Sports and Energy Drinks: Aspects to Consider

SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER

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Raquel Raizel, Audrey Yule Coqueiro, Andrea Bonvini, Julio Tirapegui Department of Food and Experimental Nutrition, Faculty of Pharmaceutical Sciences, University of São Paulo, São Paulo, Brazil

1.1 Introduction The development of nutritional beverages specifically geared toward improving the athletic performance has increased dramatically over the last decades (Park et  al., 2013). The sports beverage industry has evolved from a single electrolyte drink to a multibillion dollar category within the larger sports drinks, sports food, & sports supplements markets. According to the report titled “Sports Nutrition Market (Sports Food, Sports Drink & Sports Supplements): Global Industry Perspective, Comprehensive Analysis, and Forecast, 2016–2022,” published by Zion Market Research, the global sports nutrition market accounted for USD 28.37 billion in 2016 and is expected to reach USD 45.27 billion by 2022. Sports and energy drinks/beverages are sold with the aim of providing real or perceived enhanced physiological and/or performance effects by delaying the onset of fatigue (Thomas et  al., 2016). These drinks commonly contain a source of carbohydrate, electrolytes (minerals such as chloride, calcium, magnesium, sodium, and potassium), stimulants (such as caffeine, guarana, and taurine), vitamins, and others. Although sports drinks are primarily formulated to meet the needs of athletes during strenuous physical exercise, these products are increasingly attracted by lifestyle and recreational users (Higgins et al., 2010). According to the 2010 National Health Interview Survey data for 25,492 US adults (18 years of age or older; 48% males), 31.3% of adults were sports and energy drink consumers, with 21.5% consuming sports and energy drinks one or more times per week and 11.5% consuming three or more times per week (CDC, 2010). Worryingly, a high proportion of children have consumed sports drinks regularly and outside of sporting activity, increasing the risk of dental caries and erosion, since sports drinks are acidic and high in sugar (Broughton et al., 2016). Sports and Energy Drinks. https://doi.org/10.1016/B978-0-12-815851-7.00001-2 © 2019 Elsevier Inc. All rights reserved.

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Although sports drinks can hydrate and replenish electrolytes and carbohydrates, assisting to meet thermoregulation, and athletes’ nutrition recovery goals, the elevated levels of stimulants, such as caffeine, in energy drinks may increase urinary output and natriuresis (Higgins et al., 2010; Riesenhuber et al., 2006). These conditions, as well as the intake of an excessive amount of hypotonic fluid, may lead to exertional hyponatremia, a common electrolyte disturbance that, if not treated properly and promptly, may be potentially fatal due to encephalopathy (Casa et al., 2012). Long-term exposure to the various components of energy drinks may also result in significant alterations in the cardiovascular system and, although energy drinks may promote benefits to physical performance, this has raised the question about the safety of these beverages (Riesenhuber et  al., 2006; Alsunni, 2015). Despite several studies showing ergogenic effects of sports and energy drinks and manufacturers of energy drinks claiming they are suitable and safe for consumers, currently, significant concerns have been raised about the need and safety of these products (Alsunni, 2015). In this chapter, we summarize important aspects of these beverages, including their nutritional composition, applicability, biological properties, and beneficial and adverse health effects, focusing on physical exercise and sports.

1.2  Component of Sports and Energy Drinks The main role of a sports beverage is to stimulate rapid fluid absorption and speed rehydration, supply carbohydrate as energy substrate for use during exercise, and promote overall recovery after exercise. Energy drinks are marketed as products contributing to the increase of mental and physical energy boost, enhancing physical and cognitive functioning. Nonetheless, evidence to support these declarations is limited. The main components of sports and energy drinks are illustrated in Table 1.1.

1.2.1  Sports Drinks Sport drinks are a unique category within the beverage industry and are formulated for quick replacement of fluids and electrolytes that are lost by sweating during exercise, and to provide carbohydrate (sugar) to replenish glycogen stores, thus sustaining performance capacity (Campbell et al., 2013). The hydration effect of sports beverages is not immediate since the fluid must be absorbed in the proximal small intestines, where 50%–60% of any given fluid ingested orally is absorbed (Riesenhuber et  al., 2006). Thus, the “ideal” sports drink should provide a rapid gastric emptying rate, a body fluid balance,

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Table 1.1  Composition of Sports and Energy Drinks and Their Use in Sports Sports drinks

Energy drinks

Composition

Sports-Related Use

6%–8% CHO (including glucose, fructose, sucrose, maltodextrin) 10–25 mmol/L sodium 3–5 mmol/L potassium 9%–10% CHO or sugar free Caffeine Amino acids Herbal substances Vitamins and other ingredients

Optimum delivery of fluid + CHO during exercise Postexercise rehydration Postexercise refuelling Not formulated for rehydration Claimed to give energy “burst” Excessive consumption results in mainly caffeine-related adverse effects

CHO = carbohydrates.

minerals that are typically lost through sweat during exercise and an adequate carbohydrate source to aid in energy supply and performance (Maughan et  al., 2016). Among the available sports drinks, there are three main types (isotonic, hypertonic, and hypotonic) containing different amounts of fluid, electrolytes, and carbohydrate.

1.2.1.1 Isotonic Isotonic drinks are produced with salt and sugar levels similar to those found in the human body. It quickly replaces fluids lost by sweat offering a boost of carbohydrate. They are the preferred choice for most athletes, including middle and long-distance running or those involved in team sports. Most sports drinks are moderately isotonic, containing between 13 and 19 g of sugar per 250 mL and small amounts of electrolytes in the form of salts, most commonly sodium (Colakoglu et al., 2016).

1.2.1.2 Hypertonic When compared to the human body, hypertonic drinks contain high concentrations of salt and sugar. Normally consumed postworkout to supplement daily carbohydrate intake and refuel muscle glycogen stores. Can be taken during ultradistance events to meet high-energy demands, but must be used in conjunction with isotonic drinks to replace lost fluids. Hypertonic drinks have been suggested to cause gastrointestinal distress via water retention in the human

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i­ ntestines and incomplete absorption of carbohydrates, because of its excess (de Oliveira and Burini, 2014).

1.2.1.3 Hypotonic Hypotonic drinks contain lower levels of salt and sugar in comparison to the human body. These beverages quickly replace fluids lost by sweating and are suitable for athletes such as gymnasts, who require fluid without a carbohydrate boost. Evidence suggests that a hypotonic sports drink provides minimally to moderately faster fluid absorption than more concentrated isotonic-hypertonic sports drinks. However, although hypotonic carbohydrate-electrolyte sports drinks might offer benefits over more concentrated drinks in shorter duration performances, larger carbohydrate intakes may be more beneficial over longer durations (Rowlands et  al., 2011). Supplementation with low carbohydrate plus protein or amino acids, in small amounts, has been suggested to improve aerobic capacity compared with traditional sports beverages, which may facilitate recovery improving subsequent performance (Martínez-Lagunas et al., 2010). Moreover, it may be an effective strategy to enhance aerobic capacity while limiting the carbohydrate and caloric consumption.

1.2.2  Components of Sports Drinks Sports drinks typically provide a small amount of carbohydrate (e.g., 6–8 g/100 mL) and electrolytes (sodium, potassium, calcium, magnesium).

