Do you know your BMI, or body mass index? I’ve got news for you: using BMI as a way to classify you as obese, overweight, underweight or at your ideal weight is flawed. People love to talk about BMI because it’s a simple way to get a reading on your weight. There are all sorts of online BMI calculators, and your doctor may even ask if you know your BMI. What’s the problem then? It’s so simple, it’s inaccurate. Your body mass index only uses your height and weight to determine where you fall. What it doesn’t account for is your body type/frame and your body composition—your ratio of body fat and muscle.
Let me put it this way, if I was to use BMI to determine if I am at a healthy weight, I would be one number away from being classified as overweight. Using the standard chart below, I am a 24. But I am a 24 because of muscle.
Underweight, BMI = <18.5
Normal weight, BMI = 18.5-24.9
Overweight, BMI = 25-29.9
Obesity, BMI = 30 or greater
An ideal BMI (the measurement considered to be healthy) is between 20.5 and 21.5. How can a specific number be ideal when it makes absolutely no distinction between body weight from muscle and body weight from fat? BMI ends up labeling a broad segment of the athletic and similarly healthy populations as overweight and obese when they are not.
5 More Reasons Why You Should Not Use BMI To Judge Your Health
Aside from it being inaccurate, here are few more reasons that using BMI as a health indicator is a flawed system.
1) People are not created equal.
Ever notice when you look at special weight loss editions of magazines or TV shows that people can look dramatically different even if they are the same height and weight? People look significantly different at the same weights, because they are. BMI doesn’t account for proportions of bone, muscle and fat. BMI doesn’t know if you sit on the couch all day or if you are a gym rat—so how can it be the basis for determining if you are a healthy weight?
2) The BMI ignores your waist size.
Your height and weight alone aren’t the only factors that determine your health. If you have abdominal obesity and tend to carry most of your fat around your waist instead of your hips—you are more of an apple shape than pear—you’re at increased risk for coronary heart disease and type 2 diabetes. Your waist size should always be less than half of your height in inches. So, for a woman who is 5 feet, 4 inches, or 64 inches tall, her waist size should be less than 32 inches around. (Use a tape measure at the belly button, just above your hipbones.) The risk for health-complications goes up with a waist size that’s greater than 35 inches for women or greater than 40 inches for men.
3) Thin doesn’t mean healthy.
Yes, you love to hate them, but there are people who are thin and eat lots of junk food and rarely exercise. Thin or a low weight on a scale doesn’t necessarily translate into health. It’s only one piece of information. (And by the way, we call those people “skinny fat!” meaning just because someone is thin but eats whatever they want doesn’t make them healthy!) There are so many factors aside from your physical weight that determine your health such as what you eat, how often you exercise, your level of stress, how you handle that stress, and how much sleep you get most nights.
4) Other numbers are more important.
I love how Dr. Mehmet Oz advocates knowing your FIVE numbers to assess your health. He encourages people to know their blood pressure, waist size, weight, cholesterol and fasting blood sugar. That’s a more comprehensive overview of your weight and overall health than a BMI chart.
5) Track body composition, not body weight.
As a personal trainer, this is the most important concept to me. People tell me their goal is to lose weight and reshape their body. Therefore, stepping on the scale will indicate weight loss, but monitoring body composition is just as important. Body composition is the amount of body fat and lean muscle you have, not just what you weigh in pounds.
We all know what body fat is; lean mass is everything except the fat. It includes muscle, water, bone, and internal organs. Muscle is the “metabolic engine” of the body that burns calories and plays an important role in maintaining strength and energy. Healthy levels of lean mass contribute to physical strength and may prevent conditions such as osteoporosis. Metabolism is related to your lean body weight. How many calories you burn in a 24-hour period is dependent on your lean mass.
So how can you change your body composition?
The most appropriate way to improve your health and reshape your body is through a good nutrition plan and exercise, both cardiovascular exercise to burn off calories and strength training to increase muscle. The most accurate way to measure body fat is through hydrostatic weighting or the BOD POD—an air displacement method. But most accessible is skinfold measurements and body fat scales.
You’d never go to the doctor for a check-up and just provide your height and weight and go home—so make sure you don’t let your BMI number have the final say on your weight and well-being.