Nutritional Supplements in Sport, Exercise and Health

An A-Z Guide

Linda M. Castell, Samantha J. Stear, Louise M. Burke, Linda M. Castell, Samantha J. Stear, Louise M. Burke

• Publisher: Routledge
• Year: 2015
• ISBN:
  9781317678618
• Edition: 1
• Topic: Medicine
• Subtopic: Nutrition, Dietics & Bariatrics

Nutritional Supplements in Sport, Exercise and Health is the most up-to-date and authoritative guide to dietary supplements, ergogenic aids and sports nutrition foods currently available. Consisting of over 140 evidence-based review articles written by world-leading research scientists and practitioners, the book aims to dispel the misinformation that surrounds supplements and supplementation, offering a useful, balanced and unbiased resource.

The reviews are set out in an A-Z format and include: definitions alongside related products; applicable food sources; where appropriate, practical recommendations such as dosage and timing, possible nutrient interactions requiring the avoidance of other nutrients, and any known potential side effects; and full research citations. The volume as a whole addresses the key issues of efficacy, safety, legality and ethics, and includes additional reviews on the WADA code, inadvertent doping, and stacking.

Combining the most up-to-date scientific evidence with consideration of practical issues, this book is an essential reference for any healthcare professional working in sport and exercise, any student or researcher working in sport and exercise science, sports medicine, health science or nutrition, and for all coaches and support teams working with athletes.

Nutritional Supplements in Sport, Exercise and Health

An A–Z Guide

AMINO ACIDS

Arash Bandegan, Linda M. Castell and Peter W.R. Lemon

Amino acids (AA) contain both amine and carboxyl functional groups. Most are the building blocks for protein and are absorbed into the bloodstream following digestion of ingested animal and/or vegetable protein sources. However, not all proteins in the diet have the same nutritional value because each contains different proportions of the essential (or indispensable) AA. The essential and non-essential (or dispensable) AA terminology (see Figure 12) refers to whether or not a specific AA can be synthesised by the body at a rate sufficient to meet the normal requirements for protein synthesis. When sufficient essential AA are present, the protein is considered ‘first-class’ or ‘complete’, e.g. dairy products, eggs, fish and meat. In contrast, plant proteins are described as ‘second-class’ or ‘incomplete’ proteins and must be combined to equal ‘complete’ proteins. Specifically, if combinations of grains plus legumes (peas, beans and peanuts), grains plus nuts or seeds, and/or legumes plus nuts or seeds are consumed throughout the day, adequate amounts of the essential AA are available and protein synthesis is normal (these are often called complementary proteins). Otherwise, growth and/or tissue repair is impaired. As a result, strict vegetarians need to plan their diet carefully to ensure their daily ingestion of plant foods provides them with adequate quantities of each essential AA. Further, several AA (known as conditionally indispensable) including arginine, cysteine, glutamine, proline, tyrosine and perhaps others, can become essential under conditions of stress, e.g. trauma, exercise, etc.

Several studies have measured changes in total plasma AA with exercise in an attempt to understand whether exercise alters AA requirements; however, this information is of limited value because both intracellular (Wolfe, 2002) and extracellular (Bohe et al., 2003) AA are the more relevant precursor pools for protein synthesis. Although debated for decades (Lemon and Nagle, 1981), it is likely that exercise increases dietary AA requirements (Philips and van Loon, 2011). The confusion on this issue is due, at least in part, to several complicating factors including age, gender, protein quality, overall dietary energy, time since last meal, type of exercise training, etc. Recent consensus indicates that AA needs are increased with regular exercise (both endurance and strength) suggesting that protein intakes as high as ~150–200% of current recommendations might be necessary for those involved in regular exercise training (Phillips and van Loon, 2011).

Furthermore, the quality of protein is important as milk protein induces a greater muscle protein synthesis (vs. some plant proteins; Wilkinson et al., 2007). Also, the peak response is greater with faster-digesting protein (whey) compared with a slower-digesting protein (casein) (Pennings et al., 2011; Tang et al., 2009), due to the associated rapid aminoacidaemia (West et al., 2011a). Fortunately, it appears that only the essential AA are needed to achieve an increased muscle protein synthesis. Consequently, those who need to be energy conscious may opt to consume sufficient essential AA rather than a whole protein source. Further, some of these essential AA, especially leucine, appear to be key signallers of muscle protein synthesis (Xu et al., 2014; Norton et al., 2012) so for those attempting to increase/preserve muscle mass-specific AA supplementation may be most important.

FIGURE 12 The amino acid composition of myosin, one of the two major proteins in muscle and therefore in lean meat, and the biosynthetic role of some of these amino acids. Reproduced with permission from E.A. Newsholme, L.M. Castell. In: R. Maughan (ed.) (2000) Nutrition in Sport, Ch. 11. Oxford: Blackwell Science.

