A validation study of body composition by bioelectrical impedance analysis in human immunodeficiency virus (HIV)-positive and HIV-negative Hispanic men and women.

Bioelectrical impedance analysis (BIA) is a potentially useful tool for measuring body composition in people with human immunodeficiency virus (HIV). However, it is not clear that equations derived in healthy non-Hispanic whites can be applied to people who are of other races or ethnicities and who are infected with HIV. Body composition measures done by BIA, using the equations of Lukaski, were compared to measures of body composition derived from dual-energy x-ray absorptiometry (DXA) in Hispanic men and women of Caribbean origin (predominantly Puerto Rican) with and without HIV infection. In cross-sectional analyses, body composition was measured by BIA and DXA in four groups of Hispanics: 97 HIV-positive men, 70 HIV-negative men, 38 HIV-positive women, and 14 HIV-negative women. The method of Bland and Altman was used to evaluate the validity of BIA compared to DXA. Compared to DXA, BIA provided accurate measures of fat-free mass in HIV-positive and HIV-negative Hispanic men. Fat-free mass by BIA compared to DXA was overestimated by 2.7 kg (standard deviation=2.5; P<0.0001) in the HIV-positive Hispanic women and by 3.4 kg (standard deviation=2.6; P<0.01) in the HIV-negative women. The magnitude of the bias in fat-free mass was dependent on fat mass in both the men and the women. BIA, using the equations of Lukaski, appears to be useful in this Hispanic population of Caribbean origin with and without HIV, for whom it provided reasonable estimates of body composition. Fat mass affects the accuracy of estimates.

Fetal and infant head circumference sexual dimorphism in primates.

Studies have shown that after controlling for the effects of body size on brain size, the brains of adult humans, rhesus monkeys, and chimpanzees differ in relative size, where males have a greater volume of cerebral tissue than females. We assess whether head circumference sexual dimorphism is present during early development by evaluating sex differences in relative head circumference in living fetuses and infants within the first year of life. Head circumference is used as a proxy for brain size in the fetus and infant. Femur length is used as a proxy for body length in the fetus. Ultrasonography was used to obtain fetal measures, and anthropometry was used to obtain postnatal measures in humans, rhesus monkeys, baboons, and common marmosets. We show that statistically significant but low levels of head circumference sexual dimorphism are present in humans, rhesus monkeys, and baboons in early life. On average, males have head circumferences about 2% larger than females of comparable femur/body length in humans, rhesus monkeys, and baboons. No evidence for head circumference sexual dimorphism in the common marmoset was found. Dimorphism was present across all body size ranges. We suggest that head circumference sexual dimorphism emerges largely postnatally and increases throughout maturation, particularly in humans who reach adult dimorphism values greater than the monkeys. We suggest that brain dimorphism is not likely to impose an additional energetic burden to the gestating or lactating mother. Finally, some of the problems with ascribing functional significance to brain size sexual dimorphism are discussed, and the energetic implications for brain size sexual dimorphism in infancy are assessed.

A new method for quantifying encephalization in the growing individual.

Here we describe a new method for quantifying encephalization in the growing individual and provide a worked example of the methods. The new method is based on the use of conditional SD scores derived from brain and body growth references. These encephalization SD scores control for age, sex and body size effects on brain size, and therefore, control for the confounds associated with allometry as well as growth differences between the brain and body and between the sexes. The methods also control for distribution skewness. Encephalization SD scores derived from pre- and post-natal data may be directly compared and changes in SD score over time assessed. These methods may be applied to a broad range of data where relative size during growth is to be quantified. Derived SD scores may also be applied to correlation and regression analyses where statistical relationships with other variables are of interest.