Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2012.)
Cycling
Diet, nutrition for cyclists:
some facts and fallacies
Dr D. P. Van Velden
M.B.Ch.B. M. Prax. Med.
Director: Students’ Health Service
University of the Orange Free State
o d o u b t th a t a fte r th e re c e n t R a p p o rt T o u r and th e
u p su rg e o f c y c lin g as a s p o rt a n d as an
e c o n o m ic a l m e a n s o f tra n s p o rt fo r th e la ym an , m a n y
d o c to rs w ill be c o n fro n te d w ith c y c lis ts in q u irin g on the
s u b je c t o f d ie t a n d n u tritio n fo r o p tim u m p e rfo rm a n c e .
N
In th e past, th e re w a s no s p h e re o f d ie te tic s in w h ic h
fa d d is m a n d ig n o ra n c e w a s m o re c o n s p ic u o u s th a n in
th e fie ld o f a th le tics. It is n o w kn o w n th a t th e d ie te tic re­
q u ire m e n ts o f th e a th le te in tra in in g a re b a se d on th e
s a m e fu n d a m e n ta l p rin c ip le s w h ic h g o v e rn th e n u tri­
tio n o f h u m a n b e in g s in g e n e ra l.
It ca n th u s be s ta te d c a te g o ric a lly :
1. th a t n o n e o f th e o rd in a ry fo o d s e a te n by m an a re
e ith e r o f s p e c ia l va lu e o r c o n tra -in d ic a te d in a th le tic
tra in in g .
2. th a t p re p a ra tio n s o f v ita m in s a n d m in e ra ls, g ive n in
a d d itio n to g o o d m ixe d d ie t, d o n o t im p ro v e a th le tic p e r­
fo rm a n c e .
P ro vid e d th e re q u ire m e n ts fo r p ro te in , c a rb o h y d ra te ,
fa t, m in e ra ls a nd v ita m in s a re p ro p e rly sa tisfie d , th e
d ie t fo r th e a th le te in tra in in g d iffe rs o n ly fro m th e o r­
d in a ry w e ll-b a la n c e d d ie t in th a t it m u s t p ro vid e e xtra
s o u rc e s o f e n e rg y.
B ro a d ly sp e a kin g , th e fiv e d iffe re n t fo o d g ro u p s m u st
s u p p ly th e b o d y w ith th e fo llo w in g th re e typ e s o f
n u trie n ts !
F ro m th e c y to p la s m th e p ro d u c ts o f g ly c o ly s is
(pyru va te ) and lip o lysis (A ce tyl C o A) a re tra n s p o rte d
in to th e m ito c h o n d rio n w h e re th e m a jo r e n e rg y p ro d u c ­
tion o c c u rs in o x id a tive (a e ro b ic) m e ta b o lis m and
w h e re p re c u rs o rs fro m e ith e r fa t o r c a rb o h y d ra te sh a re
a c o m m o n p a th w a y in th e K re b s cycle .
Figure 1
Vluscle Cell
Blood
G lu co se
La ctic
A cid
'
Blood Free
Fatty A cid s
Cell
C yto p la sm
“ A n a e ro b ic ”
or
C yto p la s m ic
M e ta b o lis m
“ A e ro b ic
or
M ito c h o n d ria l
O xid a tive
M e ta b o lis m
M ito c h o n d rio n
1. Nutrients which provide energy.
M a in ly c a rb o h y d ra te s a n d fa ts a nd s o m e tim e s p ro ­
teins.
2. Nutrients concerned with growth and repair.
M a in ly p ro te in s, c a lc iu m , so d iu m , iron a nd w a te r.
3. Nutrients regulating body processes.
M in e ra l e le m e n ts , w a te r, so m e p ro te in e n z y m e s and
v ita m in s.
It is n o t th e p u rp o s e o f th is a rtic le to o u tlin e all the
c o n s titu e n ts o f a n o rm a l w e ll-b a la n c e d d ie t, o r to g ive
d e ta ile d re c o m m e n d a tio n s on th e v a rio u s n u trie n ts the
b o d y n e e ds w ith th e ir s p e c ific fu n c tio n s . T he g o a l is, to
d e s c rib e s o m e in te re s tin g p rin c ip le s o f s o u n d n u tritio n
a p p lic a b le to cyclin g .
