucose, thus allowing the maintenance of a higher power output. This was the first study to provide evidence that increased exogenous carbohydrate oxidation improves endurance performance.¹⁷

The series of studies conducted by researchers at the University of Birmingham in the United Kingdom demonstrates that consuming between 1.8 to 2.4 g/min of carbohydrates (108 to 144 g/hr) from a mixture of carbohydrates increases oxidation up to 75 to 104 g/hr of carbohydrates.¹⁷ Further research from this group also determined that the athlete’s gut is “trainable” and that adopting a high-carbohydrate diet and consuming multiple transportable carbohydrates during exercise can, over time, improve the absorptive capacity of the intestine, thereby diminishing gastric upset.¹⁸

As stated, protein has a number of benefits in the overall diet of athletes and potentially as part of the pre-and post-exercise feedings. The addition of protein to sports drinks, though, does not improve performance when carbohydrate intake is adequate.¹⁹

High concentrations of pure fructose should be avoided due to the risk of gastrointestinal upset. Fructose is absorbed relatively slowly and must be converted to glucose by the liver before oxidized in the muscle. Since the maximum rate of oxidation of ingested fructose is less than for glucose, sucrose or glucose polymers, ingesting fructose alone does not improve performance. However, in combination with other carbohydrate sources, fructose is well tolerated and increases exogenous carbohydrate oxidation and improves performance.^1,5

Sports drinks that include several different carbohydrate sources (glucose and fructose) may also enhance water absorption, compared with solutions containing only one carbohydrate source. The addition of a second carbohydrate activates additional mechanisms for intestinal transport and involves transport by separate, non-competitive pathways.¹⁷

Carbohydrate Dose and Timing of Intake

Updated recommendations for carbohydrate intake during exercise are absolute (g/hr), rather than based on body weight.^1,17 Athletes should consume 30 g/hr to 60 g/hr of carbohydrates from carbohydrate-rich fluids or foods during endurance and intermittent, high-intensity exercise lasting 1 to 2.5 hours.¹ As the duration of the event increases, so does the amount of carbohydrates required to enhance performance. During endurance and ultra-endurance exercise lasting 2.5 to 3 hours and longer, athletes should consume up to 80 to 90 g/hr of carbohydrates. Products providing multiple transportable carbohydrates are necessary to achieve these high rates of carbohydrate oxidation.¹

Athletes should decide on a refueling plan that meets their nutritional goals (including hydration) and minimizes gastrointestinal distress.¹

Carbohydrate Intake Guidelines²
Duration of Exercise	Amount of CHO Needed	Recommended Type of CHO	Additional Recommendations
30 to 75 minutes	Small amounts or mouth rinse	Single or multiple transportable CHO	Nutritional training recommended
1 to 2 hours	30 g/hr	Single or multiple transportable CHO	Nutritional training recommended
2 to 3 hours	60 g/hr	Single or multiple transportable CHO	Nutritional training highly recommended
>2.5 hours	90 g/hr	Only multiple transportable CHO	Nutritional training ESSENTIAL

Eating for Recovery

The restoration of muscle and liver glycogen stores is important for recovery following strenuous training. It is common for an athlete to engage in prolonged, high-intensity workouts once or twice a day, with a limited amount of time (six to 24 hours) to recover before the next exercise session. Using effective refueling strategies helps to optimize recovery and promote the desired adaptations to training. During competition, especially multi-day events such as bicycle stage races, there may be less control over the exercise-to-recovery ratio. In this case, the goal is to recover as much as possible for the next day’s event. Several factors limiting recovery include:²⁰

Fatigue interfering with ability to obtain or eat food
Decrease in appetite following high-intensity exercise
Limited access to suitable foods at exercise location
Other commitments (e.g. coach meetings, equipment maintenance)
Celebration with excessive alcohol intake or “cheat” meals (high sugar, high fat) after competition

When there are fewer than eight hours between workouts or competitions, the athlete should start consuming carbohydrates immediately after the first exercise session to maximize the effective recovery time between sessions.¹ The athlete should consume 1 to 1.2 g/kg/hr of carbohydrates for the first four hours after glycogen-depleting exercise. Consuming small amounts of carbohydrates frequently further enhances muscle glycogen resynthesis (every 15 to 30 minutes).¹ Recovery meals/snacks contribute to the athlete’s daily carbohydrate and energy requirements.²⁰

During longer periods of recovery (24 hours), it does not matter how carbohydrate intake is spaced throughout the day as long as the athlete consumes adequate carbohydrates and energy (6 to 10 g/kg). The type, pattern and timing of carbohydrate intake can be chosen according to what is practical and enjoyable.^1,7

