Calls to scrap BMI over eating disorder concerns – is it an accurate measurement?

The use of body mass index (BMI) to determine whether an individual's weight is healthy should be scrapped due to concerns it contributes to eating disorders, according to an MP report.

The Women and Equalities Committee has warned the use of a person's BMI by medics to decide whether the individual should be put on a weight loss or gain programme can lead to issues like anorexia and poor mental health.

BMI "inspires weight stigma" while "disrupting people's body image", argues the committee.

It recommends Public Health England focuses on a "health at every size" approach that takes into account differences in people's age, sex and ethnicity.

Read more: Overweight people are coronavirus superspreaders

The new approach should also highlight healthy lifestyle choices, rather than focusing on correcting a person's weight, adds the committee.

"This past year has been particularly difficult for those affected by eating disorders, with Beat's helpline alone delivering 100,000 support sessions and seeing a 302% increase in demand," said Tom Quinn, from the eating disorder charity.

Scientists from Anglia Ruskin University previously revealed coronavirus lockdowns may be linked to a rise in eating disorder symptoms.

Read more: Why are obese people more at risk of coronavirus?

"BMI should never be used as the sole factor in diagnosing eating disorders or for determining who is 'unwell enough' to access treatment," added Quinn.

"This can lead to potentially dangerous delays and drive people deeper into eating disorders in order to be taken seriously."

What is BMI?

A person's BMI is calculated by dividing their weight in kilograms by their height in metres squared.

A healthy BMI for most adults is considered to be between 18.5 and 24.9. Below 18.5 is underweight, 25 to 29.9 overweight, and 30 or above obese.

Among adults, BMI does not traditionally take into account an individual's age or sex, which is considered when assessing a child's weight.

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The NHS' BMI calculator, however, asks a user's age, sex, ethnicity and activity level in order to "personalise" the results.

Non-white people have a higher risk of certain conditions, like type 2 diabetes. Among these adults, a BMI of 23 or above poses an "increased risk", while 27.5 or more constitutes a "high risk".

Watch: Obesity rising among children amid pandemic

Is BMI an accurate measurement?

BMI is generally considered a good rule of thumb, however, it has some shortcomings.

For a start, it fails to take into account where excess weight is distributed on the body.

Carrying too much fat around the abdomen – an "apple" physique – has been linked to heart disease, type 2 diabetes and strokes.

This may be better assessed by measuring someone's waist. This measurement can be carried out by wrapping a tape measure midway between the bottom of the ribs and top of the hips, breathing out before noting the reading.

Regardless of height or weight, a waist size of 94cm (37 inches) or more in men, or 80cm (31.5 inches) in women, should encourage healthy weight loss, according to the NHS.

A reading of 102cm (40 inches) in men or 88cm (34 inches) in women, or more, puts a person at "very high risk".

Waist measurements are not generally recommended for children because they do not account for their height. A youngster's BMI may also be expressed as a "centile", which describes how their frame compares to children in national surveys.

BMI also fails to differentiate between the weight of fat and that of muscle or bone. Muscular athletes may therefore be classed as "overweight" or even "obese", despite their body fat being low.

Adults who naturally lose muscle with age may also measure as having a healthy BMI, but carry excess fat.

BMI increases during pregnancy, with women being advised to use their pre-pregnancy weight when taking the measurement.

The NHS stresses: "If you have an eating disorder, the BMI calculator results do not apply. Please get further advice from a GP.

"Apart from these limitations, the BMI is a relatively straightforward and convenient way of assessing someone's weight," it added.

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