Plasma-Free Amino-Acids Of Infants And Children Consuming Wheat-Based Diets, With And Without Supplemental Casein Or Lysine

Plasma free amino acids (AA) were measured in children consuming five diets: (a) 44–50% of calories (kcal) and all 6.6% protein (Pro) kcal from wheat; (b) same + casein to 8.0% pro kcal; (c) 75% kcal and all 9.8% pro kcal from wheat; (d) same with 0.2% Lys; and (e) identical to c, but following c and d. On day 9 of diet a, inadequate in available Pro because of Lys deficiency, 16 subjects had low fasting TEAA/TAA (total essential/total AA) molar ratios, with significant declines 3 and 4 hours postprandially (p.c.). Fasting molar fractions of each essential AA (EAA/TEAA) were not different from subjects consuming isonitrogenous milk protein diets, except slightly lower Lys/TEAA and higher Thr/TEAA; significant declines p.c. in Lys/TEAA and increases in Ile, Tyr and Phe/TEAA, modest decline in Thr/TEAA. After more than 3 months of diet b, four subjects had higher fasting Lys/TEAA, marked declines p.c.; lower fasting Thr/TEAA and significant increases p.c. in Ile, Tyr and Phe/TEAA. After 28–89 days of diet c in 10 subjects, there was significant increase p.c. in TEAA/TAA; fasting Lys/TEAA was lower than after diet a and significant greater decline p.c.; fasting Thr/TEAA was elevated with modest 3-hour decline; significant increases p.c. in Ile, Tyr and Phe/TEAA. When Lys was added in seven of 10 subjects (diet d), after 8–50 days fasting Lys/TEAA was significantly higher with no p.c. decline; fasting Thr/TEAA lower; only significant p.c. change was increase in Phe/TEAA. After 15–29 days without added Lys in five of seven (diet e), plasma AA were similar to those after identical diet c; fasting Lys/TEAA lower, suggesting greater depletion of body pools. Fasting plasma AA reflect diet TEAA/TAA and Pro kcal ratios, protein “status” and first-limiting EAA (after prolonged consumption). Second-limiting EAA may be elevated. Postprandial EAA/TEAA declines identify first-limiting EAA; increases may be due to relative diet excess or delays in plasma clearance.