The goal of sports nutrition is to help an athlete optimize performance potential and overall health. For adolescent athletes, the top priority is healthy growth, development, and maturation. In practice, this means assessing nutrition to ensure growth and development is not negatively affected when intense training is combined with poor nutrition.1 The sports physician can assess food habits, timing, and amounts of foods and fluids to give helpful tips during the visit. Physicians can also be the first line of defense for dispelling myths about fad diets. Referral to a registered dietitian can be made for a more comprehensive nutrition assessment.
FOOD SELECTION AND HABITS
Adolescent athletes have a wide range of nutritional needs based on body size, training intensity, age, and sex. Some factors that influence the food choices of adolescents are convenience, cravings, time, peer/parental influence, cost, and food preparation skills.1 For busy teens and working parents, food that is easy to access and carry without much preparation time is appealing. Adolescents tend to depend on snacking because they balance school schedules during the day with training before or after school. Knowing how to choose healthy snacks and having access to healthy options is important for this population.
Collecting a quick diet history can help identify specific eating patterns and raise “red flags” to anything that may need to be addressed in more detail (ie inconsistent eating patterns, disordered eating, lack of food groups, etc.). Food group quantity checklists or 24-hour recall methods are more useful than food logs for providing a snapshot into eating habits, especially if time is limited. Refer to Figures 1 and 2 for templates for daily and weekly food group frequency charts, respectively. It is important to keep in mind that eating habits and patterns can change drastically from training to competition days and from weekdays to weekends.
Collecting a diet history can also help gauge eating times and identify missed eating opportunities during the day. Helping an athlete plan eating opportunities during his/her scheduled day can be beneficial to ensure energy needs are met. It can also be used as a planning tool to guide food selection. See Figure 3 for a sample planning tool.
As stated previously, consuming enough calories to maintain a healthy body weight and keep up with growth/maturation standards should take precedence with performance and training goals coming in second. Energy is usually in deficit or surplus in adolescents, rarely is energy balance seen.1 That being said, research on energy balance for adolescent athletes is limited. There are not specific nutrition and energy recommendations for the adolescent athlete. Currently, young athlete nutritional recommendations are based on the energy calculations of adult athletes and dietary reference intakes for age and sex for micronutrients.1 Estimates of average time and intensity of training are needed to calculate energy expenditure in addition to energy needed for appropriate growth.
The United States Department of Agriculture MyPlate website provides an easy way for athletes to estimate energy requirements: https://www.choosemyplate.gov/MyPlatePlan.2 Athletes who desire more precision may want to consider a referral to a sports dietitian for an assessment using the Cunningham or the Harris–Benedict equations with an appropriate activity factor to estimated energy expenditure.3–5 Although these equations are included in the 2016 joint position statement “Nutrition and Athletic Performance” by the American College of Sports Medicine, it should be noted that the specific nutritional needs of child and adolescent athletes are not addressed in the statement.3 Measures of growth, development, and physiological function should be used to make sure energy intake in meeting the individual's needs.6
Like energy balance, evidence-based recommendations of carbohydrate, protein, and fat intake for the active adolescent are nearly nonexistent. Refer to Table 1 for general macronutrient recommendations for athletes.3 Again, suggested intake is based on adult athlete recommendations.
Carbohydrates are the main source of energy for the body, muscles, and brain. Carbohydrate should provide most of the increased calorie needs of a young athlete.7 Not having enough carbohydrate in the diet can cause early fatigue, and the body can start to break down muscle for energy. Young athletes also store less glycogen than adults, which may cause them to experience fatigue faster.7
Carbohydrate foods cannot seem to get rid of the stigma that carbohydrates cause weight gain or are unhealthy. Low carbohydrate consumption in athletes, no matter what age, can cause poor energy levels because of depletion of glycogen stores.3 Dehydration and cramping is also a concern with low carbohydrate intake because carbohydrates store water in the muscle. It is important to help an adolescent athlete recognize the importance of carbohydrates as an energy source for improved performance and overall health. Priority should be placed on selecting healthy carbohydrate sources around/during training periods, then working on specific amounts. It is a common misconception that carbohydrates only come from grains. Fruit, milk, yogurt, and starchy vegetables (legumes, potatoes, winter squash, etc.) also are sources of carbohydrates. Figures 4, 5 and 6 highlight some easily digestible carbohydrate sources to use during and around training.
Protein intake is usually easily met by a “typical” mixed diet. Vegetarian, vegan, or energy-restricted athletes should be assessed to make sure protein needs are being met. Although there is a misconception that meat is the only source of protein, legumes, nuts, seeds, milk, yogurt, soy, and eggs are examples of nonmeat protein foods. Usually a protein supplement is not necessary.
