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?
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.
National BMI Stats
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.
When discussing health, single measurements - by themselves - are rarely of value. It is important to know other numbers or biomarkers such as: cardiovascular risk from an ApoB test, diabetes risk from an HbA1c test and blood pressure.
And BMI does matter. There are a wealth of studies that look at populations (in the millions), their BMI and risk of chronic illness. (please see examples at bottom of page) In broad terms we can clearly see what the risk is, at what bodyweight / BMI. This has value.
Additionally, are you meeting weekly recommendations for diet, exercise and sleep? How is your stress or work-life balance? These factors (also known as the pillars of health) are the foundations of health, good or bad. Irrespective of testing, they need to be addressed to enjoy lifespan and healthspan.
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.
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.
Stay Healthy,
Alastair
Singapore HealthHub, BMI, info and calculator
UK NHS, BMI calculator
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Related Resources and Studies
Tham KW, Lim AYL, Baur LA. The global agenda on obesity: what does this mean for Singapore? Singapore Med J. 2023 Mar;64(3):182-187. doi: 10.4103/singaporemedj.SMJ-2023-018. PMID: 36876624; PMCID: PMC10071858.
Larsson SC, Burgess S. Causal role of high body mass index in multiple chronic diseases: a systematic review and meta-analysis of Mendelian randomization studies. BMC Med. 2021 Dec 15;19(1):320. doi: 10.1186/s12916-021-02188-x. PMID: 34906131; PMCID: PMC8672504.
Bhaskaran K, Dos-Santos-Silva I, Leon DA, Douglas IJ, Smeeth L. Association of BMI with overall and cause-specific mortality: a population-based cohort study of 3·6 million adults in the UK. Lancet Diabetes Endocrinol. 2018 Dec;6(12):944-953. doi: 10.1016/S2213-8587(18)30288-2. Epub 2018 Oct 30. PMID: 30389323; PMCID: PMC6249991.
Global BMI Mortality Collaboration, Di Angelantonio E, Bhupathiraju ShN, Wormser D, Gao P, Kaptoge S, Berrington de Gonzalez A, Cairns BJ, Huxley R, Jackson ChL, Joshy G, Lewington S, Manson JE, Murphy N, Patel AV, Samet JM, Woodward M, Zheng W, Zhou M, Bansal N, Barricarte A, Carter B, Cerhan JR, Smith GD, Fang X, Franco OH, Green J, Halsey J, Hildebrand JS, Jung KJ, Korda RJ, McLerran DF, Moore SC, O'Keeffe LM, Paige E, Ramond A, Reeves GK, Rolland B, Sacerdote C, Sattar N, Sofianopoulou E, Stevens J, Thun M, Ueshima H, Yang L, Yun YD, Willeit P, Banks E, Beral V, Chen Zh, Gapstur SM, Gunter MJ, Hartge P, Jee SH, Lam TH, Peto R, Potter JD, Willett WC, Thompson SG, Danesh J, Hu FB. Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents. Lancet. 2016 Aug 20;388(10046):776-86. doi: 10.1016/S0140-6736(16)30175-1. Epub 2016 Jul 13. PMID: 27423262; PMCID: PMC4995441.
Aune D, Sen A, Prasad M, Norat T, Janszky I, Tonstad S, Romundstad P, Vatten LJ. BMI and all cause mortality: systematic review and non-linear dose-response meta-analysis of 230 cohort studies with 3.74 million deaths among 30.3 million participants. BMJ. 2016 May 4;353:i2156. doi: 10.1136/bmj.i2156. PMID: 27146380; PMCID: PMC4856854.