As I toed the line at the start of the 2007 Chicago Marathon, two things quickly became obvious: One, the sweat running down my face as I waited for the gun to go off served as a warning that I had better remember to seriously monitor my fluid intake. Two, the extremely long lines for everything from water to the porta-potties confirmed that the popularity of the sport of marathoning was growing in leaps and bounds.
Indeed, the challenge of running 26.2 miles seems to be appealing to more and more people. According
to MarathonGuide.com, approximately 403,000 runners competed in marathons in the United States in 2007, a 2.3% increase from 2006. Last year, more than 340 marathons were held, with the largest race, the New York City Marathon, drawing nearly 39,000 finishers, according to the website.
As I waited my turn to cross the starting line that day in Chicago, I reflected back on my exacting nutrition plan leading up to race day. Having spent more than 4 months scrutinizing my fluid, calorie and vitamin/mineral intake, I was banking on reaping the rewards of that attention to detail. Yet even with my nutrition education and experience, I knew there were no guarantees that I would fare better than my opponents.
Books that cover the science of sports nutrition may be able to quantify exactly how many grams of carbohydrate to load up on before a marathon, how many ounces of fluid to consume daily at each stage of training, and which vitamin deficiencies to avoid. But no one can really tell you the specific foods and beverages that give runners an edge over the competition, as what works for one athlete may not work for the next. The goal of this article is to help you share with your marathon clients the recommended ranges of macronutrients, micronutrients and fluids for most runners, along with practical tips and menus to try
before, during and after the event. While much of this advice
applies to long-distance runners in general, those who run in triathlons and other longer endurance events would require higher intakes of certain nutrients, such as fat and protein.
Tour the aisles of any grocery store and there seem to be as many energy bars, drinks, gels, beans and chews as there are marathons nowadays. While these products vary in taste, palatability, flavor and nutrient composition, they all have one thing in common: they really help out on race day because they provide quick-acting carbohydrate—a must during marathons. Carbohydrate is the primary fuel used during physical activity, and adequate stores are needed for optimal performance.
Carbohydrate is stored in muscles and the liver in the form of glycogen. In most athletes, the amount that can be stored ranges from approximately 375 grams (g) to 500 g, depending on intensity of training and dietary intake (American Dietetic Association [ADA] 2006). Because stores are limited, carbs must be consumed daily during training and before, during and after training runs and races. The following ranges of carb intake are for athletes of all shapes and sizes. In general, athletes with a low body mass
index (BMI) should consume carbs at the low end of the range, whereas those with higher BMIs or those looking to gain weight should consider selecting from the higher end of the range.
Recommended Carbohydrate Intake. The amount of carbs athletes need ranges from 6 to 10 g per kilogram per day (g/kg/dy), which equates to about 2.7–4.5 g per pound per day (g/lb/dy) (ADA 2006). This range can be further quantified
based on an individual’s training level and the type of event. Some experts suggest that athletes in general training should consume 5–7 g/kg/dy (2.3–3.2 g/lb/dy) of carbohydrate, whereas
endurance athletes should consume 7–10 g/kg/dy (3.2–4.5 g/lb/dy) (Burke et al. 2001). Based on these recommendations, a typical 150-pound athlete in training would need about 345–480 g of carbs each day, whereas an endurance athlete or a marathon runner would require about 480–675 g per day.
Anyone who competes in a marathon knows that you need a ton of protein to run your personal best and feel your fittest. Right? Wrong!
Although protein is involved in numerous physiological processes, such as supporting the immune system and building up muscle, most people get enough protein in their daily diet without increasing intake. That’s because the human body uses fat and carbohydrate for energy before drawing on protein.
What we do depend on protein for is maintaining nitrogen balance. Put simply, nitrogen balance is the difference between the amount of nitrogen taken into the body and the amount
excreted or lost. Protein, the only macronutrient that supplies the body with nitrogen, is broken down into nitrogen-rich amino acids during the digestive process. These amino acids are used to synthesize protein, which is then transformed, via the process of protein turnover, back into amino acids. Most of these amino acids are then recycled to create new body proteins, but a small proportion are oxidized and excreted through sweat, feces, urine and other routes. During exercise and at rest, the body tries to conserve protein and therefore does not typically rely on protein as a fuel source. In properly fed individuals, protein provides for less than 5% of energy expended during activity (ADA 2000).
