L M Castell

A to Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—Part 31

This issue deals with the increasingly interesting topic of probiotics and also, slightly out of alphabetical order, with pycnogenol, a product usually associated with pine bark. Probiotics are food supplements containing live microorganisms. They modify intestinal microbiota in a way that enables beneficial bacteria to increase. An additional benefit is that probiotics in sufficient quantities also tend to decrease those species of bacteria which are considered harmful. It is suggested that this situation produces many potential benefits for the health and functioning of the digestive system, and also has a beneficial effect on immune function. In the short review below, the effects of probiotics and their efficacy in reducing infection incidence (or symptom severity/duration) in athletes are summarised. Pycnogenol supplementation has previously been considered to have a range of beneficial effects, including antioxidant and anti-inflammatory properties.nn### M GleesonnnProbiotics are food supplements that contain live microorganisms which when administered in adequate amounts can confer a health benefit on the host.1 There is now a reasonable body of evidence that regular consumption of probiotic strains that are proven to survive gut transit can modify the population of the gut-dwelling bacteria (microbiota) and influence immune function2,–,5 though it should be noted that such effects are dose- and strain-dependent. Probiotics modify the intestinal microbiota such that the numbers of beneficial bacteria increase and usually numbers of species considered harmful are decreased. Such changes have been associated with a range of potential benefits to the health and functioning …

A-Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance--Part 33.

Quercetin was first introduced to our A–Z series in the article on flavonoids.1 In Part 33, the author of the flavonoid review, Dr Nieman, updates this topic. We also cover another intriguing plant-based compound with proposed benefits as an antioxidant and stimulator of mitochondrial biogenesis, resveratrol. Rhodiola rosea, a claimed adaptogen, concludes this issue.nn### D C NiemannnEpidemiological studies support multiple disease prevention benefits for individuals consuming foods rich in the flavonol quercetin. In vitro and animal studies indicate that quercetin is a strong antioxidant and anti-inflammatory agent, and exerts antipathogenic and immune regulatory influences.2 Quercetin supplementation studies in community-dwelling humans do not reflect these positive benefits, but research is continuing in order to determine the proper outcome measures, dosing regimen and adjuvants that may amplify any perceived bioactive effects of quercetin in vivo.nnQuercetin supplementation studies in athletes have focused on potential influences on post-exercise inflammation, oxidative stress and immune dysfunction, illness rates following periods of physiological stress and exercise performance.nnResults thus far have been negative for quercetins countermeasure effects on postexercise physiological stress indicators, such as immune perturbations.3,–,5 However, when quercetin supplementation is combined with other polyphenols and food components such as green tea extract, isoquercetin and fish oil, a substantial reduction in exercise-induced inflammation and oxidative stress occurs in athletes, with augmentation of innate immune function.6nnQuercetin exerts strong antiviral activities when cultured with a wide variety …

A-Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance--Part 22.

Practitioners who work with elite athletes know that the pressure and considerable rewards involved with success provide a high level of motivation to look for any safe and legal strategy that might enhance performance, even by small margins. Dietary supplements operate in this space, whether they promise a large performance boost or just create the fear that an athlete cannot afford to miss out on what everyone else is using. It is often tempting to overlook the lack of evidence to support the claims made about a supplement on the basis that the stakes are higher for elite athletes; therefore the cost:benefit ratio favours experimentation in the absence of clear proof. Over the past decade, however, we have become aware that the cost of getting it wrong has also escalated for elite athletes. A new hazard related to supplement use has emerged: inadvertent ingestion of substances that are banned under the antidoping codes in place in elite sport, but present in supplement products. In some cases, the level of the presence, or contamination, of banned substances in supplements presents a health hazard for all consumers. In some cases, the concentration may be too small to achieve any health or performance effect but large enough to record an infringement for athletes who submit to doping tests. Newspapers, the internet and Courts of Arbitration in Sport now bear stories of dedicated athletes whose careers have been or are being jeopardised because of the ingestion of a banned substance via a dietary supplement. This problem was first brought to scientific recognition by Hans Geyer and his colleagues from the Centre for Preventive Doping Research in Cologne. The following article provides an update of a recent review by this team.1nnnnIn the past years, an increasing number of dietary supplements containing undeclared doping …

