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Your guide to learning about the Body Mass Index (BMI)

By Jake Biggs, Nutrition Longevity


1. What is body mass index (BMI)?

BMI is the most widely used indicator to classify overweight and obesity.


2. How is BMI calculated?

WEIGHT ÷ HEIGHT ÷ HEIGHT

Eg: 70 (weight) ÷ 1.74 ÷ 1.74 = 23.12


3. BMI results interpretation


4. What are the advantages of using BMI?

• Easy to perform

• No expense

• Approximate estimation of body fat

• Useful tool to assess body composition


5. What are the disadvantages of using BMI?

• Guideline for assessing body composition

• Not accurate measure of overall health & disease risk

• Does not take into consideration overall fat distribution eg: difference between subcutaneous and visceral fat (visceral fat upsurges risk of heart disease, diabetes, metabolic syndrome and cancer)

• There are substantial differences in overweight and obesity at the same BMI amongst diverse ethnic groups

• Pacific Islanders and Maori have elevated cut off places for healthy/overweight and obese due to genetic disparities in body types than Caucasians

• Asian and Indian individuals have lower cut off points for healthy/overweight and obese due to their propensity to have higher levels of visceral fat at a lower body mass than Caucasians. A heightened risk of diabetes and cardiovascular disease begins at a BMI of 23 in Asian populations.

• Undervalues adipose tissue (body fat) for the elderly population, physically impaired/disable individuals and individuals with suboptimal levels of lean muscle mass

• Overestimates the amount of body fat of pregnant women, high performance athletes, bodybuilders and individuals who have a large of lean muscle mass due to BMI not measuring lean muscle mass vs fat mass. It is a measurement of overall weight.

• Regularly overestimates obesity in shorter people and underestimates obesity in taller individuals, therefore it is hypothesis that BMI should not be used in people <150cm and >190cm.


Case Study

1. LeBron James: One of the greatest basketball players in history and requires an extremely high level of fitness with a high level of muscle mass is 2.06m height and 113kg weight. His BMI is 26.63 which would place him in the overweight category, but as the BMI doesn’t take into consideration muscle/fat ratio; this isn’t a correct evaluation of his current health. As the picture tells he is definitely not visibly overweight 😊


2. Helmut Strebl: Currently the most muscular/shredded/lean natural bodybuilder in the world (no performance enhancing drugs) is 190.5cm and 93kg. His BMI calculation is 25.76 would also place him in the overweight category. Again due to not taking into consideration lean muscle mass vs fat mass, this also isn’t a correct assessment of his current health. Again the picture shows the evidence 😊


In summary: BMI can be used a ‘tool’ for measurement of overall health but as a nutritional medicine practitioner, I want to meticulously measure my clientele’s health and wellbeing (which I will be covering in future posts), so I would not be using this very often!