Body Mass Index - An Overview

BMI, or Body Mass Index, is a measure used to assess an individual's body weight relative to their height. It's calculated by dividing a person's weight in kilograms by the square of their height in meters (BMI = weight / height^2). The result is a numerical value that categorizes individuals into different weight categories: underweight, normal weight, overweight, or obese.

BMI can be used as a guide for what is a healthy weight for your height:

  1. Underweight: A BMI below 18.5 typically indicates that a person is underweight for their height. This may suggest inadequate nutrition or certain health conditions.

  2. Normal weight: A BMI between 18.5 and 24.9 is considered normal. Individuals falling within this range usually have a healthy weight relative to their height.

  3. Overweight: A BMI between 25 and 29.9 suggests that a person is overweight, which may increase the risk of certain health problems such as heart disease, diabetes, and high blood pressure.

  4. Obese: A BMI of 30 or higher indicates obesity. This significantly increases the risk of various health issues, including cardiovascular disease, stroke, type 2 diabetes, and certain cancers.

However, BMI has several shortcomings when used as a sole indicator of health:

  1. Limited assessment of body composition: BMI does not differentiate between fat mass and muscle mass. Therefore, individuals with high muscle mass, such as athletes or bodybuilders, may have a high BMI despite having a low body fat percentage.

  2. Doesn't account for distribution of fat: BMI does not consider where fat is distributed on the body. Central obesity (excess fat around the abdomen) is associated with higher health risks compared to fat distributed elsewhere on the body.

  3. Doesn't consider age or gender: BMI standards are based on general populations and may not be suitable for specific demographic groups. For example, older adults may have different body composition changes that affect their BMI interpretation.

  4. Not applicable for certain populations: BMI may not be accurate for children, pregnant women, or individuals with certain medical conditions.

  5. Health risks at lower BMI: While a high BMI generally indicates increased health risks, having a low BMI can also be associated with health problems, such as malnutrition, weakened immune system, and osteoporosis.

Given these limitations, BMI should be used cautiously and in conjunction with other measures, such as waist circumference, body fat percentage, and overall health assessment by a healthcare professional, to provide a more comprehensive evaluation of an individual's health status.

 

For more information, some of the following pages may be useful:

Irish Heart Foundation: https://irishheart.ie/how-to-keep-your-heart-healthy/weight-loss/

Health Service Executive: https://www2.hse.ie/conditions/type-2-diabetes/living-with/managing-your-weight/

Back to blog