Effects of dietary methionine supplementation on preferences for NaCl solutions

Preferences for eight concentrations of sodium chloride were measured in 10 control rats, 10 rats fed a diet supplemented with 2.5% methionine, and 10 rats fed a diet supplemented with 2.5% methionine and 2% zinc sulfate. All rats received the applicable diet for 21 days before testing was initiated with a 48-hr, two-bottle preference paradigm. Results of the study indicated that rats supplemented with methionine alone had significantly greater preferences for the salt solutions than rats from either of the remaining groups. Dietary treatment did not affect total volume intake (milliliters per gram body weight). Further analysis of the separate water and sodium chloride solution volume intakes demonstrated that while all groups consumed essentially equivalent amounts of water, the rats supplemented with methionine alone consumed significantly increased amounts of the salt solutions, thus manifesting an increased percentage preference. The results indicate that methionine, a thiol-containing amino acid, can alter preferences for sodium chloride solutions and that this effect can be reversed by zinc supplementation. The etiology of this change in preference behavior may be related to either decreased gustatory sensitivity (mediated by zinc depletion and/or thiol supplementation) or to salt craving (mediated by kidney and/or adrenal dysfunction).