Although studies have thoroughly documented the protein needs of most individuals, there continues to be much debate as to whether physically active individuals require more protein than their sedentary counterparts. Indeed, personal experience often leads athletes to believe that higher-protein diets lead to better finish times and generally enhanced performance (Phillips 2006). Recently, more and more nutrition experts seem to agree that athletes do in fact have higher protein needs than individuals who are less active. According to the most recent joint position statement issued by the ADA, the Dietitians of Canada and the American College of Sports Medicine (ACSM), the mechanisms for these potentially greater protein needs include exercise-induced muscle breakdown and rebuilding, use of small amounts of protein for energy and the need for additional protein to support gains in lean muscle mass (ADA 2000).
Recommended Protein Intake. Although the scientific jury is still out, endurance athletes (along with those performing resistance exercise) probably do need more protein than nonactive
individuals. The Recommended Dietary Allowance (RDA) for the general adult population is 0.8 g/kg/dy of protein (0.36 g/lb/dy) (ADA 2000). Compare this to the protein recommendations for endurance athletes, which range from 1.2 to 1.4 g/kg/dy (0.55–0.64 g/lb/day) (ADA 2000). During times of intense training (including resistance exercise), this recommendation
increases to 1.6–1.7 g/kg/dy (0.73–0.77 g/lb/dy) (ADA 2000).
Most athletes have little difficulty achieving these recommended protein intakes. However, vegetarian and vegan athletes, as well as those concerned with caloric intake and weight, do need to pay close attention to their protein choices and serving sizes. When a healthy body weight is maintained and sound nutrition practices are followed, few runners are at risk for protein deficiency.
No longer a bad word, fat is a necessary source of fuel for athletes. Fat, along with carbohydrate, is oxidized during exercise to provide energy to working muscles. In endurance events, or those lasting longer than 90 minutes, carbohydrate stores are often quickly depleted and the body relies on fat for fuel. At 9 calories (kcal) per gram, fat packs quite a punch in terms of caloric density and energy provision.
Fat-containing foods are key for runners; these foods both provide energy and aid in the absorption of such key nutrients as vitamins A, D, E and K. Because there are no enhanced performance benefits to maintaining a very high fat diet (greater than 70% of total calories from fat) or a very low fat diet (less than 15% of total energy intake), athletes should aim to consume within the Acceptable Macronutrient Distribution Range (AMDR) for fat.
Recommended Fat Intake. The fat AMDR for athletes and most of the adult population is 20%–35% of their total daily calories (National Research Council 1989; ADA 2000). The best way to accomplish this is to get fat from heart-healthy sources, such as plant oils and nuts, and to avoid items that contain saturated fat, trans fat or cholesterol.
Vitamins and minerals play a vital role in energy production; growth and development; and maintenance and protection of bones, tissues, organs, blood and the immune system (ADA 2000). Exercise can increase the need for these nutrients in various ways; for example, by increasing the amount of tissue repair that is required. For most athletes with adequate energy intakes, the respective RDA or Dietary Reference Intake should suffice for vitamins and minerals.
Vitamin and mineral supplementation in an attempt to improve athletic performance is both controversial and likely
unwarranted. However, athletes who have excessive losses of micronutrients in the urine, sweat and feces may require supplementation. The same applies for athletes who severely restrict their overall energy intake, those who have eliminated food groups from the diet and those who follow a special diet—such as vegan or vegetarian.
Common micronutrients that runners should closely monitor and potentially supplement include the minerals calcium, iron and zinc. Mineral deficiencies are most common in female athletes and can have dire consequences. These deficiencies are usually related to a low intake of animal products, including red meat and dairy. Calcium deficiencies can lead to low bone density and stress fracture risk, whereas low iron levels can affect performance and cause fatigue. Zinc deficiencies can negatively impact muscle growth, development and repair, and may also lead to fatigue.
Runners should ensure that they get an adequate daily intake of all B vitamins, especially B12 and folate. Because these two
vitamins are metabolically intertwined, deficiencies in either or both can lead to megaloblastic anemia, a condition that increases serum homocysteine levels, a risk factor for cardiovascular disease. By consuming a diet rich in whole grains and complete proteins, runners can usually avoid micronutrient deficiencies.
