BMI and its limitations
BMI and its limitations
While Body Mass Index (BMI) is a widely used measure for assessing weight status and obesity, it has several limitations when used to assess the weight of an individual. It does not take into account factors like body composition, muscle mass, and distribution of fat, which can affect its accuracy in determining an individual’s health risk. When assessing an individual’s weight in your clinic it is important to consider how these metrics affect your treatment decision and use BMI as only a starting point before further investigation.
As BMI solely considers weight relative to height and doesn’t differentiate between muscle and fat, individuals with a high muscle mass may be classified as overweight or obese, even if they have a low body fat percentage, which is not indicative of health risk.1 Consider using a body fat scale or even a Dexascan to provide more detailed information for the patient.
Central obesity or visceral fat (fat around the organs near the waist) is associated with a higher risk of health problems, including cardiovascular disease and diabetes. However BMI doesn’t differentiate between central and peripheral fat so the patient’s risk may be misjudged based solely on BMI. 2
BMI doesn’t consider changes in body composition that can occur with age and hormonal changes therefore BMI may not be equally relevant for men and women. 3 BMI’s accuracy in assessing health risk varies among different populations, such as older adults and athletes. It also may not be an appropriate measure for these groups. Please see the table below for BMI classification for the Asia Pacific population. 4
| World Health Organization classification (BMI) | Asia-Pacific classification (BMI) | |
| Underweight | <18.5 kg/m2 | <18.5 kg/m2 |
| Normal weight | 18.5 – 24.9 kg/m2 | 18.5 –22.9 kg/m2 |
| Overweight | 25 – 29.9 kg/m2 | 23 – 24.9 kg/m2 |
| Obese | >30 kg/m2 | >25 kg/m2 |
References
- Gallagher, D., Heymsfield, S. B., Heo, M., Jebb, S. A., Murgatroyd, P. R., & Sakamoto, Y. (2000). Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. The American Journal of Clinical Nutrition, 72(3), 694-701.
- Després, J. P., Lemieux, I., & Prud’homme, D. (2001). Treatment of obesity: need to focus on high risk abdominally obese patients. BMJ, 322(7288), 716-720.
- Heo, M., Faith, M. S., Pietrobelli, A., & Heymsfield, S. B. (2012). Percentage of body fat cutoffs by sex, age, and race-ethnicity in the US adult population from NHANES 1999-2004. The American Journal of Clinical Nutrition, 95(3), 594-602.
- Romero-Corral, A., Somers, V. K., Sierra-Johnson, J., Thomas, R. J., Collazo-Clavell, M. L., Korinek, J., … & Lopez-Jimenez, F. (2008). Accuracy of body mass index in diagnosing obesity in the adult general population. International Journal of Obesity, 32(6), 959-966.
- Lim JU et al. Int J Chron Obstruct Pulmon Dis. 2017;12:2465–2475. 2. NICE. Public health guideline PH46 – BMI: preventing ill health and premature death in black, Asian and other minority ethnic groups. 2013
- Dietz, W. H. (1998). Health consequences of obesity in youth: childhood predictors of adult disease. Pediatrics, 101(3), 518-525.