More protein is often thought of as better, especially for athletes trying to gain muscle or “bulk up.” To gain muscle, or weight, in general, an individual must be taking in more calories than expending. If an athlete is eating more protein than recommended, but still taking in less total calories than expending, weight or muscle gain will not occur.
With protein, try to stress a “food first” approach as well as spreading protein “feedings” throughout the day. Food is the superior source of dietary protein compared with supplements. Consuming protein 3 to 5 times per day in about 20 to 30 g doses provides multiple stimuli to maintain and build lean muscle mass.7 One of these doses should be postworkout when nutrients are delivered to muscles and cells quicker. Protein, along with carbohydrate, post-exercise will help prevent further muscle breakdown and activate muscle repair.3Table 2 provides examples of 20-g protein servings, while Figure 7 gives examples of postworkout snacks and meals.
Fat in the diet is essential for absorption of fat-soluble vitamins and production of cholesterol and sex hormones. Although adolescents use fat more readily as a fuel source during exercise compared with adults, adult recommendations are still used.1 Around 25% to 30% of total daily energy intake should come from fats with less than 10% to 15% from saturated fat sources.7 This is where snack and convenience foods come into play. For many adolescents, snack and convenience foods contribute a bulk of total calorie intake—most of which are higher in fats and saturated fats (along with simple sugars). Finding healthier substitutions for “junk food” or decreasing the occurrence of snack/convenience foods in the diet is the best place to start making changes for this macronutrient. Refer to Figure 8 for examples of healthy snack foods.
VITAMINS AND MINERALS
If an athlete is consuming a well-balanced diet that provides enough calories to meet standards of growth and activity levels, a multivitamin supplement is, most likely, not required. Consider a multivitamin for those who are amenorrheic, iron-deficient, experience food insecurity, restricted food groups such as vegetarians and vegans, or have restrictions due to multiple food allergies.1 Multivitamins have not been shown to enhance athletic performance, and mega supplements or ultrasupplements are not recommended.
Calcium and Vitamin D
Calcium is essential for bone growth, bone mass, nerve impulses, and muscle contraction. Bone development and bone accrual is at its highest rate during adolescence and calcium is a mineral that should be assessed individually.6 The recommended dietary allowance (RDA) of calcium for adolescents is 1300 mg/d6. Milk, cheese, yogurt, calcium fortified foods/juices, soy products, and cereals are good sources of calcium in the diet. Dairy products and nondairy milks are the main source of calcium in a “typical” diet. However, many times if energy is restricted, dairy products are also restricted. Less than 15% of female atheletes 9 to 18 years old meet the recommended calcium intake.8 Calcium supplements are not good substitutes for dietary calcium in regards to impacting bone health but should be considered if dietary needs are unable to be met with food.8 Vitamin D also plays a role in bone health and the absorption of calcium. The RDA is 600 IU/d for 4 to 18 year olds.8 Supplementation should be considered and serum levels checked for those living in the northern hemisphere and/or who play and train indoors.
Iron is another mineral that may need to be evaluated individually. Iron is essential for energy metabolism and oxygen transportation through the body. Iron deficiency and/or iron depletion is a common problem in adolescent athletes due to increased requirements and turnover, but particularly female athletes.1 Iron levels are more of a concern among female athletes, with need increasing after menarche. Low iron can cause decreases in performance such as excessive fatigue, impaired muscle function, weakened immunity, and decreased ability to make decisions.1,3
The RDA for boys aged 9 to 13 years is 8 mg/d and 11 mg/d for 12 to 18 year olds.7 Girls aged 9 to 13 years also have an RDA of 8 mg/d but this increases to 15 mg/d at the 14- to 18-year age range. Food sources of iron are red meat, pork, chicken, eggs, fish, dried fruit, leafy greens, peanuts, beans, and some fortified beverages and cereals. Pairing sources of iron with food high in vitamin C (citrus fruits, orange juice, etc.) helps absorption of iron in the body.
Anemia blood tests and iron screenings should be considered for male and female athletes experiencing any of the symptoms listed above, following a vegetarian diet, or have been consuming a low-energy diet for an extended period of time.1 Iron supplementation is not advised without a diagnosis of anemia or deficiency because iron toxicity is a risk especially in the younger population.
There has been a long-held belief that adolescent athletes are at greater risk for dehydration due to greater heat stress and heat accumulation; however, current research indicates children are not uniquely vulnerable to heat illness.9 That being said, attention should be paid to adequate fluid consumption and prevention of heat illness for any athlete. Fluids should be consumed throughout the day, not just around practice. If an athlete tries to hydrate right before practice, he/she will still be dehydrated. Physicians can help encourage consumption of water or low-calorie flavored drinks throughout the day, as well as with meals (low-fat milk is also a good option at meals). Limited access to fluids during the school day, the inability to leave class to use a drinking fountain or not being allowed to carry a water bottle can be barriers to appropriate hydration.