Prior to the Chicago Marathon, I had spent months tweaking my training and race-day hydration strategy. I knew exactly how many ounces of sports drink and water I needed to consume per hour in order to maintain optimal performance. I had trained in the heat of the summer and was looking forward to a cool fall marathon. Days before the race, temperatures and humidity in my hometown where I trained began to decrease, and I acclimated nicely. I continued to hydrate appropriately in the days leading up to the race, and I arrived at the event properly hydrated and fueled. Before the gun went off, I even remembered to top off my tank. So how did all this attention to detail play out on race day? Not so well: by mile 6, I was sweating profusely, my formerly acclimated system was going nuts, my fluid tank was empty, and I had to suffer the consequences for 20 more miles.
Without optimal hydration, runners can train until the cows come home and never reap the benefits. Even a slight decline in hydration status—as little as a 1%–2% loss in body weight from fluids—can impair performance (ADA 2006; Sawka et al. 2007). Improper hydration status can lead not only to longer race times but also to decreases in muscle strength, stamina and cognitive function. These losses and impairments are further exacerbated in warm or humid environments.
Most active individuals will lose somewhere between 1 and 4 liters of fluid each hour during exercise, depending on event
intensity, weather conditions and various physiological parameters (ADA 2006). However, the majority of athletes replace only 30%–70% of the total fluid they lose during exercise (ADA 2006). Based on these statistics, it is likely that most athletes who finish a strenuous workout or a long-distance event will find themselves somewhat, if not very, dehydrated. That’s why rehydration is just as important as pre-event fueling and during-event hydration.
In the same way that athletes differ in their training and
superstitions, they are unique in their fluid needs. A blanket recommendation doesn’t work for endurance athletes because each has a unique sweat rate and a different baseline hydration status. If you take two athletes of the exact same size exercising at the exact same intensity, each will have different fluid intake
and sweat losses. Therefore, for optimal hydration, individual athletes should perform a sweat test, or hydration analysis, so they can tailor their hydration intake to sweat and fluid output (see the sidebar “Sweat Test”). The specific hydration recommendations before, during and after a marathon race are shown in the following sections on training and race-day nutrition.
Training and Race-Day Nutrition
It’s lunchtime, and while you can’t ignore the hunger pains in your stomach, you also can’t forget that a hard workout awaits you in a couple of hours. What should you choose to satisfy both of these needs?
Keep in mind that a pre-exercise meal does not contribute immediate energy for exercise. Instead, the ingested fuel is used when the exercise continues for longer than 1 hour. Your pre-exercise meal should not only stave off feelings of hunger but also prevent hypoglycemia (low blood glucose levels) and provide glucose to working muscles.
The focus in any meal eaten before an exercise session should be on carbs. The meal may also contain some protein, but it should be low in fat, which takes longer to digest. Depending on the sensitivity of the athlete’s gastrointestinal (GI) system, caution should be taken when selecting bulking, fiber-rich foods.
For each hour between lunchtime and the workout, be sure to ingest 1 g of carbohydrate per kg of body weight. For example, if the time between lunch and the workout is extensive (about 4½ hours), aim for 4.5 g/kg of carbohydrate, which equates to about 300 g for a 150-pound runner (ADA 2000 and 2006). If the time between lunch and the workout is 1 hour or less, aim for 1 g/kg of carbs, or about 70 g for a 150-pound runner (ADA 2000 and 2006). For a quick “bite” close to the workout time, consider a nutritional shake, which can quickly provide carbs while also being easily digested.
When filling up the tank before exercise, the endurance athlete should not forgo hydration. To begin an event well hydrated, ACSM and the National Athletic Trainers’ Association recommend drinking 13–20 ounces (about 1¾–2½cups) of fluid 2–3 hours before exercise (ADA 2000). (This amount assumes that the athlete has taken in generous amounts of fluid in the 24 hours preceding the workout or race.)
During exercise, athletes rely heavily on pre-existing glycogen and fat stores. By consuming carbohydrate during the workout or race, runners can be sure that there will be fuel available for the kick to the finish. Carb ingestion increases blood glucose levels, permitting greater utilization of blood glucose for energy. When glucose remains available, carbohydrate oxidation can
occur even if muscle glycogen stores are low, allowing for continued endurance and performance.
