I first learned about the Body Mass Index (BMI) calculation my junior year of college while munching a turkey and swiss wrap in the back row during my Health Psychology class. I must have heard of it before then, but I’d never taken the time to calculate my own. During class, we used a simple height/weight calculation and I remember falling within the “normal” range and thinking “well, crap, I should probably lose some weight.” Of course, that was about the time I had just begun down the whole dieting path, caloric obsessions and exercise addictions, and now I see this number as an arbitrary figure that doesn’t consider density of muscle versus fat.
But in discounting BMI, am I just rationalizing that it’s okay to have a higher BMI despite being a long-distance runner? Or are my suspicions right: is this BMI thing really just a bunch of BS?
BMI is a simple and universal measure of body fat that can determine whether or not one falls within the healthy range for their height. BMI is found by simply dividing your weight by your height and squaring the resulting number, or (w÷h)² if you like math formulas. It is used to calculate the BMI of men, women, and kids of all ages. According to the measure:
- under 18.5 is considered underweight
- between18.5 and 24.9 is “normal”
- between 25 and 29.9 is overweight
- over 30.0 is obese
I don’t like numbers. I don’t like labels. So I might be biased against BMI to begin with, but below are some common blanket statements regarding BMI that should be taken with a grain of salt, so to speak.
#1: BMI reveals accurate body composition readings
False. Body Mass Index readings are arbitrary in that they do not consider fat versus muscle. BMI is a numerical relation between one’s weight and one’s height. That’s it.
#2: A low BMI means you are healthy
False. You may mathematically fit the part; however, you could have very low physical activity and a crappy diet. You may be able to subside on Big Macs and candy and never gain weight. That’s genetics. Diet, work conditions, genetic factors: these all contribute to health and eventually such a lifestyle will result in poor health, despite an arbitrary number.
#3: A high BMI means you are unhealthy
False. A very muscular person (hello long-distance runners!) may have the same or similar BMI to that of an overweight person despite having extremely different levels of muscle and fat. Here density comes into play. Many of us think muscle weighs more than fat, but actually muscle is merely much more dense than fat. Ultimately, this means when looking at five pounds of muscle and five pounds of fat side by side, the fat takes up more volume, or space, than the muscle. One can be extremely fit and quite dense – resulting in a similar BMI to someone obese with a “lighter” volume of fat. Does that make sense?
What I’m trying to say here is: don’t stress about a number. If you follow basic guidelines of physical activity and diet recommendations, chances are you are doing just fine. I remember trying out this app during the Summer Olympics, which calculated your BMI and gave you your counterpart Olympian. According to this, I’d make a great competitive 20k walker. I wouldn’t take it too seriously, but it’s fun, nonetheless. Another tidbit of random trivia for your next cocktail party: according to the standards of BMI, Lebron James is just short of being considered obese with a 29.6 BMI (he is 6’5″ and weighs in at 250 pounds).
How do you feel about BMI? Arbitrary? A good starting point for measure of health? For the birds?
Many of us think muscle weighs more than fat, but actually muscle is merely much more dense than fat.
When people say that muscle weighs more than fat, they mean that a given volume of muscle weighs more than the same volume of fat– which is true, because of the fact that muscle is more dense than fat.
That said I agree with the rest of your points. Also worth noting is that until 1998, a BMI of up to 27.8 was considered in the ‘normal’ range, when the ‘overweight’ category was changed to start at 25. I don’t know all the scientific literature, but there are studies that put the risk of ill health effects for people in the 25-28 range as pretty much the same as those in the 19-25 range.
Hi Meaghan,
Thanks for reiterating the point that muscle doesn’t “weigh” more than fat. I used to be one of those people who thought that! But, indeed, the density is a factor that shouldn’t be ignored. I wonder what made the standards of BMI change since 1998?
What I mean is that muscle does weigh more than fat– given the same volume. A pound of muscle and a pound of fat both weigh a pound, but a 12″x 12″ x 12″ box of muscle weighs more than the same size box of fat.
So muscle does weigh more than fat– unless you would say that cotton balls and concrete weigh the same amount because 1lb of each weighs 1lb.
Ouch. This is starting to hurt my head 🙂 It sounds like you’re both saying the same thing to me?
