Children’s Nutrition Research Center Staff Publications
Publication Date
6-8-2021
Journal
Nutrients
DOI
10.3390/nu13061976
PMID
34201370
PMCID
PMC8227932
PubMedCentral® Posted Date
6-8-2021
PubMedCentral® Full Text Version
Post-print
Published Open-Access
yes
Keywords
Administration, Oral, Adult, Body Weight, Dietary Supplements, Energy Intake, Female, Health, Humans, Male, Mental Fatigue, Nutrients, Phenylalanine, Serine, Sleep
Abstract
Phenylalanine and serine are amino acids used in dietary supplements and nutritional products consumed by healthy consumers; however, the safe level of phenylalanine or serine supplementation is unknown. The objective of this study was to conduct two 4-week clinical trials to evaluate the safety and tolerability of graded dosages of oral phenylalanine and oral serine. Healthy male adults (n = 60, 38.2 ± 1.8y) completed graded dosages of either phenylalanine or serine supplement (3, 6, 9 and 12 g/d) for 4 weeks with 2-week wash-out periods in between. Primary outcomes included vitals, a broad spectrum of circulating biochemical analytes, body weight, sleep quality and mental self-assessment. At low dosages, minor changes in serum electrolytes and plasma non-essential amino acids glutamine and aspartic acid concentrations were observed. Serine increased its plasma concentrations at high supplemental dosages (9 and 12 g/day), and phenylalanine increased plasma tyrosine concentrations at 12 g/day, but those changes were not considered toxicologically relevant. No other changes in measured parameters were observed, and study subjects tolerated 4-week-long oral supplementation of phenylalanine or serine without treatment-related adverse events. A clinical, no-observed-adverse-effect-level (NOAEL) of phenylalanine and serine supplementation in healthy adult males was determined to be 12 g/day.
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