Sports Nutrition

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Macronutrients

Macronutrients are nutrients that provide calories or energy to the body. The purpose of macronutrients is to promote healthy cellular growth, metabolism, and to maintain normal bodily functions. The macronutrients, as suggested by the name “macro,” are needed in the body in large amounts to provide the full and proper effect [1].
There are three types of macronutrients: carbohydrates, proteins, and fats. Carbohydrates are organic materials composed of hydrogen and oxygen atoms which bond together to form monosaccharides, or simple sugar molecules. Carbohydrates are found to form either a simple carbohydrate, composed of one monosaccharide, or a complex (composite) carbohydrate, composed of two or more monosaccharide molecules. When broken down, both simple and complex carbohydrates form glucose, which is the body’s main source of energy [2]. In addition, carbohydrates form an important part of waste elimination and intestinal health, Carbohydrates can be found in most fruits, vegetables and grains and provide the body with 4 calories per gram [3].

Proteins are nitrogenous organic compounds which are involved with many of the body’s most crucial functions including: providing the primary workforce in the cells, making hormones and enzymes, and a high involvement with tissue repair. Proteins also provide energy when there are not enough carbohydrates available as well as sustain lean body mass [4]. Just as carbohydrates are composed of monosaccharides, proteins are composed of chains of amino acid molecules. Also just like carbohydrates, proteins provide the body with 4 calories per gram. Proteins are most commonly found in animal products, nuts, and beans [3].

Fats, which are collectively referred to as triglycerides, are molecules comprised of fatty acids and glycerol. Fats provide essential elements of cell membranes and also provide the body with the ability to absorb the fat-soluble vitamins A, D, and E [5]. As fats are the most energy dense macronutrient, they also provide the highest calorie count, providing the body with 9 calories per gram instead of the 4 provided by one gram of either carbohydrate or protein. The three primary types of fat include: saturated fat, unsaturated fat, and trans fat. Saturated fat, such as that found in butter and cream, as well as trans fat, which is found in snack foods and fried foods, have been shown to increase the risk for heart disease. While in turn, unsaturated fats, which are found in olive oil and canola oil, has been shown decrease the risk of developing heart disease [3].
In regards to athletes, the knowledge of what carbohydrates, proteins, and fats provide the body with will allow them to make the best dietary decisions regarding their performance goals.

Micronutrients

Micronutrients are chemical elements comprised of thirteen organic essential vitamins and seven inorganic minerals [6]. When consumed in the human body, micronutrients play an important role in energy production, hemoglobin synthesis, healthy growth, bone and immune health, and maintain a normal metabolism. Despite the importance of maintaining the correct level of these vitamins and minerals in the body, as the name “micro” suggests, these chemical elements are only required to exist in the body in small amounts to provide ample effect [7].

The thirteen essential vitamins fall into one of two categories, water-soluble and fat-soluble. The water-soluble vitamins, the eight vitamins which compose the vitamin B complex and vitamin C, must be consumed daily as the body is unable to store what it does not immediately use. In contrast, the fat-soluble vitamins, vitamin K, A, D and E, can be stored in the body’s adipose tissue and therefore does not have to be consumed on daily basis to maintain the correct levels in the body [3].

Minerals are inorganic nutrients that also play a key role in ensuring an athlete’s health. The seven minerals needed to maintain accurate energy and hydration levels include: calcium, iron, zinc, magnesium, sodium, chloride, and potassium [3]. These are important because proper hydration prior, during, and after an activity is crucial in the effect on an athlete’s performance.

According to multiple sources, the most important vitamins and minerals for athletes include: calcium, iron, zinc, magnesium, the vitamin B complex, and vitamins C, D and E due to their role in the efficiency of muscle contraction; both smooth and cardiac muscle. These vitamins and minerals can be obtained in a wide variety of food or through added supplementation [5]

Nutritional Recommendations for Athletes

Nutrition is very important to every athlete, and at high levels, where talent and training are relatively equal, it can be the difference between winning and losing. The American College of Sports Medicine (ACSM) published data they complied from multiple sources on recommended nutrition for athletes in which they state, “that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition.”[8] Therefore, athletes are advised to take a careful look at their daily intake of food to make sure their body is getting the nutrients it needs to repair, maintain, and build muscle. There are many recommendations for what athletes should be eating but below we looked at the ACSM and the U.S Anti-doping Agency (USADA) official recommendations.

