BMI, a valuable tool?

7 July, 2015 ,

According to the WHO, BMI (Body Mass Index) is a tool that evaluates the general level of obesity. Different weight categories can be associated with a risk of developing certain diseases. BMI has the advantage of being easy to use: only two pieces of information are required, namely weight and height. This tool is so simple that it must be used with caution, because it has certain limitations.


BMI is quick as a screening tool, but in order to properly interpret build, health professionals must equally take into account the individual’s age, sex and muscular mass. For example, a muscular person can be considered as overweight, and an older person could seem to be a healthy weight despite the loss of muscular mass caused by aging. It should be noted that persons under 18 years of age and pregnant women cannot be evaluated with this tool. According to the WHO, a BMI of between 25 and 30 indicates a person could be overweight, and a BMI above 30 indicates a person could be obese.


Health Risk Classification According to Body Mass Index (BMI) [I]
Classification BMI Category (kg/m2) Risk of developing health problems
Underweight < 18,5 Increased
Normal Weight 18,5 – 24,9 Least
Overwight 25,0 – 29,9 Increased
Obesity class I 30,0 – 34,9 High
Obesity, class II 35,0 – 39,9 Very high
Obesity, class III >= 40,0 Extremely high

To calculate your BMI, you can use the following formula:
BMI = weight(kg)/height(m)2

BMI represents therefore only one of the stages of the evaluation. Abdominal girth is an indicator of adiposity additional to that of BMI. Indeed, waist size determines whether there is an excess of visceral fat, which is directly linked to an increased health risk. And a final indicator, the waist-hip ratio makes it possible to assess the individual in question’s body shape. The “apple” body shape is to be avoided, because it is marked by an excess of fat around the abdomen. The “pear” body shape on the other hand, is characterized by a surplus around the hips and buttocks.

Experts are unanimous on this point: weight is only one factor of disease risk. It is necessary to also take into considerations other factors such as age, sex, unhealthy diet, smoking, sedentary lifestyle, education level and heredity.


[1] Source : Health Canada

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Marie-Maxime Bergeron

Marie-Maxime Bergeron

Registered Dietitian, RD at

Changing eating habits gradually and adapting to the needs of my clients is the cornerstone of my approach. Eating well for fun and for health is the goal and everything begins with a return to simplicity in our habits. I am a nutritionist and have offered counselling in nutrition for 10 years.

Marie-Maxime Bergeron

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