Preference for sodium chloride is reduced in protein-deprived juvenile rats

The influence of dietary protein levels on the preference for sodium chloride 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 between aqueous solution of NaCl (2-51 mmol/L) or deionized water were conducted. Blood samples were collected for measuring the serum zinc concentration. Scanning electron microscopy was performed to observe the rats' tongue epithelia. Only the rats fed 50 g purified egg protein/kg diet preferred the lowest concentration of 2 mmol/L NaCl solution to deionized water, whereas the rats fed protein-free diet did not discriminate diluted NaCl solution until the concentration was 9 mmol/L. The filiform papillae of the protein-free diet fed group showed significantly 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 diets contained, the higher was the serum concentration of zinc. Significant correlations were observed between protein intake and discriminated 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 present study suggests that taste preference is impaired by protein malnutrition and this may be related to zinc status.