Overall, the most important recommendation is that an athlete needs to track the amount of energy they are expending each day and make sure they are replacing this energy with a balanced diet of carbohydrates, protein, and fat. The recommended replenishment for maintaining carbohydrate levels in the body is eating 0.68 grams per pound of body weight within the first 30 minutes after training and again every two hours for four hours [8]. For example if a 180 lb. athlete completes their training for the day they need to have a meal/snack with about 122 g of carbohydrates, which could be a multi-grain bagel with peanut butter and an oatmeal bar[9] Importantly, studies have shown it is not necessary for athletes who rest one or two days in between training bouts to follow this post training carbohydrate recommendation as long as they are they are meeting their daily requirements, which are explained below[8].

The ACSM, and many other publications, recommend that an athlete should never train on an empty stomach. They recommend that an athlete eat between 200 and 300 g of carbohydrate three to four hours prior to exercising [8]. The USADA says to add in small amounts of protein to help slow the breakdown of carbohydrates and aid in regulating energy levels by sending carbohydrates to muscles at a steadier rate throughout the training[9]. However, they also say this is up to the athlete and the size of the meal they can tolerate before training. Athletes should experiment with different pre-training meals to find what they feel comfortable with and eat that meal at a time consistent to when they eat the pre-training meal before a game.

Research has shown a strong benefit to endurance performance for athlete performing in events lasting longer than one hour if they eat about 30-60 grams of carbohydrates every hour during the event [8]. This equates to eating a banana, a food bar, or something with equal carbohydrates every hour[9]. The ACSM takes it even further and says it is much more beneficial to the body’s energy storage to eat small snacks or bites of carbohydrates every 15-20 minutes (about 10-20 grams each time) rather than waiting and eating 60-120 grams every two hours[8].The USADA says an athlete can intake 6-12 ounces of a sports drink that has 6-8% carbohydrates to water ratio. Anything greater than a 10% ratio increases the likelihood of cramps and an upset stomach[9]. In similar regard, research is also now showing that high quality protein consumed pre and post training at just 0.2 grams per pound of body weight, which is about 4 ounces of chicken breast, is enough for a “maximal acute anabolic effect [10]." 

For daily intake the USADA, and practically every other organization, recommends that an athlete’s daily calorie should encompass about, 50-70% carbohydrates, 10-35% protein, and 20-30% fat [9]. Therefore, an athlete needs to plan their day of meals according to these percentages so that they know their total caloric intake for a day encompasses enough of each type. Below is a detailed a recommendation from ACSM of the breakdown of each nutrient an athlete needs for their specific body weight:

Carbohydrates
1 hour of training per day 2.5 grams per pound of body wt per hour of training
More than 4 hours of training per day No more than 6 grams per pound of body wt [8]


Proteins
Endurance training 0.54-0.64 grams per pound of body wt
Strength training (to gain muscle mass) 0.72-0.81 grams per pound of body wt
Strength training (to maintain wt) 0.54-0.64 grams per pound of body wt [8]


Fats
20% of daily calories 


They do not recommend a specific value of grams per pound of fats because of the wide variety a person can consume. Almost all athletes do not need to make an attempt to consume more because foods an athlete is eating has fat in it, so the athlete just needs to be careful that he or she is choosing foods that have an adequate amount of fat[8]

For the athlete looking for nutritional recommendations, the primary point of agreement between all researchers is that while there is some flexibility in the optimal timing of nutrients, the most important factor for maximizing benefit from training is to continently meet your daily carbohydrate, protein, and fat needs[10].

