Beljakovine, esencialno hranilo za človeka. Kdaj, kaj in koliko?

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Abstract
Beljakovine igrajo v človeškem telesu po-membno vlogo, še posebej pri športni-kih, saj so mišice v večji meri sestavljene prav iz beljakovin. Gradniki beljakovin so aminokisline, od katerih jih 9 imenuje-mo tudi esencialne in jih moramo v telo vnesti s prehrano. Aminokislina levcin igra pri mišični sintezi najpomembnejšo vlogo, saj lahko, podobno kakor vadba, aktivira kompleks mTOR, ki sproži sintezo mišičnih beljakovin. V članku so predsta-vljeni izsledki raziskav o vplivu kvalitete, količine, časovnice vnosa beljakovin in zdravstvenem vidiku povečanega vnosa beljakovin. Na koncu so predstavljene smernice o vnosu beljakovin za splošno populacijo, športnike in starostnike. Ključne besede: beljakovine, mišična masa, športna prehrana, levcin.
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šport in zdravje
87
Proteins, essential nutrient for humans. When, what and how much?
Abstract
Proteins play a very important role in humans, especially in athletes given that proteins are the building blocks of muscles. Pro-
teins consist of dierent amino acids, of which 9 are called essential and humans need to consume them with a diet. Amino acid
leucine appears to play a crucial role in muscle protein synthesis because of its ability to activate mTOR pathway, which in turn
initiates muscle protein synthesis. This article presents current evidence about the quality, quantity and timing of protein intake
and health consequences of increased protein intake. At the end of article guidelines for protein intake for general public, athletes
and elderly are presented.
Keywords: proteins, muscle mass, sports nutrition, leucine.
Tim Podlogar,
Jure Kolar, Tina Goršek
Beljakovine, esencialno hranilo
za človeka.
Kdaj, kaj in koliko?
Izvleček
Beljakovine igrajo v človeškem telesu po-
membno vlogo, še posebej pri športni-
kih, saj so mišice v večji meri sestavljene
prav iz beljakovin. Gradniki beljakovin so
aminokisline, od katerih jih 9 imenuje-
mo tudi esencialne in jih moramo v telo
vnesti s prehrano. Aminokislina levcin
igra pri mišični sintezi najpomembnejšo
vlogo, saj lahko, podobno kakor vadba,
aktivira kompleks mTOR, ki sproži sintezo
mišičnih beljakovin. V članku so predsta-
vljeni izsledki raziskav o vplivu kvalitete,
količine, časovnice vnosa beljakovin in
zdravstvenem vidiku povečanega vnosa
beljakovin. Na koncu so predstavljene
smernice o vnosu beljakovin za splošno
populacijo, športnike in starostnike.
Ključne besede: beljakovine, mišična
masa, športna prehrana, levcin.
http://elitefitpersonaltraining.co.uk/benefits-of-a-high-protein-diet/
88
Uvod
Poimenovanje beljakovin oziroma protei-
nov (angleško proteins) izhaja iz grške be-
sede proteion, kar v prevodu pomeni 'prvo
mesto, prva nagrada'. S takšnim poimeno-
vanjem je mišljeno ali 'prvovrstna (spojina)'
ali 'prvobitna (spojina)' (Snoj, 2015). To kaže,
da so beljakovinam velik pomen pripisovali
že starodavni Grki.
Beljakovine so prisotne povsod v telesu,
približno 40 % jih je del mišičnega tkiva,
več kot 25 % v človeških organih, ostalo pa
predvsem v koži in krvi. Beljakovine poleg
maščob in ogljikovih hidratov uvrščamo
med makrohranila, saj jih vnašamo v re-
lativno velikih količinah in nam služijo kot
vir energije ter so ključne pri drugih po-
membnih funkcijah. Kemijsko gledano so
beljakovine organske spojine, sestavljene
iz verižno povezanih aminokislin. Vnesene
beljakovine v prebavilih razpadejo na ami-
nokisline, slednje pa človeški organizem
potrebuje za sintezo (izgradnjo) primernih
novih beljakovin in dušikovih spojin, ki so
nujno potrebne za življenje. V telesu opra-
vljajo pomembne funkcije encimske,
prenašalne, strukturne, imunoprotektivne,
pufrske, uravnalne itd. (Gropper in Smith,
2012).
Mišice v telesu imajo glavno vlogo pri
metabolizmu beljakovin in predstavljajo
zalogo aminokislin za sintezo beljakovin v
času, ko te niso bile zaužite s hrano oziroma
absorbirane iz črevesja. V primeru pomanj-
kanja glukoze (hipoglikemija) pa služijo kot
substrat za glukoneogenezo (Wolfe, 2006).
Beljakovine so tako ves čas v fazi gradnje in
razgradnje (Phillips, 2004).
