Chapter 17 Nutrition for the Athlete

After studying this chapter, the reader will be able to do the following:

1. Estimate daily total energy needs

2. Describe the appropriate amount of carbohydrate, protein, and fat for an athlete’s diet

3. Describe the appropriate protocol for carbohydrate loading

4. Identify the appropriate nutrient for consumption, before, during, and after exercise

5. Describe optimal fluid intake guidelines for exercise

6. Evaluate ergogenic aids for safety and effectiveness

7. Understand the influence of exercise on gastrointestinal function and the effect of diet

8. Describe how to evaluate the optimal body weight and composition for an athlete

Nutritional recommendations for an athlete depend on many factors including (1) type of exercise; (2) duration of exercise; (3) intensity of exercise; (4) performance goals; and, of course, (5) personal preference. Simply consuming a “sports” bar or “sports” drink does not constitute a top-notch sports nutrition diet plan. This chapter helps to alleviate the confusion about what to eat for peak performance and provides an overview of the basic and essential considerations when choosing foods to fuel an athlete.

ENERGY NEEDS

A top concern for any athlete is making sure the appropriate amount of energy (i.e., calories) is consumed to meet daily needs. This energy is used to fuel not only exercise but any other muscular activity and all the metabolic processes in the body.¹ For an athlete, determining how much energy to consume is the first step in designing his or her sports nutrition diet plan. The three major components of an individual’s energy requirement include the following²:

1. Resting energy expenditure (REE): the amount of energy necessary to maintain basic body systems and body temperature at rest

2. Thermic effect of food (TEF): the amount of energy used following consumption of food/nutrients for absorption, digestion, metabolism, and storage of the food/nutrients

3. Activity energy expenditure (AEE): the amount of energy used during both activities of daily living (e.g., cooking, showering, dressing), involuntary muscular movements (e.g., shivering), and planned physical activity

The average person’s total energy requirement is predominately (60% to 80%) determined by his or her REE,² which varies with body size and composition. A higher body weight will increase REE, while a higher muscle mass will do the same. The second component, TEF, accounts for approximately 6% to 10% of an individual’s total energy requirement and varies by macronutrient composition of the diet, as well as the energy density of a meal.² The final component, AEE, is the most variant factor in determining an athlete’s total energy requirements and typically accounts for 20% to 40% of total energy requirements, but for some elite athletes it can account for closer to half of their total energy needs.¹ This latter factor is the most essential in determining an individual athlete’s energy needs and is heavily influenced by an athlete’s training duration, intensity, and frequency.

CALCULATING AND MEETING ENERGY NEEDS

Most athletes want to know exactly how much energy they need to train and perform, but simply telling them they need to consume 3000 calories daily does little to support their training and improve their performance. In addition to estimating daily energy needs, athletes need guidance in choosing foods and drinks to meet these needs. Several methods exist to measure energy needs including laboratory-based measurements; however, these methods can be complicated and time consuming with limited availability; therefore more simple prediction equations have been developed. Prediction equations have been developed to estimate an individual’s REE on the basis of factors including gender, age, and body weight. Table 17-1 provides some commonly used equations. Most equations were developed using data from sedentary populations, limiting the applicability to athletes.^2,³ Once the REE is estimated, it can then be multiplied by an appropriate factor, which accounts for daily level of activity, to provide an estimate of total energy needs.² For an athlete, choosing the appropriate activity factor is critical and may vary with training and competition (Table 17-2).

Table 17-1 Equations for Estimating Resting Metabolic Rate in Healthy Individuals

Equation 1	Males: REE calories = 11 × body weight in pounds
	Females: REE calories = 10 × body weight in pounds
Equation 2	Males: REE calories = 66.47 + 13.75 (weight, kg) + 5 (height, cm) − 6.76 (age, yr)
	Females: REE calories = 655.1 + 9.65 (weight, kg) + 1.84 (height, cm) − 4.68 (age, yr)
Equation 3	Males and females: 500 + (22 × lean body mass)

REE, Resting energy expenditure.

Data from Cunningham JJ: Am J Clin Nutr 33(11):2372-2374, 1980; Frankenfield DC, Muth ER, Rowe WA: J Am Diet Assoc 98(4):439-445, 1998.

