Body Mass Index is a way to measure whether or not a person is underweight, overweight or normal weight. It is a calculation that evaluates body mass compared to height. It is widely used to determine if people fall within a weight range that is healthy.
We are living in a time when people are more obsessed than ever in being thin.
The visual images put forth in the media are that of super skinny women and body builder men, which can make us normal people feel a bit self-conscious. Recently a few actors and models have come forward to show the contrast between their photoshopped selves and what they look like before alteration. However, it is difficult to remember when we open a magazine that we are looking at an artistic creation, not a true reflection of the real world. A measurement like BMI can bring us back to reality with a more realistic assessment of what it means to be healthy. It can also enlighten us to the reality of weight problems. Having said that, BMI does have its limitations.
BMI is calculated by comparing weight in kilograms to height in centimeters. If you’re like me and live in the U.S., you probably have absolutely no clue whatsoever what your weight is in kilograms or what you measure in meters. I remember hearing as a child about how we were inevitably going to convert to the metric system, but I’m a fully grown adult and I’m still waiting. So before we get started, us Americans need to do a little extra calculating.
*First, we need to multiply our weight in pounds by .45.
So I weigh about 120 pounds (I think, Honestly, I only weight myself once a year when I go to the doctor’s office.) So, my first step would be to multiply 120 x .45 which equals 54 kg.
*Then we Americans have to multiply our height in inches by .025.
I’m 5 foot, 5 inches, or 65 inches to be exact. So my calculation is 65x.025 which equals 1.625 m. Ok, now we are working with the metric system. Whew, that’s a lot of math, and we haven’t even gotten to the real equation yet!
The equation to determine BMI is weight divided by height squared.
So the first thing we need to do is determine our height squared. Back to using myself as an example, I’ll multiply my height by itself (1.625 x 1.625) which equals 2.64. And the final step is then to divide my weight (54) by my height squared (2.64). This means my BMI is 20.45.
So here is a summary of the results per the World Health Organization:
But here’s the catch.
This evaluation doesn’t account for someone’s build. Is the person small boned, stocky or muscular? Having extra pounds of muscle is very different than having extra pounds of fat. Someone who gains weight by muscle lifting will have an increase in BMI, just as someone does who is sedentary and gaining fat. So BMI can be a helpful indicator of health for many, but it doesn’t tell the entire story for everyone. Therefore, it is important when calculating BMI to really evaluate someone’s build. We can quickly see that a body builder is not obese, but muscular. BMI does not evaluate and that is where BMI falls short
There are other, more accurate ways to evaluate body composition.
One of the best ways is to measure body fat directly. Excess weight is usually only problematic when it is composed of fat. There are many ways to measure body fat. First, there’s hydraulic testing which involves measuring fat by submerging a person in water. Next, there’s Dexa scans, which can also be used to measure bone density and evaluate risk for osteoporosis. A Dexa scan uses beams of light to determine body fat as well as bone density. These methods can give a very accurate reading, however, they also can cost a pretty penny.
Skin Calipers are a cheaper method, often used in gyms to pinch the skin and take fat measurements. The skin calipers literally grab the skin and then measure the skin fold. This method is commonly used due to its convenience along with its low price tag. However, because fat is only measured in a few select areas, it is difficult to get a truly accurate reading of overall body fat this way.
For this reason, BMI remains one of the most commonly used measurements to determine body composition. No, it is not a perfect way to evaluate a person. BMI needs to be taken with a grain of salt, and a person needs to be honest with themselves in evaluating their own muscle mass. This can be difficult as, not only do people overestimate the amount of muscle they have, they also underestimate it. My suggestion when looking at a questionable BMI is to follow-up with skin calipers. BMI doesn’t create the entire picture of whether a person is healthy, but it is a convenient tool to start exploring the topic.
Do you know your BMI?
I’m glad you included some of the “catches” and limitations with BMI. But, as you’ve said, some of the other more complete options for judging a healthy body mass index can be costly, so it still remains a good means for gauging where you fall on the weight spectrum.
Yes, I wish some of the other options were cheaper, but for most of us, this is the only affordable option.
My previous doctor was big on BMI and did calculate mine. But like you I agree there are to many variables. It is a great place to start but other factors, like body build, metabolism and even age play a role. However, the range, such as 18-25 for normal helps a lot. I guess if you are able to stay within that range you are doing well.
I feel best when I weight 125 pounds (56.25Kg)22.68BMI, a weight that that I am always working towards and seldom achieve – I normally run around 110 pounds (49.5kg)19.95BMI.
Interesting exercise.
Lenie, you probably will be best served focusing on adding muscle as opposed to worrying about fat. I imagine you already do muscle building exercises. They are especially important for us women as we age and can be helpful for someone who wants to gain weight.
My physician is big on BMI, but does factor in variables when using it in my overall heath assessment. She has just purchased a fancy scale that shows tons of other data, so now the variables can be factored more precisely! It’s called Lookin Body…completely fascinating to me. Measures Weight, skeletal muscle mass. body mass fat, total body water, and then shows a lean mass evaluation!