Poznamo esencialne in neesencialne ami-
nokisline (Rose, 1957). Devet esencialnih
aminokislin (histidin, izolevcin, levcin, lizin,
metionin, fenilalanin, treonin, triptofan in
valin) telo ne more sintetizirati samo, zato
jih je potrebno v telo vnesti s hrano. Telo
zdravega odraslega človeka lahko nee-
sencialne aminokisline v zadostni količi-
ni proizvede samo, v primeru določenih
zdravstvenih stanj je lahko potreben vnos
tudi neesencialnih aminokislin, zaradi česar
mnogi kritizirajo delitev na esencialne in
neesencialne aminokisline ter predlagajo
delitev na esencialne, pogojno esencialne
in neesencialne.
Smernice v Evropski uniji narekujejo odra-
slemu prebivalstvu vnos 0,83 g beljakovin
na kilogram telesne mase na dan (v nada-
ljevanju g/kg/dan) (EFSA Panel on Dietetic
Products Nutrition and Allergies (NDA),
2012). Priporočilo je nastalo na podlagi
analiz dušikovega razmerja. Slednja meril-
na tehnika pa ima kar nekaj pomanjkljivosti
(Millward idr., 2001; Rafii idr., 2015), saj so pri-
dobljene vrednosti z uporabo te metode
velikokrat podcenjene. Novejši, državnim
organizacijam neodvisni pregledi raziskav
posledično priporočajo veliko višji dnevni
vnos beljakovin – 1,2–1,6 g/kg/dan za splo-
šno populacijo (Phillips, Chevalier in Leidy,
2016)
Športnikom moči konvencionalne smerni-
ce priporočajo vnos 1,2–1,7 g/kg/dan, vzdr-
žljivostnim športnikom pa 1,2–1,4 g/kg/dan
(Rodriguez idr., 2009), večinoma na podla-
gi raziskav, ki so potrebe vnosa beljakovin
raziskovale s preučevanjem dušikovega
razmerja. V nadaljevanju predstavljene
študije, ki so uporabile novejšo in natanč-
nejšo metodologijo, tako ugotavljajo, da
so potrebe po beljakovinah tudi v športni
populaciji večje od vnosa, ki ga priporočajo
konvencionalne smernice.
Industrija prehranskih dodatkov dosega v
zadnjih letih enormno rast in je ena izmed
najhitreje rastočih panog (Lariviere, 2013).
Na Danskem tako večina elitnih športni-
kov in obiskovalcev fitnes centrov redno
uživa vsaj enega izmed športnih dodatkov
(Solheim idr., 2016), podobno poročajo tu-
di v drugih evropskih državah (Petroczi in
Naughton, 2008) in glede na viden porast
trgovin s športno prehrano v Sloveniji gre
o podobnem deležu sklepati tudi pri nas.
Med te dodatke štejemo tudi beljakovinske
preparate, zato so na znanstvenih dogna-
njih bazirana priporočila o najbolj smisel-
nem in tudi varnem vnosu še toliko bolj
potrebna.
V nadaljevanju so predstavljeni izsledki ak-
tualnih študij o najoptimalnejšem beljako-
vinskem vnosu z ozirom na mišično maso
in zdravstvenem vidiku povišanega vnosa
beljakovin. Na koncu so podane smernice
za širši krog ljudi (športniki, nešportniki in
starostniki).
Razprava
Beljakovine v telesu so ves čas v procesu
fluktuacije, torej razgradnje (katabolizem)
in sinteze (anabolizem) (Slika 1). Beljakovin-
ska fluktuacija je energijsko relativno po-
traten proces in lahko predstavlja tudi 20
% dnevne porabe energije posameznika.
Razpolovna doba beljakovin zelo variira, od
le nekaj minut (npr. encimi) do nekaj dni ali
celo tednov (encimi v mišicah) (MacLaren
in Morton, 2012).
Poenostavljeno je katabolna faza čas vad-
be in stradanja ter se odraža na mikropo-
škodbah mišičnih struktur (Clarkson in
Hubal, 2002; Proske in Morgan, 2001) ter
razgradnji v mišicah shranjenih aminokislin
za potrebe proizvodnje glukoze v proce-
su, imenovanem glukoneogeneza (Owen,
2005). Katabolni fazi sledi anabolna faza, v
kateri pride do povečane sinteze beljako-
vin, vadba pa predstavlja še dodaten dra-
žljaj za sintezo mišičnih beljakovin (Phillips,
Tipton, Aarsland, Wolf in Wolfe, 1997). Iz
tega logično sledi, da je zadosten vnos be-
ljakovin (»gradbenega materiala za mišice«)
ključen iz vidika ohranjanja in pridobivanja
mišične mase.
Sinteza beljakovin je za športnike izjemno
pomembna, saj omogoča izboljšanje ce-
ličnih zmogljivosti proizvodnje ATP-ja v
procesu oksidativne fosforilacije (Gollnick
idr., 1973; Holloszy in Coyle, 1984) ter aku-
mulacijo miofibrilarnih beljakovin, ki se od-
razi v povečanem prečnem preseku mišic.
