Body Mass Index

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton, Kim Jackson and Naomi O'Reilly  

Introduction[edit | edit source]

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Body mass index, or BMI, is used to determine a person’s healthy weight range for their height.

  • It is useful to consider BMI alongside waist circumference, as waist measurement helps to assess risk by measuring the amount of central fat.
  • BMI is a useful measurement for most people over 18 years old. However it is only an estimate and not taking into account age, ethnicity, gender and body composition.[1]
  • At the cellular level, an increase or decrease in BMI can have a significant effect on physiology. Research has shown associations with BMI to insulin resistant states, inflammatory states, and cognition.[2]

Definition and Classification[edit | edit source]

Overweight biker.jpg

Body mass index or BMI is a statistical index using a person's weight and height to provide an estimate of body fat in males and females of any age. It is calculated by taking a person's weight, in kilograms, divided by their height, in meters squared, or BMI = weight (in kg)/ height^2 (in m^2). The number generated from this equation is then the individual's BMI number.

Individual variations do exist, and BMI is insufficient as the sole means of classifying a person as obese or malnourished.

  • in elite athletes and body-builders, an elevated BMI does not directly correlate to their health status due to their increased muscle mass and weight falsely increasing their BMI.[3]

The BMI number and classifications are listed below, these classifications for BMI are in use by the NIH and the World Health Organization (WHO)

White, Hispanic and Black individuals

  • Severely underweight - BMI less than 16.5kg/m^2
  • Underweight - BMI under 18.5 kg/m^2
  • Normal weight - BMI greater than or equal to 18.5 to 24.9 kg/m^2
  • Overweight – BMI greater than or equal to 25 to 29.9 kg/m^2
  • Obesity – BMI greater than or equal to 30 kg/m^2

Asian and South Asian Population:

  • Overweight - BMI between 23 and 24.9 kg/m^2;
  • Obesity - BMI greater than 25 kg/m^2[3]

Related Tests[edit | edit source]

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When individuals are identified as an abnormal weight, certain testing should be done.

  • A BMI greater than 30 kg/m2: a lipid panel, thyroid level, and diabetes screening should always be done. These patients should be counseled about a healthy diet and exercise.
  • A BMI less than 18 kg/m2: thyroid level, comprehensive metabolic panel, psychiatric screening for an eating disorder, and conditions of malabsorption should be done. If weight loss was rapid and unintentional, a cancer workup should also be done.[2]

BMI and Physiotherapy[edit | edit source]

The main issue of concern in regards to BMI involves the growing obesity epidemic and the increasing population with high BMI numbers. See The Emerging Role of the Physiotherapist in the Current Obesity Epidemic

In eating disorders BMI is used to see what specific exercise guide lines are appropriate, see Anorexia Nervosa

References[edit | edit source]

  1. Heart Foundation BMI Available: (accessed 13.8.2021)
  2. 2.0 2.1 Zierle-Ghosh A, Jan A. Physiology, Body Mass Index. [Updated 2020 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan Available: 13.8.2021)
  3. 3.0 3.1 Weir CB, Jan A. BMI Classification Percentile And Cut Off Points. [Updated 2021 Jun 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-.Available:!po=81.2500 (accessed 13.8.2021)