Is BMI Accurate? Learn More About BMI and Other Health Measurements

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If you’re interested in bariatric surgery, or if you’ve already undergone the procedure, you’re likely well-acquainted with your Body Mass Index (BMI). For the uneducated, BMI is a mathematical formula based on weight and height that’s used to calculate percentage of body fat. Use our BMI calculator to determine your own body mass index. 


If you have a BMI of over 25, you’re considered to be overweight. If your BMI is less than 18.5 you’re underweight, which comes with its own set of potential health risks. 


BMI is ultimately a tool millions of health care professionals rely on to determine the weight classification of their patients (overweight, underweight, healthy), which in turn could help to identify potential health risks. That said, is BMI accurate? This article seeks to answer that question, and offer a possible alternative. 



Is BMI Accurate?


Put simply, BMI is an easy to use screening tool that helps medical professionals screen weight categories. While widely used and convenient, BMI is not a diagnostic tool. Your doctor will need to perform additional assessments to gain a full evaluation of the health risks you potentially face in your weight category.  


These assessments include: 

  • Family history 
  • Diet  
  • Measurement of body fat percentage 
  • Exercise patterns 


Additionally, BMI doesn’t consider gender, age, or muscle mass, which could lead to inaccurate measurements as a result. Because of this, the answer to the question “is BMI accurate?” is “it depends.” BMI isn’t always accurate for every individual and there are more comprehensive ways to measure health. 


For example, a bodybuilder may have a high BMI despite having a low percentage of body fat. This is because muscle mass isn’t factored into the equation. On the other hand, an elderly person who has lost muscle mass due to aging may appear to have a healthy BMI, even if they don’t. 


How Does BMI Correlate to Health? 


The rule of thumb is that if your BMI classifies you as being overweight or obese, you’re unhealthy. If your BMI reads within a normal range, you should be in top form. It’s a simple process, but it’s far from error-free. 


Research published in 2016 found this assessment to be grossly inaccurate. In the study, researchers found that more than 54 million Americans classified as overweight or obese were considered to be completely healthy upon analysis of other cardiometabolic measurements (cholesterol, blood pressure, blood sugar, etc.). 


On the opposite end of the spectrum, 21 million Americans who were classified as having a normal BMI was determined to be unhealthy based on the same cardiometabolic measurements. 

To conduct the study, researchers turned to data from the U.S. National Health and Nutrition Examination Survey and compared BMI measurements against a range of additional health markers, such as blood pressure and cholesterol levels. The results revealed the inaccuracies of BMI measurements on both ends of the weight spectrum.



Alternative Health Measurements to BMI


Some experts believe the limitations of BMI makes it an ineffective method of determining weight classifications. Instead, many of these experts advocate that measuring the circumference of the waistline is a more accurate method.  


This is primarily because BMI doesn’t take into consideration where fat is located on the body. For example, excess weight gain around the hips and buttocks is generally less worrisome than excess fat around the abdominal region which could lead to an increased risk of obesity-related health complications.  


A study by the National Institute of Health found that a bigger waist circumference – generally larger than 35 inches for women and 40 inches for men – is linked to an increased risk of heart disease, Type 2 diabetes, abnormal cholesterol levels, and high blood pressure. 


Despite the supporting statistical data, there are still those who believe that measuring the circumference of the waistline is still not an entirely accurate method of determining potential health risks. Though effective, this method still fails to consider crucial health factors such as race, age, and activity levels. 


What Can You do to Lower Your BMI and Shrink Your Waistline? 


Regardless of which method of measurement you prefer, you’ll still want to get your waistline and your BMI to healthy levels. You can do this by regularly exercising and eating a healthier diet. 


If you’re seriously considering bariatric surgery, or if you’re already undergone surgery, lifestyle changes are a mandatory step to keeping unhealthy levels of body fat at bay. 


Even losing a small amount of weight, as little as 5 – 10%, can have a massive improvement in your cholesterol, blood pressure, and blood sugar levels. 


What BMI Should You Have to be Considered a Candidate for Weight Loss Surgery? 


Weight loss surgery is the most effective method for fighting obesity. Most medical professionals agree that morbid obesity falls within a BMI of 35 – 39.9. At this level, obesity-related conditions such as obstructive sleep apnea, Type 2 diabetes, osteoarthritis, and high blood pressure are a risk. 


To be a good candidate for weight loss surgery, you will need to meet the following criteria: 


  • You’re unable to maintain a healthy body weight for any given period, even under a medically-supervised dieting plan
  • You are more than 100 lbs. heavier than your ideal body weight
  • You have a BMI of over 35 and are experiencing a range of adverse health complications, such as diabetes or high blood pressure
  • You have a Body Mass Index (BMI) of over 40



Final Thoughts 


Is BMI accurate? Not completely. Research clearly shows that the system is prone to miscalculations. That said, when BMI is used as a diagnostic tool in combination with other types of health tests, it can still be an effective method of determining weight categories and identifying potential health risks. 


At the end of the day, BMI is an easy to use system that’s recognized around the world. While prone to inaccuracies, its wide acceptance is a clear indicator that health care professionals will continue using it for the foreseeable future. 


A good doctor should recognize the limitations of the BMI system, and offer additional tests if needed to give you a full picture of the potential health risks you may face in your weight category. Our bariatric surgeons would be happy to answer any questions you have about your BMI and possible weight loss procedures. Contact us today to learn more. 


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