NUTRITION IN SPORT

containing 2.4 g protein · kg–1· day–1. Further,
amino acid oxidation increased with the 1.4 and
2.4 g · kg–1· day–1diet in the sedentary group but
only with the 2.4 g · kg–1· day–1 diet in the
strength athletes. This suggests that at an intake
of 1.4 g protein · kg–1· day–1, the amino acids con-
sumed in excess of needs were removed from the
body via oxidation in the sedentary subjects but
were used to support an enhanced protein syn-
thesis rate in the strength group. Obviously with
time this should lead to increases in muscle
mass and potentially in strength. These results
confirm the Fern et al. (1991) data (that increased
dietary protein combined with strength exercise
enhances muscle growth over training alone)
and further indicate that 2.4 g protein · kg–1· day–1
is excessive. These data and the nitrogen balance
data (Lemon et al. 1992; Tarnopolsky et al. 1992)
indicate that optimal protein intakes for male
strength athletes are likely about 1.4–1.8 g
protein · kg–1· day–1(175–225% of current recom-
mendations). Finally, it should be understood

that these studies all involved men who were not

taking any anabolic substances. Although not

condoned due the potential adverse side-effects,

it is possible that the ceiling effect relative to

muscle growth observed in the vicinity of 1.4–

1.8 g protein · kg–1· day–1might be extended to

higher intakes if combined with pharmacologic

manipulations known to enhance muscle devel-

opment (Bhasin et al. 1996). If so, this could

explain why the athletes’ beliefs about the bene-

fits of very high protein diets differ from the

scientific data. Finally, these studies need to be

repeated in women to assess whether there are

gender differences in the protein needed to

enhance muscle growth.

Campbellet al. (1995) studied protein turnover

and nitrogen status (balance) in older men and

women (ages, 56–80 years) consuming either 1.62

or 0.8 g protein · kg–1· day–1while participating in

a 12-week, whole-body, heavy resistance training

programme. They observed a negative nitrogen

status and a tendency for whole-body protein

effects of exercise on protein metabolism 143

Whole-body protein (mg

.kg

–1

.h

–1)

300

50

250

100

200

150

0.9 1.4 2.4

Protein intake (g.kg–1.day–1)

a

a a a

b

b

Fig. 10.12Whole-body protein synthesis in sedentary (
) vs. strength-trained ( ) men consuming 0.9, 1.4 or 2.4 g
protein · kg–1· day–1(112%, 175% and 300% of the current recommended protein intake). Note that the protein
synthetic rate increased in the strength-trained men when going from 112% to 175% of the current recommended
protein intake, indicating that this latter protein intake would facilitate mass and strength development. However,
there was no additional increase when protein intake was further increased to 300%, suggesting that this quantity
exceeded the optimal protein intake. Note also that strength training is necessary to increase the protein synthetic
rate with additional dietary protein, as no increase was observed in the sedentary men. Unlike letters, P< 0.05.
Adapted from Tarnopolsky et al. (1992).