Although the timing of any protein or AA ingestion related to exercise plays a role (Lemon et al., 2002), the total quantity consumed in a day may be most important (Schoenfeld et al., 2013). In the case of strength training an intake of ~20–25g of a high quality protein source within one hour following exercise appears to produce the maximum rate of muscle protein synthesis, at least in acute studies with young adults, whereas the amount to induce the same response in older adults is 35–40g (Moore et al., 2012; Kakigi et al., 2014; Pennings et al., 2012; Yang et al., 2012a). Also, it has been suggested that ingestion pattern (evenly spaced intakes throughout the day of ~20–30g protein per meal; 3 times/day) might be the best approach to maximize muscle protein synthesis (Moore et al., 2012; Areta et al., 2013; Mamerow et al., 2014). However, these studies may not reflect net protein anabolism because protein breakdown must be considered (Deutz and Wolfe, 2013). Further, it has been shown that these acute increased muscle protein synthesis measurements after a bout of strength exercise do not correlate well with long-term hypertrophy (Mitchell et al., 2014), indicating that other factors are involved. Clearly, therefore, the adaptations to strength training are more complicated. For example, desensitization with training may create a need for a greater AA intake for the same response (Bucci et al., 1990; Fogelholm et al., 1993a; Lambert et al., 1993). Consequently, long-term training studies (months or even years) are needed to confirm AA or protein intake recommendations for physically active individuals.

Finally, whenever individual AA are consumed, concerns arise because an imbalance with other AA is possible. Therefore, caution is recommended until these dietary recommendations can be confirmed. Amino acids that have been researched individually or in combination as an ingredient of a supplement will each be the focus of separate articles in this book.

Competing interests None

γ-AMINOBUTYRIC ACID (GABA)

Romain Meeusen and Bart Roelands

γ-aminobutyric acid (GABA) is synthesized through the decarboxylation of glutamate by the enzyme glutamatic acid decarboxylase. Glutamate is the main excitatory neurotransmitter, and GABA is the major inhibitory neurotransmitter in the mature brain. GABA acts primarily by activating CL^– channels called GABA_A receptors, and by eliciting metabotropic G-protein mediated responses by GABA_B receptors (Kornau, 2006; Möhler, 2006). GABA is considered to act as a natural tranquilizer and anti-epileptic agent in the brain.

GABA_A receptors are the site of action of benzodiazepines, barbiturates and anaesthetics (Whiting et al., 2001) and known to mediate sedation. GABA_B agonists may be useful for the treatment of pain and drug dependence (Kornau, 2006). Baclofen, the first synthetic GABA_B receptor agonist, is used clinically for the treatment of spasticity and skeletal muscle rigidity (Bowery, 1993). GABA_B antagonists on the other hand have shown antidepressant and cognition-enhancing effects (Cryan and Kaupmann, 2005; Kornau, 2006). Furthermore, recent data (Banuelos et al., 2014) suggest that the age-related dysregulation of GABAergic signalling in the prefrontal cortex may play a crucial role in impaired working memory, making GABA_B a potential target to provide a therapeutic benefit for age-related impairments in cognitive function.

In rats, baclofen has shown to prolong time to fatigue, possibly because of a boost in glycogen due to the effect of IL-6 release in the muscle (Abdelmalki et al., 1997). In humans, on the other hand, Collomp et al. (1985) found no effect on performance after administration of lorazepam (a benzodiazepine drug). Recently it was shown that GABA ingestion at rest increases immunoreactive growth hormone (irGH) and immunofunctional GH secretion (ifGH), which may enhance the skeletal muscle response to resistance training. Moreover, when GABA ingestion was combined with exercise, concentrations of irGH and ifGH rose even higher (Powers et al., 2007). Although some effects have been found, specifically for the response to resistance training, much more research regarding the effects of GABAergic manipulations on exercise performance is needed to elucidate the role of GABA.

Competing interests None

ANDROSTENEDIONE (‘ANDRO’ OR ‘DIONE’)

Gregory A. Brown, Matthew D. Vukovich and Douglas S. King

Androstenedione (‘Andro’ or ‘DIONE’), an androgenic steroid hormone that is a precursor to testosterone, was marketed in the late 1990s and early 2000s as a ‘natural’ alternative to anabolic steroid use. Androstenedione was purported to raise blood testosterone levels and subsequently promote muscle size and strength.

A review of the research on androstenedione supplementation published between 1999 and 2006 (Brown et al., 2006) concluded that it does not support the efficacy or safety of this product. In young men, a single dose of 100–200mg Andro does not increase blood testosterone levels or stimulate muscle protein synthesis, and chronic intake of 100mg Andro (three times per day for eight weeks or twice per day for 12 weeks) does not augment increases in muscle size and strength during resistance training. Although a single dose of 300mg Andro may raise blood testosterone levels slightly (~15%) in young men, it is unlikely that this increase in testosterone would increase muscle size or strength. In women and middle-aged men, Andro intake raises blood testosterone levels, although an anabolic effect of androstenedione has not been demonstrated in either population.

