Abstract
OBJECTIVES: To evaluate the association between percent body fat (%BF) and body mass index (BMI) among BMI-defined non-obese individuals between 40 and 69 years of age using a population-based Canadian sample.
DATA AND METHODS: Cross-sectional data from the Canadian Health Measures Survey (2007 and 2009) was used to select all middle-aged individuals with BMI < 30 kg/m2 (n = 2,656). %BF was determined from anthropometric skinfolds and categorized according to sex-specific equations. Association of other anthropometry measures and metabolic markers were evaluated across different %BF categories. Significance of proportions was evaluated using chi-squared and Bonferroni-adjusted Wald test. Diagnostic performance measures of BMI-defined overweight categories compared to those defined by %BF were reported.
RESULTS: The majority (69%) of the sample was %BF-defined overweight/obese, while 55% were BMI-defined overweight. BMI category was not concordant with %BF classification for 30% of the population. The greatest discordance between %BF and BMI was observed among %BF-defined overweight/obese women (32%). Sensitivity and specificity of BMI-defined overweight compared to %BF-defined overweight/obese were (58%, 94%) among females and (82%, 59%) among males respectively. According to the estimated negative predictive value, if an individual is categorized as BMI-defined non-obese, he/she has a 52% chance of being in the %BF-defined overweight/obese category.
CONCLUSION: Middle-aged individuals classified as normal by BMI may be overweight/obese based on measures of %BF. These individuals may be at risk for chronic diseases, but would not be identified as such based on their BMI classification. Quantifying %BF in this group could inform targeted strategies for disease prevention.
Key Words: Obesity, body mass index, body fat percentage, adipose tissue
Résumé
OBJECTIFS: Évaluer l’association entre l’indice de masse grasse (IMG) et l’indice de masse corporelle (IMC) chez des personnes âgées de 40 à 69 ans, non obèses selon la définition de l’IMC, à l’aide d’un échantillon populationnel canadien.
DONNÉES ET MÉTHODE: À partir des données transversales de l’Enquête canadienne sur les mesures de la santé (2007 et 2009), nous avons sélectionné toutes les personnes d’âge moyen ayant un IMC < 30 kg/m2 (n = 2 656). L’IMG de ces personnes a été déterminé à partir de mesures anthropométriques des plis cutanés et catégorisé à l’aide d’équations sexospécifiques. Les associations avec d’autres mesures anthropométriques et indicateurs métaboliques ont été évaluées pour différentes catégories d’IMG. Le caractère significatif des proportions a été analysé en utilisant le test du khi-carré et le test de Wald corrigé à l’aide de la technique de Bonferroni. Nous avons fait état des indicateurs de performance diagnostique des catégories de surpoids définies selon l’IMC comparées à celles définies selon l’IMC.
RÉSULTATS: La majorité (69 %) de l’échantillon était en surpoids ou obèse selon la définition de l’IMG, tandis qu’une proportion de 55 % était en surpoids selon la définition de l’IMC. Pour 30 % de la population, la catégorie d’IMC ne concordait pas avec la classification de l’IMG. La plus grande discordance entre l’IMG et l’IMC a été observée chez les femmes définies comme étant en surpoids ou obèses selon l’IMG (32 %). La sensibilité et la spécificité de la définition du surpoids selon l’IMC comparativement à la définition du surpoids ou de l’obésité selon l’IMG étaient de (58 %, 94 %) chez les femmes et de (82 %, 59 %) chez les hommes, respectivement. Selon la valeur prédictive négative estimative, si une personne est catégorisée comme n’étant pas obèse selon la définition de l’IMC, cette personne a une probabilité de 52 % de faire partie de la catégorie de surpoids ou d’obésité selon la définition de l’IMG.
CONCLUSION: Les personnes d’âge moyen classifiées comme ayant un IMC normal pourraient être en surpoids ou obèses selon les indicateurs de l’IMG. Ces personnes peuvent être vulnérables aux maladies chroniques, mais ne seraient pas identifiées comme telles d’après leur IMC. La quantification de l’IMG dans ce groupe pourrait éclairer des stratégies ciblées de prévention des maladies.
Mots Clés: obésité, indice de masse corporelle, indice de masse grasse, tissu adipeux
Footnotes
Acknowledgement and disclaimer: The views expressed in this paper are solely those of the authors and do not reflect those of Statistics Canada. We thank Claudia Sanmartin for her contributions related to data access and analysis.
Conflict of Interest: None to declare.
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