Slednja športnikom omogoča razvoj moči
(Wackerhage in Ratkevicius, 2008). Naspro-
tno pa se lahko zgodi v primeru neaktiv-
nosti in stradanja, ko mišična masa začne
Slika 1. Prikaz razmerja med sintezo in razgradnjo skozi čas. Obrok predstavlja dražljaj za sintezo. Po obroku
pa nastopi obdobje razgradnje. V kolikor želimo vzdrževati mišično maso, mora biti na koncu dneva sinteza
enaka razgradnji. Prirejeno po (Phillips, 2004).
šport in zdravje
89
upadati, kar poimenujemo atrofija (Phillips,
Glover in Rennie, 2009).
Četudi je teoretično izhodišče o pomemb-
nosti zadostnega vnosa beljakovin jasno,
rezultati dolgoročnih študij o dodajanju
beljakovin v prehrano niso tako jasni. Pa-
siakos, Lieberman in McLellan (2014) so
v nedavnem sistematičnemu pregledu
raziskav in metaanalizi ugotovili, da je na
voljo le omejena količina dokazov o učin-
kovitosti dodatka beljakovin pri regenera-
ciji mišičnih funkcij. A to še ne pomeni, da
je dodatek beljakovin nesmiseln, saj je bila
metodologija mnogih študij neoptimalna
(npr. suboptimalna količina beljakovin v
dodatku ali že dosežen dnevno potreben
vnos beljakovin). V populaciji starostnikov,
kjer je pojavnost sarkopenije in dinapenije
v porastu, je dodaten vnos beljakovin pri
posameznikih, ki so del trenažnega pro-
cesa vadbe z obremenitvijo, povezan s
povečanjem puste (nemaščobne) mase, ne
pa tudi povečanjem mišične mase ali večje
mišične moči (Finger idr., 2015).
Že omenjeni sistematični pregled raziskav
in metaanaliza Pasiakosa, McLellana in Lie-
bermana (2004), opravljena na raziskavah,
ki so preučevale zdrave odrasle, zaključuje,
da dodaten vnos beljakovin vzpodbudi
mišično rast in napredek v mišični jakosti
tako pri treniranih, kot tudi pri netrenira-
nih. V primeru, ko se pogostost treningov
močno poveča, pa po njihovem obstajajo
dokazi, da dodatek beljakovin pomaga
pri izboljšanju kratkotrajne in dolgotrajne
vzdržljivosti. Razlog za nejasne zaključke
omenjenih raziskav gre po vsej verjetnosti
iskati predvsem v njihovi metodologiji, saj
se večina vpraša, ali dodaten vnos beljako-
vin (en dodaten beljakovinski obrok) izbolj-
ša merjene parametre, navadno pa ni ugo-
tovljeno, če so bile beljakovinske potrebe v
času študije dosežene ali ne. Pridobivanje
mišične mase je počasen proces, prirastki
so majhni in tako nezaznavni pri navadno
majhnem raziskovalnem vzorcu in relativ-
no kratkem raziskovalnem času. Zato so
potrebne dodatne dolgotrajne študije z
uporabo natančnih merilnih inštrumentov
(npr. magnetna resonanca), da se ugotovi
učinkovitost dodatnega vnosa beljakovin.
Stimulacija sinteze beljakovin
Sintezo beljakovin v mišicah sproži obre-
menitvena vadba skupaj z zadostno količi-
no beljakovin ali zadosten vnos kvalitetnih
beljakovin, najučinkovitejša pa je kombina-
cija ustreznega beljakovinskega vnosa in
vadbe (Biolo, Tipton, Klein in Wolfe, 1997;
Morton, McGlory in Phillips, 2015; Tipton in
Wolfe, 2004; Witard, Wardle, Macnaughton,
Hodgson in Tipton, 2016).
V zadnjem desetletju se veliko pomena pri
mišični masi pripisuje signalnemu sistemu,
ki bazira na Ser/Thr proteinski kinazi, ime-
novanem mTO R-u (angleško mechanistic
target of rapamycin). mTOR sestavljata dva
kompleksa mTORC1 in mTORC2, slednji
igra ključno vlogo pri kontroli prepisovanja
mRNA, kar vodi v beljakovinsko sintezo (Je-
well in Guan, 2013).
Sinteza beljakovin je posledica aktivacije
mTOR in kasnejše aktivacije ribosomske be-
ljakovine S6K (p70S6K), kar izhaja iz podatkov
raziskav, v katerih je bila rast mišic prepre-
čena z inhibitorjem mTOR-a rapamycinom,
medtem ko je stimulacija mTOR-a povzroči-
la mišično rast in preprečila atrofijo (Bodine
idr., 2001; Drummond idr., 2009). Delovanje
mTOR okrepi vadba z obremenitvijo (Philp,
Hamilton in Baar, 2011).
