NUTRITION IN SPORT

142 nutrition and exercise

recommended intakes of 1.7 and 1.8 g protein ·

kg–1· day–1, respectively. Moreover, Fern et al.

(1991) found a greater gain in mass over 4 weeks

of training in body builders who consumed 3.3

vs. 1.3 g protein · kg–1· day–1. This study is fasci-

nating because it supports the age-old (but

poorly documented) belief of strength athletes

that very large amounts of dietary protein (and

the resulting highly positive nitrogen balance)

in combination with the anabolic stimulus of

strength exercise may be able to stimulate muscle

growth (Lemon 1991). However, amino acid oxi-

dation also increased by 150% in this study, sug-

gesting that the optimum protein intake was

likely exceeded. Subsequently, Tarnopolsky et al.

(1992) observed an increase in whole-body

protein synthesis (Fig. 10.12) when athletes

participating in a strength training programme

increased their protein intake from 0.9 to

1.4 g · kg–1· day–1. Interestingly, there was no

additional increase when they consumed a diet

Leucine oxidation (

μmol

.kg

–1

.g

–1)

Rest Exercise

*

*

70

**

60

50

40

30

20

10

0 4 3 2 1 0

Protein intake (g

.kg

–1

.day

–1

)

–10 –5 0 5 10 15

Nitrogen balance (g.day–1)

Fig. 10.10Effect of gender on oxidation of the amino
acid leucine both at rest and during an endurance
exercise bout in humans. Note that exercise increases
leucine oxidation (*, P<0.01, exercise vs. rest) and that
both at rest and during exercise the leucine oxidation
rate is greater in the men (**, P<0.01, men vs. women).

, men; , women. Adapted from Phillips et al.
(1993).

Fig. 10.11Estimated dietary requirements (protein intake necessary to elicit nitrogen balance) in novice body-
building men. Note that while consuming 0.99 g protein · kg–1body mass · day–1(125% of the recommended dietary
intake for protein) (
), all subjects had a negative nitrogen status and a strong linear relationship between protein
intake and nitrogen status (r=0.82,P< 0.01, y=0.13x+1.43). Using these data, the estimated dietary requirement for
protein (yintercept) is 1.43 g protein · kg–1· day–1. Typically, recommendations for protein are equal to this value (y
intercept) plus a safety buffer equal to 2 SD of the sample mean (in order to account for the variability in the
population relative to the sample studied). Here, the recommendation would be 1.63 g protein · kg–1· day–1(204% of
the current recommendation). The linear relationship between protein intake and nitrogen status is lost at the high
protein intake studied (2.62 g protein · kg–1· day–1) () and the nitrogen status was highly positive indicating that
this intake exceeded protein need (r=0.11; P< 0.05; y=– 0.93x+2.76). For both treatments combined, r=0.86;
P< 0.01; y=– 0.11x+1.53. Adapted from Lemon et al. (1992).