BMI Perception:  A potential cheap alternative to objectively measured BMI?

Abstract Background Accurately measuring BMI in large epidemiological studies is problematic as objective measurements are expensive, so subjective methodologies must usually suffice. A number of subjective methodologies have been shown to be inaccurate, resulting in misclassification to a lower BMI category and a subsequent underestimation of obesity prevalence. The purpose of this study is to explore a new subjective method of measuring BMI, BMI perception. Methods A cross-sectional analysis of the Mitchelstown Cohort Rescreen study, a random sample of 1 354 men and women aged 51–77 years recruited from a single primary care centre. Data were collected using self-administered questionnaires. BMI perception was measured by asking “Do you think you are underweight, normal weight, overweight or obese?” Weight and height were also objectively measured. Results 79% of the cohort were overweight or obese: 86% of males, 69% of females, P<0.001. The sensitivity for correct BMI perception for normal weight, overweight and obese was 77%, 61% and 11% respectively. 59% of overweight/obese participants underestimated their BMI. In multivariable analysis, gender, higher education levels, being told by a health professional to lose weight, and being on a diet were significantly associated with correct BMI perception. There was a linear trend relationship between increasing BMI levels and correct perception of BMI; participants in the highest BMI quartile had an approximate eight-fold increased odds of correctly perceiving their BMI when compared to participants within the lower overweight/obese quartiles (OR=7.72, 95% CI: 4.59, 12.98). Conclusions BMI perception as a subjective measurement of BMI has the potential to be an important measurement tool in large epidemiological studies. Clinicians need to be aware of disparities between BMI perception at the higher and lower BMI levels among overweight/obese patients and encourage preventative action for those at the lower levels to avoid weight gain and thus reduce their all-cause mortality risk.