NUTRITION IN SPORT

lower relative exercise intensity, and perhaps as a
result, an improved nitrogen status. To examine
this possibility, we decided to repeat the initial
investigation of Gontzea et al. (1974) with a
few minor but significant changes. First, we
studied experienced endurance runners (> 5
years’ training experience, 94±21 km · week–1,
V

.
o2max.= 71 ±5ml·kg–1· min–1) and, second, we
used an exercise bout which simulated their
daily training load. We observed a negative
nitrogen status in the trained runners when they
consumed 0.9 g protein · kg–1· day–1and a posi-
tive nitrogen status when they consumed 1.5 g ·
kg–1· day–1(Friedman & Lemon 1989). The fact
that these experienced endurance runners
responded similarly to the untrained subjects
who were unaccustomed to the exercise stimulus
in the Gontzea et al. (1974) study indicates that
the negative nitrogen status in the endurance
runners on the diet of 0.9 g protein · kg–1· day–1
reflects an inadequate protein diet rather than a
transient response to the initiation of an exercise
programme.
In another study, Tarnopolosky et al. (1988),

140 nutrition and exercise

using various protein intakes (1.0–2.7 g · kg–1·

day–1) and the nitrogen status (balance) tech-

nique, not only observed an increased protein

need in the endurance athletes studied, agreeing

with the other studies mentioned above, but also

in a group of strength athletes (see discussion

of strength studies below; Fig. 10.9). Typically,

regression procedures, i.e. protein intake that

elicits nitrogen balance plus a safety margin

(twice the standard deviation of the subject

sample) to cover the needs of 97.5% of the popu-

lation of interest (US Food and Nutrition Board

1989), are used with these kinds of data to deter-

mine a recommended dietary allowance (RDA).

In this study the investigators used this proce-

dure but utilized only 1 SD to arrive at re-

commended protein intakes of 1.6 g · kg–1· day–1

for endurance athletes and 1.2 g · kg–1· day–1for

strength athletes (167% and 112% of the current

RDA in the United States, respectively). This

conservative approach was used because they

wanted to minimize any overestimation that

might result when extrapolating from protein

intakes as high as 2.7 g · kg–1· day–1 to those

Nitrogen balance (g

.day

–1

)

1

0

–1

–2

–3 –4 –2 0 2 4 6 8 10 12 14 16 18 20

Time (days)

Fig. 10.8Effect of adaptation to an exercise programme on nitrogen status while consuming 1 g protein · kg–1· day–1
(125% of the recommended protein intake) in humans. Note that nitrogen status (balance) appears to recover over
several weeks of the same exercise stimulus. These data have been interpreted to mean that this protein intake,
although inadequate for a few days at the beginning of an endurance exercise programme, becomes adequate over
a few weeks as a result of some adaptation. However, this apparent improved nitrogen status could also be an
artifact of a decreased exercise stimulus due to an increasing endurance capacity over the several weeks of training.
Adapted from Gontzea et al. (1975).