Energy restriction increases longevity and life span of B/W mice as it does in mice of other long-lived or short-lived strains. Mice of autoimmune-prone strains that develop certain diseases of aging experience an increase in median longevity when energy intake is restricted early in life. The present experiments analyze the influence of restricting energy intake while feeding constant, adequate and greatly excessive amounts of protein, and constant amounts of minerals and vitamins. The experiments assess the influence of excess protein intake in mice fed ad libitum versus those restricted in energy intake. Ad libitum feeding of diets with protein composition ranging from 15 to 50% did not alter longevity or onset and manifestations of renal disease in B/W mice. In mice consuming a restricted energy intake of a diet providing identical amounts of protein to those consumed by ad libitum-fed mice, whether the protein intake was very high or normal, longevity was equally greatly prolonged. Ad libitum feeding of diets of greatly differing protein content is well tolerated by B/W mice. Both the 15 and 50% protein diets, when ad libitum fed, permitted expression of autoimmune disease and glomerulonephritis in B/W mice but did not adversely influence development or progression of disease. Restriction of energy intake of either the normal protein diet or the high protein diet greatly prolonged the life of mice of the autoimmune-prone, glomerulonephritis-prone B/W strain.
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