Beljakovine in šport

Kakšen pomen imajo beljakovine v prehrani športnika, rekreativca? Koliko beljakovin potrebuje športnik? Je vrsta zaužitih beljakovin pomembna? Ali večja količina zaužitih beljakovin športniku lahko škodi? Osteoporoza, obremenitev ledvic? Je res, da vzdržljivostni športniki ne potrebujejo več beljakovin kot neaktivna populacija? Kaj pa težkoatleti; je res, da več beljakovin pomeni večji napredek, prirast mišične mase in moči? Ali obstaja kakšna povezava med potrebami po beljakovinah in skupno dnevno zaužito količino energije? Je timing uživanja beljakovin pomemben?

Prehranske beljakovine so že zelo dolgo vroča tema v okviru strokovnih (in laičnih) debat o športni prehrani.  Tudi na Cenim.se je bilo na to temo spisanih že nekaj člankov, kljub temu pa skoraj ne mine teden, da v elektronski nabiralnik ne bi prispelo vprašanje, povezano z beljakovinami v športni prehrani.

Namen tega članka ni podati podrobne odgovore na zgoraj zastavljena in podobna konkretna vprašanja, pač pa v strnjeni obliki nanizati nekaj – za športnike – najpomembnejših dejstev o beljakovinah v prehrani, ki imajo podlago v spodaj našteti strokovni literaturi.

Šport in prehranske beljakovine

Številne fiziološke funkcije prehranskih beljakovin in ključnih aminokislin, kot sta npr. glutamin in levcin (ena od treh aminokislin z razvejano verigo oz. BCAA), odpirajo za športnike in rekreativce najrazličnejše možnosti uporabe oz. manipulacije uživanja teh hranil. Vendar pa te možnosti niso omejene zgolj na npr. uravnavanje običajnih ergogenih učinkov ali spreminjanje telesne sestave, pač pa imajo prehranske beljakovine in določene aminokisline – oz. optimizacija / manipulacija njihovega vnosa – tudi druge, za športnike zelo pomembne funkcije / učinke.

  1. Beljakovine so gradniki kontraktilnih, strukturnih, hormonskih, imunskih, encimskih in vseh drugih telesnih beljakovin. Potrebne so za rast in obnovo vseh telesnih tkiv.
  2. V stanju relativne inzulinske odpornosti, npr. zaradi povečanih ekscentričnih obremenitev ali povečanega psihološkega stresa in pomanjkanja spanja, prispevajo k energijskemu ravnovesju in regeneraciji mišičnega glikogena (Layman DK, 2002; Meijer AJ, 2003; Varnier M et al, 1995).
  3. Preskrba mišic (levcin oz. BCAA) in črevesja ter levkocitov (glutamin) z oksidativnim gorivom med imunskim stresom.
  4. Spodbujanje izgradnje telesnih beljakovin v sicer kataboličnem stanju. Ta učinek se pripisuje predvsem aminokislini levcin.
  5. Možno zamnjšanje kataboličnih procesov med vadbo. Tudi ta učinek se pripisuje predvsem levcinu oz. BCAA. Ena od raziskav, leta 2000 objavljena v Journal of sports medicine and physical fitness (2 tedna po 12 g BCAA na  in dodatnih 20 g pred in po testiranju / vadbi), je pokazala, da uživanje BCAA zmanjša dvig encima kreatin kinaze po vadbi, kar kaže na manjši obseg kataboličnih procesov v mišičnem tkivu. Do podobnih rezultatov je prišla tudi raziskava (Training journal, 2003), v kateri so testiranci pred in po treningu zaužili mešanico aminokislin, ki je vsebovala 37% BCAA ter še 2 enaka odmerka dnevno 4 dni po testu. Izkazalo se je, da je uživanje aminokislinske mešanice bistveno omililo mišične bolečine / muskelfiber (primerjava s placebo skupino). Da zaužitje BCAA pred vadbo zmanjša dvig kreatin kinaze je pokazala tudi raziskava iz leta 2007, objavljena v International journal of sport nutrition and exercise metabolism.
  6. Povečana antioksidativna kapaciteta preko glutationa. Glutation je telesu lastna snov, ki jo sestavljajo tri aminokisline: glicin, glutamat in cistein. Poleg antioksidativnih ima glutation še nekatere druge pozitivne učinke, med drugim sodeluje pri nevtralizaciji raznih strupenih snovi, zaščiti pred ionizirajočim sevanjem, izgradnji beljakovin, prostaglandinov itd. Intenziven trening znižuje koncentracijo glutationa v telesu, kar zvišuje oksidativni stres. Dokazano je, da lahko sirotkine beljakovine omilijo znižanje glutationa v krvi. Obstaja tudi visoka korelacija med koncentracijama mišičnega glutamata in mišičnega glutationa, dodatki prekurzorjev glutamata (glutamin, BCAA, ornitin-alfa-ketoglutarat) pa lahko povečajo koncentracijo mišičnega glutamata in s tem glutationa (Jackson AA et al, 2004; Middleton N et al, 2004; Rutten EP et al, 2005).
  7. Izboljšana izgradnja kolagena (Karna E et al., 2001).
  8. Možna pospešitev oz. optimizacija hitrosti celjenja športnih in drugih poškodb. To velja tako za mikropoškodbe kot tudi večje poškodbe gibalnega aparata. Večina poškodb poveča bazalni metabolizem, zato lahko ob nespremenjeni prehrani pride tudi do kaloričnega in beljakovinskega deficita.
  9. Zmanjšana pojavnost infekcij zgornjih dihalnih poti in povečana količina nazalnega imunoglobulina-A. Ti učinki so bili dokazani za dodatke glutamina (Krieger JW et al, 2004;  Castell LM et al, 1996).
  10. Znižanje ravni in obramba proti škodljivemu delovanju povečane količine stresnih hormonov (kortizol, kateholamini), ki se izločajo med intenzivnimi treningi in so lahko tudi kronično povišani. Ti hormoni delujejo katabolično in zvišujejo bazalni metabolizem, uživanje določenih aminokislin in beljakovin (npr. glutamin, beljakovinska frakcija alfa-laktalbumin) pa lahko omili povišanje koncentracij in negativne učinke (Kanaley JA et al, 2001; Markus CR et al, 2000; Markus CR et al, 2005; Salehian B et al, 1999).

