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Downloaded from bjsm.bmj.com on January 14, 2010 - Published by group.bmj.com BJSM reviews: A−Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance Part 4 L M Burke, L M Castell, S J Stear, et al. Br J Sports Med 2009 43: 1088-1090 doi: 10.1136/bjsm.2009.068643 Updated information and services can be found at: http://bjsm.bmj.com/content/43/14/1088.full.html These include: References This article cites 22 articles, 8 of which can be accessed free at: http://bjsm.bmj.com/content/43/14/1088.full.html#ref-list-1 Email alerting service Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article. Notes To order reprints of this article go to: http://bjsm.bmj.com/cgi/reprintform To subscribe to British Journal of Sports Medicine go to: http://bjsm.bmj.com/subscriptions Downloaded from bjsm.bmj.com on January 14, 2010 - Published by group.bmj.com Nutritional supplement series BJSM reviews: A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance Part 4 L M Burke,1 L M Castell,2 S J Stear,3 P J Rogers,4 E Blomstrand,5 S Gurr,6 N Mitchell,7 F B Stephens,8 P L Greenhaff8 1 Australian Institute of Sport, Canberra, Australia; 2 University of Oxford, Oxford, UK; 3 English Institute of Sport, London, UK; 4 ASPARTAME, BRANCHED CHAIN AMINO ACIDS, BEE POLLEN, BORON, CARNITINE 4 Department of Experimental Psychology, University of Bristol, Bristol, UK; 5 Åstrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden; 6 Sports Nutrition, Australian Institute of Sport, Belconnen, Australia; 7 British Cycling, English Institute of Sport, Sheffield, UK; 8 School of Biomedical Sciences, The Medical School, The University of Nottingham, Nottingham, UK Correspondence to: L M Castell, University of Oxford, Green Templeton College, Oxford OX2 6HG, UK; lindy. [email protected] LB, LC and SJ edited this series. Accepted 9 October 2009 INTRODUCTORY REMARKS Welcome to Part 4 in our A–Z of nutritional supplement series. One of the enjoyable aspects of reviewing the many supplements in a fairly logical order from A to Z means that, every now and then, a review comprises a real assortment of supplements, and Part 4 is certainly one of them! In Part 4, the review takes us from aspartame, a sweetening ingredient found in many foods and drinks, to BCAA, the three branched chain essential amino acids; then onto bee pollen, marketed as a ‘‘superfood,’’ followed by the ultra trace element boron, known more for its association with bone health, and finally to L-carnitine, a supplement which is widely used in the sporting arena and seems to be gaining in popularity. We are grateful for the excellent contributions from our invited reviewers, which facilitate the provision of access to impartial advice on the value of these individual ingredients and supplements. These contributions are establishing that, for some, the performance evidence is limited or simply does not yet exist. In the January 2010 issue, we will be turning our attention to ‘‘buffers,’’ where we will be covering the key ones used by many athletes, such as betaalanine and carnosine, together with the two more established compounds of sodium bicarbonate and sodium citrate. ASPARTAME PJ Rogers Aspartame (C14H18N2O5) is an example of an intense or non-nutritive sweetener and an ingredient of many thousands of drink and food products consumed worldwide. It is a methyl ester of a dipeptide composed of the amino acids aspartic acid and phenylalanine, which are constituents of all protein-containing foods. Aspartame is about 180 times sweeter than sucrose with, for most individuals, minimal bitterness and a good quality of sweet taste. Being composed of amino acids, it has an energy value of 4 kcal/g; however, at the concentrations needed to sweeten foods and drinks, its nutritive value is negligible. In products it may be blended with one or more other intense sweeteners (eg, acesulfame K and sucralose) and/ 1088 or with sugars, including sucrose, fructose and glucose. The safety of aspartame has been the subject of much, often ill-informed, debate. After ingestion, aspartame is broken down to its constituent amino acids and methanol, and some further minor products. Even at high dietary intakes of aspartame, the amount of methanol produced is too small to be harmful. Because high intakes of phenylalanine are undesirable for those born with phenylketonuria,1 products with aspartame may contain information such as ‘‘Contains a source of phenylalanine.’’ A recent comprehensive review concluded that ‘‘The weight of existing evidence is that aspartame is safe at current levels of consumption as a non-nutritive sweetener.’’2 By replacing sugars in products, intense sweeteners can potentially aid control of energy intake and weight, but the extent of any benefit would appear to be dependent on the context of use.3 Additionally, aspartame reduces appetite independent of its sweet taste by a physiological action which is currently unknown.4 Aspartame, and other intense sweeteners, are used in sport drinks to allow adjustment of nutrient profile and tonicity, while maintaining a pleasant level of sweetness. The flavour and sweetness of such products are important for motivating consumption, and thereby achieving desired levels of hydration and nutrient intake. BRANCHED CHAIN AMINO ACIDS E Blomstrand The three branched chain amino acids (BCAA; leucine, isoleucine and valine) cannot