Rita Wellens

Body size and fatness in young adults in relation to age at menarche

The relationships among age at menarche, body size, and body composition were considered in university students surveyed in 1970 (n = 342) and 1987 (n = 109). Recalled ages at menarche, stature, weight, and the triceps skinfold thickness were measured. Subjects ranged in age from 17.5 to 22.5 years in both surveys and were divided into four categories by age at menarche: before 12 years, 12.0 through 12.99 years, 13.0 through 13.99 years, and older than 14 years. In both the 1970 and 1987 surveys, later maturers had significantly more linear physiques than those experiencing menarche earlier. Late maturers also showed a tendency to lower values for the body mass index (BMI) and triceps skinfold compared with early maturers. Comparative data for women of the same age from the Fels Longitudinal Study (n = 234) showed similar findings. Women who reached menarche at ages older than 14 years were significantly taller than women with menarcheal ages less than 13 years. Women with menarcheal ages younger than 12 years were significantly heavier and had higher BMIs than those from any older menarcheal category. They also had significantly thicker triceps skinfolds than those with menarcheal ages older than 14 years.

A Comparison of Body Composition Models

There has been ample interest in body composition of special populations such as children and older adults. A significant problem occurs when applying the conventional two-component body composition model to these special groups. This two-component model assumes body composition is composed of fat and fat-free components and the composition of the fat-free component is constant across ages, sexes, and races. The fat-free component of the human body can be chemically separated into water, mineral, and protein. In a multicomponent model, the fat-free component varies by age, sex, and race as each subcomponent in the fat-free mass changes according to biological conditions. Changes in water content are important because body water is a major and variable fraction of the fat-free component. Infants and juveniles tend to have a larger water fraction than men. Consequently, in a two-component model, FFM is underestimated in the young. The assumptions in a multi-component model are biologically true but limited in accuracy because measurement errors for each component may accumulate and inflate the errors in the body composition estimates. An alternative is to use dual-energy X-ray absorptiometry (DXA) to obtain body composition measures. Software to allow soft tissue measurements from DXA has become recently available. The equipment is simple to use but the theory behind this soft tissue measurements is not well-defined.

Head circumference for Mexican American infants and young children from the Hispanic health and nutrition examination survey (HHANES 1982–1984): Comparisons with Whites and Blacks from NHANES II (1976–1980)

This study presents descriptive statistics for head circumference in Mexican American children 6 months to 7 years of age using data from the Hispanic Health and Nutrition Examination Survey (HHANES, 1982–1984) and compares these statistics with national estimates of head circumference for non‐Hispanic White children and non‐Hispanic Black children from the Second National Health and Nutrition Examination Survey (NHANES II, 1976–1980). Head circumference was measured in the same standardized fashion in the two surveys. The patterns of change with age in means and in empirical percentiles were similar for both genders and for all three ethnic groups. Values for head circumference increased with age, but the rate of increase became less as age advanced. Analyses indicated that at 1, 2, and 4 years of age, mean values for head circumferences for non‐Hispanic White boys were significantly larger than those for Mexican American boys. The differences in mean values for head circumferences ranged from 0.7 to 1.1 cm. Because ethnic differences in head circumferences are small in magnitude, ethnic‐specific sets of reference data for head circumference are not needed for clinical evaluation of Mexican Americans, non‐Hispanic Whites, and non‐Hispanic Blacks. Further analyses may be necessary when additional information from NHANES III allows the calculation of the 5th and 95th percentiles for Black and Mexican American children with small confidence limits.

The Use of High Frequency Energy Absorption to Measure Limb Musculature

Muscle mass is an important indicator of nutritional status invariably linked with protein status. Through the use of anthropometric data, arm muscle mass has been shown to be a useful predictor of mortality. Arm muscle circumference was an important predictor of all cause mortality in a 25year prospective study of 4,267 men from three European countries1 and arm muscle area below 12 cm2 is related to impending death in cancer patients2.

Fat-Free Mass and Percent Body Fat Assessments by Dual-Energy X-ray Absorptiometry, Densitometry and Total Body Water

In recent years, noninvasive measurements for determining body composition have included dual-energy projection methods, which provide skeletal as well as soft tissue measurements for total and regional body composition1. The use of dual photon absorptiometry for body composition measurements is based upon the differential attenuation by tissue of photons from two different energy levels emerging from an X-ray source or from a radionuclide. The acronym DXA will be adopted for dual-energy X-ray absorptiometry throughout this text in accordance with the recommendations of Wilson et al.2. Dual-energy projection methods are independent of assumptions about biological constancies of tissue densities that characterize traditional methods such as hydrometry and the two-component densitometric model. These are based on the main assumption that the density of fat-free mass is constant. However, the density of fat-free mass varies depending on the amounts of water, protein and mineral present and according to ethnicity, gender, age and determinants of fatness such as exercise and illnesses3. For clinical and research purposes, it is important to compare results from methods developed recently such as DXA with body composition techniques that have a longstanding tradition. The purpose of this study is to compare fat-free mass (FFM) and percent body fat (%BF) as obtained by dual-energy X-ray absorptiometry (DXA), densitometry (DENS) and deuterium dilution for total body water (TBW).

Reference data for arm muscle and arm adipose tissue areas in Mexican Americans from the Hispanic Health and Nutrition Examination survey (HHANES 1982–1984): Comparisons with whites and blacks from NHANES II (1976–1980)

Data for arm muscle area (AMA) and arm adipose tissue area (AATA) from 3695 Mexican American children 6 months to 18 years of age included in HHANES (1982–1984) were used to obtain age‐and gender‐specific means and selected percentiles. These statistics were compared with those for non‐Hispanic white and non‐Hispanic black children from NHANES II (1976–1980). In comparison with non‐Hispanic white and non‐Hispanic black children, the Mexican American children tended to have smaller means and percentile values for AMA but larger values for AATA. There was considerable sexual dimorphism in AMA and AATA. Within each population, boys tended to have larger means and percentile values for AMA than girls, and girls tended to have larger values for AATA than boys. Within each population of boys, there was a prepubescent gain in AATA, followed by a midpubescent loss, and then an increase near the middle of the second decade. This “fat wave” pattern was not noticeable in girls. Population differences in age‐ and gender‐specific mean values for AMA and AATA were small. Few statistically significant differences were observed; these were no more common than would occur by chance. Therefore, population‐specific reference data for AMA and AATA may not be needed for the clinical evaluation of Mexican Americans, non‐Hispanic blacks, and non‐Hispanic whites.

Relationship of skeletal age to limb composition during pubescence

The relationships between skeletal age (SA) and limb composition (arms, legs, and all four limbs) in terms of fat mass (FM), fat‐free mass (FFM), muscle mass (MM) and bone mineral content (BMC) were investigated in 55 males and 53 females aged 9–15 years. The Fels method was used to assess hand‐wrist SAs which were expressed as SA/chronological age (SA/CA). The limb composition data were obtained from a Lunar dual‐energy x‐ray absorptiometer using 3.6z software. The means for the limb composition variables increased gradually with age except in males for whom FM decreased from 12 to 13 years, and FFM and MM increased markedly from 13 to 14 years. There were similar findings when the limb composition data were expressed as percentages of body weight. All of the regressions of SA/CA on limb composition variables had positive slopes. Each of the slopes was significant for males, but nonsignificant for females.