1.2.2.1 Carbohydrate Carbohydrate provides a fuel source for the muscles and the brain, and contributes to the palatability of sports drinks. It is well known that consuming carbohydrate can have benefits on performance in a range of sporting events. According to the Academy of Nutrition and Dietetics, sports drinks ideally should contain a 6%–8% carbohydrate concentration and isotonic level, allowing faster gastric emptying during exercise. Most sports drinks offer a blend of carbohydrate sources, such as sucrose, glucose, fructose, and galactose. A few beverages may also add maltodextrin, a glucose polymer that is rapidly digested and behaves identically to glucose being preferentially utilized in exercise (Rowlands et al., 2015). Some research suggest that sports drinks offering a blend of carbohydrates, such as glucose and sucrose, rather than a single carbohydrate source may improve intestinal carbohydrate absorption, since different sugars are absorbed through different routes in intestinal tract (de Oliveira and Burini, 2014). This means increased carbohydrate is supplied to active muscles to

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r­ eplenish glycogen stores, which may improve sports performance (de Sousa et al., 2007). Despite all the evidences, the majority of beverages consumed during some sports (such as an ultra-endurance triathlon) does not contain an optimal saccharide profile (Wilson et al., 2015). Multiple transportable monosaccharides intake (glucose  +  fructose) during prolonged exercise increases gastric emptying, intestinal fluid absorption, and fluid delivery because glucose and fructose are absorbed by different transporters. Glucose transport across the intestinal brush border occurs by sodium-dependent glucose transporter 1 (SGLT1), whereas fructose is absorbed by GLUT 5 (Jeukendrup and Moseley, 2010). Moreover, the intake of solutions containing glucose and fructose increases exogenous carbohydrate oxidation and endurance performance, relative to single carbohydrate solutions (O'Brien et  al., 2013). High intake of glucose plus fructose (90 g/h) prevents stomach fullness sensation, compared with glucose intake (Jeukendrup et  al., 2006). Studies have suggested that a glucose-to-fructose ratio of 1.2:1 to 1:1 is optimal to increase the exogenous carbohydrate oxidation while minimizing gastrointestinal distress during exercise (O'Brien et al., 2013; O'Brien and Rowlands, 2011; Rowlands et al., 2008). Enhanced high-intensity endurance performance with a 0.8 ratio of fructose-maltodextrin-glucose drink is characterized by higher exogenous-carbohydrate oxidation efficiency and reduced endogenouscarbohydrate oxidation (O'Brien et al., 2013). In general, fructose and glucose composites enhance exogenous carbohydrate oxidation, gut comfort, and endurance performance, relative to single-saccharide formulations. Studies showed that when 0.5:1 ratio composites are ingested at 1.7 g/min, improvements are larger than at 1.4–1.6 g/min. Authors concluded that solutions containing a 0.7–1.0: 1 fructose: glucose ratio are absorbed faster; when ingested at 1.5–1.8 g/min, a 0.8:1 fructose: glucose ratio conveyed the highest e­ xogenous carbohydrate energy and endurance power compared with lower or higher fructose: glucose ratios (Rowlands et  al., 2015). It has been also observed that stomach fullness, abdominal cramping, and nausea are lower with solutions containing 6% and 7.5% of fructose and maltodextrin, respectively, followed by the 7.5% and 6% solution. The intake of carbohydrate at high rate, such as solutions containing 6% and 7.5% of fructose-maltodextrin, may be beneficial to endurance performance, as well as to promote gastrointestinal comfort (O'Brien and Rowlands, 2011).

1.2.2.2 Electrolytes The adequate fluid reposition by sports drinks can also prevent and/ or treat other conditions that affect athletes, such as heat exhaustion and muscle cramps, improving physical performance. Excessive sweating ­results in salt loss, which has been implicated in exercise associated

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­ uscle cramps and in salt loss hyponatremia during long-duration (98 h) m endurance events in the heat (Armstrong et al., 2007). These requirements have led to the development of different products with a large range of added electrolytes (less than 1%) by the food industry, to cover the nutritional needs of athletes. However, most commercial sports drinks contain sodium, chloride, and potassium, which are lost in sweat in high amounts during strenuous physical exercise (Thomas et al., 2016). Sodium, an electrolyte lost in large amounts during and after exercise through sweat, helps to regulate fluid balance, nerve transmission, and acid-base balance, promoting the intestinal uptake of fluid and improves hydration. Athletes have higher sodium requirements compared to the general population and the poor fluid balance induced by sodium loss may induce muscle cramps and hyponatremia in extreme situations (i.e., blood sodium levels much lower than normal). Sports drinks containing sodium have better palatability and trigger the thirst mechanism, which make athletes increase the fluid intake enhancing hydration and improving physical performance. The sodium added in sports beverages will replace sodium lost through sweat during intense and long-duration exercises, and help to maintain electrolyte balance. The replenishment of sodium is necessary when individuals exercise at high intensities or in hot environments with high humidity (Kreider et al., 2010; Thomas et al., 2016). Potassium assists in muscle contraction besides maintaining electrolyte balance and regulating blood pressure. Thus, the combination of sodium and potassium in sports beverages may prevent muscle cramps, a crucial aspect to improve performance. Although sodium and potassium are the electrolytes lost in large amounts in sweat, the addition of magnesium and calcium in the same drink is also important to assist in muscle contractions and to ensure optimal muscle function (Kreider et al., 2010).

1.2.2.3  Other Ingredients Flavor is an important characteristic of sports drinks. The more you enjoy the flavor of a drink, the more you drink. The most recent generation of sports drinks includes beverages without artificial ingredients, which feature stevia sweeteners and organic agave syrup as a source of carbohydrate, and natural sea salt and coconut water as a source of electrolytes. Beverages marketed as sports drinks have other added ingredients like vitamins, amino acids, and herbs. It is worth mentioning that additional ingredients may affect the palatability and subsequent consumption of a sports drink. The recovery benefits of carbohydrate and protein ingestion are well documented. However, the potential performance benefits of ingestion during exercise are mixed. Minerals, such as sodium bicarbonate, can also be added to sports drinks to buffer the acid (H+) and carbon dioxide (CO2), ­accumulated in the

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­ uscle and blood during high intensity exercise, with bicarbonate m ions. This can delay muscle fatigue and increase endurance capacity, but some people have difficulty to tolerate bicarbonate as it may cause gastrointestinal distress. B complex vitamins as well as antioxidants, such as vitamins A, C, and E, selenium and green tea extract are also common in sports products. Since B vitamins and vitamin C are water soluble, excessive intake of these vitamins may be eliminated in urine, with few exceptions (e.g., vitamin B6, which can cause peripheral nerve damage when consumed in excessive amounts) (Kreider et al., 2010). The main categories of sports drinks, their key ingredients, and functions are presented in Table 1.2.

1.2.3  Energy Drinks Energy drinks are designed for the specific purpose of providing real or perceived enhanced physiological and/or performance effects. Consuming energy drinks before exercise is thought to improve mental focus, alertness, anaerobic performance, and/or endurance performance. According to The Stimulant Drinks Committee, the

Table 1.2  Categories, Key Ingredients, and Function of Sports Drinks Category Preexercise Energy Energy + supplements During exercise Electrolyte/hydration

Postexercise Recovery Protein Meal replacements

Key Ingredients

Function

Sugar, caffeine, guarana, amino acids and herbal products (e.g., ginseng) Sugar, herbal extracts, vitamins, electrolytes, amino acids (e.g., taurine)

Energy boost, mental alertness Sport specific performance, joint health, antiinflammatory

Sugar (e.g., glucose, sucrose and fructose), electrolytes (such as sodium and potassium), sea salt, coconut water, vitamins

Endurance, hydration, glycogen replenishment

Maltodextrin, whey protein, electrolytes Whey isolate, BCAA, hydrolyzed whey protein, and milk protein concentrate Casein, milk protein concentrate, sunflower oil

Glycogen replenishment, muscle recovery Muscle growth Satiety, to gain or lose weight

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products referred to as “energy” or “stimulant” drinks belong to a class of products, in liquid form, which typically contain stimulants, amino acids, an energy source, vitamins, and/or other substance(s) (Alsunni, 2015). Evidence indicating that some of these substances are important for proper body function is widely accepted; however, it does not mean that a person has a deficiency. Thus, several studies have been performed to evaluate issues regarding overall intake and subsequent adverse effects (Higgins et al., 2010; Campbell et al., 2013). The primary ergogenic nutrient in most energy drinks appears to be carbohydrate and/or caffeine. Most of marketed brands contain large amounts of glucose while some brands offer artificially sweetened versions. The most common form of added sugar is sucrose, glucose, or high fructose corn syrup. Despite being considered highly caffeinated, energy drinks also contain high levels of sugar, similar to the dose found in other soft drinks (Alsunni, 2015). The amount of carbohydrate, above the recommendations for physically active people, has potential health issues since high-energy drink intake potentially contributes to an increased risk of type 2 diabetes and obesity in sedentary individuals. Moreover, high sugar levels can slow the rate at which fluid is absorbed into the bloodstream or lead to gastrointestinal distress (Bedi et al., 2014; Higgins et al., 2010). The main ingredients of popular energy drinks are illustrated in Table 1.3, and the specific components are subsequently discussed in more detail.