Carbohydrate-rich foods should be emphasized in recovery meals and snacks to supply a readily available source of carbohydrates for muscle glycogen synthesis.^1,20 There is no difference in glycogen synthesis when liquid or solid forms of carbohydrates are consumed; however, liquid forms may be appealing when athletes have decreased appetites due to fatigue and/or dehydration.²⁰

Glycogen repletion. There are several reasons why glycogen repletion occurs faster after exercise:

Blood flow to the muscles is much greater immediately after exercise
Active muscle cells are more likely to take up glucose
Muscle cells are more sensitive to the effects of insulin during this time period, which promotes glycogen synthesis
Phosphorylases and other enzymes are more active immediately following exercise

Glucose and sucrose are more effective than fructose in restoring muscle glycogen after exercise, as fructose must first travel through the liver. The type of carbohydrate (simple vs. complex) does not seem to influence glycogen repletion, although like pre-exercise fueling, high-fat, -protein and -fiber foods may slow digestion.²⁰

The foods consumed during recovery meals/snacks should contribute to the athlete’s overall nutrient and energy intake. Nutrient-rich carbohydrate foods and lean protein and dairy also contain vitamins and minerals that are essential for health and performance. These micronutrients may be important for post-exercise recovery processes.²⁰ Endurance athletes should avoid consuming large amounts of foods high in fat and/or protein when total energy requirements or gastrointestinal distress limit food intake during recovery. These foods can displace carbohydrate-rich foods and reduce muscle glycogen storage.^1,20

Unaccustomed exercise that results in muscle damage and delayed-onset muscle soreness may impair muscle glycogen synthesis. Such muscle damage appears to decrease both the rate of muscle glycogen synthesis and the total muscle glycogen content. While a diet providing 10 g/kg of carbohydrates daily will usually replace muscle glycogen stores within 24 hours, the damaging effects of unaccustomed exercise result in significant delays to muscle glycogen repletion. Even the normalization of muscle glycogen stores does not guarantee normal muscle function after unaccustomed exercise.²⁰

Protein. Consuming protein with the recovery meal or snack helps to increase net muscle protein balance, promote muscle tissue repair and enhance adaptations involving synthesis of new proteins.²¹ Adding protein to the recovery feeding, though, does not enhance muscle glycogen storage when the amount of carbohydrates is at or above the threshold for maximum glycogen synthesis (1 to 1.2 g/kg/hr).^1,20 Adding a small amount of protein (0.2 to 0.4 g/kg/hour) to a suboptimal carbohydrate intake (less than 1 g/kg/hour), however, can accelerate muscle glycogen restoration.^4,21

Recommendations for carbohydrate and protein intake following exercise include:¹

When there are fewer than eight hours between exercise sessions, start consuming carbohydrates immediately after exercise to maximize recovery time
Consume 1 to 1.2 g/kg/hr of carbohydrates for the first four hours after glycogen-depleting exercise
Early refueling may be enhanced by consuming small amounts of carbohydrates more frequently (e.g. every 15 to 30 minutes)
Add a small amount of protein to first feeding to stimulate muscle protein synthesis/repair: 15 to 25 grams or 0.2 to 0.4 g/kg

The beneficial 15 to 25 g of high-quality protein in addition to carbohydrates can be provided by 16 oz of skim milk (16 g), two to three large eggs (14 to 21 g) or 2 to 3 oz of lean red meat (14 to 21 g).^1,22

Putting it All Together

Giving competitive athletes or “weekend warriors” good advice on how to optimally fuel for exercise helps them improve their performance. The take-away messages that you can share with your clients, family and friends include:

Carbohydrate-rich foods are typically the easiest to digest, tolerate and utilize before, during and after exercise
Carbohydrate intake for exercise performance is well-supported in the research, whereas low-carb, high-fat and high-protein regimens are not yet well-documented (despite the fact that they may be appropriate for some individuals)
Various forms of carbohydrate (liquid, solid, gel) are equally effective; base the recommendations on an athlete’s tastes, likes, dislikes, trained status and intensity of exercise
The Glycemic Index (GI) is less useful than previously determined
Multiple sources of carbohydrates (glucose, fructose, starches and glucose polymers) are important for increased oxidation
With the use of multiple transportable carbohydrates, the body can oxidize more than 60 g/hr of carbohydrate during exercise
Provide absolute carbohydrate intake recommendations during exercise (30-90 g/hour)
Provide relative carbohydrate intake recommendations (based on body weight) before exercise and during recovery
Carbohydrate intake is also effective in exercise sessions lasting 30 to 60 minutes
A dose response for carbohydrate intake and race day performance may exist
Any sports nutrition protocol needs to be specific to the needs of the athlete and familiar to the athlete.

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Fueling for Exercise and Recovery How to Optimize Carbohydrate Intake by Justin Robinson, MA, RD, CSSD, FAFS, CSCS

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