If you’ve ever had a standard medical exam with your doctor or other healthcare professional, chances are they’ve calculated your BMI. This is a simple formula using your height and weight to determine if you are carrying too much fat.
It’s been a standard way of judging a person’s health since the turn of the 20th century (with tweaks along the way) but while it gives a good overview of a person’s condition, being such a simple test, it is not the full picture and should be looked at alongside other considerations.
To get the most accurate picture of an individual’s health status, it is important to consider what the BMI doesn’t take into account. While BMI is a good starting point, considering a person’s age, gender, ethnicity, and build will help create a better picture of where that person is and whether she needs to make any lifestyle changes. There are also other ways to measure body fat (opens in a new tab) it could be more accurate – but these are usually based on more complicated calculations.
Contributor: Dr. Juliet McGrattan
A practicing doctor for 16 years, UK-based Dr Juliet McGrattan is now an award-winning author and running coach. As well as her years as a GP, she was also the North West’s leading Clinical Physical Activity Champion for Public Health England. (opens in a new tab).
What exactly is BMI?
BMI stands for “body mass index” and it is commonly used to determine if a person is at risk for obesity or underweight. BMI measurements correlate with many obesity-related health issues, so it’s a valid starting point for looking at a person’s health status. It is also easy to understand because it is based on a numerical scale.
Each entry on the scale relates to the number of kilograms per square meter (so a BMI of 25 would be 25 kg/m²).
According to the CDC (opens in a new tab), a BMI of less than 18.4 on the scale is considered “underweight”. For most individuals, a BMI between 18.5 and 24.9) is considered normal or acceptable, while people between 25 and 29.9 are classified as “overweight.” Anyone with a BMI of 30 or more is considered “obese”.
Yet, since a person’s BMI does not focus exclusively on fat and also includes muscle and other tissues, it is not a complete assessment on its own.
|18.5 – 24.9||Normal|
|25.0 – 29.9||Overweight|
|30.0 and above||Obese|
How do I calculate my own BMI?
To calculate your BMI, you need to know:
- How much do you weigh
- What is your size
This can be in metric or imperial measurements. There is a formula for both.
For the metric, you simply calculate your height in square centimeters, then use that number to divide your weight into kilograms (weight ÷ height²).
For the imperial system, determine your height (in inches) and use the number to divide your weight into pounds (weight (lbs) ÷ height (in)²). This time, also multiply by 703.
For an easy way to calculate your BMI, you can use one of the many online calculators available, where you enter your weight and height and it calculates it for you.
What is the BMI used for?
Healthcare professionals use BMI to help them assess their patients’ risk factors for certain weight-related health problems.
“Measuring your BMI can help you and your nurse or doctor determine if you are at a healthy weight.” says Dr Juliet McGrattan, former GP and author of Sorted: The Active Woman’s Guide to Health (opens in a new tab). “There are health risks associated with being overweight and underweight.”
However, calculating your BMI isn’t just useful on a personal level. “BMI can be used at the individual level to help you decide whether to gain or lose weight, but it’s also used at a broader level where it indicates the health of populations,” adds Dr McGrattan.
So, knowing the average BMI of a population, in conjunction with other health statistics, can give healthcare professionals more information on how to target communities that may need additional help. with their lifestyle and health care options.
Should I be worried about a high or low BMI?
If you’ve entered your details into a calculator and the results aren’t within “healthy” ranges, don’t panic.
“It is important to know that BMI is only a guide and can be misleading for some people. For example, if you’re very muscular, your BMI may indicate that you’re overweight when you’re actually very healthy,” says Dr. McGrattan.
But it’s still worth checking if you’re unsure, as there are risks associated with being on either side of “unhealthy” settings:
“If your BMI is outside the healthy range, then it’s a good idea to discuss this with your doctor,” adds Dr. McGrattan. “A very low BMI could put you at increased risk for health problems, including osteoporosis, where bones are thin and fracture easily.
“There are also many known health risks associated with being overweight or obese, such as type 2 diabetes, heart disease and many types of cancer. Your doctor can help you determine what your BMI means to you personally and if there are steps you need to take to correct it.
Is BMI an accurate measure of my health?
BMI is a good place to start, but some researchers would argue that BMI is not a good measure of healthy weight. As McGrattan explains, “Your BMI doesn’t tell the whole story. Someone with a BMI in the normal range can be in very poor health if they don’t exercise regularly, or if they smoke or drinks excessive amounts of alcohol.
“Similarly, a person with a high BMI may be fitter and healthier than a person with a low BMI. It all depends on their lifestyle and habits. BMI should always be interpreted alongside d other factors such as lifestyle, ethnic group and other medical conditions a person might have.
As mentioned earlier, the main disadvantage of BMI is that it does not exclusively measure fat, or where that fat is distributed on the body. It is therefore important to look at a BMI score in conjunction with other tests such as waist circumference to quickly determine if a person is healthy or in need of further assistance.
“Also remember that overall good health includes both physical and mental health, and BMI does not measure your mental health,” says Dr. McGrattan.
BMI is still a good way to quickly get a picture of a person’s health, but is not a one-size-fits-all and should be considered alongside other considerations such as lifestyle, build, gender, age, ethnicity and overall health of the individual.
If you’re the least concerned about your health in relation to your BMI, ask your doctor or nurse for advice.
This article is not intended to offer medical advice and readers should consult their doctor or health care professional before adopting any diet or treatment.