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A Piece of String is Better to Check for Body Fat than BMI

By Magdeline Lum

Body Mass Index may not be the best measure of obesity and risk of cardiovascular disease.

New research published at this year’s European Congress on Obesity in Prague suggests that a piece of string can provide a more accurate measure of weight gain than the Body Mass Index (BMI). Currently most doctors use BMI to determine whether a patient is at risk of disease, but the use of BMI is becoming contentious as there is evidence that it can overestimate the danger posed to people who have a large muscle mass or a heavy bone structure.

Dr Margaret Ashwell of Oxford Brookes University, who led the study, has found that using a person’s waist-to-height ratio is a better predictor of a person’s risk of obesity and cardio­vascular disease. Previous work by Ashwell has demonstrated that using only BMI and ignoring other measures of obesity, like the waist-to-height ratio, resulted in an incorrect classification of 10% of the UK population. More than one-quarter of these people were deemed to be of normal weight and not at risk. Many global studies have also concluded that a person is at lower cardiovascular risk if they keep their waist measurement to less than half their height measurement.

The results in this latest study showed that from a cohort of 2917 people aged 16 years and over, 12% of the total population would be missed by BMI screening, and over one-third of those classified as “normal” by BMI have a waist-to-height ratio exceeding 0.5. These could be called non-overweight “apples”: people who have a lot of fat around the waist but not a high BMI.

The authors concluded: “This study not only supports our previous findings on the superiority of waist-to-height ratio over BMI as a primary screening method for mor­bidity and mortality risk, but also demonstrates the potentially severe im­plications of misclassification by BMI alone in screening for cardiometa­bolic risk factors. Checking that waist-to-height ratio is less than 0.5 could not be simpler: all that is needed is a piece of string, not even a tape measure.”

Minimal training and resources is all that is needed with the measuring of the weight-to-height ratio. What is needed is to take a piece of string to measure the height and fold it in half to see whether it fits around the waist of the patient. The authors also believe that this is a more efficient means of first-stage screening for the health risks of obesity.

The authors of the study also hope that this will provide an impetus for medical practitioners to consider measuring weight-to-height ratio when determining the health risks associated with obesity.

“We would like to show that waist-to-height is not only superior to BMI in first-stage screening for the health risks of obesity but is also more efficient in practice and can be done by personnel with minimal training and resources.”