Wow, you are the second person who said your doctor focuses on BMI. I’ve never had a doctor mention BMI to me, even when I was heavier. I love that your doctor has that modern scale. I’m sure it gives you really valuable information!
I was just wondering about this the other day! My husband and I have a running debate on whether he weighs enough. (He runs and bikes a lot.) His BMI is normal, but I think he’s too skinny. Now I can tell him you said I’m right! 🙂
Haha! Well, from one woman to another, I’m always happy to help a wife say, “I told you so” to her husband! 🙂
The fact that you only weigh yourself once a year is probably as much a sign of good health as your BMI.
I love that, Ken! I never thought of that!
Yes, I know my BMI as well as my ideal weight range. I try to ensure my weight does not exceed this which is a little difficult.
It’s great that you have that information, Phoenicia! The more you know, the more empowered you are to make good choices!
I also have never had a doctor mention BMI but I do know what mine is. There certainly are other factors to be considered. I think it is more important to live a healthy lifestyle. There is too much emphasis on being ultra thin and this results in awful illnesses that can even result in death.
The interesting thing, Beth, is that I had a trial at a gym a couple years ago where they measured my BMI. They told me if I worked with them, they would help me lose 9 pounds of fat and gain 5 pounds of muscle so my BMI would somehow be 16. I think it is important to realize that less fat isn’t always better. Also, they had to have me lose fat to gain muscle or my BMI would have gone up!
I’m so glad that you pointed out that BMI is not the absolute basis when it comes to evaluating our body’s composition and using this to see how healthy we are. Nevertheless, it’s still very important to make sure that we try to at least keep our BMI within the normal range to increase our chances to live a healthy life.
I would say BMI is one of the best “easy” measurements we have right now. However, it is nuts when people give it too much weight (pardon the pun!)
This is so interesting Erica and I have to admit that I’ve never had a doctor even mention BMI. It’s one of those things I was aware of but relegated it to something only those who buy muscle magazines would care about. Thanks for providing some clarification on this issue!
Glad this was helpful, Marquita. BMI is definitely something that is good to know, despite its imperfections.
I’ve always wondered about BMI, and glad to have you explain it. Last time my doctor checked, I was in the “normal” range, thank goodness. However, as you so rightly point out, it should be just one of the ways in which we monitor our health – although some people do seem fixated on it!
While BMI doesn’t tell the whole story, knowing that your BMI falls into the normal range is a good place to start. Unless you notice that you have very little muscle tone, you probably are in a good range.
My BMI has always been at the upper-end of “healthy,” but people always think I weigh less than I do. We all carry weight differently I guess. I try not to weigh myself often. For years, I’ve gauged myself by whether or not I fit into my favorite brand and size of jeans. It seems to work as I stay motivated enough so the jeans don’t cut off my circulation 😉
I’m certainly not an expert in this, but I believe that some of us have heavier bone structures, and of course, some of us are naturally more muscular. I gauge my weight the same way. As long as my jeans fit, I’m good!
This is interesting. I read the only accurate way to get BMI is to be submerged in water. That always sounded a bit extreme to me. I have to admit, I’m one of those people who uses a scale, it’s the surest way I know to monitor my weight. As far as body fat, I hope that a healthy diet and 2 hours of Ashtanga Yoga 6 days a week is monitoring that. And if it’s not, I surrender to that and choose to let it go : )
I believe that is via the hydraulic body fat testing, and yes, that is way more accurate. It also has a very steep price tag. I’ve always wanted to get that done, just out of curiosity. Wow, 2 hours of yoga, 6 days a week! That is commitment!
For the mathophobes out there, the National Heart, Lung, and Blood Institute offers a BMI calculator that accepts ‘English unit’ inputs (height in feet and inches, weight in pounds):
http://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm
Thanks for that link, Andy! I didn’t know of that. That really makes it so easy!
You are absolutely correct about not taking in the person’s body type. I am a wrestler, I am 6 feet tall and 260 lbs, 50 inch chest with 19 inch arms. I can tell you the bigger I am the better shape I am. When I loose body weight, it is because I am not exercising, and although I weigh less, I have more body fat.
Yes, William. BBI would not be a good measurement for an athlete that needs bulked-up muscle. Most of us don’t need or have that much muscle so that makes BMI a better measurement. It, of course, depends on the person.
Did the math and my BMI is 23.36. About what I expected. But I’ve always been “small”. But I’ve lately noticed that Im getting a little softer in the middle. Again I’m still considered skinny by most who don’t know me, but to those who do, myself included, I’m growing as a person in a way I don’t want to. like you mention how a person needs to have their build assessed with the addition of BMI, I think you need to also look at the persons personal build history. Have they always been big and its always been a struggle to lose weight/mass? Or like me, have they also been small and struggled to put on weight. Trust me, it goes both ways. As much weightlifting as I have done (when trying to bulk up…not lately obviously) while taking in as many calories as I can to help with that, its still damn hard for me to gain any significant mass. So any significant change (like I mentioned) is definitely noticeable.