Validation of body mass index (BMI) adjusted for fat mass using the bioelectrical impedance analysis.

Author(s)

Mirele Savegnago Mialich Grecco

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2012-06-22

Examining board members

Alceu Afonso Jordao Junior; Carlos Eduardo Andrade Chagas; Maria Cristina Foss de Freitas; Rosa Wanda Diez Garcia; Mayra Mayumi Kamiji

• Advisor: Alceu Afonso Jordao Junior

Abstract

Obesity is defined as the excess fat and BMI has been one of the most widely used methods for the diagnosis of obesity because of its ease of application and low cost. However, this index has a major limitation of not differentiating adipose tissue and fat- free mass. This study aimed to validate the Body Mass Index adjusted for fat mass obtained by bioelectrical impedance analysis previously developed by Mialich et al., 2011. We conducted a cross-sectional study with 501 subjects of both genders, aged between 17 and 38 years, enrolled in graduate courses at the USP campus at Ribeirao Preto. The subjects underwent measurement of weight, height and body composition assessment by bioelectrical impedance analysis. In addition, information was collected regarding the eating pattern by applying a questionnaire develops by the researchers, and also on the physical activity questionnaire using the IPAQ. The student participation was voluntary and all subjects were evaluated only one time in the study and by a group of trained examiners. For validation we used the linear regression model, being the BMI-adjusted the independent variable and BMI-traditional the dependent variable. The sample consisted of 366 women and 135 men and it had a mean age of 20.8 ± 3.2 years and 20.3 ± 2.7 years, weight 76.9 ± 13.6 kg and 57.8 ± 9.2 kg, height 177.3 ± 6.7 cm and 163.1 ± 6.3 cm, BMI 24.4 ± 3.8 kg/m2 and 21.7 ± 3.0 kg/m2, fat-free mass, 60.0 ± 7.7 kg and 39.8 ± 3.8 kg, fat mass 17.0 ± 6.2% and 26.6 ± 6.2% for men and women, respectively. With respect to validation were found high and satisfactory R2 values, 91.1%, 91.9% and 88.8%, considering all individuals, men and women, respectively. We also defined new range classification of nutritional status for both genders, considering this new BMI, as follows: 1.35 to 1.65 (nutritional risk for malnutrition), > 1.65 and 2.0 (normal) and > 2.0 (obesity). It was also found that this new index has the capacity to capture more accurate obese subjects (0.980, 0.993, 0.974) whereas all individuals, men and women, respectively, and the cutoff points for body fat of 25% (men) and 35% (women), rather than the traditional BMI (0.932, 0.956, 0.95). Moreover, this study allowed the definition of new points to traditional BMI cutoff for the classification of obesity, and: 25.24 kg/m2 and 28.38 kg/m2 for women and men, respectively. The new BMI set was validated for the population studied and may be adopted in clinical practice. Further studies should seek their implementation in different ethnic groups as well as the comparison of this index with other previously described in the literature. (AU)

• FAPESP's process: 10/01189-1 - Validation of Body Mass Index (BMI) adjusted for fat using the bioimpedance
• Grantee: Mirele Savegnago Mialich Grecco
• Support Opportunities: Scholarships in Brazil - Doctorate