Table 17-2 Activity Factors

	Activity Factor
Activity Level	Male	Female
Resting: Sleeping, reclining	1	1
Sedentary: Minimal movement, mainly sitting/lying down; activities include watching television and reading	1.3	1.3
Light: Office work, sitting, day consists of sleeping 8 hrs with 16 hrs of walking or standing; activities include walking, laundry, golf, ping pong, walking on level ground at 2.5-3 mph	1.6	1.5
Usually includes 1 hr of moderate activity
Moderate: Light manual labor; activities include walking 3.5-4 mph, carrying a load, cycling, tennis, dancing, weeding, and hoeing	1.7	1.6
Very active: Full-time athletes, agricultural laborers, active military duty, hard laborers (mine and steel workers); activities include walking with a load uphill, team sports, climbing	2.1	1.9
Extremely active: Lumberjacks, construction workers, coal miners, some full-time athletes with daily strenuous training	2.4	2.2

Data from ESHA Research, Food Processor, version 8.3, Salem, Ore.

Given that these prediction equations only provide estimated daily total energy needs, evaluating if these estimates are correct can occur through monitoring body weight (i.e., is weight stable or decreasing/increasing as desired? is body weight within a healthy range?), body composition (i.e. fat mass, muscle mass at appropriate levels for sport and health of athlete), and performance.

Once total energy needs are estimated, it is important for athletes to consume foods and drinks that will not only meet these energy needs but also the recommended carbohydrate, protein, and fat needs of the athlete. Tables 17-3 and 17-4 provide an overview of more specific recommendations for carbohydrate and protein intake by exercise level and duration.

Table 17-3 Carbohydrate Intake Guidelines for Athletes

Exercise Intensity	Daily Carbohydrate (grams/pound body weight)
Low intensity (moderate duration)	2.3 to 3.2
Moderate to heavy intensity	3.2 to 5.5
Extreme intensity^*	4.5 to 5.5+
Immediately (0-4 hr) following exercise	0.45 to 0.55

* Elite level.

Data from Burke LM, Kiens B, Ivy JL: J Sports Sci 22(1):15-30, 2004.

Table 17-4 Protein Intake Guidelines

Activity Level	Protein Needs (grams/pound body weight)
Sedentary	0.36
Recreational endurance^*	0.36
Recreational resistance (strength training)	0.36
Moderate-intensity endurance^†	0.54
Elite female endurance athletes	0.53-0.63
Elite male endurance athletes	0.72
Resistance (strength) training athletes (consistent training, midseason, for maintenance of muscle mass)	0.53-0.63
Cross-training or intermittent, high-intensity training athletes (basketball, soccer, hockey)	0.63-0.77
Resistance (strength) trained athletes (early training or promotion of muscle mass growth, or both)	0.68-0.81

* 4-5 times/week for 30 min at <55% VO₂ max.

† 4-5 times/week for 40-60 minutes.

Data from Tarnopolsky M: Nutrition 20(7-8):662-668, 2004; Lemon PW: J Am Coll Nutr 19(5 Suppl):513S-521S, 2000

SPECIFIC RECOMMENDATIONS FOR SPORT AND NUTRIENT INTAKE

Recommendations for nutrient intake vary by sport and should focus around enhancing energy stores, reducing risk of dehydration, preventing nausea and gastrointestinal discomfort, and enhancing muscle and energy recovery while replacing fluid losses.⁴ Recommendations will also vary depending on weight and body composition goals of an athlete. For instance, athletes desiring muscle mass gains must first ensure that overall energy needs are met (including an increase in energy intake if necessary) and second that adequate protein is consumed at appropriate times throughout the day (more on this later).⁵ For all athletes, the key to maximizing the benefit of optimal nutrient intake is timing. Macronutrients and fluid intake in relation to exercise are covered in detail next.

