NUTRITION IN SPORT

to effectively strengthen cellular antioxidant
defences and protect against oxidative stress.
Nutritional manipulations that have significant
potential to circumvent exercise-induced oxida-
tive stress are discussed below.

298 nutrition and exercise

Dietary restriction

Dietary restriction delays the loss of several

cellular immune functions, retards age-related

functional disorders and has been proven to sig-

nificantly extend lifespan in laboratory animals

(Sohalet al. 1994). Several studies suggest that

dietary restriction may strengthen tissue antioxi-

dant defence systems and alleviate oxidative

stress-related damage including cataractogene-

sis (Taylor et al. 1995). Activities of certain

components of the physiological antioxidant

defence system are upregulated during the

course of ageing, perhaps to cope with age-

related increased oxidative stress. In the skeletal

muscle, activities of catalase and GSH peroxi-

dase increased progressively and markedly with

ageing in rats fed ad libitum. Dietary restriction

clearly suppressed such responses, suggesting

that the ageing tissue may have been exposed to

less oxidative stress challenge than that of rats

fedad libitum(Luhtalaet al. 1994). In mice, ageing

has been observed to be associated with marked

oxidative protein damage in organs such as the

brain, heart and kidney. This adverse effect could

be considerably limited when mice were fed with

a diet 40% lower in energy. Ageing increases the

resting respiratory rate of mitochondria resulting

in increased generation of mitochondrial super-

Total glutathione (

μmol

.g

–1

wet wt)

1.4

0

1.2

0.4

SOL

0.2

GS

1.0

0.8

0.6

EDL PL QF

*

** * Fig. 22.1Sprint-training-

dependent increase in skeletal

muscle glutathione. Rats were

either not trained () or treadmill

trained 5 days per week for

6 weeks on a treadmill at speed

close to the physiological limit of

rats (
) (see Atalay et al. 1996).

EDL, extensor digitorum longus;

GS, gastrocnemius; PL, plantaris;

QF, quadriceps femoris; SOL,

soleus. Effect of sprint training: *,

P<0.001; **, P<0.01.

Table 22.2Endogenous proteins with antioxidant
properties.

Protein Function

Superoxide dismutases Dismutases superoxides to
(Cu, Zn, Mn) hydrogen peroxide
Catalase (Fe) Hydroperoxide
decomposition
Glutathione peroxidase Hydroperoxide
(Se) decomposition
GlutathioneS-transferase Hydroperoxide
decomposition
(secondary property)
Glutathione reductase Glutathione recycling
Thioredoxin peroxidase Hydroperoxide
decomposition
Methionine sulphoxide Oxidized –SH repair in
reductase proteins
Thioredoxin Reduces oxidized protein
disulphides
Transferrin Iron transport
Ferritin Iron storage
Ceruloplasmin Copper storage
‘Peroxiredoxin’ Hydroperoxide/
(a 24 kD thiol-specific radical scavenging
protein)