1.2.4  Components of Energy Drinks Energy drinks can contain more than 15 ingredients, which typically include high amounts of carbohydrate along with nutrients marketed to improve perceptions of attention and/or mental alertness (Higgins et  al., 2010). Low-calorie energy drinks are also marketed to increase mental alertness, energy metabolism, and performance. Besides containing caffeine and a sweetener, energy drinks can also contain one or more amino acids (e.g., taurine, l-carnitine), glucuronolactone, vitamins, and other herbal supplements such as ginseng, gingko biloba, milk thistle, and guarana among others (Campbell et al., 2013). Additives such as guarana, yerba mate, cocoa, and kola nut may increase the caffeine content of energy drinks; however, the impact of these additives on sport performance remains controversial. Other commonly used constituents are methylxanthines, B complex vitamins, acai, maltodextrin, inositol, creatine (Cr), bitter orange, and ginkgo biloba (Ishak et al., 2012).

1.2.4.1 Caffeine Caffeine (1,3,7-trimethylxanthine) is a lipid-soluble purine, readily absorbed after oral ingestion, with an onset of action within 15–45 min

Table 1.3  Comparison of the Amount of Ingredients of Popular Energy Drinks Brand name

Caffeine (mg/250 mL)

Taurine (mg/250 mL)

Glucuronolactone (mg/250 mL)

Absolute Bull American Bull Dynamite Full Throttle

80 80 80 141 mg Part of a 3000-mg “energy blend” 62.5a 50 Only listed as part of a 5000mg “energy blend”

1000 # 1000 Only listed as part of a 3000mg “energy blend”

600 § § §

1000 1000 2000 mg Part of a 5000-mg “energy blend” 1000 2000 mg Part of a 1.35-g “energy blend” 1000 1000

§ § Only listed as part of a 5000-mg “energy blend”

Indigo Extra Lipovitan B3 Monster

Red Bull Rockstar

Shark Spiked Silver

80 160 mg Part of a 1.35-g “energy blend” 75a 80a

#, not given; §, not listed in the ingredients list. a Includes caffeine in the form of guarana.

600 §

# 600

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and peak plasma concentration within 1 h, regardless of the dose ingested. This compound belongs to the methylxanthine family and is known as a naturally occurring alkaloid obtained from leaves, seeds, and nuts of more than 63 plant species (Lisko et  al., 2017). Caffeine is extracted from Coffea arabica (coffee bean), Cola acuminate (kola nut), and Camellia sinensis (tea leaves) plants. Dietary sources of caffeine such as tea, coffee, chocolate, cola, and energy drinks typically provide 30–100 mg of caffeine per serve and the inclusion of this substance in energy drinks and sports supplements has increased the opportunities for athletes to consume caffeine (Duchan et  al., 2010; Goldstein et al., 2010). Caffeine is known as an ergogenic compound that raises the rate and force of the heart increasing the blood pressure, and has a broad range of metabolic, hormonal, and physiological effects. In sports field, this substance enhances sport performance in trained athletes when consumed in low-to-moderate dosages (~3–6 mg/kg) and in an anhydrous state, having greater ergogenic effects relative to coffee. Caffeine improves vigilance during exhaustive exercise and sleep deprivation; is ergogenic for maximal endurance exercise such as cycling, running, and swimming (duration superior to 5 min); is highly effective for time-trial performance; is beneficial for high-intensity exercise, including team sports (e.g., soccer and rugby, both of which are categorized by intermittent activity with long duration), but not resistance exercises (Goldstein et al., 2010). Caffeine administration has been suggested to promote benefits 30–120 min after ingestion. However, administration under 30 min may promote detrimental effects due to over-arousal and consequent difficulties to keep fine motor control, compromising performance (Salinero et al., 2014). The doses used in sports vary from 3 to 13 mg/kg of body weight per day and the main ergogenic effects are: delay in fatigue, improvement in mental alertness, concentration, visual vigilance, and reaction time, as well as reduction in pain perception (Armstrong et al., 2007; Campbell et al., 2013). An overview of beneficial and the adverse effects of caffeine is presented in Table 1.4. Caffeine is widely accepted as a central nervous stimulant and modulator of cardiovascular function. In this sense, several action mechanisms are proposed to explain the ergogenic effects of caffeine, such as (i) adenosine receptor antagonism in the central nervous system, (ii) calcium mobilization from sarcoplasmic reticulum, improving muscle contraction, (iii) inhibition of phosphodiesterase, increasing intracellular cyclic adenosine monophosphate (cyclic-AMP), and lipolysis, sparing glycogen for muscle utilization, and (iv) improvement in pulmonary function (Cappelletti et al., 2015). The direct effect of caffeine on cyclic-AMP may act to increase lipolysis in adipose and muscle tissue, increasing plasma free fatty

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Table 1.4  Effects on Performance and Adverse Effects of Caffeine Effects on Performance

Adverse Effects

Improved muscle contractibility Increased time to exhaustion Improved concentration Enhanced alertness Reduced fatigue

Abdominal pain Diarrhea Dehydration Insomnia, anxiety, and irritability Headaches Increase of blood pressure Interference with recovery and sleep patterns Increased muscle tension

acid concentrations and availability of intramuscular triglyceride, which may delay depletion of muscle glycogen during moderate-­ intensity exercise and allows for prolonged exercise. Despite some studies suggesting an antioxidant capacity, caffeine may also be immunomodulatory in vivo depending on subject characteristics, exercise characteristics, and immune parameters (Senchina et al., 2014). Breakdown products of caffeine such as paraxanthine (84%) followed by theophylline (12%) may also have actions within the human body (Cappelletti et al., 2015).

1.2.4.2 Glucuronolactone Glucuronolactone is a metabolite naturally synthesized from g­ lucose in the liver, which is involved in ascorbic acid ­synthesis, metabolized and excreted in urine as glucaric acid, xylitol, and ­ ­l-­xylulose (Mora-Rodriguez and Pallarés, 2014). This substance is found in a small number of foods and wine, is the richest source of glucuronolactone, and present in an amount up to 20 mg/L (Campbell et  al., 2013). In energy drinks glucuronolactone is present in doses from 250 to 2,500 mg/L. Supplementation with d-glucarates, including glucuronolactone, may favor the body’s natural defense mechanism for eliminating carcinogens and tumor promoters and their effects. However, it has also been suggested that glucuronolactone might contribute to detrimental effects of energy drinks (Worthley et al., 2010). Preworkout dietary supplements containing glucuronolactone have been suggested to improve anaerobic peak and mean power (Martinez et al., 2016). On the other hand, evidence is lacking relative to its impact on exercise performance, and little research has been done in humans,

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making it difficult to conclude whether this compound is harmful or beneficial (Higgins et al., 2010; Mora-Rodriguez and Pallarés, 2014).

