Aging in the rat: longitudinal and cross sectional studies of body composition

G. T. Lesser, S. Deutsch, J. Markofsky

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Two rat colonies were maintained through life and the individual rats studied repeatedly for total body fat content and fat free mass (FFB). The design permitted comparison of cross sectional (population means at given ages) with longitudinal observations of the individual rats. Detailed autopsies allowed distinction of aging changes from those due to disease. The longitudinal data identified a long lived subgroup within each colony, characterized by lower body weight and smaller FFB, and also by maintenance of stable body composition in old age. There was no significant difference in their proportion of body fat. Due to selective longevity, these lighter rats came to represent a majority of the population at late ages. An implicit assumption in cross sectional investigations of aging that older subjects represent random survivors of a population was not valid in this instance. Average colony FFB decreased in senescence. However, the longitudinal data demonstrated this from selective longevity for rats of smaller FFB, rather than to loss of lean tissue by healthy aged rats. The findings emphasize the potential of longitudinal aging study and also suggest that the widely held concept of senescent loss of lean tissue in mammals be reevaluated.

Original languageEnglish
Pages (from-to)1472-1478
Number of pages7
JournalAmerican Journal of Physiology
Issue number6
StatePublished - 1973
Externally publishedYes


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