BMI should be preferred option when checking adolescent weight

BMI should be the preferred option when assessing weight in adolescents with eating disorders, US researchers say.

Clinicians also should refer to body weight as being ‘expected’ rather than ‘ideal’ to avoid unrealistic expectations in patients, the University of Chicago team suggest.

Exact determination of expected body weight for adolescents is ‘critical’ for accurate diagnosis and management of eating disorders such as anorexia and bulimia, they argue.

The researchers assessed almost 400 adolescents seeking treatment for an eating disorder. The trial took into account weight, height, age, gender, ethnicity and diagnosis.

They looked at BMI, the McLaren method and the Moore weight assessment methods. Both the McLaren and Moore methods presented limitations when dealing with extreme height and weight measurements, the researchers found.

The BMI method revealed the fewest limitations and could be applied to children and adolescents of all ages, heights and weights.

Dr Damian Wood, paediatrician at Nottingham Children’s Hospital, specialises in eating disorders and is chair of the RCPCH young people’s group. Dr Wood helped lead a similar study in the UK which came up with the same result.

He said: ‘Nobody has come up with a perfect method, so for the time being BMI is the best measure we’ve got.

‘If you’re a parent or a patient you want to know how serious the eating disorder is and how close to recovery you are.’

BMI measures the percentage weight for height, which is simple for people to understand.

Dr Wood is concerned that GPs are not routinely plotting growth in young people, either because they do not have enough time or don’t have access to a BMI chart.

‘For improved diagnosis and treatment of eating disorders this does require a shift in practice for GPs,’ he said. ‘It is so important that we use a common language and a standard method so that there is no confusion.’

Dr Laurel Edmunds, a child and adolescent weight management at the University of Oxford, said BMI was easily measured but may not be any more accurate in terms of diagnosing eating disorders. 'It is a rather crude measure applied to a scale which disguises the amount of body fat a patient has.’

The Royal College of Psychiatrists have been working on a new set of guidelines for eating disorder patients, called Marsipan, after NICE guidance was criticised for neglecting treatment in young people and adolescents.

The new guidelines are expected to be published early this year.

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