Animal studies on the cellular basis of obesity suggest that the number of adipocytes is determined by nutritional factors soon after birth, while size is affected by the same factors at later ages; the tenability of this hypothesis is questioned in a review of relevant studies. Present methodologies for estimating total body fat and adipocyte size and volume can vary considerably and validity has not been established. Some of the problems include sampling variations and the impossibility of identifying empty adipocytes. Observations and serial data on human beings yield mixed results; age-to-age correlations of obesity at birth and later ages are almost nil, and while those between 6 and 16 are higher, they still do not tend to support the theory of determination of obesity by numbers of adipocytes in infancy.
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