Peer review

Because of the poor digestibility of rice protein, plasma amino acid fluxes after a rice meal might be expected to be less than those seen after a meal of more readily digested protein. This would militate against finding the changes in plasma essential amino acid concentrations indicative of inadequacy of lysine, the first limiting amino acid of rice protein relative to the FAO/WHO provisional scoring pattern. The postprandial changes of plasma free amino acids were analyzed in 15 children after consuming a meal in which one of the two varieties of rice (IR 32 or IR 480-5-9) protein provided 6% of 20 to 25 kcal/kg body weight. The fasting concentrations of total amino acids (TAA), total essential amino acids (TEAA) and their ratio (TEAA/TAA), reflecting 7 to 14 days rice consumption, were low (TAA = 2353 ± 435 µmole/liter, TEAA = 530 ± 59 µmole/liter, TEAA/TAA = 0.230 ± 0.036). There were no significant postprandial changes in TAA, TEAA, TEAA/TAA, or in the concentrations of Lys or Thr. The Lys/TEAA molar ratio was significantly less than the fasting value at 3 hours (fasting = 0.150 ± 0.030, 3 hour = 0.129 ± 0.021, P < 0.02) but not at 4 hours (0.10 > P > 0.05). No significant change of Thr/TEAA occurred. Analysis by variety showed more marked changes of the plasma concentration of Lys and of the Lys/TEAA molar ratio after consuming IR 32. Despite the generally muted plasma amino acid response to rice protein, the changes previously seen with wheat when lysine is the first limiting amino acid in the diet were found to occur in these studies.

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