1.2.4.3  Amino Acids Amino acids are thought to enhance performance in many ways, such as increasing the secretion of anabolic hormones, improving fuel use during exercise, preventing adverse effects of overtraining, and delaying fatigue (Williams, 2005). Taurine Taurine (2-aminoethanesulphonic acid) is the most abundant intracellular amino acid in humans and a normal constituent of the human diet. This sulfur-containing amino acid is considered conditionally essential, since in severe stress, such as strenuous physical exercise, its stores became depleted (Williams, 2005). In humans, taurine is present in high amounts in skeletal muscles, heart, and central nervous system, while its dietary sources include meat, seafood, milk, and other foods of animal origin (Schaffer et al., 2010; De Luca et al., 2015). The main mechanisms of the action of taurine are: (i) modulation of skeletal muscle contractile function in response to neuronal input, and (ii) antioxidative effects, attenuating exercise-induced DNA damage (Higgins et al., 2010; Schaffer et al., 2010). Taurine has numerous other biological and physiologic functions, including cell membrane stabilization, osmoregulation of cell volume, detoxification, bile acid conjugation, and cholestasis prevention, effects such as antiarrhythmic, inotropic, and chronotropic, retinal development and function, endocrine or metabolic effects, antiinflammatory and antiapoptotic properties (Ripps and Shen, 2012; Chesney et al., 2010; Lambert et al., 2015). This amino acid is commonly found in energy drinks and provides the main ergogenic effects of these beverages for the improvement of physical performance after a short period of supplementation (7 days), when compared with sports drinks containing only sugar and caffeine (Ballard et al., 2010). Supplementation with taurine has been demonstrated to increase its levels in skeletal muscle, promote greater force, and to improve resistance and recovery due to its role in keeping excitation-contraction coupling (De Luca et  al., 2015). Taurine supplementation seems to be effective in decreasing oxidative stress markers, suggesting that it may prevent oxidative stress in triathletes (De Carvalho et al., 2017), as well as reduce late-onset muscle soreness induced by eccentric exercise in young men (Ra et  al., 2015). Although there is evidence showing the ability of taurine in improving exercise performance, its ergogenic effects are not completely elucidated (Ballard et al., 2010). Therefore, the amounts of taurine in energy drinks are sometimes below the amounts expected to deliver therapeutic benefits or adverse events (Higgins et al., 2010; Warnock et al., 2017; Jeffries et al., 2017; Mora-Rodriguez and Pallarés, 2014).

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Beta-Alanine Beta-alanine is an amino acid nonproteinogenic, endogenously synthesized in the liver in combination with histidine, thus forming the dipeptide carnosine within skeletal muscle. In humans, muscle carnosine concentrations generally range from 10 to 40 mmol/kg dry weight and tend to be higher in fast-twitch than in slow-twitch muscle fibers. In diet, this amino acid is found in animal sources, such as poultry and meat. Recent studies have investigated the ergogenic properties of beta-alanine. Interestingly, beta-alanine has limited ergogenic effects by itself, but its supplementation raises intracellular carnosine concentrations that in turn improve muscle’s ability to buffer protons, attenuating cellular acidosis during exercise. For this reason, beta-­ alanine may best act as an ergogenic aid, improving physical performance in anaerobic activities (de Salles Painelli et al., 2014; Saunders et al., 2017), when metabolic acidosis is the primary factor for compromised exercise performance (Trexler et al., 2015; Caruso et al., 2012). In sports drinks, the inclusion of beta-alanine is uncommon, because the evidence about this amino acid is still recent. Optimal ­beta-alanine dosages have not been determined according to different ages, genders, and nutritional conditions; however, it is worth mentioning that supplementation of beta-alanine (4–6 g daily) during 4 weeks is linked to increased concentrations of muscle carnosine (Chung et  al., 2014), acting as an intracellular pH buffer, but doses have to be divided in 2 g or less, since the intake of higher doses promotes paresthesia, a well-known side effect related oral beta-alanine ingestion (Kreider et  al., 2010). Daily administration of beta-alanine has been reported to improve exercise performance (activities from 1 to 4 min), attenuate neuromuscular fatigue, and improve tactical performance (Hoffman et  al., 2014). However, the beneficial e­ ffects of beta-alanine ­supplementation on endurance performance from activities lasting less than 25 min, and strength are still unclear. Considering that the severity and duration of paresthesia episodes are dose-dependent, the formulation of future beta-alanine-containing beverages should take into account this adverse effect (Caruso et al., 2012; Trexler et al., 2015). Branched Chain Amino Acids The branched chain amino acids (BCAA) (leucine, isoleucine, and valine) are considered nutritionally essential because they cannot be synthesized endogenously by humans and must be supplied by diet. The BCAA has been suggested to participate in protein synthesis, in recovery from high-intensity exercise and improvement of cognition, focus, and psychomotor function (Fernstrom, 2005; de CamposFerraz et al., 2011). The addition of BCAA in energy drinks has become popular and mainly used in an attempt to delay fatigue, since BCAA administration reduces tryptophan levels and serotonin synthesis

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during prolonged physical activity (Fernstrom, 2005). The BCAA supplementation may delay central nervous system fatigue and enhance performance in prolonged aerobic endurance events by increasing the BCAA: free tryptophan ratio and mitigating the brain synthesis of serotonin (Williams, 2005). Central/mental fatigue has been related to increased levels of serotonin during long periods of endurance activity (Davis et al., 2000; Falavigna et al., 2012), when muscle glycogen become depleted increasing the utilization of BCAA as fuel, and decreasing the plasma BCAA: free tryptophan ratio. Endurance exercise may be benefited from the combination of arginine and BCAA, as it attenuates muscle proteolysis (Matsumoto et al., 2007). Additionally, the inclusion of BCAA in sports drinks may improve immune function and glucose metabolism, attenuate muscle damage and oxidative stress, as well as delay fatigue and improve body composition in athletes (Walsh et  al., 2010). Although there is evidence of the benefits of BCAA supplementation on exercise performance (de Araujo et al., 2006), the effects are mixed with some studies suggesting an improvement and others showing no effect (Kreider et al., 2010; Chen et al., 2016; Ribeiro et al., 2010). l-Carnitine

l-Carnitine was discovered in muscle tissue and identified as 3-hydroxy-4-N,N,N-trimethylaminobutyric acid, a water soluble quaternary amine. This amino acid is synthesized predominantly by the liver and kidneys and is essentially involved in energy production by increased fatty acid oxidation (Stephens et al., 2007). l-carnitine can be obtained by including red meats and dairy products in the diet. Dietary supplementation with l-carnitine has been shown to increase maximal oxygen consumption, indicating stimulation of lipid metabolism; prevent cellular damage, enhancing recovery from exercise stress (Higgins et al., 2010). There is evidence of a beneficial effect of l-carnitine supplementation in training, competition, and recovery from strenuous exercise (Karlic and Lohninger, 2004). However, benefits may decrease when supplementing an oral dose greater than 2 g at once, since absorption studies indicate saturation at this dose (Bain et al., 2006). More recent studies show that human muscle total carnitine can be increased by dietary sources, elevating lipid utilization, and sparing muscle glycogen during low-intensity exercise, as well as a better matching of glycolytic, pyruvate dehydrogenase complex, and mitochondrial flux during high-intensity exercise, while decreasing muscle anaerobic adenosine triphosphate (ATP) production, and these changes promoted an improvement in exercise performance (Wall et al., 2011). l-carnitine supplemented at a dose of 3 g provides antioxidant action by increasing antioxidant molecules capacity and d ­ ecreasing lipid ­peroxidation