Energy metabolism of cyclists
It has b e e n c a lc u la te d th a t d u rin g a ty p ic a l 160 km
bike ra ce a c y c lis t w o u ld c o n s u m e o v e r 4 186 kJ p e r
hour.
T he m a jo r e n e rg y s o u rc e s a v a ila b le to ske le ta l m u s ­
c le a re its o w n s to re s o f fa ts (trig ly c e rid e s ) and
g ly c o g e n . F ro m th e b lo o d s tre a m it e x tra c ts g lu c o s e
a n d c irc u la tin g fre e fa tty a c id s (F.F.A.).
In th e cyto p la s m , o r m u s c le ce ll, th e se e n e rg y
s o u rc e s a re b ro ke n d o w n b y a n a e ro b ic m e ta b o lis m by
th e p ro c e s s o f g ly c o ly s is (g lu co se ) and lip o lysis
(trig ly ce rid e s). It is a w a s te fu l fo rm o f e n e rg y th a t c a n ­
n o t be s u s ta in e d fo r m u c h m o re th a n 20 s e c o n d s
b e fo re e n e rg y b re a k s d o w n , o r a d e p le tio n o f m u s c le
g ly c o g e n ca u s e s m u s c le c o n tra c tio n to ce a se .
2
The importance of Carbohydrate-rich diet to
long distance endurance cyclists
By 1 939 C h ris te n s e n a nd H a n se n had d is c o v e re d
th a t in te n se p h ysica l a c tiv ity co u ld be m a in ta in e d fo r
fo u r h o u rs o r m o re if th e a th le te had p re v io u s ly e a ten
m a in ly c a rb o h y d ra te s , tw o h o u rs in th e c a s e o f a m ixe d
d iet, a n d 9 0 m in u te s in a p ro te in rich d ie t. R e ce n tly D r
B e rg s tro m fo u n d th a t if a b o u t o f p ro lo n g e d e x e rc is e
w a s fo llo w e d by th re e d a ys o f e x e rc is e and a c a r­
b o h y d ra te fre e , high fat, high p ro te in d ie t — w h ic h w a s
in tu rn fo llo w e d by a high c a rb o h y d ra te d ie t a n d no
e x e rc is e fo r th re e d a ys — g ly c o g e n s u p e rc o m p e n s a ­
tion o c c u rre d a n d m u s c le g ly c o g e n le ve ls c o u ld b e in ­
c re a s e d by as m u c h a s 3 0 0 p e r ce n t, (see Fig. 2)
A w e ig h t in c re a s e o f 2 to 4 kg a b o ve th e w e ig h t at
th e e nd o f th e lo w c a rb o h y d ra te p e rio d is d u e to th e
fa c t th a t e a c h g ra m o f g ly c o g e n s to re d is a c c o m p a n ie d
by 3 to 4 g ra m s o f w a te r. T his h a s a “ c a m e l lik e ” a d ­
va n ta g e b e c a u s e th e w a te r is a v a ila b le a fte r g ly c o g e n
d e p le tio n to c o n trib u te to th e p re v e n tio n o f d e h yd ra tio n .
Carbohydrate intake during exercise
C a rb o h y d ra te in ta ke is n e c e s s a ry d u rin g e x e rc is e of
1 1/2 h o u rs a n d lo n g e r to m a in ta in a n o rm a l level of
blo o d su g a r, b e c a u s e in p ro lo n g e d e x e rc is e c a r­
b o h y d ra te is e sse n tia l to s u s ta in e d m u s c le e ffic ie n c y .
Fat m e ta b o lis m is to o slo w fo r it to s u p p ly all th e e n e rg y
re q u ire d d u rin g high in te n sity e x e rc is e . C a rb o h y d ra te
in ta ke d u rin g e x e rc is e b lo c k s th e g ly c o g e n b re a k d o w n
in th e liver, a n d th is has a g ly c o g e n sp a rin g e ffe c t.
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D u rin g e x e rc is e th e in su lin level is lo w e re d and
m o n o s a c h a rid e s d e riv e d fro m s u g a r ta ke n d u rin g the
ra c e w ill n o t re a c h th e m u s c le s to raise th e ir lo w level
o f g ly c o g e n .