The Role of Carbohydrates and Carbohydrate Loading

Carbohydrates are the main fuel source for the brain and muscles, thereby making them an essential component of each athlete’s diet. Carbohydrates are so essential to an athlete’s diet that the American College of Sports Medicine, American Dietetic Association, and the Canadian Dietetic Association all confer that athletes should strive to achieve optimal carbohydrate intake for peak performance.⁶ Carbohydrates can be found in most foods including grains, cereals, pasta, fruits, vegetables, dairy, nuts, and beans. Just how many carbohydrates an athlete should eat and when they should be consumed will vary by type of exercise. Prolonged or endurance exercise lasting longer than 90 minutes requires high carbohydrate consumption for optimal performance.⁷ Athletes participating in such exercise should focus their dietary practices on consuming the appropriate amount of carbohydrates at key times to maintain high carbohydrate stores (glycogen) in the liver and muscles.^4,⁸ Depletion of these stores is an underlying factor leading to fatigue and decreased performance.^7,⁹ To enhance performance in endurance athletes, the strategy of carbohydrate loading to supercompensate muscle glycogen stores was introduced to endurance training in the late 1960s.¹⁰ The original protocol called for a period of muscle glycogen depletion achieved by consuming a low-carbohydrate diet for 3 to 4 days in conjunction with intense training, followed by another 3 to 4 days, this time tapering exercise and consuming a high carbohydrate diet. This strategy has since been updated to eliminate the period of low-carbohydrate intake and instead focus on 3 to 4 days of high-carbohydrate intake in conjunction with exercise taper.^9,^11,¹² The main factors for athletes to focus on when trying to adopt this nutritional strategy for increasing glycogen stores before exercise are to (1) ensure a high carbohydrate intake (≈3 to 4.5 g of carbohydrates per pound of body weight daily) and (2) taper intensity and duration of training.¹²

Evidence-Based Clinical Application: Carbohydrate Loading

Recent research suggests that highly trained athletes may enhance their glycogen stores in less than 24 hours before competition while still training. When trained endurance athletes consumed a high-carbohydrate diet (≈4.5 g/lb of body weight) over the 24 hours following a 3-minute bout of high-intensity exercise, muscle glycogen supercompensation occurred.¹³

Although endurance athletes benefit from carbohydrate loading before events, athletes participating in exercise lasting less than 60 to 90 minutes should be able to load carbohydrate stores before competition by consuming 3 to 4.5 g of carbohydrates per pound of body weight and resting or reducing training load in the 24 to 36 hours preceding competition.⁴

Evidence-Based Clinical Application: Resting Values for Muscle Glycogen

In trained athletes resting values for muscle glycogen levels are between 100 and 135 mmol/kg wet weight. Following a period of carbohydrate loading, muscle glycogen stores can increase to 150 to 250 mmol/kg wet weight.^4,⁸

Preexercise Carbohydrate and Glycemic Index

The preexercise meal or snack is an important part of the nutritional strategy to promote adequate glycogen stores. The preexercise meal is generally recommended to be consumed 3 to 4 hours before the onset of exercise and be high in carbohydrates, containing approximately 200 to 300 g of carbohydrate.⁷ This is true not only for the endurance athlete but for athletes participating in intermittent sports like soccer matches or basketball games, which can last 1½ to 3 hours and significantly draw on glycogen stores. Even resistance-training athletes desiring muscle mass gains should consume carbohydrates in their meal or snack before exercise to provide energy from carbohydrates to fuel training while sparing protein for muscle repair and growth.⁵

Not all exercise events will permit an athlete to consume a meal containing carbohydrates 3 to 4 hours beforehand, especially if an event is early in the morning. In this circumstance, if the athlete will be engaging in exercise lasting longer than 60 minutes, consumption of carbohydrates within the hour before and also during exercise may enhance performance.^7,¹⁴ Some athletes can be weary of consuming carbohydrates in the hour preceding exercise for fear of this leading to a rapid drop in blood sugar at the onset of exercise, which could impair performance. Although this was once a prevalent theory in sports nutrition dogma,¹⁵ subsequent research and recent reviews on the topic have concluded no effect on performance^16,¹⁷ or improved endurance performance¹⁸ and suggest that any decline in blood sugar that may occur during the first 20 minutes of exercise is later self-corrected, causing no detriment to exercise performance.¹⁹ On the other hand, some individual athletes may be sensitive to fluctuations in blood sugar and consuming carbohydrates in the hour leading up to exercise may negatively affect their performance. For these athletes it has been recommended that if carbohydrates are consumed within an hour of exercise, they should be in a quantity greater than 70 g and possibly with a lower glycemic index (see later).⁴ Overall, athletes who are sensitive to carbohydrate intake close to the onset of exercise should experiment during their training with optimal timing for carbohydrate intake.

