Louise M. Burke

Dietary Supplements in Sport

SummaryStudies of the dietary practices of athletes report that nutritional supplements are commonly used. Supplementation practices vary between sports and individual athletes; however, there is evidence that at least some athletes use a large number of supplements concurrently, often in doses that are very high in comparison with normal dietary intakes.In exploring supplementation practices we propose a classification system separating the supplements into dietary supplements and nutritional erogogenic aids. The dietary supplement is characterised as a product which can be used to address physiological or nutritional issues arising in sport. It may provide a convenient or practical means of consuming special nutrient requirements for exercise, or it may be used to prevent/reverse nutritional deficiencies that commonly occur among athletes. The basis of the dietary supplement is an understanding of nutritional requirements and physiological effects of exercise. When the supplement is used to successfully meet a physiological/nutritional goal arising in sport it may be demonstrated to improve sports performance. While there is some interest in refining the composition or formulation of some dietary supplements, the real interest belongs to the use or application of the supplement; i.e. educating athletes to understand and achieve their nutritional needs in a specific sports situation.The sports drink (carbohydrate-electrolyte replacement drink) is a well known example of a dietary supplement. Scientific attitudes towards the sports drink have changed over the past 20 years. Initial caution that carbohydrate-electrolyte fluids compromise gastric emptying during exercise has now been shown to be unjustified. Numerous studies have shown that 5 to 10% solutions of glucose, glucose polymers (maltodextrins) and other simple sugars all have suitable gastric emptying characteristics for the delivery of fluid and moderate amounts of carbohydrate substrate. The optimal concentration of electrolytes, particularly sodium, remains unknown. Most currently available sports drinks provide a low level of sodium (10 to 25 mmol/L) in recognition that sodium intake may promote intestinal absorption of fluid as well as assist in rehydration. The sodium level of commercial oral rehydration fluids (used in the clinical treatment of diarrhoea and dehydration) is higher than that of the present range of sports drinks. However, even if research indicates that intestinal glucose transport is optimally stimulated at higher sodium concentrations, concern for the palatability of sports drinks may impose a lower ceiling for sodium levels. Commercial viability of a sports drink requires that it provide a refreshing and palatable fluid replacement across a wide variety of sports and exercise situations. However, in specific situations, the appropriate use of a drink may offer special advantages in meeting physiological requirements. For example, during endurance and ultraendurance exercise, suitable intake of a sports drink to preserve hydration and to supply additional carbohydrate substrate for glycogen-depleted muscles has been shown to enhance performance. Additionally, the sports drink may provide a special advantage in recovery and rehydration after prolonged exercise, particularly where more rapid restoration of body fluid and fuel levels will enhance performance in future exercise bouts.High carbohydrate liquids at higher concentrations (20 to 25% carbohydrate solutions, typically from maltodextrin sources) represent another type of dietary supplement. These high carbohydrate supplements, often known as ‘carbo-loader’ supplements, have been manufactured to assist athletes in achieving a high carbohydrate intake by overcoming problems of dietary bulk or lack of nutritional knowledge. They may be useful in situations where a short term need for carbohydrate supersedes other nutritional goals, e.g. carbohydrate loading and prolonged competition over successive days. Where long term nutritional goals and requirements for a combination of nutrients need to be addressed, liquid meal supplements provide a low-bulk, nutritionally complete choice. Liquid meal supplements may be useful as a compact nutrient-dense high energy supplement for athletes with high energy requirements, particularly when it is not practical or comfortable to consume solid foods. They may be useful in preparation for exercise, both as a pre-event meal and as a low residue preparation.Athletes who consume low energy intakes and/or restricted food variety may consume sub-optimal intakes of micronutrients, particularly minerals such as iron or calcium. Adequate vitamin and mineral status is a requirement for optimal sports performance, since many of the micronutrients play a key role in exercise metabolism, recovery and adaptation. A heavy exercise programme may increase requirements for some nutrients, including the B-group vitamins and iron. Athletes at high risk of inadequate micronutrient intake or nutritional deficiencies such as iron deficiency should benefit from nutritional counselling. Supplementation may be required in cases of ongoing suboptimal dietary intake, or to rapidly restore a diagnosed nutrient deficiency state. While many athletes regard iron supplements as a low cost ‘safety net’ against iron deficiency, there are many disadvantages to unsupervised long term intake of high doses of iron. The debate surrounding biochemical and haematological markers of optimal iron status remains unresolved. In general, screening and individual treatment of athletes in high-risk groups is preferred to a mass treatment programme.There is a need for nutrition education of athletes to explain the appropriate use of these dietary supplements. In many cases, the information is specific to the individual athlete or sports situation and may require one-to-one counselling. In most situations, the use of the supplement will simply be a part of a larger plan of optimal sports nutrition or the clinical management of a nutritional disorder. Effective education will not only ensure that dietary supplements are used correctly, but will highlight the importance of optimal sports nutrition.

Diet Patterns of Elite Australian Male Triathletes

In brief: The triathlon makes heavy demands on the body and especially on glycogen supply. This article describes the self-reported diet practices of 25 elite Australian male triathletes during training and racing. They consumed a mean of 4,095 kcal/day, 59.5% of which was carbohydrate, 13% protein, 27% fat, and 0.5% alcohol; glycogen and protein intakes met or surpassed recommended levels. Intakes of five vitamins and two minerals also exceeded recommendations, and iron status was satisfactory. The athletes ate carbohydrate mostly in complex form, snacking frequently to get enough for energy needs. Few subjects trained deliberately to build up a tolerance for consuming food and fluids during competition.

