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

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... rcentage. Although skeleton weight and tail length increased through out 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 . Energy restriction has a beneficial effect on life extension in experimental animals (1-4). This life-prolonging action has been considered to be the result of delaying the onset of some age-related diseases and retarding several physiological aging processes (1, 2). On the other hand, though the relationships between protein EFFECT OF PROTEIN INTAKE LEVEL 471 EFFECT OF PROTEIN INTAKE LEVEL 477 EFFECT OF PROTEIN INTAKE LEVEL 479 with energy restriction.