Tuesday, May 22, 2012


Kyra Sedgwick says she threw her scale away because it never showed her the right number.  I know how she feels.  Since I was eleven or twelve I’ve had a love/hate relationship with scales.  Even if your diet and exercise habits stay the same, there are all kinds of circumstances that can cause your weight to go up or down:  getting a cold (up) or stomach flu (down), taking a long plane trip (up) or eating a naturally diuretic vegetable like spinach (down).  Most restaurants use a lot of salt in the food they prepare.  Oddly, places that serve spicy foods, like Indian or Mexican, tend to be especially bad about this.  If I eat at one of those I can put on five pounds overnight.

The Tanita Ironman Scale
About ten years ago I started to get serious about losing body fat.  At the time a test with calipers showed mine to be 38%, well into the “Excess Fat” category.  I bought a Tanita body fat scale and worked the number down into the mid-20’s.  Four years ago I decided to do even more and invested in a Tanita Ironman.  The Ironman won’t mow your lawn or do your taxes but it has a lot of cool features, as well as one major drawback.  In addition to your weight, muscle mass, and percentage of body fat, it will give you a separate read-out for the muscle mass and body fat in each of five areas:  right and left arm, right and left leg, and torso.  This can clue you in to asymmetries in your body that might interfere with athletic performance.  It shows visceral fat (the nasty stuff around your internal organs), bone mass (not very precise), basal metabolism rate (ditto), and body water percentage.  There are also a couple of vanity features: metabolic age and physique rating.  There are separate settings for men and women and for male and female athletes.  Anyone with a resting heart rate of less than 60 beats per minute is considered an athlete and that includes me.

Now for the bad news.  Even when I use the “female athlete” setting I don’t get sensible results for muscle mass and body fat; apparently I fall too far outside the Tanita algorithm for women.  If I pretend to be a male athlete, the numbers are closer to accurate; even if they’re not precisely right, they give me an indication of whether my condition is improving or getting worse.  The Ironman has a memory and can display previous results by day (for the past year only), week, and month.  

Like all body fat scales, the Ironman works by sending a harmless electrical current through your body and evaluating the data it produces (bioelectrical impedance analysis).  In the case of muscle mass, body fat, and water, the calculation process can cause the results to interact in unexpected ways.  For example, on days when I am dehydrated, muscle mass will go down and body fat will go up.  This may be simply an artifact of the measuring process.  Muscle is about 75% water so less water will be “read” as less muscle.  At the same weight, less muscle means more fat.

In spite of these limitations, I feel a real sense of accomplishment when I look at my numbers in 1/2008 and today:  weight 162/148, body fat 23%/13%, muscle mass 118/121.

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