Reevaluation of the protein requirement in young men with the
indicator amino acid oxidation technique.ABSTRACT
Background: The current estimated protein requirements are based
on the nitrogen balance method, which has many limitations. An
alternate approach is needed to permit a reevaluation of protein
requirements.
Objective: The objective was to determine protein requirements in
men by using the indicator amino acid oxidation technique.
Design: Eight healthy men randomly received graded protein intakes
(0.10, 0.30, 0.60, 0.90, 1.2, 1.5 and 1.8 g
kg
1
d
1) as a
crystalline amino acid mixture along with L-[1-13C]phenylalanine.
The mean protein requirement was determined by applying a biphase
linear regression crossover analysis on F13CO2 data, which identified
a breakpoint at the minimal rate of appearance of 13CO2 to
graded protein intakes.
Results: The mean and population-safe (recommended dietary
allowance; RDA) protein requirements were found to be 0.93 and
1.2 g
kg
1
d
1, respectively. These requirements are comparable
with those estimated by the application of a biphase linear regression
model to the data from nitrogen balance studies (0.91 and
1.0 g
kg
1
d
1, respectively). These requirements are 41% and
50% higher than the current recommendations for the estimated
average requirement (EAR) of 0.66 g
kg
1
d
1 and the RDA of
0.80 g
kg
1
d
1, as determined by applying a linear regression
model where it intersects the zero balance line.
Conclusion: The indicator amino acid oxidation technique defined
a protein requirement that is comparable with that estimated by the
application of a biphase linear regression model to nitrogen balance
data in the literature. Our data and the reanalysis of the preexisting
nitrogen balance data suggest that the current recommended protein
requirements are too low and require reassessment. Am J Clin
Nutr 2007;86:995–1002.


In the discussion:

The current EAR recommendation and RDA for protein are
0.66 and 0.80 g
kg
1
d
1, respectively. We believe that these
recommendations are tentative because no long-term studies
have suggested that these values would maintain nitrogen balance
along with lean body mass, muscle mass, serum protein
concentrations, immunity, functional capacity etc. Previously, a
series of long-term balance studies (67– 69) showed that intake of
the proposed safe allowance of 0.57 g (70) egg protein resulted in
negative nitrogen balance, loss of lean body mass, and deteriorating
serum protein and transferase values unless additional
energy or nonessential nitrogen was supplied.

Again, you don't need it, but it certainly doesn't hurt. This is particularly true if you workout.

Michael