Most people are familiar with the BMI measuring system, which is often displayed on charts from your doctor’s office, next to your weight. But what the numbers mean – and whether they’re a true measure of your health – is up for debate.
While we know a healthy weight is important, the factors that define healthy aren’t clear cut. Two people can have the exact same BMI, but wildly different states of health. So, what gives?
What Is BMI?
BMI stands for body mass index, and is a number calculated using certain ratios of height and weight. It was designed as a tool for researchers to calculate overall weight of population bodies, not of individuals. It still works well as a public health tool in the hands of researchers. However, as a one-on-one health marker between patients and doctors, it doesn’t allow for enough individual health factors and is two-dimensional. (1)
The problem with BMI is that it leaves no room for genetic individuality. Take two people of the exact same height and weight. One of them regularly lifts weights and has a relatively low percentage of body fat; the other lives a sedentary lifestyle and has a high percentage of body fat. Still, their weights are the same. BMI calculations would give them both the same number, which will be a poor reflection of health for one person. The active person could be falsely given an overweight classification, while the inactive person could be lulled into a feeling of health security.
Health is much more than a single number calculation or marker. We are three-dimensional human beings with multiple considerations needed to assess health.
How Was BMI Developed?
BMI is calculated by taking your weight in pounds and dividing it by your height in inches squared (your height in inches x your height in inches), and then multiplying that number by 703. (2) The final number is your BMI, and any number that is 25 or higher is considered too high.
The BMI is a way of measuring the body fat of individuals and categorizing them. What it does not measure is muscle, bone structure, or other individual elements, like fitness level or what type of fat a person has (with visceral or belly fat being more harmful than other types). (3)
Forms of BMI measurements have been around since the 1800s, but in 1993, the World Health Organization established the four BMI categories we know today: underweight (15-19.9), normal (20-24.9), overweight (25-29.9), and obese (30-35+). (4) In 1997, BMI categories were expanded to take into account differing degrees of obesity. The previous overweight category was renamed “pre-obesity” (25-29.9) and included new obesity categories of class I obesity (30-34.9), class II obesity (34.9-39.9), and class III obesity (40+).
In the U.S., the average BMI ranges between 24 and 27, meaning that almost half of the population falls into the “pre-obesity” category. (5) While it’s not a hard sell that many people in the U.S. could be overweight, is that an actual reflection of health? As demonstrated above, a fit, healthy person with more muscle and less fat could still be lumped into an unhealthy BMI category.
Other Markers for Health
While BMI is not going to be replaced any time soon from research perspectives, many doctors and other health professionals argue that there are better ways to assess a person’s health. The following are common ways that health professionals assess health, with or without BMI taken into account.
Waist Circumference or Waist-to-Hip Ratio
Doctor offices frequently measure waist-to-hip ratio to evaluate visceral fat and risk for possible associated issues, like type 2 diabetes. (6) Waist circumference is a basic measurement of your waist around your belly button using a tape measure. Men who have waist circumference measurements of 37 inches and lower and women 31.5 inches and lower are considered low risk, while anything above falls under intermediate or high risk. (7)
To measure waist-to-hip ratio, get the measurement of the smallest part of your waist in inches. Next, find the measurement around the widest part of your hips/buttocks. Your waist-to-hip ratio is calculated as follows: waist number divided by hip number. A healthy number is considered 0.9 or less in men and 0.85 or less in women. (8)
One marker that can be used to help assess heart health is the resting pulse rate. This is calculated by taking your pulse first thing in the morning before getting out of bed. Place your fingers on your wrist and find your pulse. Count the number of beats in 30 seconds and multiple by two to reach your resting heart rate. Alternatively, you can count your beats in 60 seconds and not have to do any extra math.
A resting pulse of 60 to 100 is considered normal, but athletes and extremely fit people may have a rate lower than 60, indicating an even more efficient heart. If you notice that your resting pulse is almost always pushing the upper limit, be sure to talk to your doctor.
Resting pulse measures health when paired with other factors, like glucose levels, blood pressure, and weight, and can help indicate how healthy your heart is. (9)
Blood pressure measures the amount of pressure in arteries and veins as blood travels throughout the body. The higher the number, the more pressure there is, which can indicate stress or even potential plaque problems in arteries, problems with the heart, or extreme stress. (10) One in three adults has high blood pressure. (11)
Blood pressure is measured in systolic (top) and diastolic (bottom) numbers. A normal, healthy reading is considered to be 120/80 or lower, with stage 1 high blood pressure defined as 130-139 over 80-89. As numbers get higher from there, more serious stages of hypertension (high blood pressure) are diagnosed. (12)
You can check your blood pressure at home using a digital cuff that you secure on your left arm, around your bicep. While these may not be as precise as doctor offices, using the same cuff at home on a regular basis to measure blood pressure can indicate increases or decreases over time.
People with diabetes often have to test their blood glucose at home on a regular basis, but measuring glucose can also be used as a marker for health. A normal, healthy fasting glucose should be less than 100 when taken 8-12 hours after last eating or drinking (so, first thing in the morning). (13) Optimal ranges for fasting glucose fall between 70 and 100. While you’re not considered diabetic until fasting glucose is 130 or higher, consistently ending up with readings between 100 and 125 is considered prediabetes. (14) Stress, diet, lack of exercise, lack of sleep, dehydration, and many other factors can increase fasting glucose levels – but regardless of what increases them, glucose levels are a major indicator of health. (15)
Relative Fat Mass (RFM)
Researchers are looking for better ways to uniformly measure body fat that are more applicable than BMI. The relative fat mass is still being studied, but one which some researchers claim is more relevant. It can be calculated easily, has slightly different formulas for men and women, and the final numbers aren’t as likely to class people incorrectly, as with BMI. (16)
The Bottom Line
Ultimately, BMI is a not a total measure of health – it is simply a way to categorize someone’s size. And while BMI has its useful applications, it only gives you a limited perspective on how healthy you may (or may not) be. 17)
Using these other health markers together presents a more three-dimensional picture of health, many of which you can monitor yourself at home. If your measurements indicate out-of-range numbers, you can go to your doctor and express your concerns.
Measuring your health at home also offers you a more personal connection to your state of wellness and can allow you to be more on top of your health than just waiting for your doctor to discover via annual wellness check-ups. By being proactive with your health, you can notice slight changes and be able to proactively respond.