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(Atalay Guzel et al., 2015). Taken before physical exercise, the ingestion of 3 or 4 g of l-carnitine prolongs exhaustion (Orer and Guzel, 2014). Acetyl-l-carnitine is the short-chain ester of carnitine, claimed to improve energy levels and muscle strength, and has been linked to a decrease in glucose metabolism to lactate, increased energy metabolite, and altered monoamine neurotransmitter levels (Smeland et al., 2012). In sports drinks, carnitine is claimed as a fat burner. Carnitine is supplemented by endurance athletes to increase fat oxidation and spare muscle glycogen (Jeukendrup and Randell, 2011). However, evidence of the benefits is currently unclear. Creatine Cr (or methylguanidine-acetic acid) is a naturally occurring nonprotein amino acid compound, stored primarily in skeletal muscle (95% of total storage). About two-thirds of intramuscular Cr is phosphocreatine (PCr) and one-third constitute free Cr. The total creatine pool (PCr + Cr) in muscle reaches typical concentrations of 100–150 mmol/kg of dry muscle mass in a 70-kg individual. The daily turnover of Cr is approximately 1%–2%, degraded into creatinine and excreted in the urine. This can be partially replaced by dietary Cr intake, found in animal muscle products such as red meat, eggs, and seafood, and typically consumed in amounts of ∼1–3 g/day in an omnivorous diet. Additional Cr needs are endogenously synthesized from arginine, glycine, and methionine, mainly in the liver, kidneys, and to a lesser extent in the pancreas, and transported to the muscle for uptake (Kreider et al., 2017; Cooper et al., 2012). Cr is a popular dietary supplement, used by athletes to increase anabolic hormonal response, muscle mass, strength, and sport ­ ­performance (Mendes et  al., 2004). Intramuscular PCr provides a rapid and brief source of phosphate for the resynthesis of ATP during maximal exercise, being an important fuel source in maximal sprints of 5–10 s (Kreider et al., 2017). Other functions of PCr metabolism comprise buffering hydrogen ions produced during anaerobic glycolysis and transporting ATP generated by aerobic metabolism, to be utilized for muscle contraction. The Cr monohydrate form has been shown to be beneficial to health due to its antioxidant potential (Rahimi, 2011). Its antioxidant properties are related to a decrease in lipid peroxidation and DNA susceptibility to oxidative stress, as well as to an ability to boost the antiinflammatory and neuroprotective activities (Rahimi et al., 2015). In this sense, Cr is also studied in the prevention/treatment of diseases, such as Alzheimer and Parkinson diseases (Cooper et al., 2012). In sports, Cr requires long periods of loading to promote performance benefits. The use of short-term high-dosage Cr loading (20 g/ day during 5 days) and long-term low-dosage (3–5 g/day during

16  Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER

≥3 weeks) have been shown to increase total Cr stores and improve exercise performance (Branch, 2003). Even though not all individuals respond similarly to Cr supplementation, it is generally accepted that, combined with resistance training, Cr supplementation increases its storage and promotes a faster regeneration of ATP to increase performance and promote greater training adaptations at a cellular and subcellular level (Cooper et al., 2012). Energy drinks are popular among young adult population. Energy sport drinks are composed of distinct ingredients that can promote ergogenic effects and have been investigated as a preworkout supplement (Williams, 2006b). Despite its effects on delaying the muscle fatigue onset, Cr has been reported to intensify the ergogenic effect of other ingredients such as caffeine. The administration of a supplement composed of caffeine, B vitamins, amino acids, beta-alanine, and Cr for preworkout is shown to delay fatigue, improve reaction time and muscular endurance capacity (Spradley et al., 2012). Despite delaying fatigue, evidence suggests that Cr, in combination with BCAA, taurine, caffeine, beta-alanine, glutamine, and glucuronolactone can improve the volume of training, as well as increase the response of growth hormone and insulin during the training session (Hoffman et  al., 2008; Gonzalez et al., 2011; Fukuda et al., 2010). Glutamine Glutamine is the most abundant free amino acid found in human muscle and plasma, which has a key role in transferring nitrogen between organs, in maintaining the acid-base balance during acidosis, participates in the regulation of protein synthesis and degradation, provides glutamate for nucleotides synthesis, and, finally, is a fuel source for intestinal cells and cells of the immune system, such as lymphocytes and macrophages, which may be decreased with prolonged intense exercise (Finsterer, 2012; Petry et al., 2015). This amino acid is considered conditionally essential, since its metabolism is increased in catabolic situations, such as sepsis, inflammation, and long-­ duration physical exercise. In these conditions, the immune response, as well as the synthesis of key molecules may be impaired (e.g., antioxidants, peptides, proteins, purines, and pyrimidines) (Petry et al., 2014; Cruzat et al., 2014; Raizel et al., 2016; Leite et al., 2016). Numerous studies have been performed to investigate the effects of glutamine supplementation on the immunosuppression induced by strenuous exercise. Acute glutamine ingestion has been shown to modulate lymphocytic responses to exhaustive exercise in the heat (Zheng et  al., 2017). Glutamine may also promote muscle glycogen synthesis (Williams, 2005) and in combination with BCAA, glutamine has been demonstrated to improve run time to an exhaustion test at 70% VO2 max (Walsh et al., 2010). Additionally, supplementation with

Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER   17

glutamine along with alanine attenuates muscle damage and oxidative stress caused by strenuous resistance training (Raizel et al., 2016; Leite et al., 2016). It is worth mentioning that free glutamine supplementation has lower efficacy in increasing plasma and muscle glutamine levels in comparison to the administration of the dipeptide (l-alanyl-l-­ glutamine) (Rogero et  al., 2006) or a solution containing glutamine and alanine in their free form (Raizel et al., 2016). In free form most of glutamine is metabolized by the enterocytes before it reaches plasma and tissues (Rogero et  al., 2006). Thus, a combination of glutamine with other amino acids (e.g., alanine) in sports drinks may improve glutamine availability and its beneficial effects in exercise.

1.2.4.4  B Vitamins The water-soluble B vitamins (thiamine, riboflavin, niacin, pantothenic acid, pyridoxine hydrochloride, biotin, inositol, and cyanocobalamin) are considered essential to human health, performing important biological activities, such as acting as coenzymes for proper cell function, especially mitochondrial function and energy production. Because of the large amounts of sugar in energy drinks, these vitamins are necessary to convert the added sugar to energy, so the energy drinks companies can claim their product provide extra energy (Higgins et al., 2010; Kennedy, 2016). The amount of B vitamins found in 1 L of energy drink is approximately 150 mg, that will be metabolized by a normally functioning renal system, while any excess may be excreted (Mora-Rodriguez and Pallarés, 2014). In sports, supplementation with these vitamins is shown to improve cognitive performance and subjective mood during intense mental processing (Kennedy et  al., 2010). The health properties are more pronounced when all vitamins are taken together. For this reason, nutritional supplements often contain the whole B complex vitamins. While some studies have failed to demonstrate ergogenic effects of these vitamins, evidence indicates that niacin, for instance, may have an ergolytic effect, impairing physical performance. Moreover, B complex vitamins decrease the bioavailability of ginseng, reducing its ergogenic effects (Ballard et al., 2010). In Table 1.5 B complex vitamins and their specific biological functions are presented.

1.2.4.5  Herbal Products Guarana Guarana is a rainforest vine also known as Guaranine, Paullinia cupana, or Sapindaceae, and its seeds contain stimulants theobromine and theophylline, having four times more caffeine than any other plant in the world. Guarana is primarily produced in the Brazilian states of

18  Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER

Table 1.5  B-Complex Vitamins and Their Biological Functions Vitamin

Name

Biological Function

Vitamin B1 Vitamin B2

Thiamine Riboflavin

Vitamin B3

Niacin

Vitamin B5

Pantothenic acid

Vitamin B6

Pyridoxine

Vitamin B7

Biotin

Vitamin B12

Cobalamin

Coenzyme precursor of some key enzymes of carbohydrate metabolism Supports energy metabolism (fat, carbohydrate and protein) being a cofactor for the flavoenzymes of the respiratory chain Required to supply protons for oxidative phosphorylation playing a major part in energy production, and also stimulates neurotransmitters synthesis Precursor of coenzyme A, α-ketoglutarate, and pyruvate dehydrogenase, and is required for fatty acid oxidation Coenzyme involved in the metabolism of amino acid, homocysteine, glucose, and lipid. Required for neurotransmitter production, DNA and RNA synthesis Coenzyme of decarboxylases, important for gluconeogenesis and oxidation of fatty acids Important in DNA synthesis and regulation, and in the fatty acids and amino acids metabolism. Helps to maintain nerve cell function and red blood cell formation

Amazonas and Bahia, and approximately 70% of the production is used by the industry of soft and energy drinks (Schimpl et al., 2013). Guarana presents the same properties as caffeine, such as (i) stimulates the central nervous system, (ii) increases secretion of gastric acid, (iii) acts as a bronchodilator, and (iv) as a diuretic (Ballard et al., 2010; Higgins et  al., 2010). Although guarana and caffeine present similar effects, both are commonly added in energy drinks. Ginseng Ginseng, extracted from the roots of ginseng plants, is considered a kind of herbal medicine in the oriental countries for thousands of years, and is one of the most popular herbal supplements. Ginsenoside, steroid-like phytochemical with adaptogenic properties, is the main bioactive compound of ginseng; while Ginsenoside Re is one of the major constituents of ginsenosides, being responsible for important biological activities (Fig.  1.1) (Duchan et  al., 2010). This compound is believed to increase protein synthesis and the activity of neurotransmitters, besides improving blood circulation in the brain

Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER   19

Fig. 1.1  Bioactive compounds of ginseng and their properties.