Nutrient Timing and Sport

Nutrient timing became popular about 15-20 years ago and is defined as intentionally eating specific foods before, during, and after training. Before this time athletes were not as concerned with their nutrition, let alone when they should eat certain foods. Ivy and Portman state that nutrient timing “will allow you to build more strength and lean muscle mass in less time than ever before.”[11] They set out to debunk the fact that if protein is good for the body then more protein must be that much better to build muscle.

Ivy and Portman explains that muscles have a very specific 24-hour growth cycle that involves the muscle producing energy, recovering, and building, and athletes need to provide specific nutrients at each of these phases[11]. They break these phases down into the energy phase (occurs during training), the anabolic phase (occurs within 45 minutes after training), and the growth phase (occurs after the 45 minutes and until the next training session)[11]. During the energy phase, as explained above, the muscles use its glycogen stores so the athlete needs to already have eaten carbohydrates and protein to aid the protein synthesis after training. During the anabolic phase the athlete needs to follow the recommendations mentioned above and eat enough carbohydrates because the “muscle cell membranes are more permeable to glucose…this results in faster rates of glycogen storage”[12]. Finally, during the growth phase the athlete needs to consume carbohydrate meals with increased glycemic indexes because that helps the glycogen stores for the next workout[13].
This new, at the time, physiological research gave athletes something scientific they could look at and convinced a lot of them that nutrition was an important aspect of training that they have been missing. However, current research is now calling into question exactly how vital the 45-munute-anabolic window is and if it can be stretched [10].

Fluids and Hydration

Dehydration not only negatively alters performance, but also causes serious complications. Dehydration of 1% to 2% body weight negatively influences performance and dehydration of greater than 3% further decreases physiological function and increases an athlete’s risk of developing exertional heat illness or worse [14]. When intense exercise is combined with elevated temperatures or restricted heat loss, core temperature may rise by 2-3 °C and also result in exertional heat illness [15]. Most studies agree that total water intake should be approximately in the 3.0 L (liter) range. Researchers found when dehydration increased, work capacity decreased by as much as 35% to 48%, and work capacity decreased even when maximal aerobic power did not change[14].

One study[14] said water is the most important nutrient for athletic performance and the biggest component of the human body, accounting for approximately 73% of lean body mass. Trained athletes have higher total body water percentage values by virtue of high muscle mass and low body fat, because fat-free mass is roughly 75% water, while adipose tissue is only 10% water[16]. Individual characteristics like body weight, genetics, metabolic proficiency, and heat acclimatization tendency will influence sweat rates[16].

Each pound of weight lost during exercise represents 1 pint (0.5 L) of fluid loss. Electrolytes regulate water distribution in various components of the body, with sodium being imperative to fluid regulation. The major electrolytes lost during exercise are mainly sodium chloride and some potassium. Researchers said sweat evaporation provides is the primary means of heat loss during vigorous exercise in hot weather. The goal of fluid replacement should be to prevent dehydration in excess of 2% body mass from occurring[17].

Before Exercise

The goal of hydrating before exercise is to start the physical activity euhydrated with normal electrolyte levels[16]. Researchers recommended 500-600 mL (17-20 fluid ounces (fl oz)) of water two to three hours prior to exercise and 200-300 mL (7-10 fl oz) 20 minutes before activity[14].

During Exercise

The goal of hydrating during exercise is to prevent excessive dehydration and electrolyte imbalances that could hinder athletic performance[16]. Researchers recommended about 200-300 mL (7-10 fl oz) ever 10-20 minutes during physical activity[14]. Athletes should make sure carbohydrate-loaded drinks have a 4-6% concentration[16].

After Exercise

The goal of hydrating after exercise is to fully replenish any fluid or electrolyte deficits[16]. The athlete should ideally complete rehydration within 2 hours for hydration restoration, ingest carbohydrates (CHO) to replenish glycogen stores, and include electrolytes to prompt rehydration[14]. Sodium in post-exercise beverages conserves fluid volume and stimulates thirst, while CHOs replenish glycogen stores.

