The BMI (Body Mass Index) measurement was never intended as a measurement of health, since it was created over 100 years ago. It was originally designed to try and determine the ideal body weight of of high-income mostly white men in Belgium as a census tool to estimate appropriate distribution of resources. Somehow despite much criticism, it has stuck, and has ever since then been used for both men and women of all ages and ethnicities.

BMI is a simple measurement, (your weight divided by your height squared) that doesn’t take into account whether you are full of muscle or fat. Muscle is much denser than fat, so takes up less space. Many Olympian and other high level athletes have a BMI in the overweight (over 25) and even obese (over 30) range. Also, we have a range of different constitutions and some people really are naturally heavier and lighter.

It has also been shown that 1/3 of those who are overweight and obese according to BMI have good metabolic health. And 1/3 of those with a BMI in the ‘healthy range’ have poor metabolic health. Therefore it is a very general measure that may have some relevance at a population scale, or screening level, but very little at a personal level. Many people who are considered overweight or obese due to their BMI, avoid seeking medical care due to shame about their weight, and due to medical professionals over-emphasis on BMI as a health indicator, which it was never intended to be. 

Other types of measurements have been proposed and one that is rising in popularity is the BRI scale- the Body Roundness Indicator. It uses a more complex and nuanced calculation than the BMI and it is based on the relationship between waist circumference and height. It gives a more detailed assessment of body shape and distribution of fat around the abdomen, which is a significant risk factor for modern metabolic diseases. Studies show that BRI more accurately reflects metabolic risk, such as cardiovascular health, and risk of death, than BMI. People who are at either end of the bell curve - with both low and high BRI- are at higher risk. 

You can check out your BRI here if you are curious: https://webfce.com/bri-calculator/

BRI is much more useful at an individual level than BMI, and as evidence grows, is slowly becoming more widely used. Such tools should always be used in conjunction with other health factors such as muscle mass, fitness level and lifestyle, and indicators such as blood pressure, cholesterol levels and family health history. The BRI can help us shift attention to health, and away from BMI and an ‘ideal’ general weight. 

https://www.sciencedirect.com/science/article/pii/S000291652200185X?via%3Dihub