The influence of dietary protein levels on the preference for sodium c
hloride was studied in juvenile rats fed diets containing 0, 25 or 50
g purified egg protein/kg and 20.0 mg zinc/kg diet. Preference tests b
etween aqueous solution of NaCl (2-51 mmol/L) or deionized water were
conducted. Blood samples were collected for measuring the serum zinc c
oncentration. Scanning electron microscopy was performed to observe th
e rats' tongue epithelia. Only the rats fed 50 g purified egg protein/
kg diet preferred the lowest concentration of 2 mmol/L NaCl solution t
o deionized water, whereas the rats fed protein-free diet did not disc
riminate diluted NaCl solution until the concentration was 9 mmol/L. T
he filiform papillae of the protein-free diet fed group showed signifi
cantly less development than the 25 g purified egg protein/kg and the
50 g purified egg protein/kg diet-fed groups. The more protein the die
ts contained, the higher was the serum concentration of zinc. Signific
ant correlations were observed between protein intake and discriminate
d NaCl concentration (r = -0.93, P < 0.001), serum zinc (r = 0.90, P <
0.001) or length of filiform papillae (r = 0.93, P < 0.001). The pres
ent study suggests that taste preference is impaired by protein malnut
rition and this may be related to zinc status.