Sexual dimorphism in the energy content of weight change.

BACKGROUND: The energy content of weight change is assumed to be sex- and age-neutral at 3,500 kcal/pound or 32.2 MJ/kg. OBJECTIVES: As sexual dimorphism in body composition generally exists in mammals, the primary hypothesis advanced and tested was that the energy content of weight change differs between men and women. DESIGN: The energy content of 129 adult men and 287 women was measured by neutron activation analysis. Cross-sectional energy content prediction models were developed and then evaluated in two longitudinal samples: one that used the same methods in 26 obese women losing weight; and the other a compilation of 18 previously reported weight change-body composition studies. RESULTS: Multiple regression modeling identified weight, sex, age and height as total energy content predictor variables with significant sex x weight (P<0.001) and age x weight (P<0.001) interactions; total model r(2) and s.e.e. were 0.89 and 107.3 MJ, respectively. The model's predictive value was supported in both longitudinal evaluation samples. Model calculations using characteristics of representative adults gaining or losing weight suggested that the energy content of weight change in women (approximately 30.1-32.2 MJ/kg) is near to the classical value of 32.2 MJ/kg and that in men the value is substantially lower, approximately 21.8-23.8 MJ/kg. The predicted energy content of weight change increases by about 10% in older (age approximately 70 y) vs younger (approximately 35 y) men and women. CONCLUSIONS: Sexual dimorphism and age-dependency appears to exist in the estimated energy content of weight change and these observations have important clinical and research implications.

Seronegativity to varicella-zoster virus in a tertiary care obstetric population.

OBJECTIVE: To determine the seronegativity rate of varicella-zoster virus in a tertiary care obstetric population. METHODS: At their initial prenatal visit, all obstetric patients at Westchester County Medical Center have a varicella-zoster virus IgG antibody titer (Varicella Stat; Biowhittaker, Inc., Walkersville, MD) performed. A value of 0.99 or greater units is positive. Patients were divided into three groups: seronegative, seropositive, and those with no test results. Mean maternal age was compared among groups using the unpaired two-tailed Student t test, with P < .05 considered significant. RESULTS: From February 1, 1994, to May 30, 1996, 927 women had an initial prenatal visit. Ninety-nine patients were varicella-zoster virus antibody negative (seronegativity 11.6%, which is significantly higher than that reported in other studies); 755 were varicella-zoster virus antibody positive, and 73 had no results. The mean age of the seronegative patients was 27 years and of the seropositive patients 28 years, which was not significantly different. CONCLUSION: Varicella-zoster virus seronegativity is higher in our obstetric population than generally is reported in adults. This may reflect the number of immigrants from tropical countries attending metropolitan hospitals. Mathematic models evaluating the impact of varicella-zoster virus vaccination and decisions regarding screening and postpartum vaccination must be based on accurate epidemiologic data, particularly in view of the effect of varicella-zoster virus on pregnant women, their fetuses, and their neonates.