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BMI Scale

caviteno | Feb 12, 2010 |

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A BMI scale, or a Body Measurement Index scale, is an electronic body fat scale that allows a user to measure their weight as well as the percentage of body fat within their bodies. The BMI index is a commonly used index to rank a person's physical status - whether they are normal weight, underweight, or overweight. The higher one's BMI, the more overweight they are on the BMI scale.

BMI scales provide only an approximate measurement of one's body fat - you must use more advanced measuring systems such as hydrodensitometry weighing (underwater weighing) which measures whole body density. DEXA scanning is an X-ray absorpitometry which is the same imaging technology doctors use to measure the bone density of those at highest risk for bone loss. Even calipers, when properly used can provide as accurate a body fat measurement as a body fat scale or BMI scale.

So how does a BMI scale work?

A BMI scale is not measuring your body fat - it has no way of knowing that. Instead, the scale measures your body density by sending a harmless current through your body (via your feet) and measuring the resistance it encounters along the way. This analysis is called Bioelectrical Impedance Analysis and this is what is used to calculate your BMI based on your bone density. The current as it races through your body will pass much faster through fat free tissue such as your bones and muscles. As it encounters fat, it encounters resistance which BIA measures and returns to you as a body fat percentage, which you can then use to calculate your BMI.

My biggest tip about weighing yourself is simple - do it at the sametime every time. Whether it's in the morning as soon as you've showered or at night before you sleep, measure your weight at the same time for the most consistent results.

Unfortunately, BMI scales are often used improperly and can yield varying results and even completely false readings. Some BMI scales are notorious for being a few percentage points off your real body fat percentage. Also note, its been known that taking a shower before using a BMI scale has been known to give completely inaccurate readings. BMI scales are very sensitive to hydration or how much fluid is currently in your body. So as I recommend, do it at the same time of the day and preferably in the morning before showering and after using the toilet.

In the end, even though BMI scales are not perfect, they allow you to track changes to your body as you make changes to the way you eat and exercise in life. However, it is well known that with BMI scales, you really get what you pay for and the BMI scales that are above a $100 are usually (but not always) more accurate and consistent than the cheaper models.