What Does BMI Really Tell Us?

by Dr. Suneil Koliwad, senior medical advisor for Yes Health 

We’ve all heard the term “BMI”—whether from our personal trainer or our physician. But what does it really mean? And how important is our “score” to our overall health?

BMI, or body mass index, is calculated from our height and weight to give us a general measure of our body fat. (The exact formula is: weight (kg) / [height (m)](squared) = BMI).  According to the Centers for Disease Control and Prevention (CDC), here’s a quick overview of BMI scores:

  • below 18.5 = underweight
  • between 18.5 to 24.9 = normal
  • between 25 to 29.9 = overweight
  • 30 and above = obese

Doctors have favored BMI as a health measurement tool because it’s easy to standardize. But it doesn’t factor in age, gender, race and body composition, all of which are significant in determining a person’s overall health. For example, many studies suggest—and the American Diabetes Association confirms—that someone who has extra fat around their waist is more unhealthy than someone who carries excess weight on their hips.

So the lingering question remains: how heavily should we weigh BMI values? After all, a professional football player who builds muscle mass may have a high BMI (since muscle is denser and weights more than fat), but we wouldn’t necessarily label them as obese. A slate of early studies suggested that, at least for the general population, BMI correlated well with increased body fat and the risk of developing related diseases, such as diabetes and heart disease. This is why BMI is built into many risk calculators for diseases like type 2 diabetes. The United States Equal Employment Opportunity Commission has gone so far as to propose rules allowing employers to penalize employees up to 30% of health insurance costs if they fail to meet “health” criteria such as reaching a specified Body Mass Index (BMI)

However, using BMI as a reliable health marker has recently come under scrutiny. Several new studies are questioning BMI’s ability to assess diabetes risk. For example, a study by researchers at UCLA and UC Santa Barbara found that 16% of people with serious obesity (over 30 on the BMI scale) had no other indicators of poor health, including high fat content in their blood, high blood pressure or elevated blood sugar levels. For people with milder obesity, this percentage rose even higher. The researchers argued that many people who may be considered obese by BMI standards, may in fact also be healthy. Interestingly, the study found that about 20% of people who had one or more serious health risk, including prediabetes, were considered normal weight. The researchers concluded that on its own, BMI is not the best indicator for assessing major health risks.

Perhaps this is because BMI isn’t sensitive enough to effectively measure small fat increases deep within the belly, where it’s thought to cause the greatest harm. This means someone who is otherwise thin may be at high risk even with a normal BMI. On the flip side, a person who gains weight in their thighs, buttocks, arms and legs will likely score high on the BMI scale, despite the fact that carrying fat in these areas may not be as risky.

So, if we can’t use BMI to accurately determine diabetes risk, what should we be using? We need something everyone can easily measure, understand and improve upon by making healthy lifestyle changes. Right now, this kind of test doesn’t exist. However, there are some interesting solutions on the horizon. For example, researchers have shown it’s possible to measure chemically altered proteins in the blood. The levels of these altered proteins indicate how much processed foods and meats people eat. The blood levels of a particular class of chemically altered proteins were shown to correlate with diabetes risk more strongly than BMI. These types of studies could one day lead to a simple blood test that could help reveal our diabetes risk, and further drive home the link between eating a whole-foods diet and better health. Fitness tracking and prevention programs like Yes Health are also key because they shine a light on our daily habits and give us a road map for making small changes that can lead to better overall health.

The bottom line? Getting healthy is not all about losing weight. It’s about eating healthfully, being active and doing things that make you happy. BMI can be helpful information to know, but it won’t tell you everything. If you do have a high BMI, talk with your doctor and take it as a cue to closely examine your lifestyle as a whole. How healthy is your diet? How often do you exercise? What is the quality of your sleep? What do you do to manage stress? Answering these questions can help you paint a clearer picture of your current health and illuminate places where there’s room for improvement. 

 

 


Yes Health is a low-cost, weight loss and diabetes-prevention program committed to helping everyone live healthier, happier lives.