BJSM reviews: A to Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—Part 18

Part 18 extends the general amino acids overview in Part 2, by reviewing specifically glutamine and glutamate, and the tripeptide antioxidant, glutathione.nnGlutamine supplementation has been well studied in both clinical and exercise situations, particularly in terms of its effects on immune function. Sports drinks containing glutamine as a free amino acid or part of a dipeptide are widely available but the low levels recommended are unlikely to help improve immune or muscle function.nnThe first product of glutamine metabolism, catalysed by the enzyme glutaminase, is the excitatory neurotransmitter glutamate. The latter has sometimes been used for supplementation. This may seem rather surprising, since its appearance in plasma at a high concentration correlates neurotoxicity and sometimes with clinical problems.nnGlutathione, for which glutamine is a precursor via glutamate, is a powerful antioxidant and, in its reduced form, is a good marker of antioxidant capacity, while an increase in its oxidised form is a good marker of oxidative stress.nn### P Newsholme and M KrausennGlutathione (γ-glutamyl-cysteinyl-glycine; GSH) is the predominant low molecular weight thiol (0.5–10 mmol/l) in mammalian cells. Most GSH (85–90%) is cytosolic, with the remainder located in organelles (including mitochondria, nuclear matrix and peroxisomes).1 This tripeptide is a key antioxidant within cells, critical to regulating the reactive oxygen species (ROS) concentration.2 Reduced glutathione (GSH) may be used to remove damaging ROS such as H2O2 and convert it to harmless H2O, generating oxidised glutathione (GSSG) via glutathione peroxidase (figure 1). Disulphide formation and gluathionylation are reversible forms of protein covalent modification dependent on glutathione and can provide mechanisms for regulation of metabolic, signalling and transcriptional processes,3 including skeletal muscle adaptation to exercise and training.4 The cellular redox state is crucial for molecular signalling, and glutathione is a key regulator/sensor for redox status; thus strategies aiming at …

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance–Part 34

Part 34 is dominated by a review of prohormones, or more specifically, testosterone prohormones, which cause concern in sports nutrition related to their direct use or inadvertent intake as contaminants in other supplements. When taken specifically for their alleged effects as testosterone alternatives, they may give rise to health problems while failing to achieve the claimed benefits of enhanced strength and muscle mass. Prohormones are a Prohibited Substance on the World Anti-Doping Agency (WADA) list and, even in minute concentrations (as occurs in contaminated supplements) these products can lead to a positive doping outcome. This part also contains brief summaries of ribose and smilax, two supplements which have not lived up to any claims related to benefits to athletic performance.nn### D S King, R BaskervillennThe term prohormone strictly refers to a post-translational peptide that is cleaved by convertases into a variety of bioactive hormones .In the supplement context, prohormones refer to androgenic precursors which, when ingested, become enzymatically activated to testosterone derivatives. An understanding of the biochemical pathways emphasises the similarity between testosterone and its precursors.nnUsers see prohormones as a natural means to improve muscle strength, body composition and general well-being with fewer side effects than testosterone or synthetic androgenic steroids and a more practical (capsule) form of intake. The marketing strategy of commercial websites is to promote prohormones as ‘legal alternatives’ to testosterone with similar anabolic effects. Of course, many consumers are unaware that these prohormones are included on the WADA list of prohibited substances as well as being illegal for sale or importation in many countries. Prohormones have another concerning role in sports nutrition as contaminants in other sports supplements which account for a large proportion of inadvertent doping offences.nnFrom cholesterol, pregnenolone is produced which converts to testosterone via dihydroepiandosterone (DHEA). The path via DHEA …

