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Plasma Free Amino Acids of Infants and Children Consuming Wheat-Based Diets, with and without Supplemental Casein or Lysine¹

Instituto de Investigacion Nutricional, Miraflores, Lima, Peru and Department of Pediatrics, School of Medicine, The Johns Hopkins University, Baltimore, MD 21205

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.

KEY WORDS: • amino acids • wheat • lysine

¹ Supported by Grant HD 10111 from the National Institutes of Health, U.S.P.H.S., by Contract ta-C-1286 with the Agency for International Development, U.S. Department of State, and by a grant from the Middendorf Foundation, Baltimore, MD.

Manuscript received 19 January 1981.