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.

The aim of this study was to determine the effectiveness of prune juice on chronic constipation. METHODS:We conducted a double-blind, randomized, placebo-controlled trial in Japanese subjects with chronic constipation. RESULTS:Prune intake significantly decreased hard and lumpy stools while increasing normal stool and not increasing loose and watery stools. Prune intake also ameliorated subjective complaints of constipation and hard stools, without alteration of flatulence, diarrhea, loose stools, or urgent need for defecation. There were no adverse events or laboratory abnormalities of liver or renal function after prune intake. DISCUSSION:Prune juice exerted an effective and safe natural food therapy for chronic constipation.

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