Appetite and taste preference in growing rats given various levels of protein nutrition.

The cephalic gustatory stimuli during a meal yield nutritional information and aid in the efficient control of homeostasis. This study was focused on either appetite for flavored food or feeding behavior in growing male Sprague-Dawley rats under various states of protein nutrition. In fasted rats, endogenous protein degradation was suppressed by ingestion of glucose that was sufficient to meet energy needs. The decrease in the amount of diet intake was compensated by sugar ingestion, except for sucrose. Rats that ingested sucrose exceeded 115% of total energy intake, compared to ingestion of saccharin as a control. Appetite and meal size are primarily dependent upon the dietary protein level, whether it was beyond normal requirements or not and, thus, flavoring by certain taste material is effective for a diet sufficient in protein, but not for a deficient one. In addition, rats fed a diet containing amino acids preferred saccharin and monosodium L-glutamate (MSG) and grew normally. But, when L-tryptophan-deficient diet was offered, the preference for tryptophan was elicited, and then MSG intake was elevated and their growth became normal. However, preference for saccharin never occurred because the level of tryptophan in blood fluctuated and was not maintained within normal limits. The strong preference for sweetness that is evoked by starvation is directly regulated by the negative energy balance. The animals' primary concern was energy intake and their second concern was protein nutrition, regardless of flavoring.