Influence of tryptophan availability on selection of alcohol and water by men

To study the effects of tryptophan on alcohol selection the tryptophan levels in subjects were altered through the administration of amino acid mixtures. Male social drinkers (N = 45) with no psychiatric or medical problems were divided into three groups and consumed a drink that contained, respectively, a nutritionally balanced amino acid mixture, a tryptophan-supplemented mixture, or a tryptophan-free mixture. After a waiting period of 5 hours, blood samples were taken and subjects participated in an ad-lib taste rating of six--one nonalcoholic and five alcoholic--beverages. Water was also made available to subjects. Although there was a marked effect on total and free plasma tryptophan levels showing a dramatic increase in the case of the tryptophan-supplemented group and a decrease in the tryptophan-free group, altered tryptophan levels did not influence the amount of alcohol subjects ingested. Tryptophan supplementation was found to decrease water intake significantly by an unknown mechanism without affecting alcohol selection.