Body Mass Index is Dogsh*t? Understanding the Strengths and Weaknesses of BMI Measurement.

Alastair Hunt
Jun 4, 2024
7 min read

Updated: 6 days ago

A recent Netflix health documentary, You Are What You Eat, used an advanced test - a DEXA scan - to measure the fat and muscle mass of study participants. The provider of the test confidently stated that the popular weight / health measure Body Mass Index (BMI) is "dogshit". Is this true?

As ever, please talk to your doctor or medical practitioner most familiar with your medical history before implementing any changes in diet, exercise or lifestyle, especially if you are under treatment.

BMI Limitations

Apart from considering that the person who made the statement... runs a DEXA scan centre, there certainly are limitations to using BMI as a measure of health in isolation. But most healthcare professionals or interested members of the public are aware of these. For example:

Someone with a high muscle mass, a strength athlete or body builder, will appear to have a higher (unhealthier) BMI than the number alone suggests. Conversely, BMI may underestimate body fat in the elderly and others who have lost muscle mass.
BMI numbers differ according to race. Asians have a lower BMI cut off points than Caucasians. This can be accounted for when interpreting the results. Many online BMI calculators will do this for you.
BMI does not account for where body fat is distributed. A waist-to-hip ratio measurement can calculate this.
BMI does not measure or account for bone density.

Worth a strong mention, waist circumference is a valuable tool for health risk assessment.

National BMI Stats

In Singapore, using the BMI cut-off reflecting the health risk of excess adiposity in Asians (in 2020) 58% of adults in Singapore were living with an unhealthy weight (BMI ≥23), 21% having obesity (BMI ≥27.5).

The Health Survey for England 2021 estimated that 26% of adults in England are obese (BMI ≥30) and a further 38% are overweight (BMI ≥25) but not obese.

One fact that sometimes gets lost in translation is that it is easy to think of being overweight as simply a number, and living with it. The truth is that being overweight is linked to a number of chronic illnesses and increased risk of mortality. An indication of an unhealthy lifestyle that can affect not only longevity but also healthspan.

What is a 'Healthy' BMI?

A 2016 meta-analysis of 230 cohort studies with 3.74 million deaths among 30.3 million participants (aune et al) concluded that:

"both overweight and obesity increases the risk of all cause mortality with a J shaped dose-response relation, and the nadir of the dose-response curve seems to be in the BMI range of 23-24 among never smokers and 22-23 among healthy never smokers. With longer duration of follow-up the nadir of the dose-response curve is in the BMI range of 20- 22.

There is some evidence of increased mortality in underweight people, but we cannot exclude the possibility that this could partly be because of residual confounding from prediagnostic disease."

Update

A recent study, Aryee et al, of US adults aged 20 to 59 found that nearly all individuals classified as obese by BMI (98%) also had confirmed excess adiposity, supporting BMI’s reliability as a population-wide screening tool. While exceptions such as athletes exist, they represent a very small minority. Confirming adiposity with methods like DEXA scanning is often impractical in clinical settings due to cost, accessibility and potential for overestimation.

An increasingly validated technique (especially with Asian populations) has recently been promoted as being more accurate than BMI, the body roundness index. This is a promising and simple to calculate measure that uses waist circumference (visceral fat) in relation to height. Those with a high waist-to-height ratio carry more weight around their middle, often described as an “apple” shaped body. Learn how to measure waist-to-height ratio here. Another similar measurement that can also taken at the clinic or at home is the waist-to-hip ratio, learn more here.

Final Thoughts

By all means, if a DEXA scan is within your budget, get a DEXA scan. Body composition matters and the information it provides is valuable. In Singapore the price is approx S$300 (US$220) .

If your BMI is high, are you familiar with your other health markers?

BMI is by no means "dogshit". It is a key measure of health and risk, with some generally well understood limitations. It is also free, providing that you have a set of weighing scales and know your height.

Understanding how to properly measure one's weight is also important and discussed here.

For most people improving health - achieving a healthy weight - is about finding motivation and prioritising self-care with an ultimate goal of taking action. If you want to take effective and targeted steps that fit into your unique lifestyle, The Whole Health Practice is here to help.

Improving health is about finding motivation, prioritising self-care and taking action. If you want to take effective and targeted steps that fit into your unique lifestyle, The Whole Health If your interest is weight loss, healthspan and longevity, to beat chronic illness or to enhance your mental health and wellbeing, our consultations and programs deliver results that are customised to your needs.

FOUNDATIONS - our premier whole person health consult - identifies and prioritises the key factors, known and unknown, that affect health and wellbeing. It provides targeted recommendations tailored to you, the individual, and your unique lifestyle.

Stay Healthy,

Alastair

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Related Resources and Studies

News: AMA adopts new policy clarifying role of BMI as a measure in medicine

The Health Survey for England 2021

Aryee EK, Zhang S, Selvin E, Fang M. Prevalence of Obesity With and Without Confirmation of Excess Adiposity Among US Adults. JAMA. Published online April 17, 2025. doi:10.1001/jama.2025.2704

Kong Y, Luo Q, Zhang Q, Wei Q. Association of the body roundness index with new-onset cardiovascular disease in middle-aged and older adults with and without diabetes: evidence from the China Health and Retirement Longitudinal Study. Diabetol Metab Syndr. 2025 Apr 28;17(1):142. doi: 10.1186/s13098-025-01705-9. PMID: 40296132; PMCID: PMC12036263.

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