title: The ingestion of different dietary proteins by humans induces large changes in the plasma tryptophan ratio, a predictor of brain tryptophan uptake and serotonin synthesis.
abstract: OBJECTIVE
  The ingestion by rats of different proteins causes large differences in the plasma ratio of tryptophan to other large neutral amino acids, which predicts brain tryptophan uptake and serotonin synthesis. We evaluated in humans whether ingesting these proteins also produces large excursions in the tryptophan ratio.
  
  
  METHODS
  Fasting males (n = 6) ingested V-8 Juice containing 40 g of α-lactalbumin, gluten, zein or starch. Blood was drawn before and at 30 min intervals after ingestion for 4 h; tryptophan and other large neutral amino acids were quantitated.
  
  
  RESULTS
  Pre-meal plasma tryptophan was ~50 nmol/ml; the tryptophan ratio was ~0.010. α-Lactalbumin increased plasma tryptophan (3-fold) and the tryptophan ratio (50%); starch did not change either tryptophan variable, while gluten caused a modest (25%) and zein a large reduction (50%) in plasma tryptophan. Gluten and zein reduced the tryptophan ratio. The maximal difference in the tryptophan ratio occurred between α-lactalbumin and zein and was large (~3-fold).
  
  
  CONCLUSIONS
  Since the plasma tryptophan ratio predicts brain tryptophan uptake and serotonin synthesis in rats, the differences in the ratio produced in humans by these proteins may modify serotonin synthesis, and perhaps elicit serotonin-linked changes in behavior.
authors: Department of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, United States; Department of Pharmacology/Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, United States. Electronic address: fernstromjd@upmc.edu.
authors: John D
authors: JD
authors: Fernstrom
authors: Kathryn A
authors: KA
authors: Langham
authors: Lyndsey M
authors: LM
authors: Marcelino
authors: Zoë L E
authors: ZL
authors: Irvine
authors: Madelyn H
authors: MH
authors: Fernstrom
authors: Walter H
authors: WH
authors: Kaye
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D001921:Brain / Q000378:metabolism*; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D004044:Dietary Proteins / Q000008:administration & dosage*; D005983:Glutens / Q000008:administration & dosage; D006801:Humans; D007328:Insulin / Q000097:blood; D007768:Lactalbumin / Q000008:administration & dosage; D008297:Male; D062407:Meals; D012701:Serotonin / Q000096:biosynthesis*; D014364:Tryptophan / Q000097:blood* / Q000493:pharmacokinetics*; D055815:Young Adult; D015028:Zein / Q000008:administration & dosage
chemical_list: D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D007328:Insulin; D012701:Serotonin; D005983:Glutens; D014364:Tryptophan; D015028:Zein; D007768:Lactalbumin
keywords: Brain; Dietary protein; Human; Large neutral amino acids; Tryptophan; Tyrosine