<p>Classification Accuracy of Body Mass Index for Excessive Body Fatness in Kuwaiti Adolescent Girls and Young Adult Women</p>

Abstract

Purpose: Adolescent obesity, as defined by BMI, is amongst the highest in the world in Kuwait. This study aimed to determine the extent to which BMI might be underestimating obesity as defined by excessive fatness in Kuwaiti female adolescents and young adults. Methods: A total of 400 apparently healthy Kuwaiti female university students (mean age 18.0 years, SD 0.6) were recruited. Excessive fatness was defined as body fat percentage ≥30, measured using the Tanita model TBF-310 Bio-impedance system with the manufacturer's equation. Obesity was defined as recommended by the WHO in adult participantsthose aged ≥19.1 yearsas BMI≥30 kg/m 2. In the adolescent participants (age <19.1 years) obesity was defined as recommended by the WHO as a BMI-forage Z score of ≥2.00. The accuracy of BMI-defined obesity to identify excessively fat individuals was determined by estimating the prevalence of obesity using high BMI and prevalence of excessive fatness, and by calculating sensitivity and specificity and predictive values. Results: Median BMI was 27.8 kg/m 2 (range 15.1-51.2) and median body fat percentage was 32.0 (range 5.0-54.0). The prevalence of excessive fatness was 62% (247/400 individuals were excessively fat), while the prevalence of obesity according to BMI was 42% (169/400 individuals were obese according to their BMI). The sensitivity of BMI to identify the excessively fat individuals was moderate (66%) but specificity was high (96%). The positive predictive value of BMI was 96% and the negative predictive value was 64%. Conclusion: BMI-based measures substantially underestimate the prevalence of excessive fatness in Kuwaiti adolescent females. Obesity is even more prevalent, and requires more urgent attention, than is apparent from BMI-based measures used in most research and national surveys. BMI may also be too crude for use as an exposure or outcome variable in many epidemiological studies of Arab adolescent girls and adult women.

Differences in educational attainment between obese and non-obese Kuwaiti female university students

“…The present study used the BMI to define obesity (obesity is a high level of body fatness rather than a high BMI) (21) – while the BMI is a convenient proxy for high body fatness, it has only moderate sensitivity for high body fatness in Kuwait and in other populations (21) . In an attempt to address this potential weakness, we also tested for differences in academic attainment between individuals defined as having high body fatness (≥30% of body weight, as estimated by bio-electrical impedance) versus those with lower body fatness in the present study.…”

“…The present study recruited a convenience sample of first- and second-year Kuwaiti University College of Social Science students between March and May 2019. Sampling and recruitment have been described in detail elsewhere (21) . In brief, all first- and second-year Social Science undergraduates were invited to take part by the researcher.…”

“…The power of the present study was difficult to assess at the outset, and the power was fixed as this was part of a wider study of the ability of BMI to identify excessive fatness among female Kuwaiti adolescents (21) .…”

“…Second, the novelty of the study was high because of the non-Western setting and the contemporary sample (with most of the previous literature from undergraduates from an era when obesity prevalence and access to tertiary education were very different (16) ). Third, we examined potential confounding by socio-economic status, considered crucial by a number of previous reviews, notably Santana et al (15) The present study used the BMI to define obesity (obesity is a high level of body fatness rather than a high BMI) (21) while the BMI is a convenient proxy for high body fatness, it has only moderate sensitivity for high body fatness in Kuwait and in other populations (21) . In an attempt to address this potential weakness, we also tested for differences in academic attainment between individuals defined as having high body fatness (≥30% of body weight, as estimated by bio-electrical impedance) versus those with lower body fatness in the present study.…”

“…Anthropometric measurements and BMI calculations were carried out as described by Al-Hammadi and Reilly (21) . A Seca Stadiometer (Seca, London, UK) was used to measure the height to the nearest 0⋅1 cm.…”