BMI is a tool that gives you an idea of the risk of your weight when compared to your height. You may have heard of it before, maybe even in your doctor’s office. But what does BMI mean for your health? I want to explain that today because I think it’s a helpful assessment when you’re starting an exercise program. Just remember that one tool can’t tell the whole story.
Determining your health involves many different measurements and it isn’t just the absence of a disease or diagnosis. It includes things like bodily strength, aerobic capacity, mobility, how we manage our emotions, socialize, and how we eat. In other words, health is holistic and involves physical, mental and social factors.
So in determining overall health we need to look at many different things because each one comes together to form a bigger picture, like the branches of a tree. BMI is just one branch of health. I’d like to focus on just that today because it’s talked about so much in the health and fitness industry.
BMI is definitely a helpful tool but I want to make sure you know what it can tell you about your health and what it can’t.
What exactly is BMI?
BMI, or body mass index, is a measurement of your weight in kg divided by your height in meters squared. It basically tells you whether your body’s mass is in a healthy range for your height. And for most people, it works pretty well. But you’ll find plenty on the internet about how it isn’t a good indicator of health at all and I’ll address that in a bit.
Don’t worry, you don’t have to do the math yourself when figuring BMI! You can use this calculator to figure it for you. Just fill in your height and weight and click “calculate”.
Once you hit calculate it puts you in a category.
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- “Underweight” is 18 or less
- “Normal” weight is from 18.5-24.9
- “Overweight” is from 25-29.9
- “Obese” is anything over 30
All it tells you whether your weight is appropriate for your height. This is an important piece of information because being overweight is associated with many diseases. But each category is a large range of numbers which I think is one downside of the tool. Let me give you an example.
My own weight is 124 lbs and at my height, I’m in the “normal” range. But I can also be “normal” at 115 lbs and 154 lbs. In my opinion, under 120 lbs would be too skinny for me. And at 154 lbs I know I wouldn’t be feeling very healthy because I can’t imagine myself carrying 30 more lbs! So it’s kind of subjective.
Looking at it that way, you can see how that range is pretty big. That span of 115 to 154 is a difference of 39 lbs. So am I healthy if I fall anywhere in that range? This is why BMI alone doesn’t tell you much about your health status. That depends more on other factors in addition to BMI.
How BMI is helpful
Again, BMI is helpful because it tells you whether or not your weight is either too much or too little for your frame. Obviously, a taller person would carry more weight than a shorter person because their weight is spread out over a bigger area.
For example, if you’re 5’2″ and weigh 150 lbs you’re considered overweight with a BMI of 27.4. But if you’re 5’10” at 150 lbs then you’re at a low normal weight with a BMI of 21.5. And those two people will look very different!
So for the average person, BMI is pretty accurate for judging weight according to height. Most of the women that come to me for personal training have a goal of weight loss so BMI is one of the first things I figure for them. That way they’ve got a baseline to start with.
Related article: 6 Reasons why you need a personal trainer.
If their BMI puts them in the category of overweight or obese it might help to motivate them to work harder to get their weight down to a healthier range. It might also make them realize that what seems normal for them is actually putting them at risk for more diseases.
According to the CDC, BMI is fairly strongly correlated with various metabolic and other diseases. Just remember that any amount of weight loss lowers your risk of disease even if it doesn’t put you in the normal category. Also, regular exercise lowers your risk of disease even without weight loss!
Of course, we all know there are people out there that are a “normal” weight but don’t exercise and are very unhealthy. Some of them may be smokers! That’s why figuring BMI for your health is only part of the story.
How BMI can affect your health
If your BMI puts you in the overweight or obese ranges then you should at least be a little concerned. A higher BMI is associated with plenty of diseases and all the leading causes of death in the U.S. including:
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- Heart disease
- Cancer
- High blood pressure
- High cholesterol
- Type 2 Diabetes
- Stroke
- Covid-19
- Osteoarthritis
- Sleep apnea
- Mental illnesses like anxiety and depression
- Pain and lowered mobility
Besides the risk of death, all of these problems also lead to a lower quality of life. So it’s important to know where you stand with your weight and height even if you don’t already have a diagnosis. Preventing disease is always easier than trying to reverse it.
In general, people gain on average about 1 lb per year after the age of 20 until about their mid-50’s. After that, there’s often a decline in weight due to a loss of bone mass and muscle. Studies show that people with high BMI’s also tend to have higher rates of disability as they age compared to people in the “normal” range.
The problems with BMI
One of the main problems with BMI is that it doesn’t know how your weight is distributed over your entire body. So if you’re a pear shape with your weight around your hips, that weight isn’t very dangerous for your health. But if you’re an apple shape with your weight around your waist then you should be concerned.
This is one reason why waist circumference should also be measured along with BMI. As a woman your waist size should be less than 35 inches and men should shoot for less than 40 inches. Studies show that waist circumference is “associated with significantly increased CVD (cardiovascular disease) even among normal-weight women”.
BMI also doesn’t work as well for many adults over the age of 65. As people age, they may lose weight but that can be due to a loss of bone density and muscle making fat the predominant tissue. As I already said, BMI doesn’t account for body composition (amount of fat vs muscle) which is more important in determining your health.
This is also why athletes and bodybuilders get inaccurate results with BMI. This group has denser bones and a lot more muscle than the average person which is very healthy. Bone and muscle weigh more so they can’t be compared to an average person of the same height. BMI will label them as “overweight or obese” when they’re obviously not.
If you’re over 65 and want to know the appropriate range for BMI that puts you at a lowered mortality risk then check out this article by The Geriatric Dietitian.
My final thoughts
BMI is just a tool that gives you an idea of how appropriate your weight is for your height. But you need to understand that that’s all it can tell you in relation to your health. That’s why you should also figure other measurements like waist circumference, blood pressure, blood sugar, and cholesterol levels.
So use the BMI formula I provided here but make sure you also see your doctor to check other markers of health. From there, start exercising or just moving more and eating healthier (real) foods with lots of nutrients. You want to educate yourself first, then start making little changes that will lead you toward better health and disease prevention.
Related article: Are you getting enough nutrients for good health?
Even if you are in the “overweight” category for BMI you may be much healthier than a person who weighs much less. It all depends on how you live your life and how well you take care of yourself overall. The big picture is what matters, not just one branch of the tree!