Aminokislina levcin ima sposobnost,
da sproži sintezo beljakovin z aktivacijo
mTOR-a neodvisno od prisotnosti ostalih
esencialnih ali neesencialnih aminokislin
(Anthony idr., 2002; Crozier, Kimball, Em-
mert, Anthony in Jefferson, 2005). Študija
(Churchward-Venne idr., 2014) ugotavlja, da
pride po zaužiti majhni (najverjetneje su-
boptimalni) količini beljakovin z dodatkom
levcina do enake stopnje in trajanja sinteze
beljakovin kot v primeru, ko je količina be-
ljakovin optimalna. Iz podatkov te raziskave
je videti, da je optimalna količina levcina v
obroku po končanem treningu, ki vključuje
mišice nog, okoli 3 grame. Raziskave, ki bi
podobno preučevale pri vključeni večji mi-
šični masi, v tem trenutku ni. Rezultati tako
kažejo, da je ravno količina levcina v obroku
tista, ki narekuje sintezo mišičnih beljakovin
(Morton idr., 2015). V Tabeli 1 je prikazana
količina levcina v različnih virih beljakovin.
Kvaliteta beljakovin
Viri beljakovin se med seboj razlikujejo po
sestavi aminokislin in imajo posledično raz-
lične vrednosti ključne aminokisline levcina
(Tabela 1). Zato se sposobnost stimulacije
sinteze beljakovin v telesu razlikuje od vi-
ra beljakovin (Phillips, 2016). Med športni-
ki najpogosteje uporabljen vir dodatnih
beljakovin so po vsej verjetnosti sirotkine
beljakovine, kar pa je glede na visok delež
levcina pravzaprav logično. Nedavna me-
taanaliza ugotavlja, da so sirotkine beljako-
vine najučinkovitejše za ohranjanje ali po-
večevanje mišične mase (Miller, Alexander
in Perez, 2014). Poudariti velja, da so tudi
drugi viri beljakovin lahko enako učinko-
viti ob predpostavki, da vnesena količina
beljakovin v posameznem obroku vsebuje
zadostno količino levcina za popolno sti-
mulacijo sinteze beljakovin v mišicah.
Analiza opravljenih raziskav iz različnih
laboratorijev o najprimernejši količini be-
ljakovin (Moore idr., 2015) je pokazala, da
približno 20 gramov sirotkinih beljakovin
(~0.24 g/kg) zadošča za optimalno stimu-
lacijo mišične sinteze pri mladih po trenin-
gu nog. S staranjem pa se ta vrednost viša
(~0.40 g/kg). Večina vključenih raziskav je
bila opravljena po vadbi, ki je vključevala
le spodnje okončine, zato je ekstrapolacija
izsledkov lahko vprašljiva, kolikor je v vad-
bo vključeno celotno telo. To dokazuje ne-
davna študija (Macnaughton idr., 2016), ki je
primerjala sintezo beljakovin po vadbi mla-
dih treniranih posameznikov. Vključevala je
vadbo celotnega telesa in ugotovila, da je
bila sinteza beljakovin ~20 % višja v skupini,
ki je po vadbi zaužila 40 g sirotkinih belja-
kovin v primerjavi s skupino, ki je zaužila 20
g. To na nek način spreminja ugotovitve
Moora in sodelavcev (2015) o optimalni
količini sirotkinih beljakovin in podatke
Tabela 1
Tabela prikazuje velikost porcije in njeno energijsko vrednost, ki je potrebna, da človek zaužije
1 g aminokisline levcina (“Leucine Content in Common Foods,” 2013)
Tip beljakovin Porcija živila, ki vsebuje 1 g
levcina
Energijska vrednost živila, ki
vsebuje 1 g levcina (kCal)
Sirotka (angleško whey) 9,2 g 37
Soja 12,4 g 50
Posneto mleko 349 ml 133
Goveje meso 57 g 156
Polnozrnat kruh 256 g 1385
Piščančja prsa 57 g 59
Arašidi 60 g 350
Grški jogurt 100 g 57
Jajca 1,8 jajca 128
90
Churchewald-Venneja in sodelavcev (2014)
o optimalni količini levcina v posameznem
obroku.
Četudi je videti slika o najoptimalnejši
količini vnesenih beljakovin precej črno-
bela, je potrebno poudariti, da se študije
in resnično življenje velikokrat razlikuje-
jo. Tako ima na primer dodatek vlaknin in
maščob ter nekajkrat višji vnos beljakovin
od priporočenega v posameznem obroku
negativen vpliv na pojavnost aminokislin
v portalnem krvnem obtoku (Ten Have,
Engelen, Luiking in Deutz, 2007). West idr.
(2011) so v svoji študiji pokazali, da je hitrost
absorpcije aminokislin pomemben faktor
pri sintezi mišičnih beljakovin, in sicer, da je
sinteza večja v primeru, ko so aminokisline
hitreje dostopne v krvi. Razlog za to je naj-
brž v tem, da v primeru počasne absorp-
cije vrednosti levcina v krvnem obtoku ne
dosežejo prave vrednosti, ki je potrebna za
optimalno stimulacijo beljakovin.
