GPs urged to weigh patients to correctly identify obesity

GPs should weigh patients to establish their true weight and BMI, researchers have warned, following studies that show the majority of GPs and trainees systematically underestimate patients' weight.

Obesity: GPs struggle to classify obese patients by sight
Obesity: GPs struggle to classify obese patients by sight

NICE guidance recommends that GPs ‘routinely’ raise the issue of weight loss for overweight and obese patients, even during unrelated appointments. But, according to a Liverpool study, it is difficult to assess BMI on sight alone, meaning such discussions are not commonplace in practice.

The study, published in the British Journal of General Practice, presented 315 GPs and trainee GPs with 15 photographs of males aged 18-30. The subjects were evenly split between being of a healthy weight, overweight and obese, with BMIs ranging from 19.4 to 34.4.

The GPs, 248 of whom were trainees, correctly identified eight out of the 15 photographs in the right BMI category, on average. But whereas 80% of the healthy individuals tended to be correctly categorised, just 48% of the overweight and 34% of the obese patients were classified correctly.

When asked to estimate the subjects’ BMIs, the GPs also tended to underestimate the figures. On average, GPs estimated an obese person with a BMI of 30 as being 27.58 – which would classify them as overweight instead.

Must weigh patients

The researchers suggested that a failure to recognise patients as obese may explain lower levels of GP intervention. While the true prevalence of obesity in the UK is close to 25%, prevalence as recorded in GP records is just 10%.

They said: ‘It is not usual to think of estimating BMI by sight as a core clinical skill. It is, after all, accurately assessed by weight and height measurement, which takes less than a minute. For GPs to do this, however, they have to start talking to the patient about weight, and assessing that they may have a significant weight problem is an important cue for that discussion.

‘The present work suggests that a sample of predominantly trainee GPs had poor visual perception of weight status and underestimated weight of overweight and obese males. This was also true for the fully-qualified GPs who participated in the study. It is important that healthcare professionals do not rely solely on visual judgements when identifying patients who may benefit from weight management treatment.’

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