Blue measuring tape on glass weighing scale

On 22 April 2021, Lord Addington (Liberal Democrat) is due to ask the Government “what assessment they have made of the effectiveness of Body Mass Index as a medical guideline”.

What is Body Mass Index (BMI)?

The Body Mass Index (BMI) is a measurement used internationally to determine “healthy weight” levels by dividing a person’s weight in kilograms by their height in metres squared. The NHS says that this calculation gives a healthy weight range for a particular height, which accounts for variations in body shape. The BMI calculation used for children also takes age and gender into consideration.

The NHS says that an ideal BMI for adults is between 18.5 and 24.9. A BMI:

  • below 18.5 is classed as underweight;
  • between 25 and 29 is classed as overweight; and
  • between 30 to 39.9 is classed as obese.

How effective is BMI as a medical guideline?

The Royal College of Nursing has said that the BMI measure is the same for males and females of all ages, and as such is the most useful population-level indicator of excess weight and obesity. It said that while specific links between obesity and poor health are difficult to assess, excess weight increases an individual’s risk of developing health problems, such as heart disease, type 2 diabetes and respiratory problems.

However, BMI does not distinguish between muscle mass and excess fat. The NHS has said that, as muscle is denser than fat, BMI is not an accurate guideline to use for very muscular people, such as athletes or weight trainers, who could be classed as ‘obese’ but who are fit and healthy. However, the BBC has said that this is thought to affect fewer than 1% of the population. BMI is also not an accurate guideline for pregnant people.

In addition, in 2004, the World Health Organisation (WHO) concluded that the cut-off points for BMI measurements used internationally were “probably not appropriate” for Asian populations. It said that Asian people may be at a higher risk of type 2 diabetes and cardiovascular disease even within a ‘healthy’ BMI classification. Due to a lack of data, the WHO did not redefine the BMI thresholds, but it did suggest some additional health action points for health practitioners to follow in relation to Asian populations. In its assessment, the WHO did not consider other non-white populations.

Researchers from the University of Bristol have argued that BMI is a “good starting point”, as it can give a “rough estimate of disease risk” in a person. However, they have said that it should be used in addition to other measurements, such as lifestyle factors, blood pressure, blood sugar, blood cholesterol levels, and waist circumference measurements, in order to establish a complete picture of an individual’s health.

What recent criticism of BMI has there been?

In its recent report, Changing the Perfect Picture: an Inquiry into Body Image, published on 9 April 2021, the House of Commons Women and Equalities Committee criticised the use of BMI as a measure of health. It said that it had received evidence from people with a higher BMI who felt health professionals were more likely to diagnose their complaints as weight-related, rather than investigate fully. In its summary of the report, the committee said:

We have been hugely saddened to hear of the number of people who have faced appearance and weight-based discrimination when accessing NHS services. The use of BMI inspires weight stigma, contributes to eating disorders, and disrupts people’s body image and mental health. Public Health England should stop using BMI as a measure of individual health, and instead focus on a ‘Health at Every Size’ approach.

In an oral evidence session to the committee, the Minister of State for the Department of Health and Social Care, Nadine Dorries, said that the Government keeps the use of BMI “constantly under review, because we know that doctors, and GPs particularly, have an over-reliance on BMI as an indicator of whether or not somebody has an eating disorder”. The Government’s full response to the report is expected by 9 June 2021.

Similar concerns were raised in the House of Commons chamber during a debate about a women’s health strategy in March 2021. Dr Lisa Cameron, Shadow SNP spokesperson for mental health, said that:

Young women disproportionately struggle to be referred for treatment due to an antiquated medical model based on body mass index to identify eating disorders, rather than on a psychological model, treating the whole person.

In response, Nadine Dorries said that the Government had allocated funding to eating disorder assistance and that it was committed to helping young women with their mental health and eating disorders. In January 2020, in response to a question on the diagnosis of eating disorders, Ms Dorries referred to NICE’s [National Institute for Health and Care Excellence] guideline on eating disorders as stating:

Recognition and treatment makes it clear that a person’s body mass index is just one of the factors that should be taken into account to determine whether to offer treatment for an eating disorder, but that it should not be used on its own.

In a recent Huffington Post article, Sabrina Strings, an assistant professor at the University of California, said that the BMI scale was initially created using data from “predominantly European men”. Due to this, she argued it should not be used in determining health outcomes for women or non-white people, as they were not part of the initial clinical study.

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Cover image by Vidmir Raic on Pixabay.