Failure to Repeatedly Supercompensate Muscle Glycogen Stores in Highly Trained Men

PURPOSE It is not known whether it is possible to repeatedly supercompensate muscle glycogen stores after exhaustive exercise bouts undertaken within several days. METHODS We evaluated the effect of repeated exercise-diet manipulation on muscle glycogen and triacylglycerol (IMTG) metabolism and exercise capacity in six well-trained subjects who completed an intermittent, exhaustive cycling protocol (EX) on three occasions separated by 48 h (i.e., days 1, 3, and 5) in a 5-d period. Twenty-four hours before day 1, subjects consumed a moderate (6 g.kg)-carbohydrate (CHO) diet, followed by 5 d of a high (12 g.kg.d)-CHO diet. Muscle biopsies were taken at rest, immediately post-EX on days 1, 3, and 5, and after 3 h of recovery on days 1 and 3. RESULTS Compared with day 1, resting muscle [glycogen] was elevated on day 3 but not day 5 (435+/-57 vs 713+/-60 vs 409+/-40 mmol.kg, P<0.001). [IMTG] was reduced by 28% (P<0.05) after EX on day 1, but post-EX levels on days 3 and 5 were similar to rest. EX was enhanced on days 3 and 5 compared with day 1 (31.9+/-2.5 and 35.4+/-3.8 vs 24.1+/-1.4 kJ.kg, P<0.05). Glycogen synthase activity at rest and immediately post-EX was similar between trials. Additionally, the rates of muscle glycogen accumulation were similar during the 3-h recovery period on days 1 and 3. CONCLUSION We show that well-trained men cannot repeatedly supercompensate muscle [glycogen] after glycogen-depleting exercise and 2 d of a high-CHO diet, suggesting that the mechanisms responsible for glycogen accumulation are attenuated as a consequence of successive days of glycogen-depleting exercise.

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. ### D C Nieman Epidemiological 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. Quercetin 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. Results 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.6 Quercetin 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 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. ### D S King, R Baskerville The 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. Users 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. From 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 28

Part 28 includes a supplement purported to combat fatigue and enhance growth hormone (ornithine); a well-known ingredient (phenylalanine) of a well-known sweetener (aspartame); a possible energy enhancer via 2,3 diphosphoglycerate (phosphate); and a rather dubious supplement purported in the early 1940s to have a wide range of medicinal effects (pangamic acid). Of these, only phosphate appears to have some credible evidence to support the claims of an ergogenic effect. ### K Currell Ornithine is an amino acid which plays a key role in the urea cycle, facilitating the disposal of ammonia. Ammonia is produced during intense exercise and may be one of the causes of fatigue. There is some evidence that L-ornithine hydrochloride supplementation prior to high-intensity exercise may prevent fatigue and improve performance by modulating the metabolism of ammonia.1 At present, the evidence is far from conclusive with a need to conduct more research using valid measures of performance. It has been suggested that ornithine supplementation will promote the secretion of growth hormone within humans.2 However, research has not been conducted to show whether this may enhance the adaptation to training and ultimately lead to an improvement in the performance. One potential avenue of future research is ornithine-α-ketoglutarate. This has been shown to improve the recovery of individuals from burns, trauma and in the postoperative state. It may also be a precursor of nitric oxide.2 At present, there is not enough evidence to support the use of ornithine in sport performance. However, further research should be conducted to investigate its use. ### DR Moore Phenylalanine is …

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. ### M F Bergeron Electrolytes 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. An 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 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. ### JA Calbet Leptin 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. Leptin 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. ### L M Burke Glycerol 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 …

A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—Part 30

Part 30 includes just two supplements: potassium and prebiotics. The role of potassium in exercise metabolism has been well documented in the literature but it seems that its appearance as a component of electrolyte-replacement products is a custom, rather than a necessity, since it is widely found in the diet. By contrast, prebiotics are at the beginning of an investigative story which may conclude by finding some beneficial uses for athletes to promote immune or gastrointestinal (GI) health during times of increased stress. ### Potassium #### Nancy DiMarco Potassium (K+) is the major intracellular cation in the body, with ∼98% of the body potassium stores located inside the cells with a concentration maintained at about 145 mM. Its major functions are to promote contractility of ciac, smooth and skeletal muscle and to influence the regulation of nerve conduction through the influx of sodium (Na+) and efflux of K+ on either side of the nerve terminal, occurring at the rate of 107 ions per second. On the surface of a nerve terminal, there are voltage-dependent channels for K+. In humans, at least 15 different K+-specific voltage-dependent channels have been identified. The Na+/K+ ATPase, also known as the Na pump, is the primary active transporter system that maintains the high K+ and low Na+ intracellular concentrations. The plasma membrane ATPase of all mammalian cells catalyses the reaction: ATP→ADP+Pi with obligatory requirements for Na+ and K+ and Mg2+ required for the dephosphorylation of ATP. Muscle has an especially high activity of this P-type Na+ pump which has been estimated to use 60% to 70% of the ATP synthesised in nerve and muscle cells.1 2 For active individuals/athletes, sweat is the …