Časovnica vnosa beljakovin
O pomembnosti časa vnosa beljakovin se
navadno razpravlja v času pred ali po vad-
bi, ko naj bi obstajalo t. i. okno priložnosti.
Ideja o oknu priložnosti najverjetneje iz-
haja iz dejstva, da so vrednosti inzulina po
vadbi višje, kar naj bi pripomoglo k hitrejši
absorbciji hranil iz krvi v tkiva in posledič-
no hitrejši povrnitvi mišičnih sposobnosti.
Slednje pa se je z vidika glikogena doka-
zalo za neresnično (Parkin, Carey, Martin,
Stojanovska in Febbraio, 1997), saj 8 ur po
aktivnosti ni razlik v koncentraciji mišične-
ga glikogena, v kolikor je ogljikohidratni
obrok zaužit takoj po vadbi v primerjavi s
scenarijem, ko je prvi obrok šele nekaj ur
kasneje. Visoke vrednosti inzulina pa nima-
jo pozitivnega vpliva niti na sintezo mišič-
nih beljakovin, zato je dodatek ogljikovih
hidratov z ozirom na sintezo beljakovin v
mišici nepotreben (Trommelen, Groen, Ha-
mer, de Groot in van Loon, 2015). A razpra-
va se pri beljakovinah vendarle ne zaključi
z inzulinom, saj nekateri znanstveniki trdijo,
da obstajajo drugi razlogi, zakaj je takojšen
beljakovinski vnos po vadbi nujen, drugi pa
temu oporekajo in trdijo, da ni tako bistven
(Ivy in Schoenfeld, 2014). Četudi konsenz
na tem področju še ni bil dosežen, se av-
torji članka nagibajo k dokazom, ki pravijo,
da takojšen vnos beljakovin po treningu ni
ključen (Aragon in Schoenfeld, 2013; Scho-
enfeld, Aragon in Krieger, 2013), je pa v ve-
čini primerov priporočljiv, saj navadno od
prejšnjega obroka mine kar nekaj časa in
je najverjetneje obrok takrat smiseln iz vi-
dika enakomerne in zadostne razporeditve
vnosa beljakovin preko celega dne.
Iz rezultatov zgoraj omenjenih študij, ki
so preučevale akutne spremembe sinteze
beljakovin z ozirom na količino in kvaliteto
beljakovin, gre moč sklepati, da ni vseeno,
kakšna je dnevna razporeditev vnosa be-
ljakovin. Kljub temu da veliko športnikov
zaradi velike dnevne porabe energije in
posledično velikega vnosa zaužije dovolj
beljakovin, razporeditev le-teh ni soraz-
merna in tako nekateri obroki niso beljako-
vinsko dovolj bogati (Naughton idr., 2016).
Podobno je pri nešportni populaciji, kjer
veliko ljudi ne zajtrkuje in se tako prvi vnos
beljakovin prestavi šele na kosilo (Phillips
idr., 2016), torej je med večernim vnosom
in kosilom tudi več kot 12-urno obdobje
brez vnosa beljakovin in posledično obdo-
bje katabolizma.
Mamerow idr. (2014) so primerjali ena-
komerno razporeditev beljakovin v treh
dnevnih obrokih in pokazali, da je enako-
merna porazdelitev z vidika sinteze be-
ljakovin pomembna. Areta idr. (2013) so
prav tako pokazali, da je časovnica vnosa
beljakovin pomembna pri sintezi mišičnih
beljakovin. V tej študiji so merjenci opravili
trening mišic nog, nato pa spremljali odziv
mišične sinteze beljakovin v obdobju dva-
najstih ur v treh različnih scenarijih – sirot-
kine beljakovine so vnesli dvakrat, takoj po
treningu in po šestih urah v količini po 40
gramov; vsake tri ure (4-krat) po 20 gramov
ali vsako uro in pol (8-krat) po 10 gramov.
Ugotovili so, da je bil sintetični odziv najve-
čji v skupini, ki je beljakovine zaužila vsake
tri ure. Pomembnost ustrezne razporeditve
potrjuje še ena raziskava, ki kaže, da je sti-
mulacija sinteze beljakovin največja 1,5 ure
po pojavu aminokislin v krvi, čemur sledi
upad stimulacije, ki pa se pojavi neodvisno
od takratne koncentracije aminokislin v kr-
vi (Atherton idr., 2010).
Zelo pomembno vlogo pa očitno igra tu-
di vnos beljakovin pred nočnim spanjem,
ko je telo kar 6–9 ur v stanju brez vnosa
beljakovin. Akutna študija kaže, da se vne-
sene beljakovine tik pred spanjem v času
spanja uspešno prebavijo in stimulirajo
mišično sintezo beljakovin (Res idr., 2012).
