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Biomedical subjects

R Leenen

Publications and source records attributed to R Leenen.

21 records · Page 2Linked to original sources
PubMed1989

In obese subjects the body fat percentage calculated with Siri's formula is an overestimation.

By means of theoretical calculations it is shown that the chemical composition of the fat-free mass is affected by the amount of fat in the body. With increasing fatness the relative amounts of minerals and protein in the fat-free mass will decrease and the relative amount of water will increase. These changes in the chemical composition of the fat-free mass are confirmed by data from the literature. Because minerals and protein are the most dense components in the fat-free mass, and water is the less dense component, the density of the fat-free mass will decrease with increasing body fatness. As a consequence, the normally used computation formula for the calculation of the body fat percentage from whole-body density (Siri's equation) will systematically overestimate the real body fat percentage by as much as 2-4 per cent in severely obese subjects. This overestimation is large enough to correct for in studies on energy metabolism and body composition.

Adipose Tissue↗
PubMed1989

Body impedance is largely dependent on the intra- and extra-cellular water distribution.

Electrical impedance measurements were performed in fasting blood samples and analysed in relation to packed cell volume and calculated intra- and extra-cellular water distribution. The total blood impedance was shown to be strongly dependent on the ratio of intra-cellular water to total water (r = 0.97, P less than 0.0001). In a group of 515 subjects, with a large variation in age and body composition, the relation between the body impedence corrected for fat-free mass and body height (the specific body impedance) and the calculated ratio of intra-cellular water to total body water, was found to be similar to that in blood. From these observations a regression model was developed and applied to body compositional data of several groups of subjects before and after weight loss caused by water losses. It was possible to calculate at a group level the losses of intra- and extra-cellular water, which confirms the applicability of the model. It is concluded that the validity of the predicted fat-free mass or total body water from body impedance is largely dependent on the water distribution in the measured subjects. This means that age- and sex-specific prediction formulas have to be used for the assessment of the body composition and that the bio-electrical impedance method is only with caution applicable in subjects with a disturbed water distribution as in oedema, pregnancy and dehydration.

Adult↗