(Williams, 2006a). Moreover, ginseng has been reported to increase energy and memory by stimulating the hypothalamic and pituitary glands to secrete corticotrophin, thereby improving cognitive abilities (Higgins et al., 2010; Oliynyk and Oh, 2013). Ginseng is an adaptogen believed to be a potential source of actoprotectors, which may increase physical and mental work capacity, and enhance body stability against physical loads without increasing oxygen consumption (Oliynyk and Oh, 2013). Although ginseng is often used by physical activity practitioners and athletes for its alleged performance-enhancing attributes (Qi et  al., 2014), its ergogenic ­properties are poorly elucidated in the literature and, therefore, its recommendation in clinical practice is quite questionable (Ballard et al., 2010; Higgins et  al., 2010; Chen et  al., 2012). Therapeutic doses for ginseng often range between 100 and 200 mg/day; however, in energy drinks the use of inferior doses is common. High doses can deliver adverse effects that include hypotension, edema, tachycardia, cerebral arteritis, headache, insomnia, appetite suppression, amenorrhea, fever, pruritus, euphoria, and cholestatic hepatitis (Higgins et al., 2010). Ginkgo Biloba Ginkgo biloba extract is derived from the leaves of the ginkgo biloba tree, the world’s most ancient extant, and has been used in traditional Chinese medicine for centuries. Ginkgo biloba is believed to have beneficial properties when its active ingredients (flavonoids and terpenoids) work in concert and dosages range from 80 to 720 mg/ day for durations of 2 weeks to 2 years. Its extract has been related to antioxidant properties, modification of vasomotor function, and reduction in the adhesion of blood cells to endothelium, which may enhance muscle tissue blood flow through improved microcirculation,

20  Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER

thereby improving aerobic endurance by enhancing muscle tissue oxidation (Diamond and Bailey, 2013; Higgins et al., 2010). Most ginkgo biloba supplementation research has been conducted in the elderly, since this herbal product has vasoregulatory and ­cognition-enhancing effects, reported to increase alertness and cognitive function (LaSala et al., 2015). A modest improvement in memory performance has been observed following single dose of 120 mg of ginkgo biloba extract administered to healthy young people (Kennedy et al., 2007). Ginkgo's primary application is linked to the treatment of cerebrovascular dysfunctions and peripheral vascular disorders due to its potent antioxidant properties and effects on peripheral and cerebral circulation (McKenna et  al., 2001). However, although ginkgo biloba supplementation has been related to exercise performance improvements (evaluated by walking distance) in patients with peripheral arterial disease, there is no evidence that similar effects occur in healthy young athletes (Williams, 2006a; Higgins et al., 2010).

1.2.4.6 Antioxidants During exercise, muscle damage may be linked to inflammation and oxidative stress. In this sense, antioxidants are purported to improve the recovery phase reducing muscle cells damage (He et  al., 2016). Vitamin C, also known as ascorbic acid, is a potent antioxidant, included in foods and beverages to preserve the products and increase their shelf life. Besides its important antioxidant property, vitamin C participates in several enzymatic reactions, such as in the collagen metabolism (Kozakowska et al., 2015). Athletes commonly use vitamin C to attenuate the oxidative damage caused by strenuous exercise. Taking into account that fatigue is one of the symptoms of vitamin C deficiency, this nutrient consumed in adequate amounts is of critical importance for athletes. On the other hand, in high doses vitamin C may induce toxicity, promoting gastrointestinal distress, which may also impair physical performance and athlete’s health. In addition, evidence showing that short-term or long-term exercise changes antioxidant requirements in well-trained athletes are scarce (Higgins et al., 2010).

1.3  Applicability and Effects of Sports and Energy Drinks 1.3.1  Hydration and the Importance of Sports Drinks In exhaustive exercises, dehydration occurs due to excessive losses of water by sweat, in addition to the usual daily water losses from respiration, gastrointestinal and renal sources. Water makes up

Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER   21

50%–60% of our body weight and is the most important nutritional ergogenic aid for athletes, since it is essential for heat regulation, chemical reactions; it is used as lubrication, as a medium of transport, and as a solvent during ionization of electrolytes and acids. Performance capacity can be impaired when 2% or more of body weight is lost through sweat (McDermott et  al., 2017). Sweating assists with the dissipation of heat generated by muscle contractions during exercise, to maintain body temperature within acceptable ranges. Sweating is often exacerbated by environmental conditions, eventually leading to hypovolemia (decreased plasma/blood volume), and thus cardiovascular strain, increased glycogen utilization, altered metabolic, and central nervous system function, and a greater rise in body temperature (Sawka et al., 2007). Athletes with weight loss higher than 4% of body weight (during anaerobic or high-intensity activities, sport-specific technical skills, and aerobic exercise) may experience decrements in the performance due to heat illness, heat exhaustion, and heat stroke, which in extreme situations may lead to coma and death (Maughan et al., 2016; Guerra et al., 2004). Severe loss of body weight (6%–10%) has more pronounced effects on exercise tolerance, decreases in cardiac output, sweat production, skin, and muscle blood flow. Routinely tracking body weight prior to and following exercise training is a good strategy to ensure that individuals maintain proper hydration (Thomas et al., 2016). Furthermore, the measure of urine color is a simple way to assess hydration status; however, recommendations from the American College of Sports Medicine state that urine color is often subjective and might be confounded (Heneghan et al., 2012; Thomas et al., 2016). Despite observing urine color, athletes should be trained to tolerate greater amounts of fluid during training to keep thermoregulation (mainly in hot/humid environments), and not depend on thirst to drink, because at this point they already have lost a significant amount of fluid through sweat (Armstrong et al., 2007). In addition to water, sweat contains substantial but variable amounts of sodium, with lesser amounts of potassium, calcium, and magnesium. For this reason, pure water ingestion during exhaustive and prolonged physical exercises is not recommended and athletes are encouraged to consume a sufficient amount of water and/or glucose/electrolyte solution sports drinks during exercise in order to maintain hydration status (Thomas et al., 2016). Additionally, when exercise lasts more than 1 h, glucose/electrolyte solution drinks helps to maintain blood glucose levels, replenish glycogen stores, and reduce the immunosuppressive effects of intense exercise (Kreider et al., 2010). The presence of dietary sodium/sodium chloride helps to retain ingested fluids, especially extracellular fluids, including

22  Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER

plasma volume. Overall, keeping a good fluid balance during exercise is one of the most effective ways to maintain exercise capacity (particularly in hot/humid environments) (Maughan and Shirreffs, 2010). To meet all recovery goals, sports drinks should be ingested in combination with other foods and fluids that provide additional carbohydrate, protein, and other nutrients essential for recovery (Kreider et al., 2010). Sweat rates of athletes range from 0.5 to 2.0 L/h depending on temperature, humidity, and exercise intensity. This requires frequent consumption (every 10–15 min) of cold water or a glucose/electrolyte solution sports drink to maintain fluid balance and preserve homeostasis, optimal body function, exercise performance, and perception of well-being. The presence of flavor in a beverage may increase palatability and voluntary fluid intake (Kreider et al., 2010). While voluntary dehydration, which has been used by some athletes to qualify for a lower weight class, could have a possible detrimental effect on performance, fluid overloading (hyperhydration) prior to some distance events performed in hot, humid environments may minimize performance decrements (Thomas et  al., 2016). It is suggested that hyperhydration prior to an event may increase fluid retention, improving heat tolerance. However, this strategy has to be carefully planned; otherwise it may increase the risk of hyponatremia and may have negative impact on performance due to feelings of fullness (McDermott et al., 2017). The American College of Sports Medicine position stand for exercise and fluid replacement recommends consuming fluids containing 20–30 milliequivalents per liter of sodium, 2–5 milliequivalents per liter of potassium, and 6%–8% of carbohydrates to help sustain electrolyte balance and exercise performance (Armstrong et  al., 2007; Sawka et  al., 2007). Evidence shows that ingestion of sports drinks during exercise in hot/humid environments can help prevent dehydration and improve endurance exercise capacity (James et al., 2017). Carbohydrate is widely accepted as an ergogenic aid that can prolong exercise. Additionally, ingesting a small amount of carbohydrate and protein 30–60 min prior to exercise and use of sports drinks during exercise can increase carbohydrate availability and improve exercise performance (Thomas et  al., 2016; Cermak and Van Loon, 2013).

