Waist circumference-to-height ratio could replace body mass index (BMI) in children and adolescents after a new study found that it was an inexpensive and accurate way to measure childhood obesity.
Researchers at the University of Exeter, who led the study, found that waist circumference-to-height ratio was preferable to BMI assessment for detecting excess fat in children and adolescents.
The new measurement can make it easier for parents and caregivers to assess childhood weight quickly and easily, enabling timely interventions for obese children.
The findings published in Pediatric Research could be critical in updating future childhood obesity guidelines and policy statements.
Obesity affects almost one in four children and adolescents in the UK. It is associated with the development of cardiovascular, metabolic, neurological, and musculoskeletal diseases, as well as premature death later in life. BMI is calculated using weight-to-height ratios for each sex to diagnose obese children. BMI measurements do not distinguish between fat and muscle mass, making them inaccurate tools for measuring childhood and adolescent obesity.
Using data from the Avon Longitudinal Study of Parents and Children (ALSPAC) UK birth cohort, the researchers examined weight-related data from 7,237 (3,667 females) nine-year-old children over a 15-year period, making it the largest and longest study of its kind in the world.
BMI and waist circumference-to-height ratio were measured at ages nine, 11, 15, 17, and 24. The total fat mass (FM) and trunk FM were measured with Dual-Energy X-ray Absorptiometry (DEXA) scans, a method used to measure body composition, at ages nine, 11, 15, 17, and 24. BMI and waist circumference-to-height ratio (WHtR) were computed and compared against DEXA-measured body composition.
Using the waist circumference-to-height ratio, the researchers found that fat mass was up to 15 per cent higher and muscle mass was 25 per cent lower than when measured using BMI.
Boys with waists more than 53 per cent of their height and girls with waists more than 54 per cent of their height are likely to have excess fat. The waist size to height ratio was the most accurate way to assess whether a child had excess body fat, with excess fat detected correctly in eight out of ten boys and seven out of ten girls when compared with excess DEXA-measured fat. The method also correctly identified 93 out of 100 boys and 95 out of 100 girls who do not have excess fat.
BMI measurements were found to be highly consistent with DXA-measured muscle mass, but it was difficult to specify whether BMI measures excess fat or muscle mass.
Recently, the American Academy of Pediatrics (AAP) published a clinical guideline on childhood obesity and requested urgent research on inexpensive and accurate alternative measures of obesity. The DEXA scan is expensive and not readily available in primary health care centres in the UK, and the researchers hope that their findings may be a useful alternative measure.
Dr Andrew Agbaje from the Children’s Health and Research Centre at the University of Exeter said: ‘This study provides novel information that would be useful in updating future childhood obesity guidelines and policy statements. Unlike BMI, the average waist circumference-to-height ratio in childhood, adolescence, and young adulthood does not vary with age and among individuals – which is why it might be preferable to BMI assessment in children and adolescent clinics as an inexpensive tool for detecting excess fat.’
He added: ‘It also means parents can easily and quickly confirm whether an increase in their child’s BMI or weight is due to excess fat by examining their child’s waist circumference-to-height ratio.’