The recommended amount of carbohydrate intake during
exercise ranges from 30 to 60 g each hour (ADA 2000; Sawka et al. 2007). However, if engaging in intense exercise for longer than 2–3 hours, athletes should up their carb intake to 45–90 g per hour (Sawka et al. 2007). As with caloric needs, the amount of carbohydrate needed depends on the size and metabolism of the athlete. In general, for events lasting longer than 1 hour, 0.7g/kg/hr should meet most athletes’ needs (ADA 2000).
During the early stages of training, athletes should gradually add carbohydrate to daily meals so that on race day, they know how much to ingest and their GI system is ready to take on the load. Carbs can be supplied in the form of food or fluid, depending on individual preference and tolerance. Athletes should aim to spread out the total carb intake so that the same amount is ingested every 15–20 minutes during activity. Consuming carbs intermittently in this way is more effective than ingesting the total amount needed in a single meal.
As to which carbs are best when exercising, some athletes have great success with sports drinks or gels, while others prefer dried fruit, jelly sandwiches or flattened soft drinks. In general, most athletes prefer carbohydrates derived from maltodextrin (glucose polymers), sucrose or glucose over products that contain only fructose, which may cause cramping and diarrhea. However, drinks and gels that combine glucose with fructose or fructose with maltodextrin are more easily oxidized and thus excellent fuel sources.
The ADA recommends choosing a sports drink that contains 4%–8% carbohydrate, or 10–18 g per 8-ounce serving, the carb concentration that is best absorbed by the GI tract during training (ADA 2000 and 2006). Sports drinks also have the added benefit of supplying badly needed electrolytes to the athlete’s system. The added sodium restores lost electrolytes, and the salty taste drives the athlete to ingest more. In addition to providing necessary calories, sports drinks provide vital fluids.
Optimal hydration status depends on many factors, including pre-event hydration, weather and sweat rate. Athletes should aim to ingest fluids every 15–20 minutes. A general rule of thumb is to consume 6–12 ounces (¾–1½ cups) of fluid 3–4 times an hour to maintain optimum hydration status (ADA 2000 and 2006).
For training runs and races lasting 1 hour or less, water is a suitable fluid. However, if you do surpass the 1-hour mark, a sports drink should be the fluid of choice. In fact, because carbohydrate repletion should begin soon after the gun goes off, many marathon runners opt to kill two birds with one stone by drinking carb-containing beverages from the starting line.
During exercise, muscles are broken down and glycogen stores are often depleted. For these reasons alone, recovery is crucial to the endurance athlete. Daily training without attention paid to recovery can be disastrous. Improper recovery can lead to fatigue, malaise and susceptibility to injury.
When exercising at high intensity for longer than 90 minutes, athletes should aim to consume 1.5 g/kg (0.68 g/lb) of carbs immediately after exercise, followed by an additional 1.5 g/kg 2 hours later (ADA 2006). Ingesting carbs immediately following exercise allows for enhanced muscle glycogen reuptake and synthesis, resulting in higher stores of muscle glycogen and more available energy the next time out. If an athlete goes more than 1 or 2 days between training sessions, the timing of refueling is not as critical. When sufficient carbohydrate is provided over
a 24-hour period, the timing of the intake does not appear to
affect the amount of glycogen stored (ADA 2000).
For improved muscle repair, athletes should take in a small amount of protein with the high-carb recovery meal. Dietary protein provides vital amino acids, necessary for both building up and repairing muscle tissue. Although adding protein to carbohydrate does not enhance muscle glycogen storage, it can stimulate muscle protein synthesis.
Because many athletes fail to consume adequate fluids during an event and finish dehydrated, rehydration is of utmost
importance for both health and future performance. In fact,
rehydration is just as important as fuel recovery after exercise, and it’s easy to accomplish if you weigh yourself before heading out the door. By determining how much weight was lost during exercise, rehydration can more easily be accomplished (see the sidebar “Sweat Test”). Consuming up to 150% of the weight lost may be necessary to cover sweat losses plus obligatory urine production (ADA 2000 and 2006).
If the next workout is less than 24 hours away or if the first workout was long and intense, rehydration should commence as soon as possible. To rehydrate, the athlete should aim to consume 23–24 ounces (about 3 cups) of fluid for each pound of weight lost (ADA 2000; Sawka et al. 2007). The best fluid choices are those that contain both calories from carbs and electrolytes; while water is a good thirst quencher, it is not the best choice for
rehydration (ADA 2006). If the urine remains fairly dark, the athlete should continue to drink even more fluids.
