Plasma levels of amino acids in young and old men in Japan (nM)

Amino acids

young men (n = 36)

old men (n = 44)

ss

Histidine

78.5 ± 7.7

78.7 ± 7.5

Lysine

185.9 ± 28.6

190.9 ± 28.7

Methionine

27.3 ± 3.6

27.6 ± 4.9

Phenylalanine

56.9 ± 7.0

65.4 ± 8.8

**

Threonine

131.4 ± 21.5

136.5 ± 27.4

Tryptophan

65.8 ± 9.1

58.7 ± 9.2

Isoleucine

67.9 ± 11.2

67.5 ± 8.5

Leucine

129.8 ± 16.8

133.8 ± 17.5

Valine

221.9 ± 16.3

228.1 ± 30.6

Tyrosine

58.2 ± 8.7

70.3 ± 12.0

**

Alanine

356.0 ± 68.8

415.9 ± 75.7

**

A-Aminobutyric acid

20.9 ± 5.3

21.7 ± 6.5

**

Arginine

77.6 ± 15.0

79.3 ± 17.6

Asparagine

45.0 ± 6.1

47.3 ± 5.7

Aspartic acid

3.4 ± 1.4

3.4 ± 0.7

Citrulline

22.2 ± 3.6

27.0 ± 6.2

**

Cystine

14.1 ± 4.1

23.6 ± 6.7

**

Glutamic acid

37.0 ± 11.6

45.0 ± 16.

**

Glutamine

548.5 ± 64.0

575.6 ± 53.0

Glycine

213.5 ± 25.9

198.5 ± 28.6

Monoethanolamine

8.5 ± 1.2

8.8 ± 1.3

Ornithine

59.4 ± 12.5

72.5 ± 13.9

**

Proline

172.8 ± 58.4

169.2 ± 56.9

Serine

124.6 ± 17.2

105.5 ± 18.2

**

Taurine

49.9 ± 1.5

67.7 ± 3.1

**

Total amino acids

2751.7 ± 215

2891.4 ± 201.6

Total essential AAs

695.3 ± 89.0

985.4 ± 94.9

Total nonessential AAs

1786.4 ± 153.3

1960.4 ± 166.0

**

Total Branched chain AAs

419.5 ± 48.3

427.5 ± 52.3

Fisher ratio

3.7 ± 0.4

3.2 ± 0.4