1.3.2  Hyponatremia and Sports Drinks The popularity of sports drinks, in part, is due to the concerns about hyponatremia in athletes. The death of a participant during the 2002 Boston Marathon highlighted the importance of preventing this condition. In recent years, exercise-associated hyponatremia has

Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER   23

been identified in a wide range of sports modalities and in extreme situations linked to rhabdomyolysis development. Hyponatremia induced by exercise starts when the blood concentration of sodium ([Na+]) is reduced during or immediately after physical activity (HewButler et al., 2017). Excessive intake of hypotonic fluids, excess of sweat, urine, and other losses are suggested to be the main cause of hyponatremia during physical exercise. In addition, glycogen metabolism is also related to hyponatremia occurring without weight gain, because of water release during glycogen metabolism leading to a depletion of the serum sodium (Hew-Butler et al., 2017; Urso et al., 2014). For this reason, the nutritional composition of the fluid ingestion is of critical importance to maintain athlete's health during the competition. Thus, administration of hypertonic saline via continues infusion is recommended under the supervision of professionals observing clinical signs and symptoms. Other causes of hyponatremia are presented in Fig. 1.2. Concerning hyponatremia prevention, the data in the literature are controversial. Some authors defended the idea of drinking fluids only when thirsty, while others recommended fluid intake according to the duration and type of physical exercise, also taking into account the individualities of each athlete. The “fluid” term refers to sports drinks composed of carbohydrates and electrolytes, such as sodium and potassium (Kreider et al., 2010). Despite increased recognition of ­exercise-associated hyponatremia worldwide, orienting athletes regarding the importance of keeping hydrated to prevent hyponatremic encephalopathy remains a challenge (Hew-Butler et al., 2017; Nichols, 2014), as shown in Fig. 1.3.

Fig. 1.2  Causes of hyponatremia.

24  Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER

Fig. 1.3  Electrolyte changes and occurrence of encephalopathy.

1.3.3  Heat Exhaustion and the Use of Sports Drinks Heat exhaustion occurs in high-intensity or long-duration exercises performed in hot environments, which may lead to hyperthermia, nausea and vomiting, tachycardia, dizziness, dehydration, muscle cramping, central nervous system dysfunction, organ system failure, and collapse. This condition is also linked with increased mortality in athletes (Armstrong et al., 2007; Nichols, 2014). Heat exhaustion presents many causes, which are demonstrated in Fig. 1.4.

Fig. 1.4  Causes of heat exhaustion.

Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER   25

One of the main strategies to prevent and recovery from heat exhaustion is the oral fluid support before and during physical exercise (Racinais et  al., 2015). Sports drinks containing carbohydrate and electrolytes are the main indicated beverages to prevent and treat this condition and its consequent maladies. In cases of severe heat exhaustion, intravenous fluid administration could be necessary for the recovery of athlete’s health (Armstrong et al., 2007).

1.3.4  Exercise-Associated Muscle Cramps and the Importance of Sports Drinks Exercise-associated muscle cramps often occur in large skeletal muscles and can occur with exhaustive work in any temperature range, but appears to be more prevalent in hot and humid conditions. This state often occurs in prolonged exercise, such as long distance races, and also in tennis and American football. Muscle twitches can progress to severe and widespread muscle spasms. Heat exhaustion and exerciserelated muscle cramps do not typically involve excessive hyperthermia, but rather are a result of dehydration, high sweat rates, high sodium losses and muscle fatigue, and/or central regulatory changes that fail in the face of exhaustion (Armstrong et al., 2007; Nichols, 2014). The resting electrical potentials of nerve and muscle tissues are affected by the concentrations of Na+, Cl−, and K+ on both sides of the cell membrane, thus intracellular dilution or water expansion is believed to develop exercise-associated muscle cramps (Armstrong et al., 2007). In this scenario, the reposition of electrolytes and water by sports drinks can attenuate the development of muscle cramps, fatigue, and exhaustion, improving the exercise performance (Armstrong et  al., 2007; Racinais et  al., 2015; Okazaki et  al., 2009). According to the American College of Sports Medicine, in the position stand of “Exertional Heat Illness during Training and Competition,” published in 2007, the treatment of exercise-associated muscle cramps includes rest, prolonged passive muscle stretching, ice massage, and the oral fluid or food intake of sodium chloride (NaCl), for instance, 1–2 salt tablets with 300–500 mL of fluid. In severe cases, the intravenous fluid reposition could be necessary (Armstrong et al., 2007; Casa et al., 2012; Nichols, 2014).

1.3.5  Fatigue, Exhaustion, and the Importance of Sports Drinks All of the above-mentioned conditions (dehydration, hyponatremia, heat exhaustion, and muscle cramps) promote fatigue, which refers to reduction of muscular strength and power, impairing physical performance. Conceptually, fatigue is divided into peripheral fatigue

26  Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER

and central fatigue. Peripheral fatigue, also called muscle fatigue, designates biochemical changes occurred inside the muscle cell during physical exercise, while in central fatigue the changes occur in the central nervous system (Amann et al., 2015). On the other hand, the definition of exhaustion is the inability to continue the physical exercise, leading to its interruption (Armstrong et  al., 2007). Taking into account both definitions, exhaustion occurs after fatigue, if the athlete does not stop the physical exercise. The main causes of peripheral fatigue are the reduction of cellular pH and energy substrates for the continuity of the exercise, accumulation of metabolites, such as ammonia, and muscle damage (Finsterer, 2012). Concerning the central fatigue, the main cause is the increase in brain serotonin synthesis, optimized by the reduction in plasma BCAA and increase in the perception of exertion, lethargy, and fatigue. However, it is worth noting that this serotonin hypothesis is not completely elucidated in the literature. High concentrations of blood ammonia and hypoglycemia are also causes of central fatigue (Popkin et al., 2010). Although fatigue is reversible and attenuated after rest, the development of this state during exercise reduces muscle activity, and strategies to delay the onset of fatigue are important in order to optimize athletic performance (Amann et  al., 2015; Nichols, 2014). Some nutrients added to sports and energy drinks may delay fatigue and improve performance (Okazaki et al., 2009). Some of these substances and their biological effect are presented in Table  1.6. In summary, the intake of sports and energy drinks could improve the situations promoting fatigue and exhaustion, improve exercise performance, and influence the result of sports competitions (Armstrong et al., 2007).

1.3.6  Ergogenic Effects of Sports and Energy Drinks Several studies evaluated the ergogenic properties of Red Bull, an energy beverage that contains caffeine, taurine, glucuronolactone, and others ingredients. Studies comparing the effects of carbonated water and Red Bull on psychomotor performance (reaction time, concentration, memory), subjective alertness, and physical endurance in healthy young adults observed an improvement in endurance performance and in memory (Alford et al., 2001; Wesnes et al., 2017). Similar studies observed improvement in endurance performance after Red Bull intake. However, this drink did not affect anaerobic performance in Wingate cycling test, indicating that Red Bull ergogenic effect is limited only to aerobic exercise. Further studies confirmed these effects (Forbes et al., 2007; Ivy et al., 2009).

Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER   27

Table 1.6  Nutrients and Their Biological Properties Regarding the Delay of Fatigue and Exhaustion Nutrient

Biological Effect

Carbohydrate Electrolytes Caffeine and guarana Ginseng

Increases cellular energy supply and delays fatigue Prevent hyponatremia that affects physical performance Stimulants that improve endurance performance Presents stimulant and antifatigue properties, besides antiinflammatory and immunomodulatory roles Modulates muscle contractile function in response to neuronal input and presents cell protective properties Important in energy metabolism during high-intensity and short-duration exercises. Increases muscle strength Attenuates cellular acidosis and improves physical performance in resistance exercises Presents immunomodulatory role, attenuates muscle damage and oxidative stress, avoids ammonia accumulation and is an important energy substrate Improve body composition, present immunomodulatory role, attenuate muscle damage and oxidative stress, and are important energy substrates

Taurine Creatine Beta-alanine Glutamine Branched chain amino acids

Interestingly, sugar-free Red Bull did not present ergogenic effect, indicating that the energy source (carbohydrate) is essential to its properties in physical exercise (Candow et al., 2009). On the other hand, Celsius, a low-calorie energy drink, with ingredients similar to Red Bull, when associated with physical exercise (resistance and endurance) improved parameters of exercise performance, such as ventilatory threshold, minute ventilation, VO2 at ventilatory threshold, and power output at ventilatory threshold (Lockwood et  al., 2010). Therefore, it is still controversial in the literature if sugar-free and low-calorie drinks present ergogenic effect. Besides Red Bull and Celsius, other sports and energy drinks were evaluated in sports, such as Amino Shooter, which contains the amino acids taurine and Cr, combined with caffeine and glucuronolactone. Different from Red Bull, Amino Shooter intake is linked with anaerobic performance improvement and delay of fatigue (Hoffman et al., 2008; Ratamess et al., 2007). In 2008, an increase in squat repetitions and volume of exercise was observed in the group that ingested Amino Shooter, compared with placebo, although without statistical significant difference (Hoffman et al., 2008).

28  Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER

Competitive sprinters have also experienced increased aspects of performance in swimming after ingesting (3 mg/kg) caffeinated energy drinks (Lara et al., 2015). Finally, evidence indicates that energy and stimulant drinks increase endurance performance (Duchan et al., 2010; Goh et al., 2012; Ferguson-Stegall et al., 2010), while sports beverages, such as Amino Shooter, that contains amino acids (e.g., Cr and taurine) improve strength and anaerobic performance (Thomas et al., 2016; Hansen et al., 2016; Wang et al., 2015).

1.4  Effectiveness and Adverse Effects of Sports and Energy Drinks The main adverse effects of sports and energy drinks occur when the dose is high or when the consumer is nonathlete. Evidence indicates that the intake of these beverages may contribute to obesity and metabolic syndrome appearing in children and middle-aged adults, as well as to an increased risk of cardiovascular diseases and dental erosion or dental caries, since the sugar content in sports drinks is as high as the amount found in soft drinks. The high sugar content in energy drinks may reduce the activity, diversity, and gene expression of intestinal bacteria contributing to these pathologies (Greenblum et al., 2012). Recent studies have demonstrated that energy drink overconsumption was related to arterial dilatation, aneurysm formation, dissection, and rupture of large arteries (González et al., 2015). Caffeine-induced psychiatric disorders have been recognized and linked to caffeine excess: caffeine intoxication, caffeine-induced anxiety, caffeine-induced sleep disorder, and caffeine-related disorder. Individuals who consume more than 300 mg of caffeine per day may also experience hallucinations, which may be explained by high levels of cortisol that enhances the physiological effects of stress following caffeine intake (Alsunni, 2015; Mora-Rodriguez and Pallarés, 2014). Furthermore, psychiatric sequelae after ingestion of energy drinks by patients with known psychiatric illness have been reported. Overall, chronic use of energy drinks has been associated with mental health problems and the effects may be dependent on caffeine (Richards and Smith, 2016). The occurrence of cardiovascular events, such as cardiac arrest, supraventricular tachycardia, and stroke, after energy and sports drinks ingestion is also worrying (Ballard et al., 2010; Higgins et al., 2010). Caffeine is the component that is most linked with the adverse effects. This substance may cause insomnia, nervousness, arrhythmias, and cardiovascular diseases, disturbance in mineral metabolism, causing anemia and osteoporosis, pregnancy and childbirth complications, gastrointestinal upset, and even death. In sports, these

Chapter 1  SPORTS AND ENERGY DRINKS: ASPECTS TO CONSIDER   29

symptoms impair physical performance (Salinero et al., 2014). When caffeine is ingested with alcohol, nicotine, or illicit substances, the adverse effects are more pronounced. Since caffeine was removed from the prohibited list, its use has dramatically increased in sports and the World Anti-Doping Agency (WADA) is the responsible for monitoring caffeine consumption by athletes. Additionally, individuals should be aware of foods, beverages, and dietary supplements that contain caffeine, because of the potential to interact with drugs, including bronchodilators, antibacterial, and antipsychotics, and change drug metabolism causing side effects (Park et al., 2013). Despite the ergogenic effects of caffeine on athletic performance, caffeine acts as a diuretic, increasing the losses of water and electrolytes. Thus, chronic intake of sports drinks containing high doses of caffeine may contribute to dehydration and hyponatremia, conditions that impair athlete’s health and physical performance. Caffeinated beverages contain about 50–100 mg of caffeine and higher doses have been associated with certain adverse effects, typically manifesting with ingestion higher than 200 mg of caffeine. In this scenario, some authors have recommended the interruption of caffeine use at least for 7 days before an important athletic event. Cardiac arrest has also been reported since caffeine can influence the activity of neuronal control pathways in the central and peripheral nervous systems (Higgins et al., 2010). Although less studied than caffeine, taurine has been related to some adverse effects. This amino acid promoted renal complications to hemodialysis patients, hypothermia and hyperkalemia in patients with uncompensated adrenocortical insufficiency, itching to psoriasis patients, and nausea, headache, dizziness, and gait disturbances in epilepsy patients. The adverse effects occurred at high doses (1.5 and 7 g/day) (Ballard et al., 2010). Higher doses of ginseng also caused adverse effects, such as insomnia, decreased appetite, edema, fever, pruritus, vertigo, euphoria, amenorrhea, vaginal bleeding, hypotension, palpitations, tachycardia, cholestatic hepatitis, headache, cerebral arteritis, and neonatal death (Ballard et al., 2010). As previously mentioned, adverse effects of sports and energy drinks are more pronounced when alcoholic beverages are consumed together. Evidences indicate that adolescents are the population that ingested sports drinks most, isolated or in combination with alcohol (Higgins et al., 2010). Thus, the incidence of adverse effects in adolescents is worrying. According to Stimulant Drinks Committee, sports, energy, and stimulant drinks should be labeled with an indication that they are unsuitable for children (<16 years), pregnant women, and individuals sensitive to caffeine. Moreover, combining energy drinks, in association with alcohol or not, may cause adverse effects (Generali, 2013; Choudhury et al., 2017).

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1.5 Conclusions Sports drinks are safe and recommended for athletes when the consumption is well oriented, according to the individual variability and the exercise characteristics; however, it should not be encouraged for nonathletes. Energy drinks may show positive effects on performance in various sport activities despite being difficult to be evaluated from the nutritional and ergogenic perspective, due to the variety of ingredients they contain (e.g., water, sugars, caffeine, other stimulants, amino acids, herbs, and vitamins). Short-term, high-intensity performance could be improved by energy drinks, but it is required to ingest high volumes to deliver enough caffeine; and although ergogenic, high doses of caffeine could result in negative side effects that could counteract the caffeine’s ergogenic effect. The negative effects of excessive caffeine intake have been proven, but the positive effects of many of the other additives, such as taurine and glucuronolactone as well as the combined effect of these ingredients in energy drinks, remain unclear. Due to their high carbohydrate concentration and lack of salts, energy drinks are not a good beverage choice when prolonged exercise in a warm environment is likely to require rehydration. Thus, ingestion of energy drinks before an event or during training can increase blood pressure; and may result in dehydration. Excessive intake of energy drinks by healthy people and the combination with alcohol may lead to severe adverse events. Hence, individuals with medical illnesses, as well as children and adolescents should avoid energy drinks.

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