TECHNICAL ARTICLE

growth, the premise for this use is flawed. Glutamine depletion only occurs in times of excess stress and its loss is now being recognised as a marker of overtraining [9]. Exercise of the duration and intensity necessary to deplete glutamine levels causes increased release of catabolic hormones and suppression of growth hormone release, the opposite of what occurs during suitable resistance training programmes. Indeed, in moderate intensity exercise, especially where the workload is progressively increased (exactly like weightlifting), glutamine status improves in the body [9, 10].

Instead, it is in exhaustive exercise that glutamine depletion occurs and that supplementation serves considerable value. Glutamine is the fuel of the immune system with depletion creating a state of immunosupression [11]. It is well established that endurance athletes performing at a high intensity level experience a significant increase in the occurrence of upper respiratory tract infections. These are infections that glutamine supplementation can overcome. In marathon racers, after just one week of glutamine supplementation (5 grams before and after training), a noticeable reduction in infection rate was achieved [12, 13].

ZMA

ZMA (30 mg zinc monomethionine aspartate, 450 mg magnesium aspartate, and 10.5 mg vitamin B-6 – B6 is added to increase zinc and magnesium absorption) is primarily targeted at males, especially athletes, as a virility enhancer. It is touted to boost anabolic hormone levels; increasing strength, aiding recovery, improving sleep and generally conferring improved well-being.

Zinc and magnesium are both essential for human growth and development, used extensively by the body in over 300 metabolic processes, and key in the production of IGF-1 (the active metabolite of growth hormone) [14]. Cellular zinc concentrations are correlated with testosterone levels, and zinc restriction causes testosterone levels to plummet. In elderly men with marginal zinc deficiency, supplementation almost doubled their testosterone levels [15]. Zinc seems to also have mild actions as an aromatase inhibitor, preventing the conversion of testosterone into oestrogens [16]. Magnesium has electrolyte actions, and is required for maintaining normal potassium and calcium levels. Evidence suggests that magnesium prevents testosterone from binding to sex hormone globulin thus increasing

the amount of available active testosterone [17]. It is also critical for energy metabolism [18].

It is noteworthy that these beneficial effects occur at recommended dietary intakes of the nutrients (15-25 mg zinc & 400-800mg magnesium), with no extra benefit seen above theses levels. However, with the average UK male ingesting a mere 10mg of zinc and 300mg of magnesium from the diet, and with studies showing that those who undergo strenuous exercise need increased intakes, the inclusion of a ZMA supplement at least at a half dose daily (15mg zinc and 200mg magnesium) makes sage advice.

ANSWER THE FOLLOWING QUESTIONS ONLINE TO EARN CPD POINTS Please log into the members’ area of the REPs website to give your answers

Q1 Q2 Q3

How many mg of Creatine will an omnivore diet typically supply a day? a) 2000mg b) 1000mg c) 5000mg

What percentage of muscle amino acid does Glutamine contain? a) 30% b) 20% c) 40%

What are Zinc and Magnesium both essential for? a) Growth and development b) Defending against acid production in the skeletal muscle c) Energy for high intensity exercise

www.exerciseregister.org

References 1. Buford, T.W., et al., International Society of Sports Nutrition position stand: creatine supplementation and exercise. J Int Soc Sports Nutr, 2007. 4: p. 6. 2. Kreider, R.B., Effects of creatine supplementation on performance and training adaptations. Mol Cell Biochem, 2003. 244(1-2): p. 89-94. 3. Persky, A.M. and G.A. Brazeau, Clinical pharmacology of the dietary supplement creatine monohydrate. Pharmacol Rev, 2001. 53(2): p. 161-76. 4. Walker, J.B., Creatine: biosynthesis, regulation, and function. Adv Enzymol Relat Areas Mol Biol, 1979. 50: p. 177-242. 5. Greenhaff, P., The nutritional biochemistry of creatine. The Journal of Nutritional Biochemistry, 1997. 8(11): p. 610-618. 6. van Loon, L.J., et al., Creatine supplementation increases glycogen storage but not GLUT-4 expression in human skeletal muscle. Clin Sci (Lond), 2004. 106(1): p. 99-106. 7. Hobson, Ruth M., et al. Effects of β-alanine supplementation on exercise performance: a meta-analysis. Amino Acids, 2012. 43.(1): p. 25-37. 8 Biolo, G., et al., Transmembrane transport and intracellular kinetics of amino acids in human skeletal muscle. Am J Physiol, 1995. 268(1 Pt 1): p. E75-84. 9. Agostini, F. and G. Biolo, Effect of physical activity on glutamine metabolism. Curr Opin Clin Nutr Metab Care, 2010. 13(1): p. 58-64. 10. Williams, B.D., D.L. Chinkes, and R.R. Wolfe, Alanine and glutamine kinetics at rest and during exercise in humans. Med Sci Sports Exerc, 1998. 30(7): p. 1053-8. 11. Miller, A.L., Therapeutic considerations of L-glutamine: a review of the literature. Altern Med Rev, 1999. 4(4): p. 239-48. 12. Castell, L.M. and E.A. Newsholme, The effects of oral glutamine supplementation on athletes after prolonged, exhaustive exercise. Nutrition, 1997. 13(7-8): p. 738-42. 13. Castell, L.M., J.R. Poortmans, and E.A. Newsholme, Does glutamine have a role in reducing infections in athletes? Eur J Appl Physiol Occup Physiol, 1996. 73(5): p. 488-90. 14. Mamoglu, S., et al., Effect of zinc supplementation on growth hormone secretion, IGF-I, IGFBP-3, somatomedin generation, alkaline phosphatase, osteocalcin and growth in prepubertal children with idiopathic short stature. J Pediatr Endocrinol Metab, 2005. 18(1): p. 69-74. 15. Prasad, A.S., et al., Zinc status and serum testosterone levels of healthy adults. Nutrition, 1996. 12(5): p. 344-8. 16. Om, A.S. and K.W. Chung, Dietary zinc deficiency alters 5 alpha-reduction and aromatization of testosterone and androgen and estrogen receptors in rat liver. J Nutr, 1996. 126(4): p. 842-8. 17. Excoffon, L., et al., Magnesium effect on testosterone-SHBG association studied by a novel molecular chromatography approach. J Pharm Biomed Anal, 2009. 49(2): p. 175-80. 18. Nielsen, F.H. and H.C. Lukaski, Update on the relationship between magnesium and exercise. Magnes Res, 2006. 19(3): p. 180-9.

THE AUTHOR

Aidan is a pharmacist with a Master’s Degree in Nutritional Medicine and is the author of the award winning book ‘The Health Delusion’. As well as providing expert health advice to the media Aidan is co-founder and director of the innovative

health information website HealthUncut.com and an expert health contributor for the ‘Huffington Post’. Armed with a specialised knowledge and a passion for sports nutrition, Aidan has devised many dietary and supplementary regiments for a host of elite athletes. www.aidangoggins.com

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