How meaningful is the BMI?
Am I too fat, too thin or just right? The answer to this question is provided by the Body Mass Index (BMI). It is considered THE measurement when it comes to assessing our body weight. However, the significance of the body mass index has its limits. You can find out what these are in today's blog post.Table of contents:
- What does the BMI say?
- Why should I even care what my BMI value is?
- What does the BMI not take into account?
- What are the alternatives to BMI?
What does the BMI say?
The body mass index is calculated from the ratio of body weight to height. It is calculated by dividing the weight (in kilograms) by the height (in metres) squared.
BMI = body weight / height2
According to the World Health Organisation (WHO) classification, a person with a BMI between 18.5 kg/m² and 25 kg/m² is considered to be of normal weight.
Why should I even care what my BMI is?
Numerous studies indicate that being overweight is associated with a higher risk of cardiovascular disease. These are the number one cause of death in Germany. The body mass index can therefore be used to draw conclusions about the cardiovascular risk (cardiovascular = affecting the heart and blood vessels). These conclusions are based on epidemiological data. However, people do not always fit into this grid and a BMI in the ideal range does not automatically equate to the highest possible level of health. Exercise, diet, relaxation, stress and genes: body weight is just one of many factors that influence cardiovascular risk.
In their sensational 2013 study, Flegal et al. even came to the conclusion that overweight people (BMI = 25-30) live longer than people of normal weight. However, most experts agree that a body mass index in the normal range is associated with the lowest risk of disease. A study of 190,000 Americans published in 2018 confirms this once again. According to the results, although people of normal weight do not live longer than overweight people (BMI = 25-30), they develop cardiovascular diseases at a later stage. Strokes, heart attacks and heart failure also occurred significantly more frequently in overweight people. With obesity (BMI > 30), the risk of cardiovascular disease increases even more and life expectancy is shortened in this group.
What does the BMI not take into account?
The body mass index is a measure used to assess nutritional status. It is simple and straightforward to use and widely used. But it has its limitations. Individual circumstances such as age, gender or muscle mass are not taken into account. As a result, the BMI is not very meaningful for some people. A major point of criticism: The BMI only takes body weight into account, but not body composition. Whether the weight is due to muscle or fat makes no difference on the scales, but it does make a difference to health. This is because the fat deposits on the stomach are considered to be particularly harmful. A couch potato with a big belly can therefore have the same body mass index as a well-trained athlete, but have a completely different fat and muscle distribution.
You can find out why belly fat is so dangerous and what you can do about it in the blog post "How do you get rid of harmful belly fat?".
What are the alternatives to BMI?
A body composition analysis provides more conclusive results. This provides information about the body's fat and muscle content. Body composition can be determined, for example, by measuring skin folds with a caliper or bioelectrical impedance analysis (BIA). In addition to the fat percentage, the fat distribution also plays an important role. A simple way to keep an eye on this is to measure it with a tape measure. Ideally, the abdominal circumference should be less than 94 cm for men and less than 80 cm for women. The waist-to-hip ratio (WHR) is also often used. Here, the values for women are ideally below 0.85 and for men below 1.
WHR = waist circumference (in cm) / hip circumference (in cm)
The body mass index has its limits and only serves as a guideline and quick assessment. In addition to weight, you should also keep an eye on harmful abdominal fat. If you also regularly check your blood pressure and blood lipid levels, you will further reduce your cardiovascular risk.
- S. Khan et al. Association of Body Mass Index With Lifetime Risk of Cardiovascular Disease and Compression of Morbidity. JAMA Cardiol. 2018;3(4):280-287.
- M. Flegal et al. Association of All-Cause Mortality With Overweight and Obesity Using Standard Body Mass Index Categories A Systematic Review and Meta-analysis. JAMA. 2013;309(1):71-82.