Tyrosine- and phenylalanine-restricted formula diet augments immunocompetence in healthy humans.

Previous studies indicate that limiting tyrosine and phenylalanine intake in the diet decreases tumor growth and metastasis. General health status, immune status, and platelet function were studied in nine healthy human subjects consuming low-protein foods supplemented with formula diets free of tyrosine and phenylalanine to maintain total daily intake of tyrosine at 2.4 mg/kg body wt and phenylalanine at 3.5 mg/kg body wt. This regimen decreased plasma tyrosine (p less than 0.05) but not phenylalanine. Blood indicators of protein status were not changed. Platelet aggregation decreased in response to adenosine diphosphate and platelet activating factor in seven of nine subjects. Natural killer, T-helper, and T-cytotoxic/suppressor lymphocyte numbers proportionally increased relative to neutrophils (p less than 0.05). Natural killer cell activity increased in six of nine subjects. Increased natural killer cell activity and decreased platelet aggregation are two indices associated with decreased tumor growth and metastasis.