The glycemic index (GI) refers to the measure of how quickly a carbohydrate containing food will increase blood sugar following ingestion compared with a reference food like white bread.²⁰ Early research showed that foods with lower GIs consumed before exercise would allow for a more sustained release of glucose into the blood stream during exercise, thereby preventing large swings in blood sugar and improving performance. Additionally, it was thought that a lower-GI carbohydrate allowed for an increase in free fatty acids available for oxidation during exercise that would lead to sparing of glycogen for later energy use.²¹ Although this was a promising theory, limitations to the use of the GI included how other macronutrients (i.e., fat and protein) affect the GI when consumed with a carbohydrate food; the influence of food preparation/processing/ripeness on GI; and the fact that the GI is based on the blood glucose response of 50 g of a carbohydrate, which is an amount that may not accurately reflect the amount of carbohydrates an athlete consumed.²² Furthermore, research has failed to show consistently that lower-GI foods consumed before exercise improve blood glucose response during exercise, while most research evaluating performance and GI has failed to find an enhancement in performance when consuming low-GI carbohydrate versus high-GI carbohydrates before exercise.²³ Finally, the influence, if any, that the GI of a preexercise carbohydrate meal or snack may have on performance is likely overshadowed by the benefits from consuming carbohydrates during prolonged exercise.²⁴ As the timing of food intake preexercise nears the onset of exercise, the major concern surrounding preexercise food selection centers around tolerance.

Carbohydrate Intake during Exercise

In addition to adequate consumption of carbohydrates before exercise, consumption of carbohydrates during exercise lasting longer than 60 to 90 minutes has been shown to improve endurance performance.^8,^9,^14,²³ This improvement in performance has been linked to the following:

• Prevention of hypoglycemia (low blood sugar)

• Provision of energy during later stages of exercise

As mentioned earlier, as glycogen stores get depleted with prolonged exercise—both endurance and moderate-intensity intermittent exercise—blood sugar levels will decrease, reducing the amount of available energy to fuel the athlete. Consumption of carbohydrates during exercise can both prevent this decrease in blood sugar and provide additional fuel when energy stores are reduced. Consumption of carbohydrates during prolonged exercise is of particular importance when adequate carbohydrates to maximize glycogen stores have not been consumed before the onset of exercise. In general it is recommended that athletes consume 30 to 60 g of carbohydrates throughout each hour of exercise ⁶; however, some research suggests that smaller amounts (≈16 g/hour) are sufficient,¹⁴ and other research suggests that more should be consumed.²³ Although research supports that the form of carbohydrate, solid or liquid, does not appear to influence the performance benefits of carbohydrate ingestion,¹⁴ ultimately convenience and individual tolerance will dictate whether an athlete fchooses to drink or eat carbohydrates. As a rule of thumb, an athlete consuming a solid form of carbohydrates (e.g., an energy bar or gel) should consume it with fluid to help improve absorption and reduce stomach distress.

Athletes participating in high-intensity stop-and-go or intermittent sports like basketball or soccer, lasting 60 minutes or longer, can also improve performance through carbohydrate supplementation during exercise. The physiology explaining this benefit is currently unknown but theorized to be associated with an influence on skeletal muscle and possibly the cardiovascular and central nervous systems.²⁵ The exact mechanisms supporting a benefit, as well as the optimal carbohydrate intake during intermittent sports, require future research; however, for now it appears that following the general guideline of 30 to 60 g of carbohydrates every hour will benefit performance. Athletes participating in stop-and-go sports are at an advantage over endurance athletes engaged in long-duration continuous exercise when it comes to carbohydrate consumption and availability opportunities. A soccer player can more easily pack a variety of solid and liquid forms of carbohydrates to keep on the sidelines than a runner can during a race. For both endurance and intermittent sport athletes, consuming 30 to 60 g of carbohydrates in feedings every 10 to 30 minutes will help provide a steady delivery of fuel during exercise and alleviate risk for stomach distress.²⁵

Carbohydrate Intake after Exercise

In addition to consumption before and during exercise, consumption of carbohydrates following exercise is essential to replenishing exhausted glycogen stores, enhancing recovery, and preparing the body for the next event or training session. The postexercise recovery period can be one of the most opportune times for athletes to benefit from optimal sports nutrition practices, yet it can also be one of the most neglected because many athletes, especially following intense exercise, have little appetite or desire to eat and drink. The first hour postexercise is a time in which the highest rates of glycogen storage can occur.¹² Three major effects from exercise likely explain this enhanced period of storage and include the following:

