Old as mature LOU/c/jall rats enhance protein selection in response to a protein deprivation

Previous experiments have shown a strong decrease in protein consumption as rats grow old. This result could be induced by an impaired regulation of feeding behaviour. Present study investigated the ability of ageing rats to adapt their protein intake to protein requirements. Four groups of self-selecting LOU/c/jall male and female rats (4, 16, 22, 28 months at the beginning of the experiments) were submitted to 4-days of protein deprivation periods while their macronutrient intakes were monitored. Moreover, they were submitted to a 4-day fasting period. After reintroduction of proteins, old and senescent rats were able to increase their protein intake in response to the specific protein need created by the protein deprivation. They were also able to increase caloric intake after the fasting period. These results led to the conclusion that the loss of appetite for protein observed with ageing reflects rather an adaptation than an impairment of the regulation of macronutrient choice. Another important observation was that older animals did not recover initial body weight after a body weight loss even if they ate as many calories as younger animals. This data supports a decrease in the efficacious utilization of body fuels in old and senescent rats.