Understanding BMI

‍What is BMI?

The Body Mass Index (BMI) uses an individual’s height and weight to categorise them broadly into underweight, healthy weight, overweight, and obese categories.¹ It can identify potential future health issues such as type 2 diabetes, high blood pressure or stroke and has been used in various public health policies.²  

BMIs of 25 and over are described as a higher BMI and may cause an individual to be at higher risk of some health conditions, including type 2 diabetes.³

BMI ranges are slightly different for people from South Asian, Chinese, African-Caribbean and black African backgrounds ². Individuals from these backgrounds may be at higher risk of health problems at a lower BMI than people from other ethnicities.²  

BMI for people from South Asian, Chinese, African-Caribbean and black African backgrounds will fit into one of these bands ²:

Is BMI accurate in predicting health?

BMI is a useful tool for estimating body fat and disease risk. However, it has certain limitations because it is dependent on height and weight and does not take into consideration different levels of adipose tissue based on age, physical activity levels and sex. ⁴

This may be an issue for individuals with a higher-than-average level of lean mass, as the BMI results could put them in the overweight or obese categories 4. Similarly, an individual with a higher fat mass could be categorised in the healthy BMI range but may lead a sedentary lifestyle and practice unhealthy dietary habits. ⁴  

If BMI has limitations, then why is it still used?

As a single measure, BMI is not a perfect measure of health, but it can be a helpful starting point. BMI only requires height and weight measurements, so it is a quick and inexpensive way for health care professionals to screen individuals for further assessment. If you have questions about your BMI, please get advice from a healthcare professional.  

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Reference's

1. World Health Organization [Internet]. A healthy lifestyle – WHO recommendations [updated 2010 May; cited 2025 Febuary 19]. Available from: https://www.who.int/europe/news-room/fact-sheets/item/a-healthy-lifestyle---who-recommendations

2. NHS [Internet]. Body mass index (BMI) [updated 2025; cited 2025 February 19]. Available from: https://www.nhsinform.scot/healthy-living/food-and-nutrition/healthy-eating-and-weight-management/body-mass-index-bmi/

3. National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Health Risks of Overweight & Obesity [updated May 2023; cited 2025 February 19]. Available from https://www.niddk.nih.gov/health-information/weight-management/adult-overweight-obesity/health-risks

4. Buss J. Limitations of body mass index to assess body fat.  Workplace Health Saf. 2014 ;62(6):264