What is Body Mass Index (BMI)?
It is very unlikely that you will have lived your life without ever having your Body Mass Index (BMI) calculated. Whether you have measured it yourself, or had it recorded at a routine doctors appointment; BMI has become a vital tool in determining a person’s overall health status.
How is BMI calculated?
BMI uses height and weight to provide an estimate of a person’s body fat:
weight in KG
height in metres2
What does it mean?
So once you have been given your BMI value, what does it actually mean? And, how is it used as a measure of obesity?
Doctors classify people according to their BMI; for most adults (male and female):
- BMI < 16.5 – severely underweight
- BMI < 18.5 – underweight
- BMI 18.6-24.9 – normal weight
- BMI ≽ 25 – overweight
- BMI ≽ 30 – obese. BMI 30-34.9 – obese class I;
BMI 35-39.9 – obese class II;
BMI ≽ 40 – obese class III.
The classifications for Asian and South Asian populations are slightly different, as using the standard cut offs for people from these regions would underestimate the risk of obesity-related health problems. In Asia and Southern Asia:
- BMI 23-24.9 – overweight
- BMI ≽ 25 – obese.
The other exception to the rule is with regards to children. A child’s BMI can be calculated using the same equation, but age and gender are both taken into account. For children, the determination of whether they are a healthy weight is dependent on where they fit percentile-wise, according to their gender- and age-matched peers:
- BMI <5th percentile – underweight
- BMI >95th percentile – overweight.
Why is BMI important?
There is a worldwide obesity crisis. The World Health Organisation (WHO) estimates that globally 604 million adults are obese and, with lifestyles becoming more sedentary and people relying more on carbohydrate-rich, processed foods and calorie laden fast food; it is a problem that will not be rectified any time soon.
Within the Middle East, obesity levels are continuing to rise and certain member states of the Gulf Cooperation Council (GCC) have amongst the highest rates of obesity in the world. In the UAE 37% of the population are obese, in Kuwait 40% are, and in Qatar as many as 42% are. The reasons for these high rates are thought to be multifactorial, encompassing genetic susceptibilities, poor lifestyle choices and cultural behaviours. For example, the rates of obesity in women of the GCC are noticeably higher than for women in other parts of the world. In the region there is great emphasis put on childbearing , during which time women are encouraged to take a less active role. In general, it can be more difficult for women in this part of the world to publicly exercise and these women may have fewer sports opportunities than their Western counterparts.
With increased obesity comes rising healthcare expenses. Obesity is strongly associated with other serious health issues, including type 2 diabetes, hypertension and cardiovascular problems. It can also cause fertility issues and increase the risk of developing certain types of cancer. All of which place a financial burden on the region’s economies.
As such, preventing obesity has become a major driver of the healthcare community at large. Using a patient’s BMI can enable doctors to establish the extent of the issue. Furthermore, working on reducing the value to within the normal range can be a tangible treatment outcome. It must be considered that whilst obesity can be a side effect of other medical conditions, including PCOS, hypothyroidism and hypogonadism, or a consequence of certain medications; most cases are due to poor lifestyle choices. Thus, adopting better choices can, over time, improve quality of life and lower BMI.
What are the problems with using BMI?
BMI is widely used and, in the majority of cases, fairly accurate at depicting whether a person is of a healthy weight or not. However, there are exceptions to the rule. In those with high muscle mass, such as elite sportspeople or body builders, calculating BMI is likely to categorise them as obese. In these cases, taking an individual approach is worthwhile as quite obviously this subgroup of people will not be exposed to the same health risks as those who are genuinely obese.
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- “Calculate Your BMI – Standard BMI Calculator.” National Heart Lung and Blood Institute, U.S. Department of Health and Human Services, https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm.
- CONFRONTING OBESITY IN THE MIDDLE EAST: Cultural, Social and Policy Challenges. The Economist, Oct. 2016, https://eiuperspectives.economist.com/sites/default/files/ConfrontingobesityintheMiddleEast_0.pdf.
- Weir, C B, and A Jan. BMI Classification Percentile And Cut Off Points. StatPearls Publishing, 2019, https://www.ncbi.nlm.nih.gov/books/NBK541070/.
- “What Is the Body Mass Index (BMI)?” NHS Choices, NHS, https://www.nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi/.