Sports Nutrition for an Adult Female Endurance Athlete
Lona Sandon, M.Ed., R.D.
Ms. Sandon is Assistant Professor, UT Southwestern Medical Center, Dallas, TX.
Within the past 12 months Ms. Sandon reports no commercial conflicts of interest.
Release Date: 01/10/2011
Termination Date: 01/10/2014
Estimated time to complete: 1 hour(s).
Albert Einstein College of Medicine designates this enduring material for a maximum of 1.0 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.
Albert Einstein College of Medicine is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.
Learning ObjectivesUpon completion of this Cyberounds®, you should be able to:
The combined position of the American Dietetic Association (ADA), Dietitians of Canada and the American College of Sports Medicine (ACSM) states that physical performance and exercise recovery can be improved through quality nutrition. Active adults and athletes can improve their physical performance by making appropriate food and fluid intake choices with consideration of timing of intake.(1) In this Cyberounds®, we review the current guidelines for sports nutrition with application to adults participating in moderate endurance events.
Energy requirements are determined by age, height, weight, gender and activity level.
How Many Calories Does Anna Need To Support Her Activity Level?
Meeting energy needs in active individuals is important for the maintenance of appropriate body weight and composition, exercise endurance and recovery, and prevention of injury and illness. Menstrual dysfunction, loss of lean muscle tissue, low bone density and frequent illness may indicate inadequate energy intake. Athletes who do not consume adequate calories may find themselves feeling weak and fatigue more easily. They are also less likely to attain recommended nutrient requirements. Adequate calories help spare muscle protein (PRO) from being used as an energy source and maintain normal body function.(1)
Energy requirements are determined by age, height, weight, gender and activity level. There are two formulas commonly used to estimate energy needs of active individuals: 1) 2002 Dietary Reference Intakes (DRI) for energy and 2) Cunningham equation. Lean body mass of the athlete must be known to use the Cunningham equation.
2002 DRI Estimated Energy Requirement (EER)(1)(2)
Table 1. PA = Physical Activity Factors.(1)
BMI may not be suitable in a highly active, athletic population.
Is Anna At An Appropriate Weight?
Although body mass index (BMI) is a widely accepted method for assessing appropriateness of body weight in the general population, it may not be suitable in a highly active, athletic population. BMI is not a measure of body composition and body composition must be considered in assessing weight status in athletes. A high percentage of lean body mass may result in a higher BMI, indicating an athlete is overweight or obese, when in fact they are quite lean. Lean mass is associated with greater power, speed, endurance and desirable appearance.
Adequate muscle glycogen repletion best achieved with moderate to high carbohydrate diet.
Body composition will vary by individual, type of sport and age of the athlete. Some body fat is necessary for optimal health and physical performance. The minimum amount of body fat for health is 12% for women and 5% for men.(1)(3) Healthy body fat ranges are listed in Table 2. It is important to remind active adults and athletes that restricting calories or overtraining to achieve a minimally acceptable percent body fat is not necessarily desirable. Attempting to be leaner may actually hinder physical performance. Body fat serves as a source of energy in endurance training, protects organs and produces sex hormones. Very low body fat has been associated with low levels of estrogen and development of amenorrhea and osteoporosis, known as the Female Athlete Triad (FAT). Energy restriction is believed to be the primary cause of these symptoms, not the low level of body fat itself.(3) The FAT is discussed in depth in the ACSM 2007 position stand, The Female Athlete Triad.
Table 2. Healthy Body Fat Ranges For Physically Active Adults.(3)
What Type Of Calories Should Anna Be Eating To Support Her Physical Activity Level?
The type of calories an active adult needs is determined by their training level and sport. Most athletes can obtain sufficient calories and nutrients by following the recommendations of the Dietary Guidelines at a calorie level matched to their physical activity level.(1) Anna is an endurance athlete and therefore relies mostly on the aerobic energy production system. This energy system primarily uses muscle glycogen and fatty acids to fuel endurance activity. Other energy systems are listed in Table 3. Because she trains five times per week, it is important to adequately replenish muscle glycogen stores on a daily basis to maintain a high level of performance and spare muscle PRO as a source of energy. It has been well established in the research literature that adequate muscle glycogen repletion can be best achieved with the consumption of a moderate to high carbohydrate (CHO) diet, as compared to a high fat diet or low CHO diet.