Performance Implications

Recent research[17] found:

  • Dehydration has little to no effect on muscle strength or ballistic power but impairs the ability to perform aerobic exercise.
  • 12-15 year-old basketball players with a water deficit of ~2% body mass made fewer shots and were significantly slower at sprinting and lateral movement tests.
  • The players attempted fewer shots and were less able to make shots linked with movement when dehydration had increased to 3%. Stationary shooting was consistent up to 4% loss.
  • Soccer players with modest dehydration during games perceived exercise as more difficult compared to when fluids were consumed with a higher internal temperature. Performance times were worse on running tests that mimicked play, as well.
  • 66% of 139 college athletes surveyed recognized that body mass change is an effective method to evaluate hydration practices, but only 15% actually check their body mass.

Hyperhydration

Excessive hydration that surpasses sweating rate increases the potential of exercise-associated hyponatremia (EAH), a potentially lethal condition. Authors have linked EAH cases to mostly marathon participants, but the possibility remains with any athlete with low sweating rates and a copious amount of fluid[17][16][18].

Ergogenic Aids and Performance

An ergogenic aid is defined as any means that supports in enhancing energy and utilization. Athletes use ergogenic aids to maximize performance separate themselves from competition. Researchers[19] classified ergogenic aids as mechanical, psychological, physiologic, and the more researched pharmacological and nutritional. The general public seems mostly concerned with anabolic steroids, but a vast array of other ergogenic aids have come under scrutiny in athletics. In 2013, 0.7% of male athletes and 0.1% of female athletes reported using anabolic steroids in the last 12 months[20]. Human growth hormone (HGH) is a commonly used aid in athletics, despite no evidence that says it improves strength, power, or performance[21]. Amphetimines, creatine, erythropoietin (EPO), and androstenedione are several other ergogenic aids that are widely used that will be covered below. Numerous researchers reported the use of performance enhancing substances (PES) in athletes as variable and ranges from 5% to 31%[20]. Recent authors conducted an anonymous questionnaire to 2,987 German triathletes and found 13.0 % used PES to improve performance[20]. 15.1 % of athletes noted the usage of cognitive doping to increase focus, determination, and memorization[20].

Anabolic Steroids
The main benefits of steroids is increased muscle size, strength, and lean body mass. Researchers randomly assigned 21 male weight-training subjects to either a testosterone or a placebo group over a 12-week period and found those in the testosterone group had significantly greater increases in muscle strength and circumference and decreases in abdominal skinfold measurements than the placebo group[20]. Common side effects include acne, testicular atrophy, gynecomastia, cardiovascular disease, arrhythmias, stroke, blood clots, liver dysfunction, and cancer[20]. Anabolic steroids are banned in all major sporting associations and events.

HGH
HGH is released in the anterior pituitary gland and stimulates growth through the actions of insulin-like growth factor-1 which promotes lipolysis and protein anabolism to decrease fat and increase lean muscle[22]. Authors reported that although HGH leads to an increase in muscular size, it does not lead to an increase in strength or athletic performance[21]. Common side effects from prolonged fluid accumulation can lead to arthalgias and carpal tunnel syndrome among others[20].

Amphetamines/Stimulants
Commonly used stimulants include amphetamines, ephedrine, caffeine, phenylephrine, and methamphetamines. Stimulants release norepinephrine, which results in vasoconstriction, increased blood pressure, mood elevation, resistance to fatigue, and even an increase in anaerobic capacity in some studies[21]. A lower level of caffeine is the only accepted stimulant with drug testing.

Beta-Hydroxy-Beta-Methlbutyrate (HMB)
HMB is becoming increasingly more popular in supplementing training regimens. It is a precursor to cholesterol and is believed to diminish protein breakdown. Researchers found upper body strength and peak torque generation showed decent improvements after HMB supplementation in untrained individuals, but bench press gains and and leg press one-repetition maximums in trained athletes were not affected[21]. HMB is not tested for and completely safe.