T h e re is a lim itin g fa c to r: it is not p o ssib le fo r the
h u m a n to in g e s t c a rb o h y d ra te as q u ic k ly as it is b u rn e d
b e c a u s e th e ra te o f a b s o rp tio n a n d m e ta b o lis m o f c a r­
b o h y d ra te d u rin g e x e rc is e is p ro b a b ly b e tw e e n 0 ,5 and
1 g ra m p e r m in u te (1).
Water and electrolyte balance in cyclists
It is im p o rta n t to re m e m b e r th a t w h e n a c y c lis t is left
to fo llo w his o w n in c lin a tio n he ra re ly d rin k s eno ug h
flu id to m a in ta in a d e q u a te w a te r b a la n ce . T his is m a in ly
b e c a u s e th e th irs t re fle x it m a rk e d ly in h ib ite d d u rin g ex­
e rc is e . F u rth e rm o re , c y c lis ts s h o u ld be e n c o u ra g e d to
s ta rt a ra c e by b e in g s lig h tly o v e rh y d ra te d . T his co u ld
b e a c h ie v e d by th e in g e stio n o f a b o u t 2 5 0 m l o f fluid
ju s t p rio r to th e ra ce , fo r flu id re p la c e m e n t is o fte n
d e la y e d d u rin g e x e rc is e (2). It is im p o rta n t th a t a c y c lis t
sh o u ld not d e h y d ra te by an a m o u n t e q u iv a le n t to 3 p e r
c e n t o f his b o d y w e ig h t, b e yo n d w h ic h his te m p e ra tu re
w ill rise irre s p e c tiv e o f th e p re v a ilin g w e a th e r co n d itio n s <3).
In c re a s in g d e h y d ra tio n a nd a rise in te m p e ra tu re w ill
in c re a s e th e risk o f h e a ts tro k e a s w e ll a s im p a rie d p e r­
fo rm a n c e .
Figure 2
Hermansen Saltin Diet (1967)
C ostil et a l(2) have s h o w n th a t g a s tric e m p ty in g is b e t­
te r w ith lo w te m p e ra tu re s (at 5 d e g re e s C g a s tric e m p ­
tyin g e q u a ls 3 8 0 m l e v e ry 15 m in u te s, w h ic h is 4x
fa s te r th a n fo r flu id s a t 35 d e g re e s C). M ost c y c lis ts
p re fe r a te m p e ra tu re o f b e tw e e n 15 and 2 0 d e g re e s C.
It is a lso im p o rta n t th a t no e le c tro ly te s sh o u ld be g ive n
d u rin g e x e rc is e o f less th a n th re e h o u rs d u ra tio n
b e c a u s e th is w o u ld , in a d d itio n to th e e ffe c t o f e xe rcise ,
fu rth e r d is tu rb e le c tro ly te c o n c e n tra tio n s . In e x e rc is e
o f less th a n th re e h o u rs d u ra tio n , lo w c o n c e n tra tio n s o f
s u g a rs sh o u ld be in clu d e d , a n d fo r lo n g e r e x e rc is e
th e re s h o u ld a lso be th e a d d itio n o f sa lt in a c o n c e n tra ­
tio n 0,1 to 0,2 p e r cent.
To fa c ilita te a d e q u a te flu id a n d c a rb o h y d ra te in ta ke
d u rin g long d is ta n c e c y c lin g e ve n ts, it is s u g g e ste d th a t
th e c y c lis ts s h o u ld d rin k 2 5 0 m l o f w a te r — o r o f a co la
b e v e ra g e d ilu te d 50 p e r c e n t w ith w a te r — e v e ry 15 to
2 0 m in u te s d e p e n d in g on th e w e a th e r c o n d itio n s. C ola
b e v e ra g e s a lso c o n ta in c a ffe in e w h ic h has a m ild
stim u la tin g e ffe c t, h a ve a d e q u a te a m o u n ts o f su c ro s e
a s a c a rb o h y d ra te so u rc e , a nd a re s u ffic ie n tly lo w in
e le c tro ly te s .
C y c lis ts do not a p p e a r to h a ve th e s a m e p ro b le m of
h e a t in ju ry as m a ra th o n ru n n e rs do, m o s tly b e c a u s e o f
th e c o o lin g e ffe c t on th e b o d y o f th e w in d . The c y c lis t
c a n a ls o c a rry an a d e q u a te flu id s u p p ly w ith h im to
utilize w h e n n e c e s s a ry to c o m b a t d e h y d ra tio n .
Reproduced by Sabinet Gateway under licence granted by the Publisher (dated 2012.)
