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The Body Mass Index (BMI) is a body measurement aiming to determine the ideal balance between height and weight. Based on BMI, one can evaluate their weight and determine whether they are underweight, of normal weight, or overweight. The range goes as far as severe underweight and obesity, and may be an indicator of severe health problems. However, BMI has its limitations (which we will discuss later), and it shouldn’t be used as the sole health evaluation method.
The history of the Body Mass Index (BMI) dates back to 1830 and starts with Belgian mathematician Adolphe Quetelet’s research. Quetelet was interested in statistics rather than in medicine and sought a way to define “the average man”. He found it, although his research was based solely on European men. The concept remained hidden until 1970, when American physiologist Dr. Ancel Keys used it to estimate obesity and called it BMI. Twenty years later, BMI was adopted by the World Health Organization (WHO) and the U.S. National Institutes of Health as the standard in defining weight categories.
Almost 200 years after its first mention, the Body Mass Index remains a widely used measure, albeit with many flaws and limitations. Nowadays, specialists recommend using it as part of a more complex weight and health evaluation, and not as the ultimate way to diagnose obesity and weight issues. Read along to understand what BMI is and how it can be calculated and used to your advantage.
You need only two values to calculate your BMI: your weight and your height. If you use the metric system (i.e., weight in kilograms and height in meters), use this BMI formula:
BMI = Weight/Height2
However, if you use the imperial system (i.e., weight in pounds and height in inches), use this BMI formula:
BMI = 703 x Weight/Height2
Standard BMI categories for adults are as follows according to CDC:
You’ll find revised categories for underweight and obese that try to assess the risks better. For example, BMIs over 30 are usually categorized as:
BMIs under 18.5 are also often divided into three categories to account for their level of severity:
Of course, having a BMI on the edge of a category should be taken with a grain of salt because it can either identify a non-existent problem or fail to enliven an existing one. Recent research shows that 1 in 4 people with a normal BMI and 1 in 2 of those categorized as overweight meet the standards of clinical obesity.
Your BMI (body mass index) is your weight divided by your height multiplied by itself. The team at NIH has put together a table to help you identify your BMI based on your body measures.
The problem with BMI is that it only considers your height and weight, which leaves out a lot of other relevant factors, such as:
In conclusion, BMI provides a fairly accurate indication for the average adult. For niche categories, such as athletes or people with a high activity level, children and teenagers, people over 65, pregnant women, and people with diagnosed muscle-related illnesses (e.g., muscle atrophy), BMI shouldn’t be a variable in health evaluation. Also, for people who are genetically predisposed to a certain body type (e.g., lean, corpulent, pear-shaped), BMI should be considered alongside other measurements, such as waist circumference, fat distribution, waist-to-height ratio, waist-to-hip ratio, and body roundness index.
The main benefit of calculating your BMI is identifying disease risk as early as possible. Many of those risks are associated with being overweight, hence having a high BMI, and they are related to illnesses such as:
BMI is used as a preliminary screening tool to identify people who might be overweight and present various health risks. That’s because BMI is cost-effective and data-driven, but also because it’s efficient at flagging potential issues.
Being underweight doesn’t necessarily mean you are slim, fit, and healthy. In many cases, it may signal a health issue, such as:
Often, a sudden decrease in BMI into the underweight range may indicate poor nutrient absorption, a deficient diet, or a systemic illness. BMI is also a standard tool in assessing malnutrition.
Calculate your BMI regularly and take action whenever you notice a significant change in weight. It may be a new habit, a disruption in your exercise or sleep routine, a change in your diet, increased stress, or an indicator of a more serious health issue that you should further investigate with your physician.
So, let’s assume you are 6 ft tall and weigh 165 pounds. The corresponding BMI formula uses inches; thus, the first step is to convert feet to inches:
Height(in) = Height(ft) x 12 = 6 x 12 = 72
Now, apply the formula below:
BMI = 703 x Weight/Height2=703 x 160/722 = 21.7
A BMI of 21.7 is within the normal weight range (18.5 - 24.9).
If you’re using the metric system, the BMI formula is even simpler. So, assuming you are 1.65 m tall and weigh 70 kg, by applying the formula below, you get:
BMI = Weight/Height2 = 70/1.652 = 25.71
A BMI of 25.71 is within the overweight range (25 - 29.9).
Tip: Use a calculator to calculate your BMI, and don’t round until the end. It will help you get a more accurate result.
When to use a BMI Calculator?
Use a BMI calculator as a screening step to identify weight-related issues, whether overweight or underweight. At home, you can use it to monitor your weight and overall well-being. Medical personnel also use BMI as a variable in medication dosages and other procedures.
What are the common pitfalls of such a calculator?
Among the common drawbacks of a BMI calculator are the need for accurate height and weight measurements, not taking into account muscle mass and fat mass ratio, not differentiating based on age, gender, lifestyle, and family patterns, and the need to be utilized in combination with other measurements and data for an accurate diagnosis.
Related: BMR Calculator
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