Along with hydrating during the day, athletes should also consume fluids during activity. Table 3 displays suggested amounts of fluids before, during, and after exercise, although tolerance to amount and needs vary.10 Using preworkout and postworkout weights and adjusting fluid recommendations to fit sweat rate are the best ways to account for individual need and tolerance. See Table 4 for an example using preworkout and postworkout weights for fluid recommendations.3 Generally, for activity lasting less than 60 minutes, water is adequate. For exercise lasting longer than 60 minutes, carbohydrate ingestion during exercise may be beneficial, especially in very hot and humid environments.3Figure 6 presents methods to achieve carbohydrate consumption during exercise.
Consuming a sports drink is a convenient way to add carbohydrates, fluids, and electrolytes, when deemed appropriate, during exercise. Use of sports drinks outside of physical activity can lead to excessive sugar and calorie intake, which may lead to dental caries, being overweight, and obesity.11 Use of a sports drink during activity should be suggested on an individual basis based on training environment, duration, intensity, and the teen's overall health.
It is important to note sports drinks and caffeinated energy drinks are not one-and-the-same. A sports drink is a “flavored beverage containing carbohydrate, minerals, electrolytes (eg, sodium, potassium, calcium, and magnesium), and sometimes vitamins or other nutrients.”11 An energy drink is usually characterized by containing stimulants (caffeine, green tea extract, and guarana), along with carbohydrates, amino acids, vitamins, and minerals.11 Making sure adolescents know the difference and risks associated with energy drinks is crucial.
Some athletes may be considered “salty” sweaters and require extra sodium in their diet. Signs of excess salt loss include sweat that burns/stings the eyes, caked salt (salt on skin, clothes, and hats), and sweat that tastes salty.10 In this case, using a sports drink or adding a small amount of extra salt (1/4 teaspoon of table salt per 1 L of water) to fluids might be necessary. Encouraging the athlete to eat salty snacks such as pickles, crackers, pretzels, and/or adding salt to foods can also help.
Adolescent athletes will gain more performance improvement through healthy growth, maturation, regular training, and adequate nutrition than any supplement may provide. There is limited research on the short- and long-term risks of supplement use in athletes younger than 18 years. Education needs to start earlier within sports teams and schools about the efficacy and safety, or lack thereof, for performance-enhancing substances/supplements. As stated previously, making sure adolescents know the difference and risks between energy (caffeine-containing drinks) and sports drinks is needed.
There are a lot of fad diets touting the benefit of improved performance to the athletic population. Some of these trending diets do have merit for health, such as a gluten-free diet, when medically appropriate, but do not enhance athletic performance. Athletes who exclude certain foods or food groups are at risk of not meeting nutrition guidelines for general health and sport. There are pros and cons to any diet, as well as potential benefits and consequences for the athletic population.
Low-Carbohydrate High-Fat or Ketogenic Diet
The premise behind the ketogenic diet is to limit the amount of carbohydrate available for the body to use as fuel, thus increasing the ability of the body to use fat for energy during exercise.12–14 In most research, a high-fat, low-carbohydrate diet presents as less than 60% to 65% of total energy intake from fat and carbohydrate below 20 g per day or less than 20% of total energy intake. Although the use of a high-fat, ketogenic diet revealed higher rates of fat oxidation, no performance benefits have been shown in endurance or high-intensity exercise thus far.12–14 The capacity for high-intensity exercise is actually at risk of being compromised while following a ketogenic diet.13,14 Research is still exploring the area of ketogenic diets in sport, particularly with ultraendurance sports.
To truly follow a high-fat, low-carbohydrate diet, as described above, would be extremely difficult for the adolescent population. Personally, I do not advise eliminating foods or food groups if it is not medically necessary. Consuming less than 20 g of carbohydrates a day would remove foods such as milk, yogurt, fruit, grains, and starchy vegetables. Carbohydrate foods provide not only the body's preferred energy source, but also vitamins, minerals, and fiber necessary during the growth and development stage of adolescence. Eating a high-fat diet may also lead to a greater intake of saturated fats, playing a factor in increasing the risk of obesity, cardiac disease, etc., later in life.