The myth of a high protein diet
C y c lis ts also b e lie ve th a t a h ig h p ro te in diet is
n e c e s s a ry to s a tis fy th e u n iq u e n u tritio n a l re ­
q u ire m e n ts o f a th le te s. T he p ro te in re q u ire m e n ts for
a c tiv e a th le te s is b e lie ve d to be in th e region o f 2 g ra m s
p e r kg b o d y w e ig h t, but even this va lu e is c a te re d fo r by
a w e ll-b a la n c e d d ie t a d ju s te d to th e h ig h e r c a lo ric re ­
q u ire m e n ts o f the in c re a s e d e x e rc is e levels.
D u rin g e x e rc is e p ro te in is not an im p o rta n t e n e rg y
s o u rc e . T he b o d y uses c a rb o h y d ra te in p re fe re n c e to
fa t as a s o u rc e o f e n e rg y fo r m ost o f its a c tiv itie s . P ro­
p o rtio n a lly less oxyg e n is re q u ire d fo r b u rn in g up c a r ­
b o h y d ra te s. The e n e rg y a v a ila b le p e r litre o f o xyg e n
used b y m e ta b o lis in g is as fo llo w s: c a rb o h y d ra te s ,
2 1 ,1 4 3 3 kJ; fats, 19,63 6 0 kJ; and p ro te in s, 19,2592 kJ.
To use p ro te in as a fuel is v e ry u n e c o n o m ic a l. A p a rt
fro m th e fa ct th a t p ro te in rich fo o d s a re e xp e n sive , th e
b o d y c a n use o n ly p a rt o f th e p ro te in m o le c u le for
e n e rg y. T he b a la n c e re p re s e n ts w a s te w h ic h has to be
.h a n d le d by th e live r a n d th e kid n e ys b e fo re be in g e x ­
c re te d . T oo m u c h p ro te in , th e re fo re , o v e rta x e s th e se
o rg a n s, and an a c c u m u la tio n o f th e w a s te p ro d u c ts in
th e b o d y ca n c a u s e d ise a se . W h e n p ro te in in ta ke e x ­
c e e d s p ro te in d e m a n d , it re s u lts in an in c re a s e d urea
c o n c e n tra tio n in th e blood, a nd a g re a te r n itro g e n
e lim in a tio n in th e p e rs p ira tio n a n d u rine .
Vitamin and drug abuse by cyclists
W h e n e v e r a visitin g c y c lin g te a m fro m E urope p a r­
tic ip a te s in th e R a p p o rt T ou r, th e c y c lis ts a re a c c o m ­
p a n ie d by an a rra y of b o ttle s, a m p o u le s, vials, in­
tra v e n o u s in fu sio n c o n ta in e rs a nd o th e r m e d ic a m e n ts .
E very p ro m in e n t c y c lis t a p p e a rs to have his o w n fads
a n d fa n c ie s , o r v ita m in p re p a ra tio n w h ic h he b e lie ve s
to h ave s o m e e rg o g e n ic aid. S o m e s u b s ta n c e s a re
c la s s ifie d as d o p e by th e M e d ic a l C o m m is s io n o f th e In ­
te rn a tio n a l O ly m p ic C o m m itte e (19 7 2 ) a n d have been
b a n n e d by th e o rg a n ize rs. (All o f th e m had been
p re s c rib e d b y th e ir m e d ic a l d o c to rs , u n a w a re of the
fa c t that so m e w id e ly u se d m e d ic in e s c o n ta in b a n n e d
s u b sta n ce s).
C yclin g , m o re th a n m ost o th e r sp o rts, had b een p ro ­
m in e n t w ith re g a rd to th e d a n g e rs o f d ru g -ta kin g fo llo w ­
ing the d e a th o f T o m S im p so n in 1967 on M o n t V e n to u x
in F ra n ce . P o lice fo u n d d ru g s in his p o sse ssio n , and
th e y w e re in e vid e n c e d u rin g p o st-m o rte m .
In S outh A fric a w e have fo rtu n a te ly been s p a re d the
m a lp ra c tic e o f m a jo r d ru g a b u se in cyc lin g .