The timing of CHO impacts exercise performance.
Table 3. Main Energy Production Systems Used During Physical Activity.(5)
How Much Carbohydrate Does Anna Need?
The research literature has long recognized the importance of CHO in enhancing exercise performance. Energy production during endurance exercise relies on existing glycogen and fat stores. At intensities lower than 65% maximal oxygen consumption (VO2max), fat provides the greatest energy contribution, while CHO is used in greater proportion at higher intensities. Adequate CHO availability is essential for preventing fatigue during prolonged endurance exercise even at lower intensities.(6) It is recommended that CHO requirements be based on body weight and training condition, as shown in Table 4.(1)
Table 4. CHO Recommendations.(6)(7)
The timing of CHO impacts exercise performance. Some studies have found that consuming a pre-exercise meal rich in CHO two to four hours prior to exercise is beneficial.(6)(9) Amounts believed to enhance performance are 4.5 g/kg of CHO four hours prior to exercise and 1 g/kg of CHO 30-60 minutes prior to exercise. The closer to exercise the meal is consumed, researchers recommend less CHO and a smaller meal to prevent gastrointestinal discomfort.(8)(9) A pre-exercise snack is typically encouraged if it has been more than four hours since the last meal. The pre-exercise snack serves to top off glycogen stores, plasma glucose and prevent hunger during activity.(1)(6) General recommendations include easily digestible foods low in fat and fiber.(1)
Calories and CHOs are key to sparing the use of amino acids as an energy source.
The glycemic index of a food does not appear to affect performance; athletes may, however, find these foods more tolerable immediately prior to exercise. Many athletes find liquid meals such as Boost, Carnation Instant Breakfast or a glass of flavored milk convenient and easy to digest within an hour before exercise, dependent on activity and tolerance of lactose. A liquid meal will also help boost fluid intake.(6)
CHO consumption during exercise lasting more than one hour improves performance in both endurance and stop-and-go sports such as basketball or volleyball. CHO consumption during extended physical activity delays the onset of fatigue and maintains blood glucose at higher levels. The recommendation is to consume 30-60 g of CHO each hour of exercise to enhance performance.(6) CHO in the form of a sports drink is easily digestible and often most practical during endurance events. It will also provide needed fluid. Some athletes may find it difficult to drink enough fluid to provide sufficient CHO. Sports bars, salty snack crackers, gels or gummies may be needed. Athletes should be encouraged to try different options during training for tolerability.
How Much Protein Does Anna Need?
Both endurance and resistance training are believed to increase PRO needs above the current Dietary Reference Intake (DRI) of 0.8 g/kg.(1) Adequacy of total energy and CHO intake impact PRO needs. Calories and CHOs are key to sparing the use of amino acids as an energy source, allowing PRO to be used for muscle anabolism and body functions.(1)(3) PRO oxidation is increased as a result of endurance exercise and may account for 2% to 6% of energy expenditure.(10) Despite evidence that shows PRO turnover is more efficient in endurance trained athletes, intake recommendations range from 1.2 to 1.4 g/kg/day for maintaining nitrogen balance. Athletes who restrict calories, follow a vegetarian diet, consume limited CHO and train on consecutive days for long hours have increased needs for PRO for normal tissue repair and body functions, and should aim for the upper level of the recommended PRO intake. No benefit has been found for consuming PRO above 2 g/kg/day.(1)(10) See PRO recommendations in Table 5.
Table 5. PRO Recommendations.
