Agreement between BMI and body fat obesity definitions in a physically active population

Abstract

Objectives: Body mass index (BMI) is a widely used proxy of body composition (BC). Concerns exist regarding possible BMI misclassification among active populations. We compared the prevalence of obesity as categorized by BMI or by skinfold estimates of body fat percentage (BF%) in a physically active population. Subjects and methods: 3,822 military firefighters underwent a physical fitness evaluation including cardiorespiratory fitness (CRF) by the 12 min-Cooper test, abdominal strength by sit-up test (SUT) and body composition (BC) by BF% (as the reference), as well as BMI. Obesity was defined by BF% > 25% and BMI ≥ 30 kg/m 2 . Agreement was evaluated by sensitivity and specificity of BMI, positive and negative predictive values (PPV/NPV), positive and negative likelihood (LR+/LR-), receiver operating characteristic (ROC) curves and also across age, CRF and SUT subgroups. Results: The prevalence of obesity estimated by BMI (13.3%) was similar to BF% (15.9%). Overall agreement was high (85.8%) and varied in different subgroups (75.3-94.5%). BMI underestimated the prevalence of obesity in all categories with high specificity (≥ 81.2%) and low sensitivity (≤ 67.0). All indices were affected by CRF, age and SUT, with better sensitivity, NPV and LR-in the less fit and older groups; and higher specificity, PPV and LR+ among the fittest and youngest groups. ROC curves showed high area under the curve (≥ 0.77) except for subjects with CRF ≥ 14 METs (= 0.46). Conclusion: Both measures yielded similar obesity prevalences, with high agreement. BMI did not overestimate obesity prevalence. BMI ≥ 30 was highly specific to exclude obesity. Because of systematic under estimation, a lower BMI cut-off point might be considered in this population. Arch Endocrinol Metab. 2016;60(6):515-25

Obesity prevalence in Brazilian firefighters and the association of central obesity with personal, occupational and cardiovascular risk factors: a cross-sectional study

“…By contrast, the overall frequency of overweight plus obese firefighters in our study was quite high (59.64%). This finding is similar to what has been described for other populations of firefighters within and outside of Brazil15 16 31 34 36 39 and surpasses the prevalence observed among the Brazilian adult man (BMI ≥25 kg/m 2 ; 57.6%) 4. There are two possible explanations for these apparently conflicting results.…”

“…Our study also showed a lower obesity prevalence when compared with firefighter populations of the USA9 31–35 and Canada 36. On the other hand, two studies that described obesity (using BMI) among Brazilian firefighters from the Federal District showed similar frequencies of obese firefighters compared with our study 15 16. The low prevalence of obesity among the Brazilian firefighters could be due to a phenomenon known as the ‘healthy worker effect’ 37 38.…”

“…Some studies point out that the rate of overweight firefighters by the BMI can be overestimated 15 35 40. Similar results have been observed in other physically active population when estimating overweight through this parameter 41 42.…”

“…In particular, recent studies have highlighted that obesity measures indicative of visceral adiposity, such as central obesity (CO), have a linear relationship with mortality from cardiovascular disease (CVD) 1 11–14. In Brazil, two studies reported a high prevalence of overweight and obesity among firefighters from the Federal District 15 16. However, there is no record of studies that investigated the obesity prevalence among other populations of Brazilian firefighters.…”

Avaliação da acurácia de medidas antropométricas em relação ao diagnóstico de Síndrome Metabólica de Xavante do Mato Grosso, Brasil

“…Contudo, é uma técnica questionável por expressar apenas a massa corporal total, impossibilitando a diferenciação da massa magra e da massa gorda [40,41]. Portanto, indivíduos com a massa muscular mais desenvolvida podem ser considerados obesos, como por exemplo, os atletas e algumas populações supostamente mais ativas [42]. Este pode ser o caso de populações indígenas, nas quais muitas das suas atividades do cotidiano favorecem o maior desenvolvimento de massa magra, elevando seu IMC.…”