A Little bit about the Medical Recommendations of Ideal Body Weight
By Steven B. Halls, MD
The medical profession likes simplicity. Researchers have tested if being overweight causes health risks, using a body mass index (BMI) of 25 kg/m2 as the definition of overweight. This is obviously too simple, but it is a common method used in data analysis. Numerous studies have confirmed that having a body mass index over 25 kg/m2 is associated with increased risk of diseases. Conditions such as diabetes, high blood pressure, heart attacks, etc), and risk of a shortened lifespan3 are associated with being overweight.
It is important to point out that this simple definition of overweight by medical researchers is not representative of how people regard each other. Neither is the definition of overweight how a doctor would judge an individual patient, or a nutritionists.
Furthermore, the Body Mass Index of 25 kg/m2 definition of overweight is a unisex threshold that suits neither men or women particularly well. Nevertheless, a Body Mass Index (BMI) of 25 to 29.9 is defined as overweight by some important institutions1.
More Problem with the Ideal Body Weight Definitions
The definition of "underweight" at a BMI below 19 kg/m2 is also arbitrary. It may be sort of suitable for women but is quite unsuitable for men.
A better definition of weight categories2 is shown in the table below. It suggests that an "overweight" BMI is actually 27.3 for women, and 27.8 for men.
Better definitions of Ideal Body Weight Categories Table
|in normal range ideal weight||19.1-25.8||20.7-26.4|
|very overweight or obese||>32.3||>31.1|
|severely obese||35 – 40|
|morbidly obese||40 – 50|
|super obese||50 – 60 kg/m2|
Another problem with all of the above definitions, is that they only apply to adults. For children under age 18, the "normal" BMI changes with age. Thus, to judge a child’s Body Mass Index, you should refer to the boys BMI chart or girls BMI chart instead. In my opinion, children whose BMI is somewhere inbetween the 5th to 85th percentiles, should be considered normal, and not overweight.
There are MANY websites on the internet that offer a simple "body mass index calculator" function. The vast majority of these websites use the too-simple definition of overweight at 25 kg/m2. You should be wary of these types of websites, not only because of their simplicity.
Other problems are that BMI websites do not take into account gender, or children or different ages of adults. The halls.md Body Mass Index Calculator does all of these things.
The halls BMI calculator is a versatile tool which also computes the "percentile" statistics of the individual compared to the equivalent population.
- Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. National Heart, Lung and Blood Institute. June 17, 1998
- Standards Committee, American Society of Obesity Surgery; Obesity Surgery. Dec. 1997; 7:523
- Calle EE, Thun MJ et al, Body mass index and mortality in a prospective cohort of US adults. N Engl J Med 1999; 341:1097-105.