Plasma levels of tyrosine and phenylalanine, and ratios of tyrosine and phenylalanine to large neutral amino acids
| BAL, mean (SD) | APTD, mean (SD) | |||||
|---|---|---|---|---|---|---|
| Amino acid, μmol/L | Morning session | Afternoon session | Difference, % | Morning session | Afternoon session | Difference, % |
| Tyrosine | 49.8 (1.6) | 123.0 (10.0)‡ | 147.1 | 52.5 (1.5) | 13.6 (0.6)‡ | −74.1 |
| Phenylalanine | 44.8 (1.0) | 57.0 (4.0)‡ | 27.0 | 45.4 (1.1) | 14.8 (1.2)‡ | −67.5 |
| Tyrosine:LNAA† | 0.131:1 (0.004) | 0.151:1 (0.011) | 15.2 | 0.135:1 (0.003) | 0.015:1 (0.001)‡ | −88.8 |
| Phenylalanine:LNAA | 0.116:1 (0.002) | 0.063:1 (0.003)‡ | −45.9 | 0.115:1 (0.002) | 0.017:1 (0.002)‡ | −85.3 |
APTD = acute phenylalanine tyrosine depletion; BAL = balanced; LNAA = large neutral amino acid; SD = standard deviation.
↵* On the APTD test session, plasma concentrations of tyrosine and phenylalanine decreased significantly (tyrosine F1,26 = 151.25, p < 0.001; phenylalanine F1,26 = 79.56, p < 0.001). The APTD mixture decreased tyrosine and phenylalanine levels by 74.09% and 67.46% from baseline. In comparison, the BAL mixture increased plasma tyrosine and phenylalanine by 147.11% and 27.01%. Ingestion of the APTD mixture also significantly decreased the ratio of tyrosine to other LNAAs by 88.77% (p < 0.001), whereas the BAL mixture caused a nonsignificant change in ratio (change of 15.18%, p = 0.06). Ingestion of both mixtures significantly decreased the ratio of plasma phenylalanine to other LNAAs (F1,26 = 155.30, p < 0.001), but the reductions were more pronounced following APTD than BAL with a decrease of 85.34% versus 45.90%, respectively (p < 0.001).
↵† LNAAs include phenylalanine, tryptophan, leucine, isoleucine, valine and methionine.
↵‡ p < 0.0001.