The timing of PRO intake in relation to exercise impacts recovery and strength gains. PRO consumption immediately before and after exercise has been shown to enhance muscle PRO synthesis and muscle repair. As little as 10 g or 0.1 g/kg of PRO intake immediately following exercise increases net PRO balance in endurance and resistance athletes. High quality PRO containing essential amino acids is superior to providing non-essential amino acids. PRO consumption post-exercise may also help to restore glycogen levels when CHO or calorie intake is insufficient.(10)
Some evidence suggests that PRO intake immediately prior to exercise can enhance muscle recovery by maintaining a positive PRO balance during exercise; this leads to a higher PRO balance post-exercise when compared to consumption of PRO immediately following exercise.(10) PRO ingestion during exercise has not been shown to improve performance. Although two studies showed positive results of PRO intake during exercise, they have been criticized for their design.(11) At this time, there is insufficient evidence to recommend PRO intake during exercise.(11) Athletes should be advised to consume adequate PRO throughout the day and after exercise for recovery and muscle mass gains.
Leucine has been shown to stimulate muscle PRO synthesis.
Most athletes consume adequate amounts of PRO due to higher calorie intakes and therefore supplemental PRO is not needed.(10) A thorough dietary analysis should be conducted prior to making recommendations for PRO supplementation. The use of amino acid or powdered PRO supplements have not been shown to be more beneficial than intact, high quality PRO food sources when adequate energy is consumed.(1) Both soy and milk-based PROs (whey, casein) have been studied for their potential muscle PRO synthesis effects. The current research literature suggests that consumption of whey PRO from dairy milk is superior to that of soy for stimulation of muscle anabolism.(12) Whey PRO is absorbed more rapidly into the blood stream and is a concentrated source of leucine, a branched chain amino acid that plays a role in muscle anabolism. Leucine has been shown to stimulate muscle PRO synthesis.(12)
Athletes’ diets may vary significantly in the amount of energy coming from fat. Individualized recommendations should be based on activity level, energy needs, age and food likes or dislikes. General recommendations are to consume 20-35% of calories from fat and choose mainly poly- and monounsaturated fat sources. Dietary fat should not be restricted. Very low fat diets have been associated with inadequate calorie consumption, nutrient deficiencies and hormone dysfunction. Fat serves as an important energy source particularly during endurance training and is also necessary for absorption of fat-soluble vitamins. A well trained athlete will utilize fatty acids more effectively than a non-trained individual.(3)
How Much Fluid Does Anna Need?
The DRI for adequate intake of fluid for adult males is 16 cups per day and 12 cups per day for adult females. Active adults and athletes may need more. Daily fluid needs may be met from a variety of sources including water, milk, 100% fruit juice, coffee, tea, soup, sports drinks or high water containing fruits and vegetables.(13) Moderate consumption of caffeinated beverages, <180 mg/dL, has little effect on urine output and risk of dehydration in athletes. However, alcohol can increase urine output and it is not advised to consume it post-exercise when rehydration is important,(10) despite what is commonly seen in advertisements and in practice at charity-based and sanctioned endurance events.
Endurance athletes should be encouraged to have a fluid replacement plan to prevent dehydration and monitor their hydration status. As little as a 2% loss of body weight due to dehydration impairs both physical and mental performance. Dehydration can cause increased heart rate, core body temperature and perceived rate of exertion. Fluid needs and losses are dependent on gender, body weight, temperature, humidity, duration and intensity of exercise, heat acclimatization and metabolic efficiency. Women tend to have less sweat and electrolyte losses than men but are at greater risk of hyponatremia.(14) Athletes can be taught to monitor their hydration status by weighing themselves before and after training and paying attention to volume and color of their urine. Scant, dark urine output indicates dehydration.(13)
Regular fluid intake before, during and after exercise helps regulate body temperature and prevent fatigue. The choice of beverage for rehydration depends on duration of exercise, climate, sweat rate and composition, and taste preference. Plain water is appropriate for exercise lasting less than 90 minutes in controlled temperature environments. Specially formulated sports drinks are necessary for extended exercise duration, hot humid climates, high sweat rates and salt losers, and for those who will not adequately replace fluids with water alone due to lack of taste. Sports drinks replace CHO and fluid and electrolytes lost in sweat.(14) Sports drinks formulated with 14 g to 19 g of CHO per cup are best for rapid absorption. Heavy sweaters and high salt losers may need to add additional salt or choose higher salt-containing endurance formulas.(13)
The American College of Sports Medicine (ACSM) provides guidelines for fluid intake before, during and after exercise. Pre-exercise fluid recommendations are to consume 5 to 7 ml/kg four hours prior to exercise. This allows for adequate time for absorption and urine output prior to the start of exercise. The athlete should be in a euhydrated state prior to the start of exercise. Consuming beverages with meals and choosing beverages with a small amount of sodium such as milk, and eating foods with sodium can help retain fluid in the body. Fluid and electrolyte losses during exercise are highly variable. The amount of fluid replacement depends on sweat rate, exercise duration and accessibility to fluids during exercise. The ACSM recommendation is to calculate individual sweat rates under typical training and competition conditions.(14) Sweat rate can be determined using the formula below.