Snijders idr. (2015) so to potrdili v študiji, v
kateri so na dolgi rok ugotavljali učinkovi-
tost večernega vnosa beljakovin. Rezultati
so pokazali, da so posamezniki, ki so uživali
beljakovine pred spanjem, statistično bolj
značilno povečali mišično jakost in mišično
maso kot tisti, ki jih niso.
Beljakovine pri veganih in
vegetarijancih
Zaradi veganskega ali vegetarijanskega
načina življenja mnogi iz svojih jedilnikov
odstranjujejo izdelke živalskega izvora.
Meso, jajca in sirotka so tako velikokrat na
nezaželenem seznamu posameznikov, za-
to se mnogi sprašujejo, ali je vegetarijan-
stvo/veganstvo pri športnikih sploh varno,
saj viri beljakovin rastlinskega izvora naj ne
bi vsebovali vseh esencialnih aminokislin.
S tem so se ukvarjali tudi v različnih opa-
zovalnih študijah (Elorinne idr., 2016; Rizzo,
Jaceldo-Siegl, Sabate in Fraser, 2013). Jacel-
do-Siegl, Sabate in Fraser (2013) so primer-
jali vnos beljakovin med različnimi vrstami
vegetarijanstva (semi- vegetarijanstvo,
lacto-ovo vegetarijanstvo, veganstvo itd.)
in nevegetarijanskem načinu prehranje-
vanja. Rezultati kažejo, da je celotni vnos
beljakovin med posameznimi skupinami
primerljiv in se ne razlikuje od količine pri
nevegetarijancih. Vegetarijanci tako zado-
stno količino beljakovin dobijo z uživanjem
soje, stročnic, leč, oreščkov in žit (Rizzo idr.,
2013). Posebno pomemben vir beljakovin
predstavlja soja, katere beljakovine imajo
zelo podobno aminokislinsko sestavo kot
kazein (mlečna beljakovina). Kljub temu pa
Ameriško dietetično združenje (“Position of
the American Dietetic Association: Vegeta-
rian Diets,” 2009) vegetarijancem priporoča
višji dnevni vnos beljakovin (0,9 g/kg/dan)
(“Position of the American Dietetic Associ-
ation: Vegetarian Diets,” 2009), kar je pribli-
žno 0.1 g/kg/dan več, kakor ista organizaci-
ja priporoča nevegetarijancem. V primeru
športne aktivnosti naj bi se pri vegetarijan-
cih vnos po konvencionalnih smernicah
povišal na 1,3–1,8 g/kg/dan. A kot že ome-
njeno so konvencionalne smernice upo-
števale starejšo metodologijo raziskovanja
ravnovesja beljakovin in zato so tudi tukaj
vrednosti najbrž podcenjene. Da bi zagoto-
vili popolno aminokislinsko sestavo jedi, je
v obrok priporočljivo vključiti kombinacijo
beljakovinsko bogatih živil (npr: fižol in riž)
(Young in Pellett, 1994). Ker je pri športnikih
energetski vnos že v osnovi višji (v primeru,
da ne gre za načrtno izgubo teže), je posle-
dično tudi vnos beljakovin višji. Torej je skrb
v primeru polnovredne prehrane in dobro
zastavljenega jedilnika odveč. Veganski
športniki nemalokrat posegajo po beljako-
vinskih dodatkih, kot so na primer sojine, ri-
ževe in grahove beljakovine. Joy idr. (2013)
so nedavno primerjali vpliv dodajanja si-
rotkinih in riževih beljakovin (izolata) na se-
stavo telesa in zmogljivost. Dodatek obeh
vrst beljakovin je skupaj z vadbo moči iz-
šport in zdravje
91
boljšal telesno sestavo. Pusta telesna masa
in mišična masa sta se povišali, sočasno pa
je prišlo do znižanja maščobne mase. Prav
tako sta se izboljšali moč in zmogljivost, in
sicer v enaki meri pri obeh vrstah beljako-
vinskih dodatkov. Objavljene so nekatere
opazovalne študije in študije primerov iz
sveta veganstva in športa in videti je, da
izogibanje hrani živalskega izvora nima ne-
gativnega vpliva na zmogljivost v primeru,
ko je jedilnik pametno načrtovan (Fuhrman
in Ferreri, 2010; Leischik in Spelsberg, 2014;
Wirnitzer in Kornexl, 2014).
Zdravstveni dejavniki poviša-
nega vnosa beljakovin
V medijih se v zadnjem času pojavlja veliko
opozoril pred pretiranim vnosom beljako-
vin, kar naj bi bilo povezano z raznoraznimi
zdravstvenimi težavami. To pa v večini pri-
merov povzroča nemalo zmede.
