Enhanced preference for a protein-containing diet in response to dietary protein restriction

Rats were maintained for 10 days on either a protein-free or a nutritionally complete maintenance diet, and they were also given access to protein-rich and carbohydrate-rich test diets during separate daily 2-h test sessions. In Experiment 1, rats maintained on the protein-free diet gradually and selectively increased their intake of the protein test diet, and eventually derived 16% of their daily energy intake from the protein test diet. Rats maintained on a nutritionally complete diet ate similar amounts of the two test diets even when their total caloric intake was matched to that of rats maintained on the protein-free diet. In Experiment 2, rats that developed a preference for the protein test diet while maintained on a protein-free diet were given Purina Chow for 25 days to allow them to recover from their protein deficiency. When these rats were later returned to the protein-free diet for 10 days, their preference for the protein test diet was immediate and sustained. However, if they were maintained on the nutritionally complete diet after the 25-day recovery period, they initially preferred the protein test diet, but this preference diminished over days. Results of these studies are consistent with other findings showing that rats can learn to compensate for macronutrient deficiencies by using oral-sensory cues. In particular, the rats' diet selection was consistent with their having learned a preference for the cues paired with dietary protein.