Unlearned specific appetite for protein.

Appetite for most protein appears to be unlearned. Protein-depleted rats, in the first half hour of a test, chose a significantly larger proportion of soybean, gluten, zein, fibrin, yeast torula and ovalbumin than protein replete controls, but not of casein or lactalbumin. There had been no opportunity to learn such dietary preference before the test. The preference for the protein in protein-depleted rats manifested itself significantly from the first minute, and also in females in which protein need was induced by pregnancy rather than a diet different from the controls.