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance: Part 48

As we end this series of reviews of supplements and sports foods, it is fitting that the last words should come from the World Anti-Doping Agency. After all, the contravention of anti-doping rules due to the ingestion of prohibited substances that are ingredients or contaminants of some supplements and sports foods is a key issue which must be taken into account whenever an athlete decides whether or not to use such products.nn### A VernecnnAthletes have a long history of using substances in an attempt to gain an advantage in sporting competitions. The ancient Greeks and Romans used herbs, fungi, poppy seeds and stimulants such as strychnine in order to boost performance.1 In the modern era, this practice continued mostly with the use of stimulants and narcotics. Sports federations took notice and in 1928 the International Association of Athletics Federations (IAAF) became the first federation to prohibit the use of performance-enhancing drugs (PEDs), although there would be no testing in sport for another 40u2005years.2nnAmphetamine use was involved in the deaths of cyclists Knud Jensen and Tommy Simpson in the 1960 Olympic Games and the 1967 Tour de France respectively: this spurred the development of the International Olympic Commissions (IOC) Medical Commission, which published the first IOC Prohibited List in 1967. This became the de facto Prohibited List for Olympic Sport Federations. The ‘Festina affair’ (1998 Tour de France), where a team trainers car was found to contain a panoply of PEDs, was the catalyst to create a new organisation to harmonise, coordinate and promote the fight against doping in sport in all its forms.3 The IOC convened the first World Conference in Doping in Sport in 1999, which resulted in the formation of the World Anti-Doping Agency (WADA).nnWADA is a unique, independent body representing equally sport and …

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—Part 13

This issue begins with a brief article on electrolytes, now popularly offered to athletes in supplement form, as a discrete product or as an ingredient of sports drinks. Two herbs are also discussed: echinacea and ephedra. Both plants are popular supplements of athletes worldwide, but the similarities end there.nn### M F BergeronnnElectrolytes are negatively (anions) or positively (cations) charged substances that, when in solution, conduct an electric current. Major physiological electrolytes include Na+, K+, Cl− and HCO3−, while other electrolytes such as Ca2+, Mg2+ and trace elements are also found in the body in significant amounts. Na+, K+, Cl− and HCO3− are primarily responsible for normal water distribution and homeostasis throughout the body via their effect on osmotic pressure. These major electrolytes also play an essential role in regulating heart and muscle function, maintaining pH and a number of other important biochemical reactions.nnAn athletes demand for electrolytes increases with exercise and heat stress, as extensive sweating can mean both large water and electrolyte losses in addition to related changes in extra- and intracellular water distribution. Dehydration and an increase in plasma osmolality, which is primarily driven by Na+, will also stimulate osmoreceptors prompting an athlete to drink to maintain further or defend plasma volume.1 The primary electrolytes in sweat are Na+ (20–70 mmol/l) and Cl−, with comparatively much lower levels of K+ (∼5 mmol/l) and even less Ca2+ (∼1 mmol/l) and Mg2+ (∼0.8 mmol/l).2 As the sweating rate increases, the concentration of Na+ in sweat increases correspondingly, even with the lower sweat Na+ concentrations observed after heat acclimation.3 With Na+ being the major cation of …

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance: Part 38

Three amino acids are discussed in Part 38, which begins with an essential amino acid, threonine. In animal studies it is important for maintaining gut function, and also has a role in immune function. The amino acid tryptophan is a precursor of serotonin. It was first shown to be instrumental in promoting fatigue in rats, and this has since been confirmed in humans. It has mainly come to prominence in sports studies because of attempts to counteract its fatiguing effects by the use of branched chain amino acids (BCAA). Recently there has been some interest in the soporific effects of tryptophan, which were first observed in the 1960s. The third amino acid discussed is tyrosine: its increase across the blood–brain barrier can promote an increase in dopamine and norepinephrine.nn### N CermaknnThreonine is one of the nine essential amino acids required by humans. As such, threonine cannot be synthesised endogenously, and thus threonine must be obtained through diet or nutritional supplementation. Foods high in threonine include cottage cheese, poultry, fish, meat, lentils and sesame seeds. In animals, threonine is a primary component of intestinal mucin protein and plasma γ-globulin required for maintaining gut function.1 Threonine supplementation in chickens, pigs and mice has been shown to elevate serum antibodies against various viruses, providing support for a role of dietary threonine in modulating immune function.1 ,2 In rats, threonine deficiency has been found to depress the synthetic rate of phospholipid and nucleoprotein …

