Six skinfold measurements, and percent body fat and fat-free weight derived from the underwater weighing technique were obtained in 43 pairs of male and 44 pairs of female monozygotic (MZ) twins. A fat tissue biopsy was performed in the suprailiac region in 20 male and 16 female pairs in order to determine mean adipocyte diameter and basal lipolysis as well as epinephrine maximally stimulated lipolysis (10−4 M). Twin resemblance in body fatness is clearly demonstrated by the analysis of the between MZ sibships over the within MZ shibship means of squares for all skinfold measurements, percent body fat and fat free weight (P < 0.01). Within MZ pair similarity is as high in female as in male pairs for body fatness. Moreover, members of the same twin pair resemble one another significantly for fat cell size and fat cell lipolytic activities, particularly when epinephrine stimulated. In female MZ pairs, additional studies with control over the menstrual cycle are needed to clarify the case of isolated fat cell basal lipolysis.