Številne raziskave so pokazale, da imajo športniki in rekreativci, ki redno in intenzivno trenirajo, večje potrebe po beljakovinah kot neaktivna oz. manj aktivna populacija. Te večje potrebe so posledica večje skupne porabe energije, povišanega bazalnega metabolizma zaradi mišičnih mikropoškodb, povišanja koncentracij t.i. stresnih hormonov (kortizol, kateholamini) in citokinov ter posledičnega večjega imunskega stresa ter možnih motenj spanja. Če upoštevamo, da lahko večina teh dejavnikov še negativno vpliva na presnovo ogljikovih hidratov, postane optimizacija vnosa beljakovin in določenih aminokislin, še posebej glutamina in levcina oz. BCAA, še toliko bolj pomembna.

Literatura

  1. Lowery L, Forsythe CE. Protein and Overtraining: Potential Applications for Free-Living Athletes. J Int Soc Sports Nutr, 2006; 3: 42 – 50.
  2. Negro M, Giardina S, Marzani B, Marzatico F. Branched-chain amino acid supplementation does not enhance athletic performance but affects muscle recovery and the immune system. J Sports Med Phys Fitness, 2008; 48(3): 347 – 351.
  3. Koopman R et al. Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects. Am J Physiol Endocrinol Metab, 2005; 288: E645 – 653.
  4. Blomstrand E et al. Branched-chain amino acids activate key enzymes in protein synthesis after physical exercise. J Nutr, 2006; 136: 269S – 273S.
  5. Mero A. Leucine supplementation and intensive training. Sports Med, 1999; 27: 347 – 358.
  6. Wolfe RR. Protein supplements and exercise. Am J Clin Nutr, 2000; 72: 551S – 557S.
  7. Gleeson M, Nicolette B. Modification of immune responses to exercise by carbohydrate, glutamine and anti-oxidant supplements. Immunol Cell Biol, 2000; 78: 554 – 561.
  8. Butterfield GE. Whole-body protein utilization in humans. Med Sci Sports Exerc 1987, 19: S157 – 165.
  9. McClave SA, Snider HL. Dissecting the energy needs of the body. Curr Opin Clin Nutr Metab Care, 2001; 4: 143 – 147.
  10. LaForgia J et al. Impact of indexing resting metabolic rate against fat-free mass determined by different body composition models. Eur J Clin Nutr, 2004; 58: 1132 – 1141.
  11. Burke LM. Energy needs of athletes. Can J Appl Physiol, 2001; (26 Suppl): S202 – 219.
  12. Gleeson M, Bishop NC. Special feature for the Olympics:  effects of exercise on the immune system:  modification of immune responses to exercise by carbohydrate, glutamine and anti-oxidant supplements. Immunol Cell Biol, 2000; 78: 554 – 561.
  13. Fielding RA, Parkington J. What are the dietary protein requirements of physically active individuals? New evidence on the effects of exercise on protein utilization during post-exercise recovery. Nutr Clin Care, 2002; 5: 191 – 196.
  14. Chiang AN, Huang PC. Excess energy and nitrogen balance at protein intakes above the requirement level in young men. Am J Clin Nutr 1988, 48: 1015 – 1022.
  15. Layman DK. Role of leucine in protein metabolism during exercise and recovery. Can J Appl Physiol, 2002; 27: 646 – 663.
  16. Varnier M et al. Stimulatory effect of glutamine on glycogen accumulation in human skeletal muscle. Am J Physiol, 1995; 269: E309 – 315.
  17. Meijer AJ. Amino acids as regulators and components of nonproteinogenic pathways. J Nutr, 2003; 133: 2057S – 062S.