During prolonged exercise, fluids should be consumed early before symptoms of dehydration appear. Beverages containing CHOs and electrolytes are recommended for maintaining fluid balance. CHOs provide energy and maintain plasma glucose levels. Sodium stimulates thirst and desire to drink more in addition to encouraging fluid absorption and retention. Following exercise, the athlete should consume 2 -3 cups of fluid for each pound lost during exercise.(14) Athletes are more likely to voluntarily replace fluid losses when beverages are cold, flavored and sweetened.(13)
Table 6. General Fluid Recommendations.(13)
Scant, dark urine output indicates dehydration.
What Should Anna Eat for Recovery After Training?
The purpose of a post-exercise snack or meal is to replenish fluid losses, muscle glycogen stores and provide amino acids for muscle repair. The timing of the recovery meal can be critical for athletes who train intensely on consecutive days or twice a day. Consuming CHO within 30 minutes of training results in greater muscle glycogen synthesis when compared to delayed CHO intake. Timing is not as critical for athletes with a rest day between intense workouts if they are meeting their daily CHO goals. A post-exercise snack, however, can help meet daily CHO needs. Protein intake closely following training also positively impacts protein balance for maintenance and repair of skeletal muscle.(6)
Low-fat chocolate milk has been studied as a post-exercise recovery and rehydration beverage. It provides CHO similar in type and amount to commercially formulated recovery beverages, essential and branched chain amino acids, and is a natural source of sodium and potassium lost in sweat. Milk has been shown in multiple studies to acutely increase muscle PRO synthesis and lead to lean mass gains when consumed after exercise.(15) The ratio of casein to whey protein allows for a prolonged elevation of plasma amino acid levels producing a positive net protein balance and increased muscle protein synthesis. Whey protein is also a source of the branched chain amino acid leucine, which plays a role in promoting muscle anabolism.(12) In addition, Cockburn and colleagues found that a milk-based PRO may decrease muscle damage when consumed immediately following exercise.(16)
Chocolate milk may help replenish muscle glycogen following glycogen-depleting exercise. In one study, participants consumed either chocolate milk or a commercial recovery beverage following glycogen-depleting exercise. Four hours later they performed a cycling trial to exhaustion. Those who consumed chocolate milk performed equally as well as those who drank the commercial beverage.(15) Milk’s naturally occurring sodium and potassium may also help return an endurance athlete to normal fluid status. Shirreffs and others, as described by Cockburn et al., compared the effectiveness of low-fat milk, low-fat milk with added salt, a sports drink and water for normalizing fluid balance after exercise with sweat losses of 1.8% of body weight. After a 4-hour recovery period, those who consumed the low-fat milk or low-fat milk with added salt had less urine output and were in a state of positive fluid balance. Those who consumed the sports drink or water had greater urine output and remained in a negative fluid balance state at 4 hours.(16) This research suggests that milk is a promising recovery and rehydration alternative to commercially prepared beverages. In addition to the described benefits, milk provides calcium, vitamin D and B vitamins not found in sports drinks and, therefore, may aid in meeting nutritional needs when used as a recovery drink.
