Is Body Mass Index (BMI) an Effective Way to Measure Obesity?

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The other night I was watching Jamie Oliver’s Eat To Save Your Life where a selection of slightly over-weight to morbidly obese people were shown what eating the wrong foods are doing to their bodies.

For one of the demonstrations three men (one slightly over-weight, one obese and one morbidly obese) went through a test to see who was the fittest. It appeared that the obese man (who happened to be vegetarian) was the fittest out of the three.

So they went on to give each man a CAT scan to measure the fat inside their bodies. The surprising thing is that the obese vegetarian had considerably less fat than either of the other two men. The reason was that he also had a lot of muscle from playing rugby.

What is Body Mass Index (BMI) and How is it Calculated?

To determine the level of obesity for the show, BMI was calculated. BMI is calculated using your height and weight to give you an indication of how healthy you are. You then compare your score to those on a chart to determine whether you are over-weight or not.

The problem is that it doesn’t take into consideration muscle. People who work out at the gym, work in a manual trade or play sports will receive a high BMI score suggesting they are overweight. When in fact they are perfectly healthy.

What Alternatives Are There?

Because very few of us will ever get the opportunity to have a CAT scan purely for the purpose of finding out how much fat there is in our bodies, we need to look at some alternative for calculating our body fat percentage.

Calipers – This is the traditional method which you can have done by a professional in your local gym or do yourself at home. You use the callipers to measure how much fat you have under the skin (subcutaneous fat). The measurements are then put into an equation to provide you with the percentage.

If you want to do this at home the suggested calipers to use are by Accu-Measure as they have been recommended by Body-for-LIFE, EAS, & World Natural Bodybuilding Federation.

Although this is fairly accurate method of finding out the amount of fat in your body, it’s not 100%. The reason is that as we get older we produce more internal fat around our organs and calipers cannot measure this.

Weighing Scales – There are special scales that you can easily buy which emit a Bioelectrical Impedance Analysis (BIA). Don’t worry it’s totally harmless. It calculates the density of fat in your body by passing an electrical current through you. These currents pass through bone and muscles much more easily than fat, so the more resistance the currents experience, the less fat you have.

BMI may help give an indication to health but it has some serious flaws which make it worthless if you have a lot of muscle. Although callipers and BIA weighing scales are not 100% accurate they are a lot better and do allow you to chart changes and see the progress you are making. Many people who go to the gym to loose weight become disheartened when they don’t see any changes on regular scales. This is because although they are loosing fat, they are also are gaining muscle which weighs more.

There are certainly plenty of people who need to lose weight out there so it’s no surprise that there are weight loss camps popping up all over the place.  Most people tend to think of their appearance but of course there is a lot going on under the surface of your body that you can’t see with the naked eye.  However you should also know that there are some disorders that cause weight loss so you should be careful about this too.  There are many who enjoy going to weight loss clubs such as Weight Watchers but remember, if you stop going chances are you will become even fatter than you are now.



  1. CyberCelt says:

    Followed you from Endangered Spaces. More than anything, it was BMI that made me realize I was almost obese. Not obese enough for lapband, but close enough to realize I was in trouble.

    You may want to check out my blog about weight loss,

  2. sorina says:

    You have a very nice blog, good post…keep up the good job

  3. Nico says:

    BMI has been the standard indeed, but if you’re body type is just a little bit different (eg, length or muscles), you get misleading results.

    I think you could just aswell judge someone’s fitness level by just looking at them. One’s vascularity and face fat are a good indication to see if someone is possibly overweight.

  4. Shawn says:

    I used to be one of those people who was told by BMI that I was morbidly obese; I was weight training 3-4 days per week. After doing one of those BIA’s it was determined that I only had 20% instead of the 32% the BMI said I had.

    I just started back up training, so I probably have a much higher % of body fat now; time to get to work!

  5. I use to be very into BMI, but I have come to see it as a very inaccurate number regarding the healthy weight of a particular individual.

  6. Jenna says:

    Very interesting post. I’m glad you brought this topic up! I have been working so hard to get myself into better shape and I found your post to be both very helpful & informational! Thanks for sharing!

  7. One of the keys to fitness and health success is to stay dedicated whatever you do, no matter what.

    Come up with a plan and stick at the diet and exercise. Also, just so you don’t lose your sanity, go ahead and eat what you want at least one day of the week, but go right back to your plan after that.

    Try it off and on for a month before making it a life long decision as that is the best route to take it.

  8. Health Freak says:

    The thing is, BMI is pants. It’s only slightly more useful than knowing someone’s weight without knowing their height. It’s a piece of data, nothing more.

    Some people have ‘bad’ BMI and aren’t even actually fat, just muscular. Some people are definitely fat, but still quite healthy. And some people have ‘normal’ BMI and are totally unhealthy.

    It’s potentially useful information, because it might mean you’re slightly more at risk of something and therefore you should be careful about it, but THAT’S IT. It does not say whether you’re a good or bad person, or even whether you’re a healthy or unhealthy person.

    If, say, men are more at risk of heart attacks than women, that doesn’t mean you should turn all men into women, or that all men will die of heart attacks. It just means they should think about it once in a while.