  18. Tipton KD et al. Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise. Am J Physiol Endocrinol Metab, 2001; 281: E197 – 206.
  19. Dolezal BA et al. Muscle damage and resting metabolic rate after acute resistance exercise with an eccentric overload. Med Sci Sports Exerc, 2000; 32: 1202 – 1207.
  20. Evans WJ, Cannon JG. The metabolic effects of exercise-induced muscle damage. Exerc Sport Sci Rev, 1991; 19: 99 – 125.
  21. Ivy JL et al. Effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity. Int J Sport Nutr Exerc Metab, 2003; 13: 382 – 395.
  22. Ratamess NA et al. The effects of amino acid supplementation on muscular performance during resistance training overreaching. J Strength Cond Res, 2003; 17: 250 – 258.
  23. Curi R et al. Glutamine-dependent changes in gene expression and protein activity. Cell Biochem Funct, 2005; 23: 77 – 84.
  24. Welbourne T, Claville W, Langford M. An oral glutamine load enhances renal acid secretion and function. Am J Clin Nutr, 1998; 67: 660 – 663.
  25. Welbourne TC. Increased plasma bicarbonate and growth hormone after an oral glutamine load. Am J Clin Nutr, 1995; 61: 1058 – 1061.
  26. Rowbottom DG, Keast D, Morton AR. The emerging role of glutamine as an indicator of exercise stress and overtraining. Sports Med, 1996; 21: 80 – 97.
  27. Urhausen A, Gabriel H, Kindermann W. Blood hormones as markers of training stress and overtraining. Sports Med, 1995; 20: 251 – 276.
  28. Hooper SL et al. Markers for monitoring overtraining and recovery. Med Sci Sports Exerc, 1995; 27: 106 – 112.
  29. Fry AC et al. Catecholamine responses to short-term high-intensity resistance exercise overtraining. J Appl Physiol, 1994; 77: 941 – 946.
  30. Brillon DJ et al. Effect of cortisol on energy expenditure and amino acid metabolism in humans. Am J Physiol, 1995; 268: E501 – 513.
  31. Salehian B, Kejriwal K. Glucocorticoid-induced muscle atrophy: mechanisms and therapeutic strategies. Endocr Pract, 1999; 5: 277 – 281.
  32. Karna E et al. The potential mechanism for glutamine-induced collagen biosynthesis in cultured human skin fibroblasts. Comp Biochem Physiol B Biochem Mol Biol, 2001; 130: 23 – 32.
  33. Kanaley JA et al. Cortisol and growth hormone responses to exercise at different times of day. J Clin Endocrinol Metab, 2001; 86: 2881 – 2889.
  34. Anderson KE et al. Diet-hormone interactions: protein/carbohydrate ratio alters reciprocally the plasma levels of testosterone and cortisol and their respective binding globulins in man. Life Sci 1987, 40: 1761 – 1768.
  35. Markus CR et al. The bovine protein alpha-lactalbumin increases the plasma ratio of tryptophan to the other large neutral amino acids, and in vulnerable subjects raises brain serotonin activity, reduces cortisol concentration, and improves mood under stress. Am J Clin Nutr, 2000; 71: 1536 – 1544.
  36. Markus CR et al. Evening intake of alpha-lactalbumin increases plasma tryptophan availability and improves morning alertness and brain measures of attention. Am J Clin Nutr, 2005; 81: 1026 – 1033.
  37. Ostrowski K et al. A trauma-like elevation of plasma cytokines in humans in response to treadmill running. J Physiol, 1998; 513(Pt 3): 889 – 894.