Hurts my head, too. I think we are saying the same thing! This article puts it succinctly, in my opinion: http://www.thefitnessexplorer.com/home/2010/8/24/does-muscle-weigh-more-than-fat.html
No. Of course a pound of anything weighs the same as a pound of anything else– they both weigh a pound. That is why weight comparison is done by volume– does spinach weigh as much as rice? No, a box of spinach weighs less than the same box filled with rice.
(Not my blog, don’t have time to dig up the best source)
http://haveanamasteblog.com/2012/07/yes-muscle-weighs-more-than-fat/
I touched on my thoughts about BMI in my post about pregnancy weight gain (shameless plug: http://www.saltyrunning.com/2012/07/12/pregnancy-weight-gain/). I always weigh more than I look – or so people say. I used to assume I was fat because of my BMI or # on the scale. But ultimately, the better metric is body fat %. Actually, maybe the best metric is how the fave jeans fit (straight out of the dryer – no cheating 🙂 )
Hey Salty!
Thanks for linking back to your post about pregnancy weight gain – my sister is pregnant with her second and I’m going to share this with her to calm any of those “weight gain” anxieties! Like you said, it’s all about trusting your body and letting it do what it needs to do to produce and nurture a strong and healthy babe.
I just look at it as a number and don’t pay much more attention to it. My blood pressure is great, my cholesterol is great, everything is great! hahaha I eat a healthy diet and work out so I know I’m taking care of myself and that matters more than a ratio or number on a scale or a dress tag.
Agreed! And, people don’t love you for the size of jeans you wear. People love you for YOU.
good post. BMI also doesn’t take into account your frame size. after all, no one has the same size skeleton! i am very fine-boned (narrow hips, wrists too small to wear adult women’s watches, etc.) so that drags down the BMI calculation. initially BMI was actually intented to be a population statistical measure and not a measure of an individual’s health and it’s really unfortunate that it’s often used now as the definitive measure of healthy/fat.
Agreed! Frame size is a whole other issue! (And I have the same dang issue with watches!)
Great point! I’m also screwed here by my slavic genes 🙂
My thoughts on BMI is that when used in conjuncture with other metrics such as resting heart rate, blood pressure, etc it can be used to give a fuller picture of a person’s health. However, on it’s own it pretty much worthless.
I am home sick today, and I was watching Hoda and Kathi Lee. Apparently, they have some kind of team weight loss challenge going on because they were talking about their teams and how much weight they have lost. The trainer was so excited about their BMIs dropping! I have never been one to put so much emphasis on BMI since there are so many other factors that contribute to being healthy–similar to what Amanda said above. I enjoyed reading your post!
I appreciate this post SO much! I have always been what I call a “thick” girl. As a senior in high school, skating 6 days a week, sometimes twice a day, I was a solid 140 pounds. I was extremely fit yet my BMI was pushing “overweight.” Now, 20 years, 3 kids, 6 half-marathons and a lot of miles later, I’m pushing “obese.” I know in my heart that it doesn’t really matter, and that I am healthier now than in my 20’s, but it is alway so validating to have other people out there voice their opinions on BMI! Thanks Ladies!!
Remember, whether you are a male or female, maintaining optimum weight and staying fit and healthy is the most appropriate thing to do. While on the one hand, it allows you to avoid health problems associated with obesity you can also avoid risks and health complications such as type-2 diabetes, gall bladder disease, high blood pressure, osteoarthritis, hypertension and heart disease among others.
BMI is BS in my non-professional opinion. I was obsessed with getting to “normal”. I’m a 41 yr old male, 5′ 9″ and my normal is 169. I hit that mark and everyone commented “you look too thin, you look unhealthy” etc, I look at pics on FB of when I was that thin and I agree! Right now, I’m at 184 and in all honesty, I think the 176 range is where I should be and I’m working on that right now. But 169?!? No… The CDC will just have to call me a fatty!
Yeah… Missed the whole part about this being women’s BMI. Guess I’m the only dude who posted? Good read though and BMI is still not the end all, be all. Be well everyone.
Thanks for the comment Chris. We love our male readers 🙂
The first image totally resolves the problem and proves that BMI is useless if you want to effectively lose weight. Just look at your body with YOUR eyes and feel it. It can say many things 🙂