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If you’ve been diagnosed with obesity, chances are you’ve heard a healthcare provider talk about your body mass index, or BMI. Many providers use it as a screening tool in the process of diagnosing obesity.
There are some questions about whether BMI is accurate and whether there are other tests medical staff should use to screen for obesity. Here’s what you need to know so you can have an informed conversation the next time your healthcare provider talks about your BMI.
BMI stands for body mass index. You can calculate it by dividing a person’s weight in kilograms by the square of their height in meters. It’s a fast way for doctors to screen people for potential risks associated with having a higher body weight.
The BMI classifications are:
Different BMI ranges are associated with higher or lower risks of developing other health conditions, but a person’s BMI score is not a direct measure of their individual health. Your doctor can talk to you about how your BMI classification might relate to your overall health.
BMI scales give both healthcare providers and the general public quick, easy ways to consider possible health risks associated with a person’s body weight. While some other tests for obesity involve a lot more math or waiting to get test results, using BMI means you don’t have to wait to seek further testing or treatment. However, BMI is a very general tool, and it doesn’t measure many factors about your body and overall health.
First among these is body type. BMI classifications were developed by studying white European males. This means they may not be valid for people from other races, ethnic groups, or genders.
Even when researchers have tried to set standards for other populations, such as a 2004 effort to develop guidelines for Asian populations, there are some groups that get left out. Unless your doctor is using BMI guidelines specifically for your race, ethnicity, and gender — guidelines which may not exist — your BMI results may not be accurate.
While BMI is designed to determine how much body fat you have, it doesn’t differentiate between fat and muscle. Thus, it doesn’t tell you anything about your body composition. This means that people carrying a lot of muscle mass may have higher BMI scores without a high amount of body fat. Similarly, someone may have a high percentage of body fat but have a BMI in the normal range, and their doctor might not think to screen them for health conditions related to higher body fat.
BMI can’t tell where people carry fat on their bodies. This is important because having fat around the belly (called central obesity) increases the risk of certain diseases compared to having fat stored elsewhere in the body.
Finally, BMI doesn’t look at a person’s metabolic health. Metabolic health has to do with how well your body absorbs nutrients and whether that process produces spikes in insulin levels, blood sugar, inflammation, and blood fat. How much fat you carry can affect these levels. Your doctor can use several tests to assess your metabolic health, but the BMI doesn’t take any of that information into account.
BMI measures your body size using your height and weight, but it doesn’t provide much information about your overall health. To learn more, your healthcare provider will need to run additional tests.
Obesity is now often recognized as a chronic disease, rather than a lifestyle issue. When obesity is thought of as a direct result of personal choices, the diagnosis comes with stigma that may prevent people from seeking healthcare. The current medical approach to obesity is less about losing weight and more about testing and treating people for related health conditions they may have.
According to some doctors and scientists, the BMI is an outdated method for diagnosing obesity. Rather than focusing only on weight or body size, which BMI does, a diagnosis should focus on what else might be going on in the body. Looking at the rest of the body, not just how much it weighs, could help people get the healthcare they need.
Using other diagnostic measures might also allow healthcare providers to better distinguish between obesity with related health conditions and metabolically healthy obesity. Opening a space for this diagnosis would help people learn about health risk factors before they experience symptoms and effects on their bodies.
BMI may give a healthcare provider some indication that you’re at risk for other health problems, but other tests can better determine what’s going on. The American Medical Association recommends that BMI be used in addition to other tests when assessing a person’s weight-related health risks.
There are several tests for measuring body fat percentage. A dual-energy X-ray absorptiometry (DXA or DEXA) scan is one of the best ways to get an accurate body fat percentage. It’s not perfect, but it can tell your doctor if you have a high BMI due to carrying extra muscle or fat. Your healthcare provider will need to order one of these scans, and your insurance must approve it before you can have the scan.
A cheaper and more affordable option is a bioelectrical impedance analysis (BIA). You can even get a scale that uses BIA for your home.
If you carry more fat around your waist compared to how much you have around your hips, you might have a higher risk for certain health issues. It’s easy to measure around your waist to find out if you need additional screening based on your waist circumference.
Your waist-to-hip ratio could give you additional information. A healthcare provider will measure your waist and hips, then divide the waist number by the hip number. If it’s over 0.9 for men and 0.85 for women, you might be at a higher risk for other health issues.
This type of ultrasound can be done in your doctor’s office if they have the right equipment. It can give you more information about how much fat you have, what type of fat it is, where it’s located, and how it compares with your muscle mass. You and your doctor may use this data to decide what your next steps should be.
Rather than trying to assess your health risks with various body measurements, it might be simpler to measure them directly through blood tests. Healthcare providers can measure your fasting glucose levels, cholesterol levels, and triglycerides — all measures of your metabolic health and cardiovascular risk — with a simple blood test. Additionally, a healthcare provider can measure your blood pressure right in the office. This information can give your healthcare provider a sense of your metabolic health, regardless of your BMI. Your healthcare provider can also refer you to an endocrinologist for further testing to understand any health risks.
If you don’t feel like BMI is accurately predicting your health risks or you want more specific information about your health, talk to your healthcare provider. They can order testing for a more comprehensive picture of your overall health.
On MyObesityTeam, people share their experiences with obesity, get advice, and find support from others who understand.
What has your experience with BMI been like? Let others know in the comments below.
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