Key takeaways:
Weight and body mass index (BMI) may not be the most accurate way to measure the type of body fat that increases health risks.
Waist size is a better way to measure belly fat, which is more closely associated with health risks than overall body fat.
Other measurements related to waist size — like waist-to-hip ratio and waist-to-height ratio — can also be a good way to estimate body fat.
We live in a world that places a lot of emphasis on weight. And for better or worse, a “normal” weight or body mass index (BMI) often gets conflated with good health. But this isn’t always the case. Other factors — like body fat, particularly around the waist — may be more closely tied to health risks.
This article explains how weight and BMI sometimes get it wrong — and how measuring your waist may be a better way to predict body fat.
Is BMI an accurate way to measure body fat?
No, body mass index (BMI) doesn’t directly measure body fat. It divides your weight by your height, to place you into one of four weight categories (listed below).
BMI | Weight category |
<18.5 | Underweight |
18.5-24.9 | Healthy weight |
25-29.9 | Overweight |
>/=30 | Obese |
Both high and low BMIs are linked with health problems. For example, a high BMI may be linked to Type 2 diabetes, sleep apnea, and heart disease. A low BMI may be linked to osteoporosis.
On its own, BMI isn’t a good reflection of your overall health. Here are just a few reasons why BMI may not tell you much about your health:
It was developed for white, middle-aged men, which means it’s less accurate for other races and for women.
The ranges haven’t been updated in more than 25 years.
It doesn’t consider where fat is located on your body, which may be more important than overall amount of fat, when it comes to health.
It also doesn’t measure how much bone and muscle you have.
Experts are now learning that other measurements, like waist size, may be a better way to measure body fat. And some researchers argue that waist size should be taken at every health checkup and tracked over time.
Waist size (circumference) and health
Having a large waist size increases your risk for certain health problems — even if your BMI is in the “normal” category.
Your waist size changes based on your belly fat. Belly fat (also called “abdominal” or “visceral” fat) is linked to many different health conditions, including high cholesterol, Type 2 diabetes, high blood pressure, and joint pain.
A large waist size is sometimes referred to as “central obesity.” Whether you have central obesity depends on your background, since it differs for certain groups of people.
| Males | Females | |
|---|---|---|
| U.S. | >40 inches (102 cm) | >35 inches (88 cm) |
| European ancestry | >37 inches (94 cm) | >31.5 inches (80 cm) |
| South Asian, Chinese, or Japanese |
>35.5 inches (90 cm) | >31.5 inches (80 cm) |
To measure your waist, here are some tips for getting an accurate measurement:
Find a stretch-resistant measuring tape or string.
Locate your natural waist, which is halfway between your hips and your ribs.
Breathe out naturally before measuring.
Wrap the measuring tape or string around your waist. Make sure it’s snug, but not too tight.
While measuring, be sure to keep the measuring tape parallel to the floor.
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It can sometimes be hard to measure your waist on your own. If you’re having trouble, ask a friend or family member to help.
What about waist-to-hip ratio?
Waist-to-hip ratio is another good way to measure body fat. Waist-to-hip ratio is your waist size divided by your hip size. This means it takes into account how fat is distributed elsewhere on your body, not just your belly.
Lower waist-to-hip ratios are linked to better health outcomes. Research studies show that having a high waist-to-hip ratio is linked to health problems, like diabetes, heart disease, and premature death.
The target waist-to-hip ratio is different for men and women, as noted below.
Sex | Waist-to-hip ratio goal |
|---|---|
Female | <0.85 |
Male | <0.90 |
Compared to BMI, waist-to-hip ratio is a more accurate way to predict a person’s chances of having a premature death. Waist-to-hip ratio is also a more accurate predictor of heart attack in males and females than BMI. This is especially true for females.
What about waist-to-height ratio?
Waist-to-height ratio is another measurement that can help predict body fat. To calculate it, simply divide your waist size by your height in the same units (inches or centimeters, for example).
Scientists have concluded that an optimal cutoff for an adult’s waist-to-height ratio is 0.5. This means that your waist circumference should ideally be less than half your height.
Compared to BMI alone, waist-to-height ratio has been shown to more accurately predict your risk of heart disease. And in people with Type 2 diabetes, waist-to-height ratio better predicted high blood pressure, compared to waist-to-hip ratio and BMI.
But researchers point out that none of these measurements are perfect in isolation. For now, your healthcare team should consider your BMI, waist and hip size, and height, along with your other individual risk factors to best assess your overall well-being.
The bottom line
Good health has to do with a lot more than just weight. And BMI is falling out of favor as the best way to measure body fat. Waist size, waist-to-hip ratio, and weight-to-height ratio may be a better way to know if your body fat is putting you at risk for certain health conditions. Keep in mind that all these measurements and tools are designed to screen large populations of people. You’re unique, and individual health is complex. Having regular checkups with a trusted healthcare professional is the best way to know if and how your weight is impacting your health.
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References
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