Percent Body Fat: Overview of the BIA Machine

Percent body fat estimates can be useful measures to help people gauge where they stand for their health. It has been my experience that most people are interested in knowing their body fat % for their own goal setting rather than as a health indicator.There are many charts available online on percent body fat that I have seen over the years. My favorite chart continues to be one from the American College of Sports Medicine taken from their Guidelines of Exercise Testing and Prescription publication (8th ed.).

Women have 12% essential body fat that is the lowest percent body fat they should have for health (no lower). Men do not require as much essential body fat, and their minimum remains 8%. Body fat is helpful for many reasons. The ACSM states that “…a range of 10%-22% and 20%-32% for men and women, respectively, has long been viewed as satisfactory for health” (ACSM’s Guidelines for Exercise Testing and Prescription, 10th ed., 2018).

When I was an Adjunct Professor at Pellissippi Community College, I used to tell students, “the fat is where it’s at!” Fat helps to insulate among many other useful bodily functions. Fat distributes and stores fat-soluable vitamins (A, D, E, and K), helps to produce testosterone and estrogen, and is needed to maintain cell membrane structure for each cell in the body (Cannon, J. 5th ed., 2014).

One way to measure body fat is using the BIA (or Bioelectrical Impedance Analysis) machine. I was lucky enough to marry a man who actually bought one, so I have had access to one at home for over 8 years! How this machine works is that it sends a faint electrical current through your body to detect how quickly the current flows. The more fat mass detected, the slower the speed. The more muscle mass detected, the quicker the speed. Muscle is comprised of water which helps the current move quickly in the body. This machine “…is portable, relatively inexpensive and the procedure is simple and painless” (Franco-Villoria et. al. , 2016).

This machine is an estimate of body fat, and there is a 2-5% rate of error associated with it. Your actual body fat may be 2-5% higher, or 2-5% lower, than what the machine reads. One factor that can affect how accurate your reading is are how hydrated you are. If you are dehydrated, the speed will be slower, therefore estimating that your body fat is higher than what it actually is. If you are over-hydrated, the BIA machine may state that your body fat is lower than what your actual body fat is.

Testing with more expensive equipment is done with the DEXA scan and Underwater Weighing technique. Underwater weighing, also known as hydrodensitometry, “…is usually regarded as the nearest to a gold standard” for estimating body composition (Franco-Villoria et. al. 2016). I had the privilege of volunteering to have both of these tests done on me during my Undergraduate Degree in Kinesiology at JMU! It was thrilling to get dunked in the water tank!

For more information on your percent body fat, please reach out to me via email: This email address is being protected from spambots. You need JavaScript enabled to view it.

American College of Sports Medicine. (2018). ACSM's guidelines for exercise testing and prescription, 10th ed. Philadelphia :Lippincott Williams & Wilkins

Franco-Villoria M, Wright CM, McColl JH, et al. Assessment of adult body composition using bioelectrical impedance: comparison of researcher calculated to machine outputted values. BMJ Open 2016;6:e008922. doi:10.113

Cannon, Joe (2016). Nutrition Essentials: A Guidebook for the Fitness Professional, 5th ed. FauldHouse Publishing