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance: part 24

In this issue, we deal with three compounds. One is a hormone involved in fat metabolism, while another is a mineral whose status may be altered by exercise. The final is a fat that might be digested and metabolised more efficiently than our common dietary fat sources.nn### JA CalbetnnLeptin is a hormone secreted primarily by adipocytes from the white adipose tissue in direct proportion to the amount of body fat present. Leptin plays a crucial role in the regulation of appetite, body fat mass, basal metabolic rate and gonadal function.1 Congenital deficiency of leptin is rare, but causes morbid obesity which is normalised following leptin treatment. Circulating leptin levels change acutely in accordance with energy balance; leptin levels increase with food ingestion and reduce with prolonged exercise and fasting. When there is a severe acute negative energy balance, serum leptin levels dramatically reduce by 60–80%, despite small changes in total fat mass. Preventing this reduction in leptin levels could attenuate hunger in dieting athletes, facilitating the adjustment of body mass to specific targets. Nevertheless, there is no account of leptin misuse by athletes for this purpose.nnLeptin receptors are densely expressed in the cerebellum, even more so than in the hypothalamus where leptin is supposed to exert its main action. Leptin-related changes owing to physical activity levels may promote structural changes in the cerebellum, which is strongly implicated in motor control and learning. Leptin receptors are also expressed in human skeletal muscle,2 3 and more abundantly in women than men.3 Here, the main action of leptin is believed to be the stimulation of fatty acid oxidation via several pathways.4 Interestingly, these pathways are also activated 30 min after sprint exercise5 and, like sprint exercise, leptin induces PGC1α expression and mitochondrial biogenesis. It is known that exercise …

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—Part 19

Glycerol, guarana and the weight-loss agent, hydroxycut, occupy part 19; glycine will appear in part 20. The ubiquitous product, glycerol, is used both orally, for example, as an emulsifier in ice cream and topically, for example, as glycerine in hand cream. In the area of sports nutrition, glycerol plays a role in improving hydration status, as described in detail below. Guarana has been used for centuries as a stimulant in South America, due to its high caffeine content; it also contains xanthine alkaloids, such as theobromine and theophylline, which enhance the effects of caffeine. Further information on caffeine and sports performance can be found in part 6 of this series.1 Unlike glycerol and guarana, hydroxycut is an example of a multi-ingredient supplement with a proprietary formulation that presents special challenges when assessing safety and efficacy, including uncertainty as to which ‘active’ ingredients may provide the desired effects and frequent formulation changes.nn### L M BurkennGlycerol is a 3-carbon sugar alcohol that provides the backbone of triglycerides and is naturally found in foods as a component of dietary fats. However, its various physical and chemical properties are valuable in food technology: glycerol is added to manufactured foods and drinks as an emulsifier, humectant, sweetener, filler and thickener. Its viscosity also makes it useful as a component of lotions and creams, explaining its common availability for purchase in purified form under the name of glycerine. Although it has been suggested as a gluconeogenic precursor that could provide a substrate for exercise, the ingestion of glycerol by athletes is best known for its role as an osmolyte. When ingested or released following lipolysis, glycerol contributes to the osmotic pressure of body fluids until it is slowly metabolised. When consumed simultaneously with a substantial volume of fluid, there is a temporary retention of this fluid and …