title: Sensitivity and specificity of the body mass index to assess low percent body fat in African women.
abstract: The objective of this study was to evaluate the ability of the body mass index (BMI, kg/m(2)) to reflect low percent body fat (%BF) in a population with a rather mild but widespread prevalence of low BMI. A sample of 586 women was studied in the Plateau Koukouya, a rural area of the Republic of Congo, Central Africa. Percent BF was estimated from bioelectrical impedance (BIA). BIA parameters were assumed to reflect lean body mass. The correlation between %BF and BMI was high (r = 0.84; P < 0.001). Low %BF or low BIA parameters were defined as the first quartile of the distribution. Sensitivity, specificity, positive and negative predictive value of BMI <18.5, an accepted international cutoff for thinness, in relation to %BF was 58.5%, 93.6%, 75.4%, and 87.1%, respectively. A continuous sensitivity/specificity analysis (receiver operator characteristic [ROC] curves) for characterizing low %BF or low BIA parameters was done for a large range of BMI values. ROC curve analysis for %BF suggested that an acceptable trade-off between sensitivity (89.8%) and specificity (77.9%) occurred at a BMI of 19.7 kg/m(2). However, the positive predictive value was low (57.6%). For the prediction of low BIA parameters, results were similar, showing moderate sensitivity and high specificity for BMI <18.5, a cutoff point of BMI = 19.6, and low positive predictive values (<48%). The data suggest that BMI was not a good predictor of low %BF. This is consistent with the assumption of a decrease in both fat and fat free body mass in cases of low BMI. Am. J. Hum. Biol. 12:25-31, 2000. Copyright 2000 Wiley-Liss, Inc.
authors.affiliation: Nutrition Unit, IRD (Institut de Recherche pour le Développement formerly orstom), WHO Collaborating Center for Nutrition, Montpellier Cedex 1, France.
authors.forename: Agnes
authors.initials: A
authors.lastname: Gartner
authors.forename: Bernard
authors.initials: B
authors.lastname: Maire
authors.forename: Pierre
authors.initials: P
authors.lastname: Traissac
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Massamba
authors.forename: Yves
authors.initials: Y
authors.lastname: Kameli
authors.forename: Vincent
authors.initials: V
authors.lastname: Keraudren
authors.forename: Francis
authors.initials: F
authors.lastname: Delpeuch