Is body fat monitor worth buying?

Question

I would prefer to measure my body fat, rather than weigh myself. Is monitor like this:

worth its money or should I look for something else?

Answer 1

I stumbled on this article: Reliability and validity of bioelectrical impedance in determining body composition

They tested how reliable the bioelectrical impedance method (BIA) is compared to the golden standards. They found:

The cross-validation correlations for the BIA determinations of % fat ranged from 0.71 to 0.76, which were significantly lower than that obtained with the sum of seven (sigma 7) skinfolds equations (rxy = 0.92 for men and 0.88 for women). The correlations between the weight-to-height ratio body mass index (BMI) and hydrostatically determined % fat were 0.75 and 0.74 for men and women, respectively. The standard errors of estimate for the two BIA models ranged from 4.6 to 6.4% fat compared with 2.6 and 3.6% fat for the sigma 7 equations. The BIA method for measuring body composition was comparable to the BMI method, with height and weight accounting for most of the variance in the BIA equation.

Ironically, that would indicate that your BMI is about as accurate as using one of these fancy impedance meters!

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For those interested, here's another study by Girandola and Contarsy that found correlations of about 0.76. They conclude:

The results of the present study support the use of this bioelectrical impedance technique as simple, reliable and yet accurate method of assessing the percent of body fat in males and female in the clinical setting.

I guess it's a matter of opinions, but I would recommend a weight scale with a built in impedance meter, at least you'll get your weight from it!

Answer 2

No, use something more accurate and cheaper: a skin fat caliper.

_{This image comes from Muscle and Strength.com}