Abstract
Background Accurately measuring BMI in large epidemiological studies is problematic as objective measurements are expensive, so subjective methodologies must usually suffice. The purpose of this study is to explore a new subjective method of BMI measurement: BMI self-selection. 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. BMI self-selection was measured by asking patients to select their BMI category: underweight, normal weight, overweight, obese. Weight and height were also objectively measured. Results 79% were overweight or obese: 86% of males, 69% of females (P < 0.001) and 59% of these underestimated their BMI. The sensitivity for correct BMI self-selection for normal weight, overweight and obese was 77%, 61% and 11% respectively. 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 self-selection. There was a linear trend relationship between increasing BMI levels and correct selection of BMI; participants in the highest BMI quartile had an approximate eight-fold increased odds of correctly selecting their BMI when compared to participants within the lower overweight/obese quartiles (OR = 7.72, 95%CI:4.59, 12.98). Conclusions BMI self-selection may be useful for self-reporting BMI. Clinicians need to be aware of disparities between BMI self-selection at 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.
Highlights
Measuring body mass index (BMI) in large epidemiological studies is problematic as objective measurements are expensive, so subjective methodologies must usually suffice
Self-reported values of weight and height must suffice and time and cost-efficient, have no guarantee of accuracy.[7]. Both misclassification and misperception of weight status arising from BMI calculated from self-reported weight and height is common.[8,9,10,11,12,13]
We know this is at least true in some situations because in our recent study of children, referred to a community weight management programme, we found that parental failure to recognise their child’s overweight or obesity and denial of their child’s weight status was a key factor underlying their lack of engagement in the programme.[16]
Summary
Measuring BMI in large epidemiological studies is problematic as objective measurements are expensive, so subjective methodologies must usually suffice. The conundrum of how to accurately measure body mass index (BMI) in large epidemiological samples has prompted much investigation, in many populations, over many years.[1,2,3,4,5,6,7,8,9] Despite this research, to date, the gold standard for accurate BMI classification is objectively measured weight and height. This is prohibitively expensive and not practical in large studies, due to the high costs involved. Both misclassification and misperception of weight status arising from BMI calculated from self-reported weight and height is common.[8,9,10,11,12,13] We know that selfreported weight is significantly lower than measured weight for both men and women[2,5,8,12] and that selfreported height is significantly higher than measured height in adults.[2,5,8,9] This is problematic because it is an inaccurate measurement of BMI and leads to an overestimation between obesity and various health conditions.[12,14] It is challenging because researchers postulate that correctly identifying oneself as being overweight is a prerequisite to successful weight
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