After the final workout is completed, rehydration should
begin again, in a more leisurely fashion. Typically, ordinary consumption of beverages, meals and snacks will restore the athlete to a hydrated state within 24 hours. Most food items contain a large percentage of water, and the body uses this water for hydration needs. When combined with food, water can improve fluid retention and expedite rehydration.
Besides aiding muscle recovery and glycogen reuptake, a postexercise meal or snack may provide a burst of sodium, which is crucial to recovery of fluid status and also triggers the thirst
response. If full meals are neither attractive nor tolerable after a workout, one can forego solids and instead obtain sodium and fuel from recovery beverages and bars, sports drinks, and energy bars and gels. On the other hand, if the athlete has an iron stomach and can handle a meal following a workout, make sure it includes salty items, such as pickles, cured or marinated meats, pretzels, soy sauce, certain salad dressings or canned soup.
As I was at the starting line of the Chicago Marathon, I rummaged into a pocket and pulled out a gel. It was the same formulation and flavor I’d been training with all summer. I knew exactly how many I needed, based on how fast I hoped to run. I also knew which fluid stations I would stop at and when I would opt for water over a sports drink. Call me a nutrition nerd, but the impact of nutrition disasters at earlier marathons still haunts me. I vividly remember a race where I tried a new brand of gel—the nausea and diarrhea that began at mile 18 lasted for 2 days! And I will never forget the race where I skipped some fuel and felt the aftermath when I hit an early wall.
The moral of this story is that race-day nutrition should mimic training nutrition. The general strategy should be “nothing new on race day.” Even when given free new bars, gels and drinks at the race expo, runners should maintain the same diet they used during training. For example, if you consumed 32 g of carbs per hour from sports drinks during your training runs, you should do the same thing on race day. If your regular pretraining run meal was oatmeal, banana and orange juice, that should be your meal plan on race day.
Take care to get up early enough on the day of the event so there’s time to eat a proper (and tried-and-true) breakfast. After months of training, you don’t want to lose ground just because your alarm didn’t go off on time. Pay optimal attention to your fluid and fuel, and give yourself the best chance that your race will go off without a hitch.
Sidebar: Overall Energy Intake for Runners
Long-distance athletes come in all shapes and sizes, and so do calorie recommendations. Calorie needs for athletes and runners must be personalized, and it is difficult to recommend a set amount of calories per pound. The RDA for healthy, moderately active men and women is set at 2,900 and 2,200 calories per day, respectively (National Research Council 1989). In terms of calories per kilogram of body weight per day, this equates to 37-41 kcal/kg/dy (ADA 2000).
Runners can use these recommendations for calories and tailor them to their own needs, based on their specific training regimen and miles covered. A good rule of thumb is that you burn approximately 100 calories per mile, according to the industry website www.runnersworld.com. Whenever possible, athletes should strive to achieve the acceptable macronutrient distribution range for all macronutrients; total energy should be made up of 45%-65% carbs, 20%-35% fat and 10%-35% protein (Phillips 2006). Endurance athletes should try to get the higher range for carbs and proteins and should aim for the low end of the fat range.
Sidebar: Sweat Test
A sweat test, or hydration analysis, should be performed in a climate that mimics actual racing conditions. If you will be running a race in the fall, a summer sweat test may overestimate fluid needs. While not perfect, this overestimation may be better than testing for a summer marathon in springlike conditions. Athletes should always remember that if the sweat test was performed on a hot and humid day and the actual day of the race is marked by a cool, pleasant breeze, their fluid needs will have changed and will likely be less than estimated. If this occurs, athletes need to pay careful attention to their sodium status and avoid the dreaded hyponatremia, or water intoxication.
Here’s how to perform a sweat test:
- Warm up, hydrate, and urinate as normal before a 1-hour workout. Weigh yourself naked on your scale.
- Perform a 1-hour workout at race-day intensity. Do not urinate or eat solids during the session, but consume fluids as normal. Pay careful attention to the amount of fluids consumed.
- After completion of the workout, weigh yourself naked, using the same scale.
- Calculate the sum of your postworkout weight loss, plus the fluid ounces drunk to get your sweat rate. (Helpful hint: there are 16 ounces in a pound and 8 ounces in a cup.)