T he re a re still c y c lis ts w h o b e lie ve that V ita m in B l2
in je c tio n s s h o u ld be g ive n a t re g u la r in te rva ls. T he re is
no re lia b le e v id e n c e th a t V ita m in B 12 has a n y b e n e fic ia l
e ffe c t on h u m a n p e rfo rm a n c e , a nd c e rta in ly none
w h ic h s h o w s that it is n e c e s s a ry fo r n o rm a l he a lth, p ro ­
vid e d a n o rm a l b a la n c e d diet is given.
V ita m in C has g e n e ra te d so m e in te re s t re ce n tly,
b e c a u s e of s o m e re p o rts th a t it m ig h t h a ve so m e
e rg o g e n ic p ro p e rtie s . It has b e e n sh o w n th a t V ita m in C
d o e s p la y a role in heat a c c lim a tiz a tio n 14’ and c o u ld be
a d m in is te re d to c y c lis ts tra in in g in hot w e a th e r d u rin g
p e rio d s o f a c c lim a tiz a tio n .
It is im p o rta n t to realise, h o w e v e r, th a t a n y re su ltin g
im p ro v e m e n t as a re su lt of d ie ta ry m a n o e u v re s is likely
to be sm all but c o u ld m a ke all th e d iffe re n c e b e tw e e n
w in n in g a n d losing.
References
1. Journal of Applied Physiology, (1977) Volume 43, pages
258-261.
2. Costill, D. L. and Saltin, B. (1974): Journal of Applied
Physiology 37, 679.
3. Wyndham, C. H. and Strydom, N. B. (1969): S. Air. Med. J.,
43, 893.
4. Strydom, N. B. Kotze, H. F„ Van der Walt, W. H., Rogers, G.
G. Effect of ascorbic acid on rate of heat acclimatization. Jour­
nal o f Applied Physiology Volume 41. pp 202-205 1976.
Further reading matter
1 Williams, J. G. P. Sports Medicine (Second Edition) Edward
Arnold (1976).
2. Woodland, Les. Cycle Racing: Training to win. Pelham
Books Ltd. (1975).
3. Kleiner and Orten. Biochemistry: (Sixth Edition) The C. V.
Mosby Company (1962)
First editorial board
get-together
lin ic a l a s p e c ts p e rta in in g to the s p o rts m a n 's w e ll
be in g has e n jo y e d an in c re a s e in in te re st a m o n g
S outh A fric a n d o c to rs p o ssib ly g re a te r th a n a n y w h e re
e lse in th e w o rld in re c e n t ye a rs.
C
T his o b se rv a tio n p ro ve d to be th e c o n c e n s u s o f in­
fo rm a l c o n v e rs a tio n s w h ic h to o k p la c e d u rin g a re c e n t
g e t-to g e th e r o f S .A Sports M edicine E ditorial A d viso ry
B o a rd M e m b e rs in Jo h a n n e sb u rg .
Itf;
,
"T h a t th e sta n d a rd o f s p o rts p h y s io lo g y a nd the
tre a tm e n t o f s p o rts in ju rie s p ra c tis e d in this c o u n try
m ust ra te a m o n g the h ig h e st in th e w o rld , ca n be
s u b s ta n tia te d by th e in te re st S .A Sports M edicine
has g e n e ra te d a m o n g lo ca l m e m b e rs o f the m e d ic a l
fra te rn ity ,” M r. W. H e n ze , g e n e ra l m a n a g e r o f the
p u b lic a tio n ’s s p o n so rin g c o m p a n y , B o e h rin g e r In­
g e lh e im (Pty) Lim ited , to ld his g u e sts.
M r H e n ze a d d e d th a t th ro u g h th e c o m p a n y 's in te r­
n a tio n a l c h a n n e ls , a " tre m e n d o u s a m o u n t” o f in te re st
h a d b e e n e x p re s s e d in s p o rts m e d ic in e d e v e lo p m e n ts
in S outh A fric a by o th e r c o u n trie s w h e re th e p u b lic a tio n
has b e e n exp o sed .
4
T h re e o f S o u th A f r ic a ’s le a d in g s p o rts m e d ic in e p r a c t i­
tio n e rs (fro m le ft):
D r. Iva n C o h e n , D r. C liv e N o b le a n d C ol E tie n n e H u g o ,
in c o n v e rs a tio n d u rin g th e in fo rm a l g e t-to g e th e r o f
S.A. S ports M e d ic in e E d ito ria l A d v is o ry B o a rd
m e m b e rs in J o h a n n e s b u rg re c e n tly .