How Do You Measure Body Fat? There Are Better Ways Than BMI
Key takeaways:
Body fat gets a bad rap because too much in the wrong places can lead to serious health problems, like Type 2 diabetes or heart disease.
BMI, or body mass index, is a measure typically used to estimate body fat, but it has many limitations.
There are other tools that can estimate your body fat, including smart scales, imaging studies, and waist measurements.
Your weight matters. But it may not matter as much as what makes up your weight (fat versus muscle) or where your fat is located. For example, having central body fat in the abdomen and around the organs is associated with health problems like diabetes and heart disease.
But how can you know how much body fat you have and what it means for your health?
Despite what you may have been told, the body mass index, or BMI, is not the best way to tell how much fat you have. The BMI is used because it’s free and easy to calculate. But using other body fat measurements — from a simple waist measurement to smart scales — may be a better way to determine your health and risk factors.
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What is body fat and why does it matter?
Body fat is necessary for survival. It performs important functions like making hormones, regulating your body temperature, and storing vitamins and nutrients.
But too much body fat can cause health problems. It raises the risk of some health conditions, including:
Where you store your fat also matters. Abdominal fat, also called visceral fat, is the fat surrounding organs in the abdomen and is associated with medical conditions like diabetes and high blood pressure. Subcutaneous fat is the fat that is under the skin. This type of fat helps with regulating body temperature, cushions the body, and can store energy.
The amount of body fat you have depends on many factors, including your age, gender, and ethnicity.
What is a healthy body fat percentage?
A healthy body fat level depends on many factors and is often determined by gender and age. In women, a healthy body fat percentage is between 20% and 35%. In men, it is between 8% to 25%.
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It is normal for women to have more body fat than men and for a person’s amount of body fat to increase with age.
What is the body mass index (BMI) and how do you calculate it?
Body mass index (BMI) is calculated using your height and weight. The formula is: weight divided by height squared. It’s easy to find a BMI calculator online, which is one of the reasons why BMI is so commonly used.
BMI can help some people identify if they have excess weight or obesity. But it’s imperfect. It’s not a whole lot better than measuring how much water you displace when you get into the bath.
A healthy BMI is considered to be between 18.5 and 24.9 kg/m2. If you have a BMI of 25 to 29, then that’s considered to be overweight. At a BMI of 30 or above, you are considered to have obesity.
Why is BMI so commonly used, and what are its shortcomings?
BMI is far from a perfect tool. It estimates body fat based on a person’s height and weight, and does not take into account age, genetics, race, muscle, or fat distribution.
The important thing to understand is that it’s not just excess fat that affects a person’s BMI. So equating BMI with body fat is not a good practice.
Here are some other reasons that a person may have a “higher than normal” or “lower than normal” BMI:
Muscle mass: BMI isn’t a good measure of body fat for athletes or people with more muscle mass. They may have a “higher than normal” BMI and still have a healthy amount of fat.
Age: People tend to lose muscle mass and gain fat as they get older. Because of this, older adults’ BMI often suggests that they have lower body fat than what they actually have.
Sex and race: BMI was created using data from Caucasian (white) men, so the scoring does not work as well for women and non-white people. Women often have more body fat than men with the same BMI. In Black people, BMI often overestimates body fat, while in some Asian people, it commonly underestimates body fat.
BMI also doesn’t tell us anything about where the fat is located. This is an important shortcoming, since it is clear that people with fat around the middle abdominal area (visceral fat) have a greater risk of health problems than people with fat in their arms, bottoms, or thighs.
What are some other ways to measure body fat?
BMI is an easy and convenient tool, but with a little more time and money, it’s possible to get a more precise measurement of body fat.
Let’s look at other techniques for measuring body fat that aren’t BMI.
Body fat scales
Also called bioimpedance analysis devices, body fat scales use electrodes to measure the amount of water in your body, which can then be used to estimate body fat. These devices can provide a quick and pretty accurate measurement of body fat, but they don’t tell you where the body fat is located.
DEXA scan for body fat
A dual-energy X-ray absorptiometry (DEXA) scan is commonly used for osteoporosis screening. It is a type of X-ray scan that can identify bone, soft tissue, and body fat. In addition to measuring bone density, it can also offer information about your body fat percentage and where your body fat is located. This test needs to be ordered by your healthcare provider.
Whole body CT or MRI scans to measure body fat
CT and MRI scans image the body and can accurately identify the amount and location of body fat. There are some downsides, though: They are both expensive, and CT scans provide some radiation exposure.
Underwater weighing
Underwater weighing is just what it sounds like. This technique measures your weight underwater compared to your weight on land. It pretty accurately measures the amount of body fat you have but doesn’t tell you where your body fat is.
Body fat calipers
Skinfold calipers are a way to measure body fat at home. They are handheld devices that pinch different areas of the skin to estimate the amount of body fat under the skin. Taking these measurements doesn't involve a lot of equipment, so it’s pretty easy to do. But it’s also not very precise, since the measurements can vary if you don’t take them in a consistent way.
How do you measure body fat with tape?
You can also get an idea of whether your body fat is a health risk by measuring your waist. While it doesn’t measure the amount of fat, measuring around the front of your abdomen provides a waist circumference, and an increased waist circumference is linked with health conditions like heart disease and Type 2 diabetes.
Here is how to interpret the measurements:
For women, risk increases when waist size is over 35 in.
For men, risk increases when waist size is over 40 in.
The bottom line
Body fat matters for many reasons, and they are not all bad. In fact, body fat plays some essential roles in keeping us healthy. That said, too much of certain types of body fat, especially around the middle of your body, can be harmful and is linked with health conditions like heart disease or Type 2 diabetes.
BMI is most commonly used as an indicator of body fat, but it should be taken with a giant pinch of salt. Ultimately, your overall health is about so much more than your size and weight. Family history, genetics, medical history, environment, and lifestyle all play a role in determining how healthy you are — and how healthy you will remain.
No single number or test to measure fat can accurately capture your whole health. So eat well, move regularly, sleep, look after your mental health, avoid smoking and excess alcohol, and make time to see your healthcare provider for regular checkups. The rest will follow.
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References
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