Predvidena škodljivost (prevelikega) vnosa
beljakovin se največkrat nanaša na zmanj-
ševanje kostne gostote ter poškodbe led-
vic. Med razgradnjo beljakovin nastanejo
kisline, ki naj bi negativno vplivale na ki-
slinsko-bazno ravnovesje (Frassetto, Todd,
Morris in Sebastian, 1998). Da bi telo zago-
tovilo ponovno ravnovesje, naj bi črpalo
kalcij iz kosti, ker lahko v teoriji na dolgi rok
povzroči osteoporozo (Reddy, Wang, Sa-
khaee, Brinkley in Pak, 2002). Dolgoročne
raziskave kažejo, da se izločanje kalcija na
daljši rok ustavi, prav tako pa se na dolgi
rok pojavijo zvišane vrednosti hormona
IGF1-a (inzulinu podoben rastni faktor), ki
je pomemben pri kostni rasti ter kostnemu
metabolizmu (Dawson-Hughes, Harris, Ra-
smussen, Song in Dallal, 2004). Mnoge dru-
ge študije in analize potrjujejo smotrnost
višjega vnosa beljakovin z vidika zdravja ko-
sti in hkrati zavračajo teorije o negativnem
vplivu višjega vnosa beljakovin na kostno
zdravje (Bonjour, 2005; Cooper idr., 1996;
Genaro, Pinheiro, Szejnfeld in Martini, 2015;
Munger, Cerhan in Chiu, 1999; Rizzoli in
Bonjour, 2004; Thorpe idr., 2008; Wengre-
en idr., 2004). Vnos beljakovin z zadostnim
vnosom kalcija je tako bistven za zdravje
kosti in nadzorovanje ter rast mišične mase
(Heaney in Layman, 2008). Do podobnih
zaključkov je prišel tudi nedavni sistematski
pregled literature (Calvez, Poupin, Chesne-
au, Lassale in Tomé, 2012). Sveža raziskava
v športni populaciji pa celo ugotavlja, da
je takoj po treningu z vidika zdravja kosti
priporočljivo zaužiti obrok bogat z belja-
kovinami in ogljikovimi hidrati (Townsend
idr., 2017).
Ledvica so filtracijski organ, ki dnevno pre-
čistijo 180 litrov krvi. Kar 20 % minutnega
volumna srca je usmerjeno v ta organ. So
funkcionalna enota in sodelujejo v presno-
vi beljakovin ter izločajo dušik iz krvi. Obre-
menitev ledvic se ob povečanem vnosu
beljakovin poveča, a ne vpliva negativno
na zdravje ledvic (Landau in Rabkin, 2013).
Podatki, da je povečan vnos beljakovin
škodljiv, prihajajo iz preučevanja ljudi, ki že
imajo resne težave iz ledvic, ledvične teža-
ve pa v osnovi ne izvirajo iz povečanega
vnosa beljakovin (Levey idr., 1996), zato je
posploševanje ob pomanjkanju dokazov
na zdravo populacijo neprimerno. Do-
kazov, da je velik vnos beljakovin proble-
matičen iz vidika zdravja ledvic pri zdravi
populacija namreč enostavno ni (Antonio,
Ellerbroek, Silver, Vargas, Tamayo, idr., 2016;
Martin, Armstrong in Rodriguez, 2005). Naj-
pomembnejša vzroka odpovedi ledvic sta
hipertenzija in diabetes, višji vnos beljako-
vin pa dokazano izboljšuje obe stanji (Al-
torf-van der Kuil idr., 2010; Appel idr., 2005;
Gannon in Nuttall, 2004). Ameriška diabe-
tična organizacija (ADA) tako sladkornim
bolnikom, kot tudi tistim, ki že imajo težave
z ledvicami, ne priporoča zmanjšanja vno-
sa beljakovin (Evert idr., 2013).
Nedavno opravljene raziskave pod vod-
stvom Antonia (Antonio, Ellerbroek, Silver,
Vargas, Tamayo, idr., 2016; Antonio, Eller-
broek, Silver, Vargas in Peacock, 2016; Anto-
nio, Peacock, Ellerbroek, Fromhoff in Silver,
2014) so pokazale, da znatno povišan vnos
beljakovin pri treniranih osebah na dolgi
rok ne povzroča škode telesu. Še več, ve-
čji vnos ima celo pozitivne učinke tako na
delovanje organizma, kot tudi njegovo se-
stavo.
Priporočila
Dnevna količina
Najnovejše raziskave vzdržljivostnih špor-
tnikov kažejo, da so potrebe beljakovin
večje od doslej priporočenih vrednosti,
in sicer vsaj 1,65–1,83 g/kg/dan (Kato idr.,
2016). Podobno kažejo tudi novejši podat-
ki iz športov moči, kjer naj bi bila dnevno
potrebna količina beljakovin vsaj 2,2 g/
kg/dan (Bandegan, Courtney-Martin, Rafii,
Pencharz in Lemon, 2017). Razlog za razli-
ke med starejšimi in novejšimi študijami je
natančnost uporabljene metodologije ali
pa so se v času od prejšnjih študij trenažni
procesi tako spremenili, da so potrebe po
beljakovinah danes večje kot v času zbira-
nja podatkov za starejše študije. Novejše
smernice višji vnos beljakovin od priporo-
čenih 0,8 g/kg/dan priporočajo tudi starej-
šim, in sicer več ali enako kot 1,2 g/kg/dan
(Phillips idr., 2016), kar naj bi pripomoglo k
zmanjšanju izgube oziroma ohranjanju mi-
šične mase.
