title: Relationships between basal metabolic rate, body weight and body composition in a group of ninety women aged 18 to 30 years
Creators: name: Kindlen, Sheenan
Publisher: name: University of Glasgow
Year: 1998
Subjects: subject: Physiology, kinesiology.

description: The aim of the study was to investigate relationships between basal metabolic rate (BMR), body weight and body composition in a group of 90 women aged 18 to 30 years. Whole body basal metabolic rate /24 hours, referred to here as gross BMR (GBMR), was assessed by indirect calorimetry using the Douglas bag technique and body composition by the sum of skinfold thickness at four sites (Durnin and Womersley, 1974). When values of GBMR were plotted against body weight (BW) and against fat free mass (FFM) (kg), the data gave covariance coefficients of 0.71 and 0.75 respectively, comparable with published values. Distributions of data points however indicated that the moderate covariance was due not simply to overall variability but to a tendency to curvilinearity. In each case the data showed both linear and polynomial trends. Since GBMR is determined to a large extent by body weight, the effect of BW as a variable was removed by calculation of BMR / kg / min., referred to here as unit BMR or uBMR. uBMR values plotted against %FM showed a highly significant curvilinear distribution with lower values of uBMR in both lean and overweight sectors of the study population. While bearing in mind the problematic nature of BMR assessment, markedly low values were found for the leanest subjects. The metabolic rate of unit weight of composite tissue is determined not only by the proportions of FFM and FM compartments but also by the components of the compartments and the factors which regulate activity within any given component. These neural and endocrine factors can not only alter the rate of fuel consumption but the selection of the fuel. While it might be expected that unit weight of tissue of high %FM would have a lower overall energy expenditure, tissue with very low percentage fat might be expected to reflect the typically higher expenditure of FFM. In addition to the inherent variability due to composition and regulation, the low values of uBMR found for very lean subjects may be evidence of some adaptation, possibly to low intake. To investigate the degree of departure from linearity as it was reflected in GBMR values, the study population was partitioned according to body size (by BMI) and body composition (by %FM). Three groups, 'overweight', 'standard' and 'lean' were identified in each grouping, the membership of each group being determined by the grouping criteria. Regression analysis of group data showed that trend-lines of GBMR with BW had distinctly different slopes from group to group in each grouping. With FFM discontinuity was evident only at extremes of the range. BMR is often estimated from linear regression equations. In order to assess the effect of this tendency to non linearity in the study population data on the prediction of GBMR, linear regression equations were constructed for the full range of the study population and for each group using BW, BW0.75 and FFM. These equations were then used as 'prediction' equations to estimate the mean GBMR by substituting mean anthropometric parameters first in the full range equation then in the group specific equation. Where the extent of departure from linearity was large, the difference between an estimate obtained using a full range equation and one obtained using the group specific equation would be significant not only in statistical but in practical terms. (Abstract shortened by ProQuest.).