1. Exercise-induced glycogen depletion activates glycogen synthase (the rate-determining enzyme for glycogen synthesis)²⁶

2. Exercise-induced increase in insulin sensitivity—higher insulin will allow for higher delivery of glucose into cells ²⁷

3. Exercise enhancement of muscle cell membrane to delivery of glucose ¹²

Although glycogen synthesis is enhanced for a short time period following intense exercise, as mentioned earlier, it is not always practical for an athlete to consume the recommended amount of carbohydrate during this time. Fortunately, research shows that if the recovery time period between training sessions or competitions is 8 to 24 hours, athletes can delay the initiation of postexercise carbohydrate intake to a more favorable start time, keeping in mind that they must achieve the carbohydrate intake goal for recovery before the onset of their next training session or event.¹² For those athletes with short recovery periods, 4 to 8 hours, efforts should be made to initiate carbohydrate replacement immediately following exercise. This may be more achievable by athletes when the form of carbohydrate is fluid; however, all athletes should experiment with what works best for them.

In addition to timing of intake, the total amount of carbohydrate consumed after exercise affects glycogen storage.¹² To maximize glycogen stores, research recommends a daily carbohydrate consumption of approximately 3 to 4.5 g per pound of body weight (for a 150-lb athlete, this would equal 450 to 675 g daily) for athletes engaging in glycogen-depleting exercise.²⁹ This recommendation is only an estimate and can be lower for athletes participating in recreational exercise or exercise that does not stress glycogen stores; however, for those athletes engaged in high-intensity, long-duration training (i.e., ultraendurance athletes), daily intake of carbohydrates greater than 4.5 g per pound of body weight is recommended.

More specifically, recommendations for immediate carbohydrate consumption include consumption of 4.5 to 5.5 g per pound of body weight immediately after and then again 2 hours following exercise (see Table 17-3).³⁰ Small, frequent, high-carbohydrate snacks, either solid or liquid, can help athletes meet these recommended intakes. Athletes need to remember to follow the postrecovery nutrition diet after both training and competition.

Glycemic Index and Postexercise Carbohydrate Consumption

Although research does not support choosing preexercise carbohydrates on the basis of GI, evidence supports a benefit of consuming carbohydrates with a medium- to high-GI postexercise.^12,³⁰ The greater insulin release and faster rise of blood glucose from a medium- to high-GI carbohydrate compared with low-GI carbohydrate may explain the benefit to glycogen resynthesis, although such has not been clearly explained.¹² Worrying about the GI of a postrecovery meal or snack will not likely be a major concern for most athletes, and the majority will likely consume carbohydrates with higher GIs (e.g., sports drinks) due to the ease and comfort associated with their consumption. Overall, athletes should focus on consuming energy adequate to both replace energy expended during exercise and provide for storage.

Adding Protein to Carbohydrate Postexercise

Results evaluating whether the addition of protein to carbohydrate consumption postexercise will enhance glycogen storage are mixed.³² Some research finds that the addition of protein enhances glycogen storage,³³ while other have not.^30,³⁴^–³⁶ Evaluation of the different study designs suggests that timing/interval of consumption and total amount of carbohydrates consumed may explain conflicting results. Studies that provided exercisers with either a carbohydrate-alone or carbohydrate-plus-protein beverage at frequent intervals (e.g., every 15 to 30 minutes) after exercise found no difference in glycogen storage,^30,³⁴^–³⁶ whereas studies using feeding intervals of 2 hours did.^33,³⁷ These results suggest that more frequent consumption of carbohydrates may offset any benefit that additional protein can have on enhancing glycogen resynthesis. Additionally, with consumption of high amounts of carbohydrate (≈0.5 g of carbohydrates per pound of body weight), additional protein has not been shown to provide any further benefit to glycogen recovery.³⁰ Although these findings do not support a clear benefit of adding protein for enhancement of glycogen storage, they do not dismiss one potential benefit. A recent study found that when recovery time was limited for an athlete, such as occurs with back-to-back endurance events, the consumption of a carbohydrate-plus-protein beverage or snack immediately after exercise (within 10 minutes) improved glycogen recovery over that of a single-carbohydrate-alone beverage or snack consumed at the same time.³³ Until more research is done, it is not clear if consumption of protein with carbohydrate postexercise will improve glycogen resynthesis, but it likely will not limit it as long as adequate carbohydrates are consumed.