Dnevna razporeditev
Beljakovine je najbolje zaužiti količinsko
enakomerno porazdeljene v več dnevnih
obrokov, vsakih 3–5 ur.
Količina in tip beljakovin v posameznem
obroku
Posamezen beljakovinski obrok mladih naj
bo sestavljen iz beljakovin, ki vsebujejo vsaj
3 grame levcina in nekoliko večjo količino
le-tega v primeru obroka po treningu, ki
je vseboval mišice celotnega telesa. V pri-
meru sirotke v prahu to pomenilo nekaj
več kot 20 oziroma 40 gramov. Pomembno
je, da je z vnosom beljakovin zagotovljen
visok delež esencialnih aminokislin, vir be-
ljakovin pa v osnovi ni tako pomemben,
kakor je pomembna skupna količina zauži-
tega levcina v posameznem obroku. Pred
spanjem se priporoča vnos 40 g beljakovin,
ki se počasneje razgrajujejo, npr. kazeina
(Trommelen in Loon, 2016).
Četudi bi bilo optimalno, da bi bil vnos
beljakovin ločen od vnosa ostalih makro-
hranil, predvsem maščob in vlaknin tako
zaradi počasnejše absorpcije beljakovin
kot tudi zmanjšanja sposobnosti sinteze
(Hammond idr., 2016), je to v realnosti ne-
mogoče. Glede na dejstvo, da obrok po
vadbi najbolj stimulira mišično sintezo
beljakovin, se priporoča, da ima obrok po
vadbi čim nižji delež maščob in vlaknin, po
možnosti pa naj bo vnos beljakovin v teko-
či obliki (Burke idr., 2012), saj je absorpcija
aminokislin takrat najhitrejša.
Za primer vzemimo 80-kilogramskega
mladega moškega. Ta dnevno prespi 8 ur,
njegov dnevni beljakovinski cilj pa je 2 g/
kg/dan, torej 160 gramov. V času budno-
sti (16 ur) obrok zaužije vsake štiri ure, kar
pomeni 5 obrokov dnevno. Velikost obro-
kov razdelimo na dva dela, dvakrat po 40
gramov (po treningu za moč, ki se konča
4 ure pred spanjem, in tik pred spanjem),
preostalih 80 gramov pa enakomerno raz-
delimo med preostale tri obroke. Večje in
manjše osebe pa velikost obrokov enako-
merno prerazporedijo.
Starostnikom se priporoča enakomerno
razporejen vnos beljakovin preko celega
dne ter uživanje z levcinom bogatih virov
beljakovin (Breen in Phillips, 2011). Posame-
92
zen obrok naj bi vseboval nekje ~0.40 g/kg
beljakovin (Churchward-Venne, Holwerda,
Phillips in van Loon, 2016; Moore idr., 2015).
Zaključek
Po pregledu raziskav vidimo, da so me-
hanizmi pomembnosti zadostnega vno-
sa relativno dobro raziskani, manjkajo pa
predvsem dobre dolgoročne raziskave, s
pomočjo katerih bi lažje implementirali
rezultate akutnih študij. Vnos beljakovin je
ključen za delovanje človeškega telesa. Po-
datki novejših raziskav kažejo, da je potre-
ben višji vnos beljakovin od doslej pripo-
ročenih smernic. Aminokislina levcin je bila
spoznana kot ključna pri sprožitvi mišične
sinteze beljakovin in je zato njena količina v
posameznem obroku bistvenega pomena.
Starejše osebe morajo zaužiti večjo količi-
no beljakovin, da dosežejo najvišjo možno
stopnjo sinteze beljakovin. Vegani in ve-
getarijanci lahko tudi z izogibanjem hrane
živalskega izvora vnesejo dovolj beljakovin
oziroma aminokislin. Ena izmed najpo-
membnejših stvari pri vnosu beljakovin je,
da je vnos enakomerno razporejen preko
celega dneva v več manjših obrokov.
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Tim Podlogar
Diplomant kineziologije, Magister
(Združeno kraljestvo Velike Britanije
in Severne Irske) vadbenih in športnih
znanosti
Doktorski študent na Univerzi v
Birminghamu, VB
tim@kineziolog.si
  • ... Beljakovine igrajo v človeškem telesu izjemno pomembno vlogo, še posebej pri športnikih, sajo so mišice v večji meri sestavljene praz iz beljakovin (Podlogar, Kolar, in Goršek, 2017). Četudi raziskave zaenkrat ne kažejo, da bi dodatek beljakovin značilno vplival na regeneracijo (Pasiakos, Lieberman, in McLellan, 2014), je zadosten vnos beljakovin vendarle priporočljiv sploh, če športnik želi ohranjati ali pridobivati mišično maso. ...
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