Creatine
Creatine monohydrate is a naturally occurring compound that serves as an energy substrate for muscle contraction and is consumed in most diets. Studies show increases in strength, power, sprint times, total work to fatigue, peak force, and peak power[20]. Of 21,000 students, the NCAA reported 14% usage among all athletes[20], with other studies reporting a 41% to 48% usage among college males[21]. Caution should be observed in extreme, long-term usage, due to liver and kidney disease.

Vitamins
Athletes primarily use vitamin E, C, and A. Researchers thought these vitamins were antioxidants and therefore able to act as free-radical scavengers, but current research does not support their use for significant increases in performance[19].

L-carnitine
Researchers believed L-carnitine slowed muscle glycogen breakdown and led to a decrease in lactic acid production during exercise, which was proved inconclusive[19]. Large doses of L-carnitine can cause excessive diarrhea.

Androstenedione
As a natural precursor to testosterone, androstenedione is thought to allow for conversion to testosterone, but the majority of studies showed no significant increases in composition, strength, and testosterone concentrations[20]. Most researchers found androstenedione lowered HDL levels, which increases the risk of cardiovascular issues, as well as the potential for the down-regulation of endogenous testosterone synthesis[21]. Androstenedione is banned in all major sporting associations and events.

Erythropoietin (EPO)/Blood Doping
Endurance athletes benefit from improved delivery of oxygen to their tissues. One method which athletes attempt this is by living or training at high altitudes and another is through blood doping. Blood doping transfusions artificially increase the hematocrit, which increases the oxygen-carrying capacity of blood[21]. An alternative to doping, the drug EPO, which is produced mostly in the kidneys, increases hematocrit levels when administered in recombinant form. In response to hypoxic exposure, the body produces a greater amount of EPO[20].

After an autologous transfusion of 750 mL of red blood cells, the VO2 max increased by 12.8 %, and times on a treadmill test to exhaustion improved significantly[20]. With blood doping, researchers found a 34% increase in time to exhaustion at 95% VO2 max, and a 44-second improvement in a five-mile treadmill run time performance[21]. Other authors performed a double blind, placebo-controlled study of 4 weeks of EPO supplementation using a cycle ergometer and noted a hematocrit increase from 42.7% to 50.8% and a VO2 max increase from 63.6 to 68.1 mL kg–1 min–1[21].

Eating Disorders and Body Image in Athletes

Athletes may have a more positive body image than nonathletes.  A meta-analytic review found a small effect size which indicated athletes had a more positive body image than nonathletes.  The review found no difference between females or males, the type of athlete, age or body mass index [23].  Those who exercise regularly like athletes have been found to have a more positive body image than those who do not [24]

Despite athletes overall having a more positive body image than nonathletes, they may be more likely to develop an eating disorder.  Common eating disorders include anorexia nervosa, bulimia nervosa, and anorexia athletica.  Researchers compared the pevalence of eating disorders between 1620 male and female elite athletes with 1696 male and female controls.  They found 13.5% of athletes had eating disorders compared with 4.6% of the controls.  Females athletes were also more likely to have eating disorders than males.  Those in aesthetic sports such as gymnastics, dancing, figure skating, aerobics and diving or sports with weight classes were more likely to have an eating disorder than those in endurance, technical or ball game sports [25].  Another medical condition female athletes who compete in sports which emphasize leanness are at risk of developing is the female athlete triad.

The treatment of athletes with eating disorders requires a multidisciplinary appoach.  Coordination and support ideally should be provided from sports medicine professionals, athletic trainers, dieticians, psychiatrists, coaching staff, teammates and those close to the athlete.  Cognitive behavioral therapy, psychodynamic psychotherapy and medications such as selective serotonin reuptake inhibitors and atypical antispsychotics may also be used [26].  Eating disorders should be treated like sports injuries and require prevention, screening programs, correct treatment and timely support [27].

Recent Related Research (from Pubmed)

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References

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