Long-term effect of energy restriction at different protein levels on several parameters of nutritional assessment

Experiments were conducted to evaluate long-term effects of energy restricted diets containing different protein levels initiated in adult life on various parameters of nutritional assessment. Rats (male SPF Wistar) were fed 20%-casein diet ad libitum, or 10%-, 20%-, or 40%-casein diets (group 10R, 20R, and 40R, respectively) under energy-restricted conditions, which corresponded to about 60% ad libitum feeding, from 18 to 55 weeks of age. Energy restriction induced a decrease of body-lipid percentage. Although skeleton weight and tail length increased throughout the experimental period in all the groups, these increases were found to be depressed under energy restriction. On the other hand, protein intake level under the energy restriction did influence plasma concentrations of urea and cholesterol, hematocrit, and systolic blood pressure. The group fed the 40%-casein diet tended to be lower in total cholesterol levels at 55 weeks of age, while the group fed 10%-casein diet tended to be lower in hematocrit and higher in systolic blood pressure levels. When mature rats were fed the 60%-energy-restricted diet for a long-term period, those on the 20%- and 40%-casein diets showed somewhat more preferable levels of hematocrit and blood pressure than those on the 10%-casein diet; the 10%-casein diet did not, however, reveal symptoms of malnutrition.