Carbohydrates.
Carbohydrates should make up the largest portion of the athletes
diet. Numerous studies have concluded that increased carbohydrate
(CHO) intake can improve exercise capacity and that low-CHO diets
can be detrimental to performance. Recent studies have also suggested
that benefit of CHO consumption is not limited to maintenance
of glycogen stores, but also related to maintenance of Krebs cycle
intermediates (8) and preservation
of the bioenergetic state of exercising muscle (9)
(factors also related to muscle fatigue). Sports nutrition guidelines
recommend that 60-65% of total energy should come from CHO (10).
It may be more appropriate, however, to base recommendations on
body weight which is independent of energy intake (11).
Nutritionists should educate vegetarian athletes on good sources
of CHO and provide guidelines for meeting daily intake of 7-10
g/kg. Usually athletes understand this type of approach, especially
when CHO exchanges are used.
Protein. Protein needs
of athletes vary according to type of activity and level of training.
The American and Canadian Dietetic Associations recommend that
athletes consume 1.5 g of protein/kg of body weight (12).
Two recent reviews, however, have come to very different conclusions
regarding protein requirements of physically active individuals
(13). approximately 1.2 to
1.4 g/kg/d for endurance athletes and, approximately 1.4 to 1.8
g/kg/d and for strength athletes. These values for strength athletes,
however, are higher than those of elite body builders (1 g/kg/d)
and may actually reflect requirements during early stages of resistance
training (14). The rationale
for the additional required protein in endurance and strength
training results from increased protein utilization as an auxiliary
fuel during exercise and to a lesser degree protein deposition
during muscle development (15).
Inadequate intakes of CHO (16)
and energy (17) have also
been found to increase protein needs. During prolonged endurance
activity, athletes with low glycogen stores metabolize twice as
much protein as those with adequate stores primarily due to increased
gluconeogenesis (18). As a
final note, protein requirements in most published studies have
been evaluated in young men, and may be different in females and/or
older athletes. Recent studies have found that females, relative
to males, catabolize less protein consequent to endurance exercise
(19), and that older sedentary
men require protein in excess of the RDA (20).
Clearly, more research is needed in this area.
