Body mass index (BMI): what it is and what it is for

Body Mass Index (BMI) is a measure of a person’s body fat in relation to their height. It’s a tool used by healthcare professionals to assess the risk of various health conditions based on a person’s weight.

Body mass index (BMI): what it is and what it is for

How is BMI calculated?

The basic formula for BMI is: \[ \text{BMI} = \frac{\text{body weight (in kg)}}{\text{height}^2\ (\text{in m})} \]

For an example with a body mass of 70kg and a height of 1.75m: \[ \text{BMI} = \frac{70}{1.75^2} \approx 22.9 \]

BMI calculator

Interpreting BMI values:

  • Less than 18.5 – Underweight
  • 18.5 to 24.9 – Normal weight
  • 25 to 29.9 – Overweight (pre-obesity)
  • 30 to 34.9 – Obesity class I
  • 35 to 39.9 – Obesity class II
  • 40 and above – Obesity class III

Why is BMI important?

BMI gives a general idea of whether a person’s weight is within a healthy range. However, it’s important to note that BMI does not distinguish between fat and muscle weight, nor does it take into account variations in body structure between individuals.

Health professionals use BMI as one of many indicators to assess risk of cardiovascular, endocrine and other diseases.

Limitations of BMI:

Although BMI is useful, it has several limitations:

  • Doesn’t distinguish between muscle and fat mass.
  • Doesn’t take into account age, gender or ethnicity.
  • May not be suitable for professional athletes, bodybuilders or people with significant muscle mass.

Bottom line

BMI is a convenient way to measure the relationship between your weight and height. While it’s a useful starting point for health-related discussions with your doctor, it shouldn’t be the only measure used to guide health or dietary decisions. It’s always a good idea to seek advice from health and nutrition professionals.

Prepared by Mary Clair

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