The Paleolithic (paleo) diet is built around the approach of eating like caveman in the Stone Age nonprocessed, whole foods.15 Foods considered paleo are fresh fruits, vegetables, lean meats, poultry, eggs, fish, tofu, nuts, and seeds. Cereals, grains, legumes, and dairy are excluded from the diet. In short, the principles behind the paleo diet lead to low carbohydrate (nonstarchy vegetables and fruits), higher protein, and moderate to higher fat intake. Since dairy is eliminated, calcium intake usually is low. A study by Osterdahl et al revealed that calcium intake on the paleo diet was at 50% of the recommended dietary intake.16
While this regimen promotes intake of fruits, veggies, lean proteins, and healthy fats, it is very restrictive. The amount of fruit “allowed” in a day is restricted, and as stated before, starchy vegetables, grains, and legumes are eliminated. Such restrictions favor low carbohydrate intake, which can affect energy levels, nutrient, and total calorie intake for athletes. Many “allowed” fresh foods may also be inconvenient for an adolescent athlete to pack and keep for a period. The cost of the paleo diet is reported to be 10% more expensive than a nonrestrictive diet of similar nutritional value.17 While adhering to a paleo diet may decrease body weight and/or body fat percentage, there are less restrictive ways to get the same result.15,17
Utilization of intermittent fasting is more commonly used as a weight loss method than for increased performance. However, many athletes believe the leaner they are, the better they will perform. Intermittent fasting involves fasting for a period with little to no caloric intake.15 Normal eating then resumes after fast. The idea is that fasting curbs hunger and restricts eating opportunities to a smaller window of time and consequently decreases overall calories consumed.15 Although intermittent fasting may decrease body weight and/or body fat percentage, it holds numerous risks and disadvantages for athletes.
A common practice in intermittent fasting is to extend the nighttime fast from sleep, then allowing only a 4- to 12-hour window for eating at the end of the day. Consuming enough calories during this time frame can be a challenge, and avoidance of optimal windows for pre-exercise, during, and post-exercise fueling would cause performance and recovery detriments. For optimal recovery from exercise, athletes should consume carbohydrate and protein within 60 minutes after exercise. In the first 2 to 4 hours after workout, muscles are able to store glycogen more readily, while the introduction of protein switches the body from muscle breakdown to synthesis.18,19 Rehydration from exercise may also be impaired during intermittent fasting. As with calorie consumption, the limited time frame for consuming foods and fluids will make it difficult to drink enough liquids to rehydrate.
A gluten-free diet eliminates the protein (gluten) found in wheat, rye, barley, and triticale. Gluten-free diets are medically necessary for those with celiac disease or a nonceliac gluten sensitivity. Many nonceliac athletes believe that avoiding gluten improves competitive performance.19 There is no evidence-based research that a gluten-free diet is “healthier” or produces increases or decreases in sport performance.20,21 Gluten-free diets may be lacking in protein, fiber, iron, and vitamins while being higher in sugar and fat.20
Avoiding gluten can lead to an emphasis on consuming fruit, vegetables, proteins, and gluten-free whole grains. As diagnosis of celiac disease and gluten intolerance has increased, there has been growth in the availability of healthy and unhealthy gluten-free foods. However, athletes traveling for competition may still have issues with availability of gluten-free foods. Gluten-free foods also tend to be more expensive than gluten-containing counterparts. It may be difficult for athletes to reach carbohydrate needs with the elimination of gluten-containing foods.20 Many carbohydrate foods recommended to athletes, such as bread, pasta, cereals, granola bars, etc., contain gluten.
- See the whole person—not just the athlete. Healthy growth, maturation, and development should be the first priority, but this may not be the teen's first priority. Consideration should be made to how these physical changes are influencing self-esteem and sense of value.
- Know who does the shopping and preparing of meals and include him/her on any nutrition education.
- Do not assume nutrition knowledge is at any certain level. Parents, media, peers, and coaches are often the main sources of nutrition information for this population, and this information may not be evidence-based.
- Advise teens to eat 3 meals plus 2 to 4 snacks daily.
- High-fat, sugary foods should be limited, but not restricted (eg dessert 3x/week).
- Hydration should be an all-day event, not only during training.
- If weight loss is indicated, gradual weight loss or weight maintenance is the goal as they (adolescents) are still gaining height and can grow into their weight. A referral to a registered dietitian should be made to achieve this goal.
- If an athlete is following a “fad” diet, benefits, disadvantages, medical necessity, reason for use, and understanding should be addressed.
- Keep changes simple and link any nutritional education to performance as a motivating factor. For example, how can changing food choices and food timing boost performance.
- Take baby steps when advising more healthful, nutritious choices, so the changes seem more do-able. For example,
Take a positive approach with positive reinforcement and praise. His/her diet still may not be where you would like to see it, but if he/she is making changes in the right direction that should be acknowledged.
- • Soda → 100% fruit juice → low-calorie flavored water → water
- • Potato chips → baked chips → pretzels or baked whole grain crackers
- • Fast food 4 times per week → 2 times per week
- • Lunch out with friends daily → lunch out 3 times per week with 2 packed lunches
The author specially thanks Dr Alison Brooks, University of Wisconsin—Madison, Associate Professor Department of Orthopedics Division of Sports Medicine and Sarah Van Riet, MS, RD, CDE, University of Wisconsin Health.
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