Chronic supplementation with Andro may pose significant health risks. High density lipoprotein cholesterol is reduced with chronic Andro intake, corresponding to a 10–15% increase in cardiovascular disease risk. Andro intake raises blood dihydrotestosterone and oestrogen levels, which have been linked to benign prostate hypertrophy, baldness, increased risk of cardiovascular disease, various forms of cancer, and gynaecomastia in men. High blood levels of androstenedione may increase the risk for prostate cancer and pancreatic cancer as well as cause neural/behavioural changes such as increased hostility.

Androstenedione was explicitly included as an illegal androgenic hormone in the 2004 revision of the United States Anabolic Steroid Control Act, and has subsequently largely disappeared from the market and research. However, other hormones of structural similarity with other names can be found in nutritional supplements marketed towards weightlifters and body builders, and these products are largely of unknown safety or efficacy. In summary, androstenedione has not been demonstrated to produce either anabolic or ergogenic effects in supplement form at supraphysiological doses. There is also strong evidence of dose and time-related widespread adverse effects resulting in several negative health consequences. Androstenedione is classified as an androgenic/anabolic steroid and included on the WADA Prohibited List (WADA, 2014a).

Competing interests None

ANTIOXIDANTS

Andreas N. Kavazis and John C. Quindry

Over the last 30+ years a wealth of scientific evidence has clearly demonstrated that physical exercise results in elevated free radical production in active skeletal muscle. Understanding free radical generation during exercise is important because 1) excess free radical production during exercise can result in oxidative stress, and 2) free radicals can contribute to muscular fatigue during exercise (Powers and Jackson, 2008). This collective knowledge has motivated many athletes to use dietary antioxidant supplements as a means to prevent exercise-induced free radical stress and/or muscular fatigue. To date, however, the scientific evidence to support effective use of dietary antioxidants to prevent oxidative stress or muscular fatigue is equivocal. To understand whether supplementation with dietary antioxidants is efficacious in athletic applications, one must first address the following two questions: 1) is exercise-induced oxidative stress a bad occurrence? and 2) can dietary antioxidant supplement use prevent or prolong fatigue during exercise? This review summarises current understanding of exercise-induced oxidative stress with the purpose of addressing a perceived need to consume dietary antioxidants by many athletes and physically active individuals. The review begins with an overview of key terms and concepts related to free radical biology and antioxidants.

Free radical biology and antioxidants – key terms

Free radicals are molecules that contain one or more unpaired electrons in the outer orbital. Free radicals are formed by either losing or gaining an electron in reactions with other molecules (Halliwell and Gutteridge, 2007). Because most of the free radicals of importance to biological organisms are oxygen-centred, the term reactive oxygen species (ROS) is used to include radicals and non-radicals, and reactive derivatives of oxygen (e.g. hydrogen peroxide). Reactive oxygen species are chemically unstable and can damage important cellular constituents including proteins, lipids and DNA. ROS-mediated damage is termed ‘oxidative damage’ and results in cellular dysfunction.

Coined in 1985, ‘oxidative stress’ is a collective term that describes a prooxidant:antioxidant imbalance that favours oxidants (Powers and Jackson, 2008). In theory, oxidative stress can be caused by ROS over-production or antioxidant depletion. Independent of cause, a scientific hallmark of oxidative stress is the appearance of oxidative damage biomarkers (e.g. oxidized proteins and/or lipids). Oxidative stress is commonly quantified by the observance of increased oxidative damage markers and/or the decrease in antioxidant content within blood or muscle tissue.

Fundamental question 1: is exercise-induced oxidative stress a bad occurrence?

The notion that exercise-induced oxidative stress could be a bad occurrence seems at clear odds with undeniable evidence that regular participation in exercise or physical activity is a potent lifestyle factor for improved morbidity and mortality outcomes. While chronic oxidative stress is a cornerstone of most disease states, exercise-induced oxidative stress is a transient occurrence. Specifically, recent data suggest that the exercise-induced spike in ROS production is short-lived by biological design, in that many of the tell-tale adaptive responses to exercise training require a spike in ROS (Powers and Jackson, 2008).

If exercise-induced ROS are central to beneficial adaptations, the next logical question is what factor(s) keeps oxidative stress in check, preventing exercise from inducing pathology? Cells throughout the body have several systems in place to counteract ROS production during exercise. For example, myofibres contain a network of enzymatic and non-enzymatic antioxidant defence mechanisms used to attenuate oxidative damage. In the context of this review, an antioxidant will be defined as any substance that delays or prevents oxidative damage to a target molecule (Powers and Jackson, 2008). Enzymatic and non-enzymatic antioxidants work in concert with dietary antioxidants (e.g. vitamin C and vitamin E) serving to ‘replenish the antioxidant machine’. Cooperative interaction between dietary and endogenous antioxidants has fuelled the notion t...