be synthesised by the human body and must therefore be provided in the diet. Food sources containing BCAA are dietary proteins such as meat, poultry, fish, egg, milk and cheese, which contain 15–20 g of BCAA per 100 g of protein. The BCAA are metabolised mainly in skeletal muscle, which means they escape the liver, and ingestion of BCAA causes a rapid increase in the plasma level. The anabolic effect of BCAA on human skeletal muscle was first demonstrated under resting conditions, followed by studies showing similar effects in the recovery period after endurance and resistance exercise.5 6 More recent data indicate that the effect of BCAA, particularly leucine, is mediated through activation of regulatory enzymes in the protein synthesis machinery.7 Increasing the plasma level of BCAA during exercise may reduce the transport of tryptophan Br J Sports Med 2009;43:1088–1090. doi:10.1136/bjsm.2009.068643 Downloaded from bjsm.bmj.com on January 14, 2010 - Published by group.bmj.com Nutritional supplement series into the brain and the synthesis of 5-hydroxytryptamine (5HT). 5-HT has been suggested to be involved in central fatigue, that is, fatigue emanating from the brain rather than muscle.8 BCAA supplementation during sustained physical activity has exerted positive effects on cognitive performance and perceived exertion.8 9 Under certain conditions, BCAA supplementation can also improve physical performance, although the majority of studies have found no effect of BCAA on performance when supplied together with carbohydrates.10 The amount of BCAA recommended is 0.03–0.05 g/kg body weight per hour or 2–4 g per hour ingested repeatedly during exercise and recovery, preferably taken as a drink. Large doses (,30 g per day) are well tolerated; however, they may be detrimental to performance due to increased production of ammonia by the exercising muscle. BEE POLLEN S Gurr Bee pollen is a mixture collected by bees of pollen granules from the stamens of flowers and flower nectar. It is commercially available in granule, capsule or tablet preparations. These contain a wide and varying array of nutrients, including saccharides, amino acids, vitamins and minerals, as well as possible contaminants. Despite a long history in traditional medicine as a ‘‘superfood,’’ there is little evidence to support the range of health claims for bee pollen. Interest in its ergogenic properties stems from anecdotal reports and testimonies from successful athletes.11 However, the few available studies from the 1970s and 1980s involving athletes and bee pollen supplementation (3–12-week protocols following manufacturers’ recommended doses) have found minimal effects on: haemoglobin concentrations,12 strength and aerobic capacity,13 perceived exertion,14 time trial performance12 or repeated high-intensity exercise.14 One study13 did note fewer days lost to respiratory infections in swimmers supplementing with bee pollen. Allergic reactions including anaphylaxis have been reported in people taking bee pollen supplements.15 The limited empirical research suggests that bee pollen supplementation affords no additional benefit to athletic performance beyond that provided by a balanced diet. BORON N Mitchell Boron, an element with the atomic number 5, is an essential nutrient for plants, but the physiological role in humans is not fully understood. Boron can be considered as an ultra trace element16 therefore requirements are micrograms per day. Dietary daily human intake is estimated to range from 2.1 to 4.3 mg of boron per kilogram body weight per day. Boron enters the food chain via its incorporation into plant structure and subsequent consumption by humans. There is little evidence of boron deficiency in humans, however, oral boron supplementation is used in the general health and sports markets. Boron has been linked to increased endogenous testosterone levels, but there is little evidence in the literature using an athletic population to support this. Research17 investigating boron supplementation in postmenopausal women (after a boron-restricted diet) focused on mineral, estrogen and testosterone metabolism. A supplementation of 3 mg of boron per day was associated with an increase in testosterone levels. No Br J Sports Med 2009;43:1088–1090. doi:10.1136/bjsm.2009.068643 proposed mechanism for increased testosterone was reported; however, the authors suggested that maintenance of adequate boron levels in postmenopausal women might prevent calcium loss and bone demineralisation. Few studies have investigated the effects of boron supplementation on increasing testosterone levels in an athletic population. Fernando and Green18 used a randomised placebo-controlled design including participants who regularly weight-trained for at least 1 year (however, no data were reported describing the trained status of the participants). The volunteers were given either 2.5 mg/day of boron (n = 10) or placebo (n = 9) for a 7week period. The results suggested an increase in strength (based on one repetition maximum, squat and bench press), increases in lean tissue and testosterone in both groups. However, there was no evidence that the boron supplementation had any additional effect. Therefore, the changes could be regarded as only due to a training effect. A 10-month boron supplementation study in young female athletes,19 versus sedentary women, produced a modest effect on mineral status. This