Is body mass index (BMI) still relevant?
Published 15 Apr 2021 • By Clémence Arnaud
Weight has become something to monitor very closely to avoid the onset of health conditions related to being overweight or obese, but also to monitor body mass in case of anorexia or malnutrition.
What is body mass index exactly? What are its limitations? Is it still relevant today? What other parameters come into play?
We tell you everything in our article!
Body mass index (BMI): definition
Body mass index or BMI is a tool for calculating an individual’s body fat based on his or her height and weight.
Formula: BMI = weight (pounds) / [height (in)]2 x 703
BMI = weight (kg) / [height (m)]2
According to data from the World Health Organisation (WHO) in 2004, there are 6 different nutritional statuses which have not changed since:
- Below 18.5: Underweight
- Between 18.5 and 24.9: Normal weight
- Between 25 and 29.9: Overweight
- Between 30 and 34.9: Obesity class 1
- Between 35 and 39.9: Obesity class 2
- Over 40: Obesity class 3
BMI was developed as a risk indicator and is correlated with an individual's fat mass. The higher the BMI, the higher the risk of developing certain health conditions (diabetes, high blood pressure, etc.).
As mentioned earlier, the body mass index is used to diagnose weight issues or obesity. Otherwise, it is also used as a criterion for the diagnosis of anorexia.
It is mainly used in adults but can sometimes be used in children or adolescents.
BMI is a tool used by doctors in particular, but can be used by anyone. It was developed in the 19th century and has some limitations, especially in cases of excess weight or obesity.
BMI: Criticism and limitations
Though BMI has been a standard health assessment tool for health practitioners for years, it has received significant criticism of late, from those who find that it oversimplifies the definition of being "in good health".
The BMI formula was developed by Lambert Adolphe Jacques Quetelet, a Belgian mathematician, in 1832 to quickly estimate a given population's degree of overweight and obesity to help governments in allocating health and financial resources. Quetelet himself indicated that BMI was not useful for studying individuals, but rather for giving an overall view of a population's health.
A key "flaw" in BMI is that the calculation does not take into account a person's body fat versus muscle (lean tissue) content. Because it is denser, muscle weighs more than fat, therefore the BMI will classify someone who is athletic and/or has a lot of muscle as more overweight than he or she really is. BMI also does not take into account where fat is stored on the body, when research has found that fat stored around the stomach area places one at higher risk for chronic illness than fat stored in the hips, thighs and buttocks.
Similarly, though men and women have varying body compositions (men usually have more muscle mass and a lower fat mass than women), BMI uses the same calculation for both sexes.
Frequently, many people with a high or low BMI are in good health and contrarily, many people with a normal BMI are unhealthy. For example, a person with a normal BMI who smokes and has a family history of cardiovascular issues may be at higher risk of cardiovascular disease than someone who has a high BMI but is in good physical shape and is a non-smoker.
BMI only considers an individual's height and weight as a measure of their health, instead of them as an individual. A person's age, sex, race, body composition, medical history and a number of other factors can have a role in a person's weight and health status.
Other parameters to be taken into account
On its own, BMI is not reflective of the full picture of a person's health. Therefore it is important to look other parameters when analysing one's health.
Family health history: It is important to take note of a person's family health history. Does the person have a predisposition for certain health conditions that may affect or be dependent on his or her weight? Are there any lifestyle changes that can be put in place to help them improve their health?
Waist circumference: This measurement shows how much fat is stored around the abdomen. As mentioned previously, research has shown that fat stored in this area can have many consequences on health. It has been linked to the risk of developing cardiovascular conditions or other chronic illnesses such as diabetes or lipid problems (hypertriglyceridemia, high cholesterol, etc.).
Nutritional habits: Many questions can help make an initial nutritional assessment. Some questions include:
- Do you often feel the urge to eat? Do you often snack between meals?
- Are you full at the end of a meal?
- What are your mealtime habits? How long does a meal last? Do you eat alone, with your family, in a group? At home or in a restaurant? Standing or sitting?
- How many meals and snacks do you eat per day?
- What foods do you eat most regularly?
- Do you drink alcohol? If so, how much and how often?
It is very important to follow a balanced diet, because even when it is well respected, a person can still be overweight or obese. This is a very important criterion to take into account in these situations, because a balanced diet contributes to limiting cardiovascular risks or problems with diabetes or cholesterol.
Sex: It is important to take into account the person's biological sex, as it may have an impact on their body composition and metabolism.
Physical activity: Physical activity is very important to limit weight issues as well as the development of metabolic conditions such as those mentioned above. A doctor may ask a few of the following questions to assess the level of physical activity:
- Do you practice any physical activity? What kind and how often? What is your professional activity?
- How much time do you spend every day without physical activity: sitting, standing without walking or in front of a screen?
As an independent measure, BMI is clearly not a perfect or completely accurate measure of health. But, when used in combination with other measures it can be a good starting point for understanding and better managing a person's nutritional and physical health. It must be complemented with other data and information to assess the risks associated with excess weight and obesity.
It is important that we be aware of our BMI, but also that we be aware of its limitations.
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