In this article, I’m going to answer the question is BMI accurate? BMI is short for body mass index. And the short answer is yes for most people. But not if you regularly lift weights and have built an appreciable amount of muscle (more on why this is later in the article). I’m also going to discuss why there are better metrics that can help you get into the best shape possible.
Firstly What Is Body Mass Index (BMI)?
As previously stated BMI means body mass index and its a measurement of your body weight per unit of height.
Their are 4 tiers that BMI can class you as:
- Underweight – Is a BMI of less than 18.5
- Normal weight – Is a BMI ranging from 18.5 – 24.9
- Overweight – Is a BMI Ranging from 25 – 29.9
- Obese – BMI of 30 – 34.9
- Extremely Obese – 35
To check your BMI look at the chart or click the link below.
Using Myself As An Example To Illustrate a flaw in Body Mass Index (BMI)
Currently, I’m 170 pounds at 5’10 with roughly a 10% body fat percentage with a waist size of around 31 inches. And according to the BMI formula, I’m just at the end spectrum of a healthy weight.
But the fact is if I increased my body fat percentage to the high teens 15-17 per cent. I would be classed as overweight (by BMI). But technically I wouldn’t be overweight. I’d be at a healthy body fat percentage. Because you can be healthy in the high teens of body fat percentages (15-19% body fat).
And because I’ve been training for 2 – 3 years. I’ve got more muscle than BMI accounts for.
BMI Is Good For The General Population – Is BMI Accurate?
If you’re obese on the BMI scale (a BMI score of 30 or more) then there’s a high chance that you’re at an unhealthy body fat percentage. This is because Although BMI doesn’t work that well for natural lifters. If you’re classed as obese your either at too high of a body fat percentage ( 20% plus) or you’ve developed an abnormal amount of muscle (on steroids).
And if the BMI calculation is classing you as obese (lifter or not) you could probably do with getting to a healthy body fat percentage (10% – 20%).
Your Body Composition Is More Important Than Your BMI
Body Composition is defined as the amount of muscle, fat and water that your body is made up of. For instance, if someone has a body fat percentage of 10% and someone else has a body fat percentage of 20% then they have a different body composition. Because one has a higher proportion of fat and one has a higher proportion of lean body mass (LBM) than the other.
3 Ways To Track Your Body Composition
- The Accu Measure 3000 Body Fat Calliper
- Waist measurements And How Your Clothes Fit.
I’ll quickly go into these in detail.
The Accumeasure 3000 Body Fat Calliper
This is extremely easy to use and only costs £21.00 and it lasts. I’ve had mine for over 3 years.
It’s simple to use. And you only measure one point on your body. Which is the point above your hip bone.
And then you use the body fat chart. That it comes with, to estimate your body fat percentage.
Waist Measurements And How Your Clothes Fit
If you buy something cheap like the myotape below. You can easily gauge your waist measurement.
Generally speaking, If your waist measurement is going up. You’re putting on fat. And if your waist measurement is going down you’re losing fat. This is because most people store a high proportion of fat in their abdominal region.
And if your clothes feel looser and you need to use a tighter notch on your belt.
You’ve lost fat.
Take Progress Pictures Front, Back And Side – Is BMI Accurate?
After a while, you’ll lose fat and you’ll look back at your first pictures and you’ll see the difference in the pictures. Especially if you’ve lost a lot of fat.
But, just know that the differences won’t be night and day after only a week or two. Fat loss takes time and you will notice the differences eventually.
These methods of tracking your body composition are good. But they’re even better when you use them together.
For instance, if you’ve lost a couple of inches from your waist. Lost a few pounds. And can see the difference in your pictures. There’s no doubt about it you’ve lost fat.
Use BMI As A Rough Estimate – Is BMI Accurate?
BMI can be a great way to estimate whether or not you need to lose fat. But I’d say this only applies to you if you:
- Haven’t spent any serious time getting stronger and lifting weights.
- Are brand new to working out.
- You just want a rough estimate of whether you’re a healthy body weight or not. And you’re not interested in lifting weights and building muscle.
I’ll go into these points in more detail quickly. But first I’ll quickly explain the role fat-free mass plays in the inaccuracy of BMI.
What Throws Off The Bmi’s Level Of Accuracy Is The Amount Of Fat-Free Mass That You Have Or Also Called Lean Body Mass (LBM)
Firstly fat free mass (or lean body mass LBM) is everything in your body that isn’t fat.
For instance, if there were 2 males. Both 5ft 10 and weighing 180 pounds but one person was 10% body fat (and has been lifting for years) whereas the other person was 20% body fat (and hasn’t ever lifted). The BMI score would be the same for both individuals.
Whereas the male who is at 20% body fat would start to be crossing the threshold of an unhealthy body fat percentage ( where insulin sensitivity decreases and your body just doesn’t operate as well)
And the other male at 10% body fat would be at a perfectly healthy weight and body fat percentage.
But they would both be classed as being overweight on the bmi scale.
So as you can see the BMI scale works great for the guy who doesn’t lift. And tracking body composition is so much more important for the guy at 10% body fat.
The Body Mass Index Can Be Useful If You’re Brand New To Working Out – Is BMI Accurate?
The reason for this is simple.
If BMI gets skewed by the amount of lean body mass you have.
Then if you don’t have much lean body mass, which people don’t normally have before properly working out.
Then the BMI scale can give you an accurate gauge if you’re overweight/obese.
But I wouldn’t take BMI as gospel. I still think figuring out your body composition is so much more practical.
You Just Want A Rough Estimate Of Whether You’re At Healthy Bodyweight Or Not (For People Who Don’t Train)
If you don’t plan on taking your lifting seriously. And just want to lose a little bit of weight. Then BMI can give you a rough estimate of whether you’re at a healthy weight or not.
Because if you never start lifting properly and improving your whole body muscle mass. Then your BMI result won’t be skewed by LBM.
Conclusion – Is BMI Accurate?
- BMI can give you a rough estimate that determines if you’re at a healthy weight or not (for non-lifters).
- If you’ve spent a decent period of time building muscle and losing fat then BMI won’t give you an accurate representation of your weight. Unless you’re obese. (because it’s very hard to gain enough muscle to be classed as obese as a natural weightlifter) and there’s probably just a higher chance that you’ve put on too much body fat.
- If you’re just about to start the gym. And have never spent any time building muscle then BMI will probably be fairly accurate for you.
Thanks for reading.
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