included a decrease in serum phosphorus and increased urinary calcium excretion which was greater in athletes than in controls. There is currently little evidence to support the use of boron supplementation in the athletic population. L-CARNITINE FB Stephens, PL Greenhaff Ninety-five per cent of the body’s carnitine (3-hydroxy-4N,N,N-trimethylaminobutyric acid; C7H15NO3) store (,25 g) exists within skeletal muscle where it plays a central role in fat and carbohydrate oxidation, particularly during exercise (for a review, see Stephens et al20). The recommended upper limit of 21 L-carnitine supplementation is 2 g/day, but no adverse effects were reported following feeding up to 6 g/day for 1 year.21 22 The main food source of carnitine is meat. Non-vegetarians ingest 1 mg/kg of dietary carnitine per day, whereas strict vegetarians ingest around 0.01 mg/kg.23 Research has been directed towards supplementing dietary L-carnitine to improve exercise performance. However, neither oral (2–6 g/day for 1 day to 4 months) nor intravenous (up to 65 mg/kg) L-carnitine administration per se has been found to alter fuel metabolism during exercise or, more importantly, increase muscle carnitine content in humans.20 22 24 Despite this, L-carnitine feeding as a tool to promote apparent fat loss remains the foundation of a multimillion dollar dietary supplement industry in the present day. More recently, intravenous infusion of L-carnitine along with insulin (to stimulate Na+-dependent muscle carnitine transport) has been found to increase muscle total carnitine content by ,15% in healthy volunteers, and to have a measurable effect on muscle fuel metabolism at rest.20 This stimulatory effect on muscle carnitine accumulation occurred in the physiological range for serum insulin concentration (50–90 mU/l).20 Furthermore, feeding L-carnitine (3 g/d) together with carbohydrate (500 ml solution containing 94 g of simple sugars) for 2 weeks increased whole-body carnitine retention compared with ingestion of L-carnitine alone.25 However, because orally administered L-carnitine has a poor bioavailability (,15% for a 2–6 g dose), it is likely that this supplementation regimen would take ,100 days to increase muscle carnitine content by ,10%.25 Further research is required to determine the impact that an insulin-mediated increase in muscle carnitine content has on muscle fuel metabolism and performance during exercise. 1089 Downloaded from bjsm.bmj.com on January 14, 2010 - Published by group.bmj.com Nutritional supplement series CONCLUDING REMARKS Although aspartame is not a supplement per se, its wide use in many sports foods and drinks warrants inclusion in the review series. Non-nutritive sweeteners have been around a long time, with saccharin first being introduced back in 1878 and becoming a household name as a substitute for sugar during the sugar restrictions of World War I and World War II. Aspartame, discovered in 1965, is now the most common sweetener, and is also probably the most researched and evaluated food additive in the world. There has been much scare-mongering about the safety of using sweeteners including aspartame, in particular the association with cancer risk, which has actually been disproved regularly. We hope this brief review of the ingredient makes an important contribution towards addressing the issue. There is no doubt that taste is down to preference, and that it is individual choice which dictates whether products are selected with or without sweeteners. Despite the popularity of bee pollen supplements, this review demonstrates the lack of evidence for a performance benefit, and with the added complication of potential allergic reactions, it may be a supplement to steer clear of. With regard to boron, there is a small amount of evidence to suggest its usefulness in bone health. However, there is currently limited evidence to support the need to consume boron supplements on top of a healthy, well-chosen diet, either for bones or for sports performance. From the review summaries presented here, there appears to be some evidence of potential benefits of consuming BCAA, and future work with L-carnitine may also find some useful outcomes. Nevertheless, it is pertinent to stress again that any athlete considering using a supplement is strongly recommended to obtain advice from a sports nutrition professional first. In particular, any potential clinical issues should be discussed. Furthermore, in relation to supplement contamination issues, as discussed in the introductory review in the September issue, it must be reiterated that any athlete who competes under the World Anti-Doping Agency (http:// www.wada-ama.org) code needs to be extremely cautious about using supplements. Athletes should always work with a qualified professional to minimise the risk of supplement use. Competing interests: None. Provenance and peer review: Commissioned; not externally peer reviewed. 1090 REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. Acosta PB, Elsas LJ. Nutritional management of phenylketonuria. In: Sadler MJ, Strain JJ, Caballero, eds. Encyclopedia of human nutrition. San Diego: Academic Press, 1999:1088–96. Magnuson BA, Burdock GA, Doull J, et al. Aspartame: a safety evaluation based on current use levels, regulations, and toxicological and epidemiological studies. Crit Rev Toxicol 2007;37:629–727. 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