- If the total number is lower than your start weight, you need to increase your fluid intake by the amount of the deficit. Keep in mind that the amount lost is per hour. Because a marathon lasts much longer than that, fluids should be consumed each hour of the race to accommodate for losses.
Sidebar: Sample Race-Day Meal Plan
The following is an example of what and when to eat and drink on the day of the big race, based on the calculated needs of a 150-pound runner. This menu contains sample meal patterns for before, during and after the event and is based on current federal nutrient recommendations (U.S. Department of Agriculture 2008).
Breakfast (2 hours before race). Concentrate on carb intake, aiming for 1 gram per kilogram of body weight (g/kg) or 0.45 g per pound of body weight (g/lb) each hour before the race, which provides approximately 2 g/kg (0.9 g/lb).
- 2 (4-inch) waffles (frozen, whole wheat)
- 1 tablespoon (tbs) reduced-fat buttery spread
- 2 tbs maple syrup
- ½ cup fresh blueberries
- 1 cup sliced banana
- 8 ounces (oz) green tea
- 1 teaspoon honey
- 16 oz sports drink (drink half [8 oz] with breakfast and save half [8 oz] for 1 hour before the race, as shown below)
Basic Analysis: 647 calories; 7 g protein; 130 g carbohydrate; 11 g total fat; 2 g saturated fat; 525 milligrams (mg) sodium; 0 mg cholesterol; 8 g fiber.
Right Before Race. One hour before, drink the other half (8 oz) of the sports drink from breakfast; 20 minutes before, drink about 7-9 oz (about 1 cup) of fluids.
During Race. Aim for 0.7 g/kg (0.32 g/lb) of carbs per hour and 6-12 oz of fluid every 15-20 minutes, as follows:
- 15 minutes = 6 oz water
- 30 minutes = 6 oz sports drink
- 45 minutes = 6 oz sports drink
- 60 minutes = 1 gel + 6-8 oz water
Basic Analysis: ~190 calories; 48 g carbohydrate.
Recovery Meal. For optimal recovery after the marathon, consume 1.5 g/kg (0.7 g/lb) of carbs immediately after the race, followed by an additional 1.5 g/kg 2 hours later.
Immediately After Race. Aim for nutrient intake as follows:
- 16 oz sports drink
- 1 medium banana
- 1 small plain bagel
- additional water depending on weight loss from sweat (see the sidebar “Sweat Test”)
In 2 hours, aim for an intake of food and fluids similar to the recovery meal shown above.
Basic Analysis: 380 calories; 8.5 g protein; 83 g carbohydrate; 1.5 g total fat; 533 mg sodium; 537 mg potassium.
Sidebar: More Winning Tips
Prior to the big event, runners should research the race route and find out where the stops for fluids will be located, which beverages will be served and which gels will be provided. If unable to train using the race-sponsored gel, athletes should bring their own with them to the race.
Gels and other products of this nature may seem to the newbie marathoner to be difficult to transport. Not so. Many vendors now make lightweight, comfortable waist packs that can easily hold beans or blocks; these same manufacturers also make fuel belts designed to carry gels and fluids. Today’s running shorts typically include an interior pocket, which can carry a gel or two, and some even contain exterior pockets with zippers to keep additional fuel safe. When all else fails, you can pin these products to the waistband of your shorts.
American Dietetic Association (ADA). 2000. Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. Journal of the American Dietetic Association (JADA), 100 (12), 1543–56.
ADA. 2006. Sports, Cardiovascular, and Wellness Nutritionists Dietetic Practice Group. In M. Dunford (Ed.), Sports Nutrition: A Practice Manual for Professionals (4th ed. [Query1].) Chicago: ADA.
Burke, L.M., et al. 2001. Guidelines for daily carbohydrate intake: Do athletes achieve them? Sports Medicine, 31, 267–99.
National Research Council. 1989. Recommended Dietary Allowances (10th ed.). Washington, DC: National Academy Press.
Phillips, S.M. 2006. Dietary protein for athletes: From requirements to metabolic advantage. Applied Physiology Nutrition Metabolism, 31, 647–54.
Sawka, M.N., et al. 2007. American College of Sports Medicine: Position Stand on Exercise and Fluid Replacement. Medicine & Science in Sports & Exercise, SC, 377–90.
U.S. Department of Agriculture (USDA). 2008. Nutrient analysis retrieved from www.nal.usda.gov/fnic/foodomp/search, Apr. 20, 2008.
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