  38. Pedersen BK, Hoffman-Goetz L. Exercise and the immune system: regulation, integration, and adaptation. Physiol Rev, 2000; 80: 1055 – 1081.
  39. Miles MP et al. Blood leukocyte and glutamine fluctuations after eccentric exercise. Int J Sports Med, 1999; 20: 322 – 327.
  40. Wilmore DW, Shabert JK. Role of glutamine in immunologic responses. Nutrition, 1998; 14: 618 – 626.
  41. Antonio J et al. The effects of high-dose glutamine ingestion on weightlifting performance. J Strength Cond Res, 2002; 16: 157 – 160.
  42. Krieger JW, Crowe M, Blank SE. Chronic glutamine supplementation increases nasal but not salivary IgA during 9 days of interval training. J Appl Physiol, 2004; 97: 585 – 591.
  43. Castell LM, Poortmans JR, Newsholme EA. Does glutamine have a role in reducing infections in athletes? Eur J Appl Physiol Occup Physiol, 1996; 73: 488 – 490.
  44. Jackson AA et al. Synthesis of erythrocyte glutathione in healthy adults consuming the safe amount of dietary protein. Am J Clin Nutr, 2004; 80: 101 – 107.
  45. Middleton N, Jelen P, Bell G. Whole blood and mononuclear cell glutathione response to dietary whey protein supplementation in sedentary and trained male human subjects. Int J Food Sci Nutr, 2004; 55: 131 – 141.
  46. Tsigos C et al. Dose effects of recombinant human interleukin-6 on pituitary hormone secretion and energy expenditure. Neuroendocrinology, 1997; 66: 54 – 62.
  47. Anthony JC, Anthony TG, Layman DK. Leucine supplementation enhances skeletal muscle recovery in rats following exercise. J Nutr, 1999; 129(6): 1102 – 1106.
  48. Greer BK, Woodard JL, White JP, Arguello EM, Haymes EM. Branched-chain amino acid supplementation and indicators of muscle damage after endurance exercise. Int J Sport Nutr Exerc Metab, 2007;17(6): 595 – 607.
  49. Coombes JS, McNaughton LR. Effects of branched-chain amino acid supplementation on serum creatine kinase and lactate dehydrogenase after prolonged exercise. J Sports Med Phys Fitness, 2000; 40: 240 – 246.
  50. Nosaka K. Muscle soreness and amino acids. Training J, 2003; 289: 24 – 28.
  51. Norton LE, Layman DK. Leucine regulates translation initiation of protein synthesis in skeletal muscle after exercise. J Nutr, 2006; 136(2): 533S – 537S.
  52. Zanchi NE, Nicastro H, Lancha AH Jr. Potential antiproteolytic effects of L-leucine: observations of in vitro and in vivo studies. Nutr Metab, 2008; 5: 20.
  53. Blomstrand E, Saltin B. BCAA intake affects protein metabolism in muscle after but not during exercise in humans. Am J Physiol Endocrinol Metab, 2001; 281(2): E365 – 74.
  54. Matsumoto K, Koba T, Hamada K, Tsujimoto H, Mitsuzono R. Branched-chain amino acid supplementation increases the lactate threshold during an incremental exercise test in trained individuals. J Nutr Sci Vitaminol, 2009; 55(1): 52 – 58.
  55. Mero A, Leikas A, Knuutinen J, Hulmi JJ, Kovanen V. Effect of strength training session on plasma amino acid concentration following oral ingestion of leucine, BCAAs or glutamine in men. Eur J Appl Physiol, 2009; 105(2): 215 – 223.
  56. Howarth KR, Burgomaster KA, Phillips SM, Gibala MJ. Exercise training increases branched-chain oxoacid dehydrogenase kinase content in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol, 2007; 293(3): R1335 – 1341.