Does Anna Need a Vitamin/mineral Supplement?
Frequent moderate to high intensity exercise may increase the need for certain vitamins and minerals. Because of higher calorie intakes, athletes typically meet these needs without additional supplementation. Athletes, however, who restrict calories, are vegan or follow restrictive diets may be at risk of inadequate intake and may benefit from a supplement to correct deficiencies. Vitamin and mineral supplementation has not been shown to improve physical performance when adequate calorie and nutrient requirements have been met through whole food sources.(1)
Vitamins and minerals of greatest concern for athletes are similar to that of the general population and include calcium, vitamin D, B vitamins, iron, zinc and magnesium. Poor calcium and vitamin D intakes may manifest in stress fractures and low bone mineral density and possible muscle pain. Poor iron intake affects oxygen carrying capacity, thus impacting work capacity and endurance. Inadequate zinc can affect muscle strength and endurance, immune system and cardiorespiratory functioning. Low magnesium can impair endurance capacity. These nutrients can be obtained in adequate amounts through a balanced diet rich in fruits, vegetables, whole grains, nuts and seeds, low fat dairy and lean protein sources. Nutrient rich food sources should be encouraged over supplementation.(1)
Many athletes believe that antioxidant vitamin supplements such as vitamin C and E may aid in recovery from damaging free radicals produced during exercise and decrease muscle damage. Although exercise increases production of free radicals, habitual training strengthens the body’s ability to manage free radicals and attenuate their effects.(17) Endurance athletes may have a higher need for vitamins C and E but their effect on performance or reduction of inflammation and muscle soreness remains unclear.(1)(17)(18)
A recent (2010) study by Bailey et al. supplemented subjects for six weeks with a combination of vitamins C and E and compared results to a control group receiving a placebo. After six weeks of supplementation, subjects performed 90 minutes of strenuous activity. Results of oxidative and inflammatory markers and muscle recovery measures indicated that supplementation did not improve muscle recovery nor reduce oxidative stress or inflammation compared to the control group.(18) A review of the literature by Urso and Clarkson shows that others have found evidence to recommend vitamin C intakes between 100 mg to 500 mg per day for endurance and ultra-endurance athletes in earlier studies.(17) These levels can be met with consumption of fruits, vegetables and 100% juices. Athletes who choose to take antioxidant supplements should not take more than the Tolerable Upper Intake level (UL). The UL for vitamins C and E are 2000 mg and 1000 mg respectively.(19)
Chocolate milk may help replenish muscle glycogen.
Nutrition plays an important role in preparing the body for optimal physical performance during sports activities. Meeting energy demands is essential for preventing fatigue during training, while maintaining an appropriate body weight and body composition for peak performance. CHO intake plays a key role in the prevention of fatigue during exercise and in the replacement of glycogen stores in exercise recovery.
Together adequate energy and CHO intake spare protein, allowing it to be used for muscle repair, protein synthesis and body functions. It is believed that endurance and strength athletes require protein levels higher than the current RDA to maintain protein balance and promote muscle protein synthesis. There is no benefit, however, to protein intake in excess of 2 g/kg.
In addition to meeting macronutrient requirements, proper hydration is essential. Endurance athlete must replace fluid and electrolytes lost in sweat. The position of the American Dietetic Association and American College of Sports Medicine recommend the consumption of sports drinks for rehydration during and after endurance exercise or exercise in hot humid conditions.
Recent research supports the use of flavored milk as a recovery beverage. Milk’s nutrient profile makes it almost an ideal beverage for CHO repletion, promotion of muscle protein synthesis, and fluid and electrolyte replacement. In addition, milk consumption can boost intake of nutrients of concern such as vitamin D and calcium. Athletes generally do not need additional vitamin and mineral supplementation if adequate calories and a varied diet are consumed. There is some evidence to suggest higher intakes of vitamin C and E may be beneficial for exercise recovery. A nutrient rich diet should be encouraged over reliance on supplements to meet nutritional needs.