What is the BMI?
BMI (Body Mass Index) is one of the simplest methods of assessing the degree of obesity. Based on it, it is possible to determine the correct body weight for a person. The index was developed in 1832 by a Belgian mathematician, astronomer and statistician Adolphe Quetelet, and since then doctors, researchers and dieticians have used it as a criterion for obesity in an individual [1].
However, the method has some drawbacks: it will not indicate the percentage of body fat or how much fat there is in a particular body part. In 1993, the WHO established an Expert Consultation Group to develop uniform BMI categories.
As a result, four were created:
- underweight <18.5;
- normal range 18.5-24.9;
- overweight 25-29.9;
- obese ≥30.
Various degrees of obesity were added in 1997:
- pre-obese 25-29.9;
- obese (class I) 30-34.9;
- obese (class II) 35-39.9;
- obese (class III) ≥40.
Obesity as a global problem
According to researchers, the general population has seen an increase in BMI over the past few decades, which means we are facing an epidemic of obesity [2]. According to the National Health Fund (NFZ), one in four people in Poland is obese, and three in five Poles are overweight [3]. That’s why it is so important to strive for proper body weight: excess weight is the cause of many diseases, with diabetes as the leading one (more than 400,000 people in our country get it every year).
What is the formula for calculating the BMI?
It can be represented most simply by the following equation:
BMI = body weight (kg)/height (m)2
So we need two pieces of data: height (always given in metres, so, for example, 170 cm is 1.7 m) and weight (in kilograms). For example, a person weighing 60 kg and 160 cm tall calculates BMI as follows:
60 / 1.6 squared, and so 60 / 2.56 = BMI 23.4
You can also use online BMI calculators to make this calculation.
Disadvantages of the BMI
You can calculate your BMI yourself, but remember: such a diagnosis will not fully determine what your health condition is. It is also no substitute for professional medical tests and consultation with a specialist doctor or dietician. As we mentioned at the beginning: BMI does not differentiate between fat content and the amount of muscle and water in the body, and will not take into account the distribution of body fat. It’s also worth knowing that people with extensive muscle tissue will likely have a high BMI, because muscles “add” weight despite having little body fat.
What instead of the BMI?
To accurately determine the distribution of body fat, a better criterion would be WHR, or waist-to-hip circumference ratio. It helps determine how fat is distributed in the body. It is easy to calculate: measure the circumference of the waist and hips, and then divide the results by each other. The normal WHR for women is less than 0.8, and 1.0 for men.
In addition to this, you can undergo professional medical tests, such as dual-energy X-ray absorptiometry (DXA), which can diagnose visceral obesity. A CT scan will give similar results – and of course, you should consult your doctor.
When to use the BMI?
BMI is a very simple method that anyone can use. However, if you suspect that your BMI is above the norm, don’t hesitate to seek professional advice from a specialist. Let the self-calculation of this indicator motivate you to sign up for an appointment and take the right steps to achieve normal body weight.
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Sources:
[1] [2] Nuttall FQ. Body Mass Index: Obesity, BMI, and Health: A Critical Review. Nutr Today. 2015 May; 50(3):117-128. doi: 10.1097/NT.0000000000000092. Epub 2015 Apr 7. PMID: 27340299; PMCID: PMC4890841.
[3] Obesity – A Heavyweight Disease, https://www.nfz.gov.pl/aktualnosci/aktualnosci-centrali/otylosc-choroba-wagi-ciezkiej,7355.html, accessed on: 02.01.2023.